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Flashcards in Biology / Biochemistry Deck (73):

What is required for extracellular binding of hormones?



Some enzymes experience a decrease in activity proportional to the concentration of their products. This phenomenon could be an example of what process?

A. Feedback inhibition.

B. Non-competitive inhibition.

C. Allosteric activation.

D. Both A and B.


Many cellular enzymes exhibit decreasing activity with increasing levels of reaction product. This feedback inhibition help regulate the activity of enzymatic processes. Often this process occurs through non-competitive inhibition. The product of the chemical reaction binds to the enzyme in a location other than the active site, which causes a conformational change in the enzyme and decreases enzymatic activity. Allosteric activation describes a process in which enzymatic activity is increased because of binding of some molecule to a site other than the active site.


Which of the following is true about cholesterol?

A Cholesterol always increases membrane fluidity in cells.
B Cholesterol is a steroid precursor.
C Cholesterol is a precursor for vitamin A, which is produced in the skin.
D Cholesterol interacts only with the hydrophobic tails of phospholipids.

Cholesterol is a steroid precursor that has variable effects on membrane fluidity depending on temperature, eliminating choice (A). It interacts with both the hydrophobic tails and the hydrophilic heads of membrane lipids, nullifying choice (D). It is also a precursor for vitamin D (not vitamin A), which can be produced in the skin in a UV-driven reaction, eliminating choice (C).


What proportion of offspring with the genotype AABBCC will result from a trihybrid cross for the unlinked genes A, B, and C?


This question tests your ability to calculate the probability of a possible genotype resulting from a trihybrid cross between two heterozygotes. One method to determine the probability is to make a Punnett square. An organism that is heterozygous for three genes can produce eight different gamete possibilities. Thus, resultant Punnett square would contain an 8×8 table with a total of 64 genotype combinations. A more efficient method is to calculate the probability of each event occurring separately and then use the rule of multiplication to determine the likelihood of all three events occurring at the same time.

Probability of obtaining an AA genotype from a cross between Aa and Aa = ¼

Probability of obtaining a BB genotype from a cross between Bb and Bb = ¼

Probability of obtaining a CC genotype from a cross between Cc and Cc = ¼

Total probability of all three possibilities = ¼ x ¼ x ¼ = 1/64

Therefore, D is the correct answer.


Which ion channels are responsible for maintaining the resting membrane potential?

Ungated channels
Voltage-gated channels
Ligand-gated channels
No ion channels are involved in maintenance of the resting membrane potential.

[A] is the correct answer.

The resting membrane potential is displayed by cells that are not actively involved in signal transduction. Ungated or “leak” channels permit limited free flow of ions, while the sodium–potassium pump is also active and corrects for this leakage. Ligand-gated and voltage-gated channels are involved in cell signaling and in the pacemaker potentials of certain cells, but cause deviation from—not maintenance of—the resting membrane potential.


How do chylomicrons and VLDLs differ?

Chylomicrons contain apoproteins, VLDLs do not.
Chylomicrons are synthesized in the intestine, VLDLs are synthesized in the liver.
Chylomicrons transport triacylglycerol, VLDLs transport cholesterol.
VLDLs are another term for chylomicron remnants; they differ in age.

[B] is the correct answer.

Chylomicrons and VLDLs are very similar. Both contain apolipoproteins and primarily transport triacylglycerol, eliminating choices (A) and (C). The only major difference between them is the tissue of origin. Chylomicrons transport dietary triacylglycerol and originate in the small intestine, while VLDLs transport newly synthesized triacylglycerol and originate in the liver.


The basic premise of cladistics is organisms that are closely related share a common evolutionary history. The characteristics that are shared by group members and derived from their ancestors are called:

A. Plesiomorphies.

B. Synapomorphies.

C. Apomorphies.

D. Autapomorphies.

B. Synapomorphies

Plesiomorphies are characteristics that are original in the organism. While apomorhic means “derived characteristic”, the prefix syn- alters the meaning to “shared derived characteristic.” Using the prefix aut- causes the meaning to change to “self-derived characteristic” implying that it isn’t shared by another group. Homoplasy or homoplastic characteristics are shared among groups, but weren’t derived from an ancestral source.


Approximately what is the energy density of a lipid in kcal/g?

~9 kcal/g


Approximately what is the energy density of a carbohydrate in kcal/g?

~4 kcal/g


Approximately what is the energy density of a protein in kcal/g?

~4 kcal/g


What are the three defining features of eukaryotic cells?

1. Membrane-bound nucleus
2. Organelles
3. Mitotic division

(Exceptions include cells such as erythrocytes)


What type of enzyme is able to reverse the orientation (Or 'flip') of sections of the cell membrane? In other words, which can flip pieces so that the side that was originally facing outside the cell is now facing inside?



What is the composition and function of a lipid raft?

Mainly composed of cholesterol and sphingomyelins.

Functions include increased membrane fluidity and signaling.


During mitosis, what is a purpose of the mitotic aster spindle fibers that do not bind the kinetochore to divide sister chromatids?

To anchor the centrosome to the cell membrane.


What is the name for the points at which crossing over occurs in homologous chromosomes during meiosis?



What colors are produced during a gram staining of gram positive and gram negative bacteria, respectively?

Purple, pink (Pink only following a counterstain of safranin).


Which is more resilient? Membrane-encapsulated viruses or non-membrane-bound?

Non-membrane-bound viruses are much more resilient to desiccation, heat, and light, and they can survive intact on their own for long periods of time.


Define positive-sense RNA (In terms of viral infection).

ssRNA that is basically ready-made RNA that is immediately ready for translation.


Define negative-sense RNA (In terms of viral infection).

ssRNA that is complementary to RNA and must be synthesized into RNA using RNA replicase supplied by the virion.


Which eukaryotic organelles have a double membrane? In other words, which eukaryotic organelles are surrounded by two lipid bilayers?

Nucleus, golgi apparatus, mitochondria, endoplasmic reticulum.


T/F Peroxisomes are surrounded by a double membrane?

False. Peroxisomes are surrounded by a single bilayer membrane.


Would the cytoplasm be better defined as a reducing or oxidizing environment?



Would the lumen of the RER be closer to the reducing cytoplasm or the oxidizing ECF?

The oxidizing ECF.


T/F Proteins can fit through gap junctions.



Describe the effects of cholesterol on membrane fluidity?

At high temperatures, the rigidity of cholesterol aids in decreasing membrane fluidity.
At low temperatures, cholesterol aids in increasing membrane fluidity.


Which of the following increases membrane fluidity?
Increased or decreased saturation of the fatty acid portions of the membrane phospholipids.

Decreased saturation (Increased number of kinks).


True / False. The production of acetyl-CoA from pyruvate is reversible?



Which cellular structure/region contains the most phosphate in the cell?
A. Cell membrane
B. Nucleus
C. Mitochondria
D. Cytosol

B. Nucleus


Secondary protein structure involves what type of intermolecular bond between what groups?

Hydrogen bonding between carboxylic acids and amine functional groups, NOT the side chains.


What are the four types of lipid relevant to the MCAT?

Fatty acids, cholesterols, eicosanoids, and terpenes


What are the carbon lengths of short, medium, and long fatty acid chains?

Short ≤ 5 carbons
Medium 6 - 12 carbons
Long 13 - 21 carbons


Describe the structure and function of sphingolipids. What is the simplest sphingolipid?

Structure: Generally found on the extracellular side of a membrane. Fatty acid attached to an amine.
Function: Cell signaling
Simplest: Ceramides


What are the most important eicosanoids? What do they do? What are they synthesized from?

Prostaglandins. Function to regulate inflammation.
Arachidonic acid (20 carbons)


Describe terpenes. Which vitamin is a terpene derivative and which is the precursor for cholesterol? What vitamin is derived from cholesterol?

Repeating isoprene units.
Vitamin A.
Squalene (30 carbons).
Vitamin D.


What are the main polysaccharides to know?

Starch (Amylose and amylopectin), glycogen, and cellulose.


What are the bonding and branching characteristics of amylose, amylopectin, glycogen, and cellulose?

Amylose: alpha(1-4), unbranched
Amylopectin: alpha(1-4) + alpha(1-6 branching)
Glycogen: Same as amylopectin but more branched.
Cellulose: Beta(1-4), unbranched


How is uracil different from thymine?

Uracil is demethylated.


Which carbon is deoxygenated in DNA?



RNA is most involved in:

Gene expression


Which two RNA types interfere with specific genes?

miRNA and siRNA which bind specific genes.


What is the name of the RNA precursor?

hnRNA (Heterogeneous RNA)


What is the difference between triglyceride micelles and phospholipid bilayers?
a. Steric hinderance
b. Hydrophilicity
c. Hydrophobicity
d. Non-covalent assemblies

a. Steric hinderance


Describe the food energy per gram in proteins, carbohydrates, and fats.

Proteins and carbohydrates:
4 kCal/g
8.8 kCal/g


What three major structural/functional features define eukaryotes?

A membrane-bound nucleus, organelles, and mitotic division


True / False The term 'cytoplasm' includes the cytosol, organelles, and nucleus?

False. The nucleus is not part of the cytoplasm.


Define mtDNA

Mitochondrial DNA


Through what mechanism does material enter the lysosome?



What are the folds and 'stacks' of the Golgi apparatus and endoplasmic reticulum known as?



What do peroxisomes do with very-long-chain fatty acids (>21 carbons)?

They break them down into medium-chain fatty acids.


What do peroxisomes do with ethanol?

They detoxify it.


Which cytoskeletal filament makes up much of the structure of a cell and facilitate intracellular transport?



True / False Both prokaryotic and eukaryotic flagella use a rotary motion and require the expenditure of ATP?

False. Eukaryotic flagella beat back and forth and do require the expenditure of ATP. Prokaryotic flagella use rotary motion and a proton gradient.


What pH is the lysosome interior?

4.5 - 5


What enzymes are responsible for inverting sections of the cell membrane so that what was facing out is now facing in, or vice versa?


(This is an energetically costly process)


Describe a lipid raft.

A raft in the cell membrane held together by large amounts of cholesterol and containing high concentrations of sphingomyelins


What happens in prophase?

The chromosomes condense and connect at the centromere.
The aster forms and attaches at the kinetochore.
The nuclear envelope and nucleolus disappear.


When does the final cell checkpoint occur?

During metaphase.


What happens in anaphase?

The sister chromatids are pulled apart.


What happens in telophase?

The opposite of prophase.


What is the name for crossing over points in meiosis?



Describe archea.

Extremophiles that inhabit areas of high salinity or extreme temperature.

They use a very broad range of energy sources.


What vitamins do gut bacteria help produce?

Vitamin K and B7


What is the difficulty of treating bacteria that release toxins?

Killing them off all at once may release a large quantity of toxins in the body.


What two chemicals are added in a Gram stain that will then be washed with ethanol or acetone?
Then what is the final counterstain used to mark the Gram-negative cells as pink?

Crystal violet and iodide



What color are the Gram-negative and Gram-positive cells after staining?

Gram-negative: pink
Gram-positive: purple


How can prokaryotes use aerobic respiration?

There can be an electron transport chain built into the cell membrane.


What are the three structures of the prokaryotic flagellum?

The basal body, the hook, and the filament


True / False Bacteria have a proper cytoskeleton.



What explains Griffith and Avery's experiments with heat-killed and non-heat-killed bacteria?

Transformation of genetic material from the environment.


Which is more vulnerable to environmental conditions, lipid-bound or non-lipid-bound viruses?

Lipid-bound are more vulnerable.


What is another name for the G0 phase?

Resting phase


Is the cytosol a reducing or oxidizing environment?



Does the RER lumen resemble the mitochondrial matrix, the cytosol, or the ECF?

The ECF. It must be an oxidizing environment (As opposed to the reducing environment of the cytosol) so that proper protein folding will take place (E.g. disulfide bonding).