Biology and Biochemistry Flashcards

Question

Answer 1

**_Anealing_** is the binding of two complementary strands of DNA into a double-stranded structure In contrast, **_melting_** or **_denaturation_** is the separation of strands of DNA.

Answer 2

DNA gets wrapped around **_histones_**. Once DNA is wrapped around **_histones_**, the DNA and **_histones_** complex is called a **_nucleosome_**. When multiple **_nucleosomes_** are packed next to each other, they are called **_chromatin_**.

Answer 3

**_Heterochromatin_** is highly compact DNA with histones, and **_euchromatin_** is much less compact and has very high transcription rates when compared to **_heterochromatin_**.

Answer 4

In eukaryotes, th efirst RNA transcribed from DNA is an immature or precursor to Messenger RNA (mRNA) called the **_heterogenous nuclear RNA_** (**_hnRNA_**). Processing events (such as addition of a cap and tail and splicing) are required for **_hnRNA_** to become mature mRNA. Since prokaryotes do not process their primary transcripts, **_hnRNA_** is only found in eukaryotes.

Answer 5

Nucleotides in the DNA are covalently linked by phosphodiester bonds between the **_3' hydroxy group_** of one deoxyribose and the **_5' phosphate group_** of the next deoxyribose.

Answer 6

**_DNA gyrase_**, or simply **_gyrase_**, is an enzyme within the class of topoisomerase and is a subclass of Type II topoisomerases[1] that reduces topological strain in an ATP dependent manner while double-stranded DNA is being unwound by elongating RNA-polymerase[2] or by helicase in front of the progressing replication fork.[3][4] The enzyme causes negative supercoiling of the DNA or relaxes positive supercoils. It only exists in prokaryotes.

Answer 7

Larger proteins cannot pass through nuclear pores and are excluded from the nuclear interior unless they contain a sequence of basic amino acids called **_nuclear localization Sequence_**.

Answer 8

**_Mitochondria_** are the site of oxidative phosphorylation. The mitochondria's inner membrane is the location of the **_electron transport chain_** and **_ATP synthase_** and is the site of the proton gradient used to drive ATP synthesis by **_ATP synthase_**.

Answer 9

The **_resting membrane potential_** is an electrical potential across the plasma membrane of approximately **_-70_** mV, with the **_interior_** of the cell negatively charged with respect to the **_exterior_** of the cell.

Answer 10

**_Adaptation_** is a decrease in firing frequency when the intesity of a stimulus remains constant.

Answer 11

Hormones can be grouped into one of two classes. Hydrophillic hormones, such as peptides and amino acid derivatives, must bind to the receptors on the **_cell surface_**, while hydrophobic hormones, such as the steroid hormones, bind to receptors in the **_cellular interior_**.

Answer 12

The **_erythrocyte_** is a cell, but it has no nucleus or other organelles such as mitochondria.

Answer 13

Acetylcholine has an **_inhibiting_** effect on cardiac muscle and therefore would cause a **_decrease_** in heart rate.

Answer 14

**_Antidiuretic Hormone_** (**_ADH_**) is also called **_arginine vasopressin_**. It's a hormone made by the **_hypothalamus_** in the brain and stored in the **_posterior pituitary gland_**. It tells your kidneys how much water to conserve. **_ADH_** constantly regulates and balances the amount of water in your blood. It is also a **_peptide_**.

Answer 15

**_Aldosterone_** is a pregnane-based **_steroidal_** hormone produced by the outer-section (zona glomerulosa) of the **_adrenal cortex_** in the **_adrenal gland_**, and acts on the distal tubules and collecting ducts of the kidney to cause the conservation of **_sodium_**, secretion of **_potassium_**, increased **_water_** retention, and increased **_blood_** pressure. The overall effect of **_aldosterone_** is to increase reabsorption of **_ions_** and **_water_** in the kidney.

Answer 16

**_Erythropoietin_**, also known as **_haematopoietin_** or **_haemopoietin_**, is a **_glycoproteincytokine_** secreted by the kidney in response to cellular **_hypoxia_**; it stimulates red blood cell production (**_erythropoiesis_**) in the bone marrow. Low levels of **_EPO_** (around 10 mU/mL) are constantly secreted sufficient to compensate for normal red blood cell turnover.

Answer 17

The gastric **_chief_** cell (also known as a **_zymogenic_** cell or **_peptic_** cell) is a cell in the stomach that releases **_pepsinogen_** and **_chymosin_**. **_Pepsinogen_** is activated into the digestive enzyme **_pepsin_** when it comes in contact with acid produced by **_gastric_** **_parietal_** cells. **_gastric_** **_parietal_** **_cells_** also secretes gastric lipase enzymes, which help digest triglycerides into free fatty acids and di- and mono-glycerides.

Answer 18

The small intestine is divided into three segments: the **_duodenum_**, **_jejunum_**, and **_ileum_**.

Answer 19

The villus contains capillaries, which absorb dietary monosacharides and amino acids. The capillaries merge to form veins, which merge to form the **_large hepatic portal vein_**, which transports blood containing amino acids and carbohydrate nutrients from the gut to the liver.

Answer 20

The villus also contains small lymphatic vessels called **_lacteals_**, which absorb dietary **_fats_**. The **_lacteals_** merge to form large lymphatic vessels, which transport the dietary **_fats_** to the thoracicduct, which empties into the bloodstream.

Answer 21

**_Alpha cells_** of the pancreas secrete **_glucagon_** in response to low blood sugar. **_Glucagon_** functions to mobilize stored fuels by stimulating the liver to hydrolyze **_glycogen_** and release glucose into the bloodstream, and by stimulating adipocytes (fat cells) to release fats into the bloodstream.

Answer 22

**_Beta_** cells of the **_pancreas_** secrete **_insulin_** in response to elevated blood sugar (e.g., after a meal). Its effects are opposite to those of **_glucagon_**: **_insulin_** stimulates the removal of glucose from the blood for sorage of glycogen and fat.

Answer 23

**_ð cells_** of the **_pancreas_** secrete **_somatostatin_**. **_Somatostatin_** inhibits many digestive processes. Somatostatin, also known as growth hormone-inhibiting hormone (GHIH) or by several other names, is a peptide hormone that regulates the endocrine system and affects neurotransmission and cell proliferation via interaction with G protein-coupledsomatostatin receptors and inhibition of the release of numerous secondary hormones. Somatostatin inhibits insulin and glucagon secretion.[5] In the pancreas, somatostatin is produced by the delta cells of the islets of Langerhans, where it serves to block the secretion of both insulin and glucagon from adjacent cells. Insulin, glucagon, and somatostatin act in concert to control the flow of nutrients into and out of the circulation. The relative concentrations of these hormones regulate the rates of absorption, utilization, and storage of glucose, amino acids, and fatty acids.

Answer 24

**_Epinephrine_** (an amino acid derivative from the adrenal medulla) and **_cortisol_** ( a steroid or glucocorticoid from the adrenal cortex) are two of the three hormones that can raise blood glucose levels.

Answer 25

A **_sarcomere_** is a structural unit of a myofibril in striated muscle, consisting of a dark band and the nearer half of each adjacent pale band.

Answer 26

**_Actin_** polymerizes to form thin filaments visible under the microscope, and **_myosin_** forms thick filaments.

Answer 27

Each **_sarcomere_** is bound by two **_Z_** lines.

Answer 28

The regions of the sarcomere composed only of thin filaments are referred to as the **_I bands_**. The full length of the thick filament represents the **_A band_** within each sarcomere; this includes the overlapping regions of the thick and thin filaments. * The region only comosed of thick filaments is called the **_H zone_**.

Answer 29

The first two steps of the contractile cycle: * 1. Binding of the **_myosin head_** to a myosin binding site on actin, also known as **_cross bridge formation_**. At this stage, myosin has **_ADP_** and **_P_i_** bound. * 2. The **_power stroke_**, in which the myosin head moves to a low-energy conformation, and pulls the actin chain toward the center of the sarcomere. **_ADP_** is released.

Answer 30

The last two steps of the contractile cycle: * 3. Binding of a new **_ATP_** molecule is necessary for the **_release_** of actin by the myosin head (key!). * 4. **_ATP_** **_hydrolysis_** occurs immediately and the myosin head is cocked (set in a high-energy confromation, like the hammer of a gun). Another cycle begins when the myosin head binds to a new binding site on the thin filament.

Answer 31

**_Tropomyosin_** is a long fibrous protein that winds around the actin polymer, blocking all the myosin binding sites.

Answer 32

**_Troponin_** is a globular protein bound to the tropomyosin that can bind **_Ca²⁺_**. When **_troponin_** binds **_Ca²⁺_**, **_troponin_** undergoes a conformational change that moves tropomyosin out of the way, so that myosin heads can attach to actin and filament sliding can occur.

Answer 33

**_Type I_**, slow twitch, or "red" muscle, is dense with capillaries and is rich in mitochondria and myoglobin, giving the muscle tissue its characteristic red color. It can carry more oxygen and sustain aerobic activity using fats or carbohydrates as fuel. Slow twitch fibers contract for long periods of time but with little force.

Answer 34

**_Type IIA_** fibers, or fast oxidative fibers, are used more during sustained power activities such as sprinting 400 meters or doing repeated lifts with a weight below maximum (but not with very light weights). They contain very large amounts of myoglobin, very many mitochondria and very many blood capillaries. **_Type IIA_** fibers are red. **_Type IIA_** fibers have a very high capacity for generating ATP by oxidative metabolic processes, and split ATP at a very rapid rate. They have a fast contraction velocity and are more resistant to fatigue.

Answer 35

**_Type IIb_** fast-twitch fibers, or fast glycolytic fibres, are recruited for very short-duration high-intensity bursts of power such as maximal and near-maximal lifts and short sprints. **_Type IIB_** fibres contain a low content of myoglobin, relatively few mitochondria, relatively few blood capillaries and large amounts glycogen. **_Type IIB_** fibres are white. **_Type IIB_** fibers are geared to generate ATP by anaerobic metabolic processes, however, they are not able to supply skeletal muscle fibres continuously with sufficient ATP, and fatigue easily.

Answer 36

**_Parathyroid Hormone_** stimulates osteoclast activity. **_Parathyroid Hormone_** effects the kidneys by increasing readsorbtion of calcium and stimulating the conversion of Vitamin D into calcitriol. **_Parathyroid Hormone_** effects the intestines indirectly (via calcitriol) increasing intestinal calcium absorbtion.

Answer 37

**_Calcitriol_** effects the bones POTENTIALLY from stimulating osteoclast activity, but oseoclast activity stimulation is very small. **_Calcitriol_** effects the kidneys by increasing reabsorbtion of phosphorus. **_Calcitriol_** effects the intestines by increasing intestinal absorbtion of calcium.

Answer 38

**_Calcitonin_** effects the bones by inhibiting osteoclast activity. **_Calcitonin_** effects the kidneys by decreasing reabsorbtion of calcium. **_Calcitonin_** effects the intestine by N/A.

Answer 39

Inhaled air folllow this pathway: **_nose_** → **_nasal cavity_** → **_pharynx_** → **_larynx_** → **_trachea_** → **_bronchi_** → **_terminal bronchioles_** → **_respiratory bronchioles_** → **_aveolar ducts_** → **_aveoli_**.

Answer 40

The lungs are not directly connected to the chest wall. Each lung is surrounded by two membranes, or **_pleura_**: the **_parietal pleura_**, which lines the inside of the chest cavity, and the **_visceral pleura_**, which lines the surface of the lungs. Between the two pleura is a very narrow space called the **_pleural space_**. The pressure in the **_pleural space_** (the pleural pressure) is **_negative_**.

Answer 41

* Competitive Inhibitor * K_m **_increased_** * V_max **_unaffected_** * Uncompetitive Inhibitor * K_m **_reduced_** * V_max **_reduced_** * Noncompetive * K_m **_unaffected_** * V_max **_reduced_**

Answer 42

The sites of spermatogenesis within the testes are the **_seminiferous tubules_**. The walls of the **_seminiferous tubules_** are formed by cells called **_sustancular cells_** (also known as **_sertoli cells_**). **_Sertoli cell_**s (or **_sustenacular cells_** protect and nurture the developing sperm, both physically and chemically.

Answer 43

The **_epididymis_** is a tube that connects a testicle to a vas deferens in the male reproductive system.

Answer 44

The hormone **_inhibin_** is secreted by sertoli cells. **_Inhibin's_** role is to inhibit FSH release.

Answer 45

**_Bindin_** is a protein on the sperm's surface that attaches to receptors on the zona pellucida surrounding the ovum.

Answer 46

**_Mullerian Inhibiting Factor (MIF)_** is activated by SOX9 in the Sertoli cells of the male fetus. Its expression inhibits the development of the female reproductive tract, or **_Müllerian ducts_** (paramesonephric ducts), in the male embryo, thereby arresting the development of fallopian tubes, uterus, and upper vagina.

Answer 47

All hormones in the development and maintainence of male characteristics are termed **_androgens_**, while those involved in development and maintenance of female characteristics are termed **_estrogens_**.

Answer 48

The **_endometrium_** is the innermost lining layer of the uterus, and functions to prevent adhesions between the opposed walls of the myometrium, thereby maintaining the patency of the uterine cavity. During the menstrual cycle or estrous cycle, the **_endometrium_** grows to a thick, blood vessel-rich, glandular tissue layer.

Answer 49

In mammals, the first part of oogenesis starts in the germinal epithelium, which gives rise to the development of ovarian follicles, the functional unit of the ovary. Oogenesis consists of several sub-processes: oocytogenesis, ootidogenesis, and finally maturation to form an ovum (oogenesis proper). Folliculogenesis is a separate sub-process that accompanies and supports all three oogenetic sub-processes. Cell typeploidy/chromosomeschromatidsProcessTime of completion Oogoniumdiploid/46(2N)2COocytogenesis (mitosis)Third trimester primary oocytediploid/46(2N)4COotidogenesis (meiosis I) (Folliculogenesis)Dictyate in prophase I for up to 50 years secondary oocytehaploid/23(1N)2COotidogenesis (meiosis II)Halted in metaphase II until fertilization Ootidhaploid/23(1N)1COotidogenesis (meiosis II)Minutes after fertilization Ovumhaploid/23(1N)1C Oogonium —(Oocytogenesis)—\> Primary Oocyte —(Meiosis I)—\> First Polar Body (Discarded afterward) + Secondary oocyte —(Meiosis II)—\> Second Polar Body (Discarded afterward) + Ovum Oocyte meiosis, important to all animal life cycles yet unlike all other instances of animal cell division, occurs completely without the aid of spindle-coordinating centrosomes.[3][4]

Answer 50

**_GnRH_** from the hypothamamus stimulates the release of FSH and LH from the **_anterior pituitary_**.

Answer 51

The sudden surge in **_LH_** causes ovulation.

Answer 52

**_Estrogen_** and **_Progesterone_** causes the maintenance fo the endometrium lining.

Answer 53

The **_chorion_** is the portion of the placenta that is derived from the zygote. It secretes **_human chorionic gonadotropin_**, or **_hCG_**, which can take the place of LH in maintaining the corpus luteum.

Answer 54

During the last six months of pregnancy, the **_corpus luteum_** is no longer needed because the placenta itself secretes sufficient estrogen and progesterone for maintenance of the endometrium.

Answer 55

Once you know the anterior pituitary hormones, it is often easy to learn the names of the rest of the steps in that hormone pathway. Here is a mneumonic that can be used to memorize the anterior pituitary hormones: FLAT PEG FLAT PEG: FSH (Follicle Stimulating Hormone), LH (Leutinizing Hormone), ACTH (Adrenocorticotropic Hormone), TSH (Thyroid Stimulating Hormone), Prolactin, Endophins, and Growth Hormones.

Answer 56

Posterior Pituitary Lobe Hormones: **_Anti-diuretic hormone (ADH_**): This hormone prompts the kidneys to increase water absorption in the blood. **_Oxytocin_**: Oxytocin is involved in a variety of processes, such as contracting the uterus during childbirth and stimulating breast milk production.

Answer 57

Glucose and fructose are in sucrose.

Answer 58

Galactose and glucose are in lactose.

Answer 59

Glucose is oxidized to produce CO2 and ATP in a four step process: **_glycolysis_**, the **_pyruvate dehydrogenase complex_** (**_PDC_**), the **_Krebs cycle_**, and **_electron transport_**/**_oxidative phosphorylation_**.

Answer 60

You put a glucose and invest 2 ATP into glycolysis, and in return, you get 2 Pyruvate, 4 ATP (Netting 2 ATP), 2 NADH, 2 H₂O, and 2 H+.

Answer 61

**_Hexokinase_** catalyzes the first step in glycolysis, the phosphorylation of glucose to G6P. G6P feedback **_inhibits_** **_hexokinase_**.

Answer 62

Under **_aerobic_** conditions (that is in the presence of **_oxygen_**), the pyruvate produced in glycolysis enters the **_Pyruvate Dehydrogenase Complex (PDC)_** and **_Krebs Cycle_** to oxidized completely to CO₂.

Answer 63

**_Fermentation_** has evolved to regenerate **_NAD_****⁺** in anaerobic conditions, thereby allowing glycolysis to continue in the abscence of oxygen. **_Fermentation_** uses **_pyruvate_** as the acceptor of the high energy electrons from **_NADH_**.

Answer 64

The lactate that is produced in humans from anaerobic respiration is exported from the muscle to the liver. When oxygen becomes available, the liver cell will convert the lactate back to pyruvate, while making NADH from NAD+.

Answer 65

**_Pyruvate_** is converted to a 2 carbon molecule (**_acetyl-CoA_**). A CO2 comes off of Pyruvate, and NAD+ is oxidized to NADH + H⁺. 2 NADH per glucose is madein pyruvate dehydrogenase.

Answer 66

The **_Krebs Cycle_** is a group of reactions which take 2-carbon acetyl units from **_acetyl-CoA_**, combine it with **_oxaloacetate_**, and release **_two CO_****₂** molecules. NADH and **_FADH_****₂** are generated in this process.

Answer 67

Krebs Cycle: 6 NADH, 2FADH2, and 2 GTP per glucose. NOTE: no need to know picture level detail. Merely, look at it for 10 seconds.

Answer 68

Names the structures of the Mitochondria. * **_Intermembrane Space_** — small space to quickly accumulate protons * **_Inner Membrane_** — Contains ETC and ATP synthase for oxidative phosphorylation. * **_Cristae_** — highly folded to increase surface area to volume ration. * **_Outer Membrane_** — contains transport proteins for shuttling pyruvate into mitochondrion. * **_Matrix_** — has appropriate enzymes and a suitable pH for the Krebs Cycle.

Answer 69

**_Oxidative phosphorylation_** is the oxidation of the high-energy electron carriers NADH and FADH2 coupled to the phosphorylation of ADP to produce ATP.

Answer 70

An **_electron transport chain_** (**_ETC_**) is a series of complexes that transfer electrons from electron donors to electron acceptors via redox (both reduction and oxidation occurring simultaneously) reactions, and couples this electron transfer with the transfer of protons (H+ ions) across a membrane. This creates an electrochemical proton gradient that drives the synthesis of adenosine triphosphate (ATP), a molecule that stores energy chemically in the form of highly strained bonds. The final acceptor of electrons in the electron transport chain during aerobic respiration is molecular **_oxygen_** although a variety of acceptors other than **_oxygen_** such as sulfate exist in anaerobic respiration.

Answer 71

Each molecule of NADH provides the energy to produce approximately **_2.5 ATP_** molecules, and each molecule of FADH₂ provides the energy to produce approximately **_1.5 ATP_** molecules. Additionally, for NADH made in the cytosol, you only get **_1.5 ATP_** molecules.

Answer 72

The **_pentose phosphate pathway_** (**_PPP_**, also known as the hexose monophosphate shunt) diverts glucose- 6-phosphate from glycolysis in order to form **_NADPH_**, **_ribose-5-phosphate_**, and **_glycolytic_** intermediates.

Answer 73

(C₅H₈)_n

Answer 74

The receptors for steroid hormones are located **_within cells_** rather than **_on the cell surface_**.

Answer 75

Peptide hormones, such as insulin, exert their effects by binding at the **_cell surface_**.

Answer 76

**_ß-Oxidation_** process begins at the outer mitochondrial membrane with the activation of the fatty acid. This reaction, catalyzed by **_acyl-CoA synthetase_**, requires the investment of two ATP equivalents to generate a fatty **_acyl-CoA_** which is then transported into the mitochondrion.

Answer 77

Each round of b-oxidation cleaves a two-carbon acetyl-CoA from the molecule; however, the final round cleaves a four-carbon fatty acyl-CoA to generate two acetyl-CoA. For instance, the complete b-oxidation of lauric acid (a twelve-carbon saturated fatty acid) involves the following: an investment of two ATP equivalents to convert it to a fatty acyl-CoA and then five rounds of b-oxidation. This generates five FADH2, five NADH, and six acetyl-CoA which can then enter the Krebs cycle. When these six acetyl- CoA go through the Krebs cycle, they will generate an additional 18 NADH, 6 FADH2, and 6 GTP. We then have a grand total of eleven FADH2 (five from b-oxidation and six from the Krebs cycle), 23 NADH (five from b-oxidation and 18 from the Krebs cycle), and six ATP equivalents (from the Krebs cycle). Af- ter the electron transport chain (and subtracting the two ATP equivalents required at the beginning of b-oxidation), we obtain 78 ATP from lauric acid.

Answer 78

During periods of starvation, glycogen stores become exhausted and blood glucose falls significantly. To help supply the central nervous system with energy when glucose is in short supply, the liver generates ketone bodies via a process in the mitochondrial matrix known as ketogenesis. The ketone bodies are generated from acetyl-CoA and include acetone, acetoacetate, and b-hydroxybutyrate. These molecules can cross the blood-brain barrier and be converted back to acetyl-CoA once they arrive at their target organ; the acetyl-CoA can then enter the kreb cycle.

Answer 79

Fatty Acid synthesis takes place in the cytoplasm.

Answer 80

The adrenal cortex produces three important steroid hormones: aldosterone, cortisol, and sex steroid.

Answer 81

The adrenal medulla produces catecholamines: epinephrine and norepinephrine.

Answer 82

Stop codons are also called **_nonsense codons_**, since they do not code for any amino acid.

Answer 83

When mitosis produces two identical daughter cells from one parental cell, each daughter must have the same genome as the parent. Therefore, cell division requires duplication of the DNA, known as **_replication_**. This is an enzymatic process, just as the Krebs cycle and glycolysis are enzymatic processes. It occurs during **_S (synthesis) phase_** in interphase of the cell cycle.

Answer 84

The enzyme that unwinds the double helix and separates the strands is called **_helicase_**. **_Helicase_** use the energy of ATP hydrolysis to break the many hydrogen bonds. The place where the **_helicase_** begins to unwind is not random. It is a specific location (sequence of nucleotides) on the chromo- some called the **_origin of replication_** (abbreviated **_ORI_**).

Answer 85

When helicase unwinds the helix at the origin of replication, the helix gets wound more tightly upstream and downstream from this point. The chromosome would get tangled and eventually break, except that enzymes called **_topoisomerases_** cut one or both of the strands and unwrap the helix, releasing the excess tension created by the helicases.

Answer 86

Another potential problem is that single-stranded DNA is much less stable than ds-DNA. **_Single-strand binding proteins_** (**_SSBPs_**) protect DNA that has been unpackaged in preparation for replication and help keep the strands separated. The separated strands are referred to as an open complex.

Answer 87

An RNA primer must be synthesized for each template strand. This is accomplished by a set of proteins called the primosome, of which the central component is an RNA polymerase called **_primase_**. Primer synthesis is important because the next enzyme, DNA polymerase, cannot start a new DNA chain from scratch. It can only add nucleotides to an existing nucleotide chain. The RNA primer is usually 8–12 nucleotides long, and is later replaced by DNA.

Answer 88

DNA Polymerization occurs in the **_5' to 3'_** direction, without exception. This means the existing chain is always lengthened by the addition of a nucleotide to the **_3'_** end of the chain. There is never **_3' to 5'_** polymerase activity.

Answer 89

During replication, eventually all RNA primers are replaced by **_DNA_**, and the fragments are joined by an enzyme called **_DNA ligase_**.

Answer 90

**_DNA pol III_** is responsible for the super-fast, super-accurate elongation of the leading strand. In other words, it has high processivity. It has 5' to 3' polymerase activity as well as 3' to 5' exonuclease activity. This is when the enzyme moves backward to chop off the nucleotide it just added, if it was incorrect; the ability to correct mistakes in this way is known as **_proofreading function_**. It has no known function in repair, and so is considered a replicative enzyme.

Answer 91

**_DNA pol I_** starts adding nucleotides at the RNA primer; this is 5' to 3' polymerase activity. Because of its poor processivity (it can only add 15-20 nucleotides per second), DNA pol III usually takes over about 400 base pairs downstream from the ORI. **_DNA pol I_** is also capable of 3' to 5' exonuclease activity (proofreading). **_DNA pol I_** removes the RNA primer via 5' to 3' exonuclease activity, while simultaneously leaving behind new DNA in 5' to 3' polymerase activity. Finally, **_DNA pol I_** is important for excision repair.

Answer 92

**_Exonuclease_** means “cutting a nucleic acid chain at the end.” An **_endonuclease_** will cut a polynucleotide acid chain in the middle of the chain, usually at a particular sequence. Two important types of **_endonucleases_** are: **_repair enzymes_** that remove chemically damaged DNA from the chain, and **_restriction enzymes_**, which are **_endonucleases_** found in bacteria. Their role is to destroy the DNA of infecting viruses, thus restricting the host range of the virus.

Answer 93

**_Missense mutation_**: This causes one amino acid to be replaced with a different amino acid. This may not be serious if the amino acids are similar.

Answer 94

Eukaryotic mRNA is usually **_monocistronic_** and obeys the “one gene, one protein” principle. This means that each piece of mRNA encodes only one polypeptide (and so contains one ORF). Hence, there are as many different mRNAs as there are proteins. Because each mRNA can be read many times, each transcript can be used to make many copies of its polypeptide.

Answer 95

Note that in eukaryotes, the first RNA transcribed from DNA is an immature or precursor to mRNA called **_heterogeneous nuclear RNA_** (**_hnRNA_**). Processing events (such as addition of a cap and tail, and splicing) are required for **_hnRNA_** to become mature mRNA. Since prokaryotes do not process their primary transcripts, **_hnRNA_** is only found in eukaryotes.

Answer 96

**_Transfer RNA_** (**_tRNA)_** is responsible for translating the genetic code. **_Transfer RNA_** carries amino acids from the cytoplasm to the ribosome to be added to a growing protein.

Answer 97

**_Small nuclear RNA_** (**_snRNA_**) molecules (150 nucleotides) associate with proteins to form **_snRNP_** (**_small nuclear ribonucleic particles_**) complexes in the spliceosome.

Answer 98

A **_microRNA_** (abbreviated **_miRNA_**) is a small non-coding RNA molecule (containing about 22 nucleotides) found in plants, animals and some viruses, that functions in RNA silencing and post-transcriptional regulation of gene expression. **_miRNAs_** function via base-pairing with complementary sequences within mRNA molecules. As a result, these mRNA molecules are silenced, by one or more of the following processes: (1) Cleavage of the mRNA strand into two pieces, (2) Destabilization of the mRNA through shortening of its poly(A) tail, and (3) Less efficient translation of the mRNA into proteins by ribosomes.

Answer 99

The sequence of nucleotides on a chromosome that activates RNA polymerase to begin the process of transcription is called the **_promoter_**, and the point where RNA polymerization actually starts is called the start site.

Answer 100

The strand which is actually transcribed is called the **_template_**, **_non-coding_**, **_transcribed_**, or **_antisense strand_**; it is complementary to the transcript. The other DNA strand is called the **_coding_** or **_sense_** strand; it has the same sequence as the transcript (except it has T in place of U).

Answer 101

The average size of a mammalian **_intron_**, for example, is about 2000 nucleotides. Intervening sequences in the RNA are called **_introns_**. Note that **_introns_** are intragenic regions (and not intergenic space). Protein-coding regions of the RNA are termed **_exons_** because they actually get expressed. Before the RNA can be translated, **_introns_** must be removed and **_exons_** joined together; this is accomplished via splicing.

Answer 102

Eukaryotic hnRNA must be modified in two other ways before translation can occur. A tag is added to each end of the molecule: a **_5' cap_** and a **_3' poly-A tail_**. The **_5' cap_** is a _methylated guanine nucleotide_ stuck on the **_5' end_**. The **_poly-A tail_** is a string of several hundred adenine nucleotides. The **_cap_** is essential for translation, while both the **_cap_** and the **_poly-A tail_** are important in preventing digestion of the mRNA by exonucleases that are free in the cell.

Answer 103

This is the **_anticodon_**, a sequence of three ribonucleotides which is complementary to the mRNA codon the tRNA translates. A key step in translation is specific base pairing between the tRNA **_anticodon_** and the mRNA codon.

Answer 104

The prokaryotic ribosome sediments in a gradient at a rate of **_70S_**, so it is referred to as the **_70S_** ribosome. It is composed of a **_30S_** small subunit and a **_50S_** large subunit.

Answer 105

Eukaryotes have an **_80S_** ribosome. It has a large and small subunit. The large subunit sediments in a gradient at a rate of **_60S_**, and the small subunit sediments at a rate of **_40S_**.

Answer 106

The **_A site_** (**_aminoacyl_**-tRNA site) is where each new tRNA delivers its amino acid. The **_P site_** (**_peptidyl_**-tRNA site) is where the growing polypeptide chain, still attached to a tRNA, is loated during translation. The **_E site_** (**_exit_**-tRNA site) is where a now empty tRNA sits prior to its release from the ribosome.

Answer 107

Prokaryotes have a ribsome binding site, also known as the **_Shine-Dalgarno sequence_**, located at -10 (ten ribonucleotides upstream, or on the 5' side of the start codon). The **_Shine Delgarno sequence_** is complementary to the pyrimidine rich region on the small subunit, and thus helps position the initiation machinery on the transcript.

Answer 108

The first amino-acyl-tRNA is special; it is called the **_initiator tRNA_**, abbreviated **_fMet-tRNAf_Met_**. The "**_fMet_**" stands for **_formylmethionine_**, which is a modified methionine used as the first amnio acid in all **_prokaryotic_** proteins.

Answer 109

In translation, eukaryotes' first amino acid in translation is **_methionine_** instead of **_formylmethionine_** (as in prokaryotes).

Answer 110

Broadly speaking, **_epigenetics_** focuses on changes in gene expresion that are not due to changes in DNA sequences, but are either heritable or have long-term effects. The three most commonly studied areas in **_epigenetics_** are DNA methylation, chromatin remodeling, and RNA interference.

Answer 111

The default for repressible systems is "**_ON_**", but for repressible **inducible** systems, the default is "**_OFF_**".

Answer 112

The lac operon of E. coli contains genes involved in lactose metabolism. It's expressed only when lactose is present and glucose is absent. Two regulators turn the operon "on" and "off" in response to lactose and glucose levels: the lac repressor and catabolite activator protein (CAP). The lac repressor acts as a lactose sensor. It normally blocks transcription of the operon, but stops acting as a repressor when lactose is present. The lac repressor senses lactose indirectly, through its isomer allolactose. **_Catabolite activator protein_** (**_CAP_**) acts as a glucose sensor. It activates transcription of the operon, but only when glucose levels are low. CAP senses glucose indirectly, through the "hunger signal" molecule cAMP.

Answer 113

If lactose is missing from the growth medium, the repressor binds very tightly to a short DNA sequence just downstream of the promoter near the beginning of lacZ called the lac operator. The repressor binding to the operator interferes with binding of RNAP to the promoter, and therefore mRNA encoding LacZ and LacY is only made at very low levels. When cells are grown in the presence of lactose, however, a lactose metabolite called allolactose, made from lactose by the product of the lacZ gene, binds to the repressor, causing an allosteric shift. Thus altered, the repressor is unable to bind to the operator, allowing RNAP to transcribe the lac genes and thereby leading to higher levels of the encoded proteins.

Answer 114

DNA ligase is a specific type of enzyme, a ligase, (EC 6.5.1.1) that facilitates the joining of DNA strands together by catalyzing the formation of a phosphodiester bond. It plays a role in repairing single-strand breaks in duplex DNA in living organisms, but some forms (such as DNA ligase IV) may specifically repair double-strand breaks (i.e. a break in both complementary strands of DNA). Single-strand breaks are repaired by DNA ligase using the complementary strand of the double helix as a template,[1] with DNA ligase creating the final phosphodiester bond to fully repair the DNA.

Answer 115

4 ATP \* n Amino Acids = total ATP used to create protein.

Answer 116

A noncompetitive inhibitor is an allosteric inhibitor.

Answer 117

The three types of RNA polymerase in humans are RNA Polymerase I, II, and III. RNA polymerase I is responsible for the transcription of most rRNA. RNA polymerase II synthesizes mRNA, as well as snRNA. RNA polymerase III synthesizes mostly tRNA, some snRNA, and miRNA (choice C can be eliminated).

Answer 118

YES! They dissociate into two pieces.

Answer 119

A virus is an **_obligate intracellular parasite_** that relies on host machinery whenever possible.

Answer 120

Viruses which do not have envelopes are called **_naked viruses_**. All phages and plant viruses are **_naked_**.

Answer 121

The process of a virus binding to the exterior of a bacterial cell is called **_attachment_** or **_adsorbtion_**.

Answer 122

Some viruses are cleverer: They enter the **_lysogenic cycle_**. Upon infection, the phage genome is incorporated in the bacterial genome and is now referred to as a **_prophage_**; the host is now called a **_lysogen_**. The **_prophage_** is silent; its genes are not expressed, and viral prgeny are not produced. Eventually, the prophage becomes activated. It now removes itself from the host genome (in a process called **_excision_**) and enters the **_lytic cycle_**.

Answer 123

Transduction is the process by which a virus transfers genetic material from one bacterium to another. Viruses called bacteriophages are able to infect bacterial cells and use them as hosts to make more viruses. After multiplying, these viruses assemble and occasionally remove a portion of the host cell's bacterial DNA. Later, when one of these bacteriophages infects a new host cell, this piece of bacterial DNA may be incorporated into the genome of the new host. There are two types of transduction: generalized and specialized. In generalized transduction, the bacteriophages can pick up any portion of the host's genome. In contrast, with specialized transduction, the bacteriophages pick up only specific portions of the host's DNA. Scientists have taken advantage of the transduction process to stably introduce genes of interest into various host cells using viruses.

Answer 124

Replication strategies of plus- and minus-strand RNA viruses. (A) The plus-sense RNA genome is the same sense as mRNA and can be translated using the cellular machinery when it is uncoated in the cell to produce the single polyprotein (represented by West Nile virus, a single-stranded, plus-sense RNA virus). The polyprotein is then processed into each individual protein. The newly made viral polymerase protein, RNA-dependent RNA polymerase, copies the plus-sense genomic RNA into complementary minus-sense RNA. It is unclear how the viral translation switches to transcription using the same genomic RNA as the template. New minus-sense strands serve as the template for new plus-sense strand synthesis. The nascent plus-sense RNA can be the new mRNA for translation, a template for replication, or packaged. (B) The minus-sense RNA genome (represented by VSV) must be transcribed into mRNAs before translation takes place, while the genomic RNA can also be transcribed into a full-length plus-sense RNA that will be the template for nascent minus-sense genomic RNA replication. Transcription is performed by the viral polymerase, which is packaged in the virion. For some minus-strand RNA viruses, for example, influenza virus, primary transcription and replication of viral RNA occur in the nucleus.

Answer 125

Retroviruses must encode reverse transcriptase!

Answer 126

The prokaryotes include **_bacteria_**, **_archea_** (**_extremophiles_**), and blue-green algae (**_cyanobacteria_**).

Answer 127

Conjugation is the process by which one bacterium transfers genetic material to another through direct contact. During conjugation, one bacterium serves as the donor of the genetic material, and the other serves as the recipient. The donor bacterium carries a DNA sequence called the fertility factor, or F-factor. The F-factor allows the donor to produce a thin, tubelike structure called a pilus, which the donor uses to contact the recipient. The pilus then draws the two bacteria together, at which time the donor bacterium transfers genetic material to the recipient bacterium. Typically, the genetic material is in the form of a plasmid, or a small, circular piece of DNA. The genetic material transferred during conjugation often provides the recipient bacterium with some sort of genetic advantage. For instance, in many cases, conjugation serves to transfer plasmids that carry antibiotic resistance genes.

Answer 128

cocci [plural] & coccus [singular]

Answer 129

bacilli [plural] & bacillus [singular]

Answer 130

spiochetes or spirilla [plural] & spirochete, spirillium [singular]

Answer 131

Danish scientist Hans Christian Gram devised a method to differentiate two types of bacteria based on the structural differences in their cell walls. In his test, bacteria that retain the crystal violet dye do so because of a thick layer of peptidoglycan and are called Gram-positive bacteria. In contrast, Gram-negative bacteria do not retain the violet dye and are colored red or pink. Compared with Gram-positive bacteria, Gram-negative bacteria are more resistant against antibodies because of their impenetrable cell wall. These bacteria have a wide variety of applications ranging from medical treatment to industrial use and Swiss cheese production. Gram-negative bacteria have a lipopolysacharide layer outside the peptidoglycan layer.

Answer 132

Endotoxins are normal gram negative bacteria outer membrane components that break down. Exotoxins are used for a bacterial speciaes to compete with another bacterial species.

Answer 133

Pilli are long projections on the bacterial surface involved in the bacteria being ble to attach to different surfaces. The sex pillus is a special pilus attaching F+ (male) and F- (female) bacteria which facilitates the formation of conjugation bridges.

Answer 134

**_Fimbriae_** are smaller structures that are not involved in locomotion or conjugation but are involved in adhering to surfaces.

Answer 135

Bacteria that thrive at very ow temperatures (near 0°C) are called **_psychrophiles_**.

Answer 136

"**_Troph_**" is a latin root meaning "eat".

Answer 137

**_Autotrophs_** utilize CO₂ as their carbon source.

Answer 138

**_Heterotrophs_** rely on organic nutrients (glucose, for example) created by other organisms.

Answer 139

**_Chemotrophs_** get their energy from chemicals.

Answer 140

Bacteria which require oxygen are called **_obligate aerobes_**.

Answer 141

**_Facultative anaerobes_** will use oxygen when it's around, but they don't need it.

Answer 142

**_Tolerant anaerobes_** can grow in the presence or abscence of oxygen but do not use it in their metabolism.

Answer 143

**_Obligate anaerobes_** are poisoned by oxygen.

Answer 144

Lag Phase Bacteria do not grow during the lag phase. However, they do adjust to their environment and metabolize, that is, produce vitamins and amino acids needed for division. They begin making copies of their DNA, and if the environment supplies plenty of nutrients, the lag phase may be very short. Then the bacteria will proceed to the next phase of their life. Log or Exponential Phase During the log or exponential phase, bacteria multiply rapidly, even exponentially. The time it takes for a culture to double is called "generation time," and under the best conditions, the fastest bacteria can double in about 15 minutes. Other bacteria take days. Within a bacterium, the DNA copy drifts to the opposite side of the membrane. The bacterium then pulls apart, creating two identical "daughter cells," which begin dividing anew. This process is called binary fission. Stationary Phase During the stationary phase, bacteria growth dwindles. Due to accumulating waste and a lack of space, bacteria cannot maintain the clip of the log or exponential phase. If the bacteria moves to another culture, however, rapid growth may resume. Death Phase During the death phase, bacteria lose all ability to reproduce, which becomes their death knell. Like the log or exponential phase, bacterial death may occur as rapidly as their growth.

Answer 145

An endospore is a dormant, tough, and non-reproductive structure produced by some bacteria in the phylum Firmicutes.[1][2] The name "endospore" is suggestive of a spore or seed-like form (endo means within), but it is not a true spore (i.e., not an offspring). It is a stripped-down, dormant form to which the bacterium can reduce itself. Endospore formation is usually triggered by a lack of nutrients, and usually occurs in gram-positive bacteria. In endospore formation, the bacterium divides within its cell wall, and one side then engulfs the other.[3] Endospores enable bacteria to lie dormant for extended periods, even centuries. The metabolic reactivation of an endospore is called **_germination_**.

Answer 146

Bacteria have three mechanisms for acquiring new genetic material: **_transduction_**, **_transformation_**, and **_conjugation_**.

Answer 147

A cell with the F factor integrated into its genome is called an **_Hfr_** (**_high frequency of recombination_**) cell.

Answer 148

Smooth endoplasmic reticulum (SER), meshwork of fine disklike tubular membrane vesicles, part of a continuous membrane organelle within the cytoplasm of eukaryotic cells, that is involved in the synthesis and storage of lipids, including cholesterol and phospholipids, which are used in the production of new cellular membrane. The smooth endoplasmic reticulum (SER) is distinguished from the rough endoplasmic reticulum (RER), the other basic type of endoplasmic reticulum, by its lack of ribosomes, which are protein-synthesizing particles that can be found attached to the outer surface of the RER to give the membrane its “rough” appearance. SER occurs both in animal and in plant cells.

Answer 149

Golgi apparatus (general structure; role in packaging, secretion, and modification of glycoprotein carbohydrates) looks like stacks of pancakes. modifies and/or secretes macromolecules for the cell. RER make protein → modified in the Golgi → buds off golgi and secreted out of cell by exocytosis. Glycoprotein = protein with attached saccharides. Golgi can glycosylate proteins as well as modifying existing glycosylations. Glycosylation affects protein's structure, function, and protect it from degradation.

Answer 150

Peroxisomes have two functions: break down fatty acids to be used for forming membranes and as fuel for respiration; and transfer hydrogen from compounds to oxygen to create hydrogen peroxide and then convert hydrogen peroxide into water.

Answer 151

The nucleolus ("little nucleus") is a region within the nucleus which functions as a ribosome factory. There is no membrane separating the nucleolus from the rest of the nucleus.

Answer 152

Surrounding the nucleus and separating it from the cytoplasm is the **_nuclear envelope_**, composed of two lipid bilayer membranes. The inner nuclear membrane is the surface of the envelope facing the nuclear interior, and the outer nuclear membrane faces the cytoplasm. The membrane of the **_endoplasmic reticulum_** is at points continuous with the outer nuclear membrane, making the interior of the **_ER_** (the lumen of the **_ER_**) contiguous with the space between the two nuclear membranes.

Answer 153

Proteins with a **_nuclear localization sequence_** are translated on cytoplasmic ribosomes and then imported into the nucleus by specific transport mechanisms.

Answer 154

The **_smooth_** **_ER_** is not actively involved in protein processing but can contain enzymes involved in steroid hormone biosynthesis (gonads) or in the degradation of environmental toxins (liver).

Answer 155

All proteins start translation in the cytoplasm; however, some proteins (secreted proteins and lysosomal proteins) have an amino acid sequence at their N-terminus called a **_signal sequence_**. The **_signal sequence_** of a nascent polypeptide is recognized by the **_signal recognition particle_** (**_SRP_**), which bind to the ribosome. The rough ER has **_SRP_** receptors that dock the **_ribosome-SRP_** complex on the cytoplasmic surface (along with the nascent polypeptide and mRNA). Translation then pushes the polypeptide, **_signal polypeptide_** first, into the ER lumen. After translation is complete, the **_signal peptide_** is removed from the polypeptide by a signal peptidase in the ER lumen.

Answer 156

The default for proteins that go through the secretory path is the plasma membrane. **_Targeting signals_** are needed if a protein is going through that path needs to end up elsewhere (e.g., the Golgi, the ER, the lysosome). Second, proteins that are made in teh cytoplasm but need to be sent to an organelle that is not part of the secretory path (e.g., the nucleus, mitochondria, or peroxisomes) require sequences called **_localization signals_**.

Answer 157

Free ions in solution are called **_electrolytes_** because the solution can conduct electricity.

Answer 158

Solutes that dissociate completely (like ionic substances) are called **_strong electrolytes_**, and those that remain ion paired to some extent are called **_weak electrolytes_**.

Answer 159

The **_van't Hoff_** (or **_ionizability_** factor) factor (***_i_*** ) tells us how many ions one unit of a substance will produce in a solution.

Answer 160

Colligative properties Colligative properties = properties that depend on the # of solute particles, but not on the type. Solute particles in solution like to keep the solution in liquid phase. This is why it makes it harder to boil (raises its boiling point) and also makes it harder to freeze (lowers the freezing point). Lowering the vapor pressure is just another fancy name for raising the boiling point. Van't Hoff Factor (i): all colligative properties take into consideration of the Van't Hoff factor. Basically, it means convert concentration to reflect the total number of particles in solution. For example, glucose has i of 1 because it doesn't break up in solution. NaCl has i of 2, because in solution, it breaks up into 2 particles Na+ and Cl-.vapor pressure lowering (Raoult's law) P = χsolvent·P°solvent ΔP = χsolute·P°solvent P is the vapor pressure. ΔP is the decrease in vapor pressure. χsolute = mol fraction of the solute = # mols of solute / # total mols of both solute and solvent χsolvent = mol fraction of the solvent = # mols of solvent / # total mols of both solute and solvent P°solvent is the vapor pressure of the pure solvent alone. When you are calculating χsolute, make sure you take into account of van't Hoff. ie. 1 mols of NaCl in solution is actually 2 mols of particles. boiling point elevation (deltaTb = kb\*m \*i) ΔTb = kb·m·i ΔTb is the increase in boiling point. kb is the molal boiling point constant (like almost every other constants, the MCAT will give it to you). m is the molality (mol solute/kg solvent). i is van't Hoff factor. freezing point depression (deltaTf = -kf\*m \*i) ΔTf = -kf·m·i ΔTf is the decrease in freezing point (the negative sign shows that the change is a decrease). kf is the molal freezing point constant. m is the molality (mol solute/kg solvent). i is van't Hoff factor. osmotic pressure π = MRT \*i π is the osmotic pressure. M is the molarity in mol/L. R is ideal gas constant. T is the temperature in K. Osmotic pressure determines whether and in what direction osmosis will occur. Osmosis is the movement of solvent across a semi-permeable membrane from an area of low solute concentration (high solvent concentration) to an area of high solute concentration (low solvent concentration). Solvent will move from an area with low π value to an area with high π value.

Answer 161

**_Osmosis_** describes the net movement of water across a semipermeable membrane from a region of low solute concentration to a region of higher solute concentration in an effort to dilute the higher concentration solution.

Answer 162

There are two types of passive transport: **_simple diffusion_** and **_facilitated diffusion_**.

Answer 163

The **_microtubule_** is a hollow rod composed of two globular proteins: **_a-tubulin_** and **_B-tubulin_**, polymerized noncovalently. One end of a **_microtubule_** is anchored to the **_microtubule organizing center_** (**_MTOC_**), located near the nucleus. Within the **_MTOC_** is a pair of **_centrioles_**. Each **_centriole_** is composed of a ring of nine **_microtubule_** triplets.

Answer 164

The centromere of each chromosome contains a **_kinectochore_** which is attached to the spindle by tiny microtubules called **_kinectochore_** fibers.

Answer 165

25nm diameter for microtubules 10nm diameter for intermediate filaments 7nm diameter for microfilaments

Answer 166

S phase (Synthesis Phase) is the phase of the cell cycle in which DNA is replicated, occurring between G1 phase and G2 phase.[1] Since accurate duplication of the genome is critical to successful cell division, the processes that occur during S-phase are tightly regulated and widely conserved.

Answer 167

The relatively brief M phase consists of nuclear division (karyokinesis). It is a relatively short period of the cell cycle. M phase is complex and highly regulated. The sequence of events is divided into phases, corresponding to the completion of one set of activities and the start of the next. These phases are sequentially known as: * prophase, * prometaphase, * metaphase, * anaphase, * telophase

Answer 168

The gap phases plus the S phase together form **_interphase_**.

Answer 169

The G0 phase describes a cellular state outside of the replicative cell cycle. Classically, cells were thought to enter G0 primarily due to environmental factors, like nutrient deprivation, that limited the resources necessary for proliferation. Thus it was thought of as a resting phase. G0 is now known to take different forms and occur for multiple reasons. For example, most adult neuronal cells, among the most metabolically active cells in the body, are fully differentiated and reside in a terminal G0 phase. Neurons reside in this state, not because of stochastic or limited nutrient supply, but as a part of their internal genetic programming.

Answer 170

During G1 phase, the cell grows in size and synthesizes mRNA and proteins (known as histones) that are required for DNA synthesis. Once the required proteins and growth are complete, the cell enters the next phase of the cell cycle, S phase. The duration of each phase, including the G1 phase, is different in many different types of cells. In human somatic cells, the cell cycle lasts about 18 hours, and the G1 phase takes up about 1/3 of that time.

Answer 171

Gap 2 (G2): During the gap between DNA synthesis and mitosis, the cell will continue to grow and produce new proteins. At the end of this gap is another control checkpoint (G2 Checkpoint) to determine if the cell can now proceed to enter M (mitosis) and divide.

Answer 172

**_The G1 Checkpoint_** * The G1 checkpoint determines whether all conditions are favorable for cell division to proceed. The G1 checkpoint, also called the restriction point (in yeast), is a point at which the cell irreversibly commits to the cell division process. External influences, such as growth factors, play a large role in carrying the cell past the G1 checkpoint. The cell will only pass the checkpoint if it is an appropriate size and has adequate energy reserves. At this point, the cell also checks for DNA damage. A cell that does not meet all the requirements will not progress to the S phase. The cell can halt the cycle and attempt to remedy the problematic condition, or the cell can advance into G0 (inactive) phase and await further signals when conditions improve. * If a cell meets the requirements for the G1 checkpoint, the cell will enter S phase and begin DNA replication. This transition, as with all of the major checkpoint transitions in the cell cycle, is signaled by cyclins and cyclin dependent kinases (CDKs). Cyclins are cell-signaling molecules that regulate the cell cycle. **_The G2 Checkpoint_** * The G2 checkpoint bars entry into the mitotic phase if certain conditions are not met. As with the G1 checkpoint, cell size and protein reserves are assessed. However, the most important role of the G2 checkpoint is to ensure that all of the chromosomes have been accurately replicated without mistakes or damage. If the checkpoint mechanisms detect problems with the DNA, the cell cycle is halted and the cell attempts to either complete DNA replication or repair the damaged DNA. If the DNA has been correctly replicated, cyclin dependent kinases (CDKs) signal the beginning of mitotic cell division. **_The M Checkpoint_** * The M checkpoint occurs near the end of the metaphase stage of mitosis. The M checkpoint is also known as the spindle checkpoint because it determines whether all the sister chromatids are correctly attached to the spindle microtubules. Because the separation of the sister chromatids during anaphase is an irreversible step, the cycle will not proceed until the kinetochores of each pair of sister chromatids are firmly anchored to at least two spindle fibers arising from opposite poles of the cell.

Answer 173

Mitosis is divided into four phases: **_prophase_**, **_metaphase_**, **_anaphase_**, and **_telophase_**.

Answer 174

**_P53_** is an example of a product of a common tumor suppressor gene. Though normally at low levels in cells, its production is scaled up when genetic damage or oncogene activity is detected, and if insufficient repair is not possible, **_p53_** will cause the cell to die in a process referred to as apoptosis.

Answer 175

Each human has **_23_** pairs of chromosomes (**_22_** pairs of autosomes and 1 pair of sex chromosome). Different versions of a gene are called **_alleles_**. The two nonidentical copies of a chromosome are called **_homologous chromosomes_**.

Answer 176

If an allele is the one expressed in the phenotype, regardless of what the second allele carried is, the expressed allele is referred to as **_dominant_**. An allele that is not expressed in the heterozygous state is referred to as **_recessive_**.

Answer 177

A failure of chromosomes to separate correctly during meiosis is called **_nondisjunction_**.

Answer 178

The progeny of one test cross is called the **_F1 generation_**.

Answer 179

Some alleles of genes display neither dominant nor recessive patterns of expression. If the phenotype of a heterozygote is a blended mix of both alleles, this is called **_incomplete dominance_**, and the alleles for that trait are given different, upper-case letters.

Answer 180

Closely related to incomplete dominance is codominance, in which both alleles are simultaneously expressed in the heterozygote. We can see an example of codominance in the MN blood groups of humans (less famous than the ABO blood groups, but still important!). A person's MN blood type is determined by his or her alleles of a certain gene. An L^MLML, start superscript, M, end superscript allele specifies production of an M marker displayed on the surface of red blood cells, while an L^NLNL, start superscript, N, end superscript allele specifies production of a slighly different N marker. Homozygotes (L^ML^MLMLML, start superscript, M, end superscript, L, start superscript, M, end superscript and L^NL^NLNLNL, start superscript, N, end superscript, L, start superscript, N, end superscript) have only M or an N markers, respectively, on the surface of their red blood cells. However, heterozygotes (L^ML^NLMLNL, start superscript, M, end superscript, L, start superscript, N, end superscript) have both types of markers in equal numbers on the cell surface. As for incomplete dominance, we can still use Mendel's rules to predict inheritance of codominant alleles. For example, if two people with L^ML^NLMLNL, start superscript, M, end superscript, L, start superscript, N, end superscriptgenotypes had children, we would expect to see M, MN, and N blood types and L^ML^MLMLML, start superscript, M, end superscript, L, start superscript, M, end superscript, L^ML^NLMLNL, start superscript, M, end superscript, L, start superscript, N, end superscript, and L^NL^NLNLNL, start superscript, N, end superscript, L, start superscript, N, end superscript genotypes in their children in a 1:2:11:2:11, colon, 2, colon, 1 ratio (if they had enough children for us to determine ratios accurately!)

Answer 181

Genes that are located on the same chromosome may not display independent assortment, however. The failure of genes to display independent assortment is called **_linkage_**.

Answer 182

A **_translocation_** occurs when a piece of one chromosome is moved onto another chromosome.

Answer 183

**_Recombination_** is a process by which pieces of DNA are broken and recombined to produce new combinations of alleles. This recombination process creates genetic diversity at the level of genes that reflects differences in the DNA sequences of different organisms. In eukaryotic cells, which are cells with a nucleus and organelles, recombination typically occurs during meiosis. Meiosis is a form of cell division that produces gametes, or egg and sperm cells. During the first phase of meiosis, the homologous pairs of maternal and paternal chromosomes align. During the alignment, the arms of the chromosomes can overlap and temporarily fuse, causing a crossover. Crossovers result in recombination and the exchange of genetic material between the maternal and paternal chromosomes. As a result, offspring can have different combinations of genes than their parents. Genes that are located farther apart on the same chromosome have a greater likelihood of undergoing recombination, which means they have a greater recombination frequency.

Answer 184

The farther apart two genes are on a chromosome, the more likely **_recombination_** will occur between the genes during **_meiosis_**.

Answer 185

The **_allele frequency_** is the number of copies of a specific allele divided by the total number of copies of the gene in a population.

Answer 186

**_Hardy-Weinberg Law_** states that the frequency of alleles in the gene pool of a population will not change over time, provided that a number of assumptions are true. * Also independent assortment is not a requirement of Hardy-Weinberg.

Answer 187

After **_one_** generation, a population will reach **_Hardy-Weinberg Equilibrium_**, in which allele frequencies no longer change.

Answer 188

Natural selection acts on **_phenotypes_**, not genotypes.

Answer 189

A mutation must occur in the **_germ line_** to introduce a new allele into a population.

Answer 190

**_Homologous structures_** are physical features shared by two different species as a result of a common ancestor. **_Analagous structures_** serve the same function in two different species but _NOT_ due to common ancestry.

Answer 191

**_Pleiotropy_** (from Greek πλείων pleion, "more", and τρόπος tropos, "way") occurs when one gene influences two or more seemingly unrelated phenotypic traits. Such a gene that exhibits multiple phenotypic expression is called a pleiotropic gene. Mutation in a pleiotropic gene may have an effect on several traits simultaneously, due to the gene coding for a product used by a myriad of cells or different targets that have the same signaling function.

Biology and Biochemistry Flashcards

Memorize Amino Acids, electron transport Chain, metabolism, etc. (280 cards)