MCAT Biology

Question 1

Describe eukaryotic nuclei

Answer 1

The nucleus is a membrane bound organelle which contains DNA. It is surrounded by a double membrane envelope which contains nuclear pores for selective two-way exchange of materials into and from the cytoplasm. DNA contains coding regions, genes. DNA is linear and is wound around organising proteins known as histones (beads on a string) which further condense into chromosomes. These are what will get acylated/methylated to expose or sequester DNA regions for different gene expression desires/demands.

Question 2

Where is ribosomal RNA synthesised

Answer 2

The nucleolus

Question 3

Describe the mitochondria

Answer 3

The mitochondria is the powerhouse of the cell. It has both an outer and inner membrane. The outermost serves as a barrier between the cytosol and the inner mitochondrial environment. The inner membrane is folded into cristae and contains the ETC. The space between the two membranes is the intermembrane space. The mitochondria function semi-autonomously and replicate independently of the nucleus and are examples of extranuclear inheritance. They are also what kick-starts the process of apoptosis.

Question 4

Describe lysosomes

Answer 4

Lysosomes are the garbage men of the cell. They contain hydrolytic enzymes which break down substrates. Often function alongside endosomes which have taken in debris from the ECF to degrade it. If the lysosomes release their hydrolytic enzymes, apoptosis will follow

Question 5

Describe the endoplasmic reticulum

Answer 5

The endoplasmic reticulum (ER) is a membrane contiguous with the nuclear envelope. It is folded and has the rough ER, which is a docking station for ribosomes, and the smooth ER which is used primarily for lipid synthesis and detoxification of certain drugs and poisons.

Question 6

Describe the golgi apparatus

Answer 6

The golgi apparatus receives materials transferred from the ER in the form of vesicles. These products enter the golgi and are modified using carbs, phosphates and sulfates to help designate a function/destination as well as attaching signal sequences. These are then repackaged into vesicles and directed to their needed location (other organelles, membrane, or secretion)

Question 7

Describe peroxisomes in eukaryotic cells

Answer 7

Peroxisomes contain hydrogen peroxide which is used to break down long fatty acid chains via beta-hydrolysis and helps in the synthesis of phospholipids

Question 8

What three parts of the eukaryotic cytoskeleton?

Answer 8

• Microfilaments
• Microtubules
• Intermediate filaments

Question 9

Describe microfilaments

Answer 9

Question 10

Describe microtubules

Answer 10

Question 11

Describe intermediate filaments

Answer 11

Intermediate filaments just help reinforce everything and bind membranes in place

Question 12

Describe epithelial tissues

Answer 12

• Epithelial tissue lines the body and it’s cavities and serves as a protection against pathogens and loss of water. In different organs they can absorb, secrete or even sense. They are tightly packed and are connected to an underlying connective tissue layer called the basement membrane.
• In most organelles they make up the parenchyma which is the functional parts of the organ. For example the hepatocytes of the liver, or the nephrons in the kidneys. They are often polarised, with a polar exterior and a non-polar interior.

Question 13

How do we classify epithelial tissues

Answer 13

Question 14

Describe connective tissues

Answer 14

Connective tissue serves as a supporting framework for the epithelial cells and sets them in position to allow for them to work. Connective tissues are the main contributors to the stroma or support structure. Things such as bone, cartilage, tendons, ligaments and adipose tissue are all examples of connective tissues. Most cells in connective tissues produce and secrete materials such as collagen and elastin to form the extracellular matrix.

Question 15

What are the two classifications of prokaryotic cells

Answer 15

Question 16

Describe gram negative prokaryote cell walls

Answer 16

Gram negative will appear pink-red when stained. Very thin and contain only some peptidoglycan which is separated from the cell membrane by the periplasmic space. They also have outer membranes containing phospholipid lipopolysaccharides which trigger an immune response in human beings.

Question 17

Describe gram positive prokaryote cell walls

Answer 17

Gram positive will appear purple when stained. Contains a thick layer of peptidoglycans which are made up of amino acids and sugars. It can aid a bacterial pathogen by providing protection which can be exploited by bacterial pathogens attempting to avoid host immune surveillance. Also contains lipoteichoic acid.

Question 18

What is the use of flagella with bacterium

Answer 18

Flagella , used for propulsion, is also used to identify bacteria. Directed by chemotaxis (the sensing of the chemical environment to direct direction of prokaryote to food or away from harm).

Question 19

What are plasmids

Answer 19

Plasmids are small, circular, double-stranded DNA molecules found in many bacteria and some eukaryotic cells. They exist independently of the bacterial chromosome and are capable of autonomous replication. Plasmids often carry non-essential but advantageous genes, such as those conferring antibiotic resistance, toxin production, or metabolic capabilities.

In bacteria, plasmids can be transferred between cells through processes like conjugation, allowing rapid genetic exchange and adaptation. Because of their ability to replicate independently and carry selectable markers, plasmids are widely used in molecular biology as vectors for gene cloning, expression, and genetic modification. Unlike the main bacterial genome, plasmids are typically much smaller and vary in copy number within a cell.

A subset of plasmids called episomes are capable of integrating into the genome of the bacterium

Question 20

What is binary fission

Answer 20

• Binary Fission is the simple asexual reproduction of prokaryotes. The circular chromosome attaches to the cell wall and replicates while the cell continues to grow in size. Eventually, the plasma membrane and cell wall begin to grow inward along the midline of the cell to produce two identical daughter cells.

Question 21

What are the three ways bacteria gain genetic diversity

Answer 21

• Transformation
• Conjugation
• Transduction

Question 22

Describe bacterial DNA transformation

Answer 22

Transformation results from the integration of foreign genetic material into the host genome using plasmids. Many gram negative rods are able to carry this out

Question 23

Describe bacterial DNA conjugation

Answer 23

Conjugation is the bacterial form of mating and it involves two cells forming a conjugation bridge to facilitate the transfer of genetic material and always goes unidirectionally from the donor male (+) to the recipient female (-) . The bridge is formed by sex pili which are extended by the donor male to bind to the female. This pili is formed by a gene called sex factor, and bacteria with sex factor is deemed + and acts as the male.

Question 24

Describe bacterial DNA transduction

Answer 24

Question 25

What are the phases of bacterial growth

Answer 25

Question 26

Generally describe viruses

Answer 26

Viruses are abiotic and contain no organelles or a nucleus. Their genetic information may be circular, linear, single or double stranded RNA or DNA. They outer layer is known as the capsid and is composed of phospholipids and virus-specific proteins but is overall very fragile. However, some viruses lack an envelope and are more resistant to sterilisation and are likely to persist on surfaces for an extended time. They are obligate intracellular parasites and must replicate genetic info within the host by hijacking their ribosomes. They then can produce viral progeny called virions which go on to infect other cells.

Question 27

Describe bacteriophages

Answer 27

Bacteriophages are the weird alien looking spider thing yk what I’m talking about. They have a tail sheath with acts as a syringe and injects the genetic material into the bacterium and the tail fibres help recognise and dock them to the host cell.

Question 28

Describe positive and negative sense RNA or DNA

Answer 28

Positive sense RNA or DNA can have their genome directly translated to functional proteins by the host ribosome , just like mRNA Negative sense RNA or DNA serve as a strand that acts as a template for synthesis of a complementary strand which can be used as a template for protein synthesis. They must carry an RNA replicase in the virion to ensure that the complementary strand is synthesised

Question 29

Describe retroviruses

Answer 29

Retroviruses are enveloped, single-stranded RNA viruses in the family Retroviridae; usually, the virion contains two identical RNA molecules. These viruses carry an enzyme known as reverse transcriptase, which synthesizes DNA from single-stranded RNA. The DNA then integrates into the host cell genome, where it is replicated and transcribed as if it were the host cell’s own DNA. It is a clever mechanism because the integration of the genetic material into the host cell genome allows the cell to be infected indefinitely, so the only way to remove the infection is to kill the infected cell.

Question 30

Describe virus entry/infection

Answer 30

Viruses infect specific cells by binding to particular receptors on the host cell. Without the correct receptors, a cell remains invisible to the virus. Once attached, enveloped viruses fuse with the plasma membrane to enter the cell or may be taken up via endocytosis. Bacteriophages use tail fibres to anchor to the bacterial membrane and inject their genome through a tail sheath, with some fibres possessing enzymatic activity to penetrate the cell wall. Depending on the virus, either the entire virion enters the cell, as with enveloped viruses like HIV, or only the genetic material is injected, as seen in bacteriophages.

Question 31

Describe virus activity after infection

Answer 31

Question 32

What are three ways viruses are released from their host cells

Answer 32

1. Viral invasion can initiate cell death which will expel the virions into the host ECF and they can go on to infect new cells 2. Host cell gets so packed with virions that it lyses and expels the virus. This is somewhat disadvantageous because they can no longer use that cell for reproduction. 3. The virus can leave the cell by fusing with the plasma membrane, called extrusion

Question 33

Describe the lytic life cycle of bacteriophages

Answer 33

During the lytic the bacteriophages just abuse the cells machinery until the cell becomes so chalk full of virions it lyses and releases the virions, viruses in this lytic phase are called “virulent”

Question 34

Describe the bacterial lysogenic cycle

Answer 34

If a virus doesn’t lyse the bacterium, it may integrate into the host genome as a provirus or prophage, initiating the lysogenic cycle. The viral genome is then replicated along with the host’s DNA during cell division. Though it can remain dormant indefinitely, environmental factors like radiation or chemicals may trigger the provirus to excise itself and enter the lytic cycle. As it leaves, the virus might carry host genes, enabling transduction between bacteria. While phages can kill their hosts, integration may benefit the bacterium by reducing susceptibility to superinfection by other phages, offering a potential evolutionary advantage.