AAMC QP Biology 1

Question 1

freeze tolerant animals

• why is freezing an issue for cells
• how do these animals tolerate the cold

Answer 1

An animal that can permit some freezing of its body fluids and sustain life is said to be freeze-tolerant.

Formation of ice within cells disrupts structural organization and metabolic function, and ultimately causes cell death.

These animals can induce accelerated glucose release from glycogen stores, thus raising the osmotic pressure of body fluids and dehydrates cells protecting them from freezing; thus, it acts as an antifreeze by depressing the freezing point of cells.
– Movement of water from inside cells to the extracellular fluid ensures that the latter is frozen rather than the cells themselves, thus increasing cell survivability.

Question 2

extracellular fluid

Answer 2

Extracellular fluid includes lymph and plasma. Basically everything that is outside of the cell.

Question 3

why do we sweat

Answer 3

Water is lost through the skin primarily as a means to keep the body at normal temperatures. Therefore, raising the environmental temperature would cause a person to perspire, releasing water to the environment where it can evaporate and cool down the body.

Question 4

Conjugation

Answer 4

found in gram-negative bacteria; provides advantages of sexual reproduction onto bacteria

involves production of a special conjugation pilus (sex pilus) by one bacterium and transfer through it of DNA to another bacterium

requires special genes for the pilus and these are usually present on a plasmid, a separate extragenomic strand of DNA not incorporated into the bacterium’s own DNA
– plasmid is referred to as the fertility or F factor

Question 5

transformation

transduction

Answer 5

In transformation bacteria take up DNA from their surroundings, the media in which they are immersed.

Vs. Transduction is the process whereby genes are transferred by a virus.

Question 6

antisense drug

Answer 6

works to prevent the expression of undesirable genes but does nothing to remedy the problem of a gene that produces an ineffective product (eg by mutation)

note: The only way to cure the latter situation would be to add a gene or gene product that could lead to the production of effective enzymes to replace the ones that do not function correctly.

Question 7

qualities of a complementary strand

Answer 7

Complementary strands will have the other half of the base-pairs but will also be in the OPPOSITE DIRECTION!

Question 8

where can myoglobin be found

Answer 8

Myoglobin is the substance that holds oxygen in the muscles and organs – not bone, which is the location of red blood cell development (thus they are unable to hold oxygen at the moment).

Question 9

what do the following brain structures control

• brain stem
• cerebellum
• hypothalamus

Answer 9

brain stem = control of heart rate and other essential survival functions

cerebellum = muscle coordinator and other motor movement

hypothalamus = appetite, thirst, temperature

Question 10

diff btwn anaphases btwn meiosis and mitosis

Answer 10

During anaphase of mitosis, sister chromatids are pulled apart at the centromeres, each becoming an independent chromosome in the two diploid daughter cells.

During anaphase I of meiosis I, homologous pairs of chromosomes are separated into the two daughter cells. However, each chromosome still consists of two sister chromatids joined to each other at the centromere.
– It is not until anaphase II of meiosis II that the centromere is split and the sister chromatids separate.

Question 11

what is the function of mammalian skin

Answer 11

Mammalian skin is involved with touch sensation, with protection from disease, and internal injury (D). However, in mammals, skin is not responsible for exchanging oxygen and carbon dioxide with the environment.

Question 12

why is inbreeding dangerous for a population

Answer 12

Deleterious genes are generally rare because they tend to be eliminated through natural selection. Only when an organism is homozygous (has two copies of a gene, one from each parent) does a recessive gene reveal its presence. Because recessive genes can be masked by dominant genes, they are less exposed to natural selection. So most organisms carry many deleterious recessive genes.

The chances of having offspring that are homozygous for a given recessive gene are rare when a mate is chosen randomly from the population. The chances of getting a pair of deleterious recessive genes increase enormously when the mate is a relative, because relatives are likely to have a similar genotype.

Question 13

how does blood pressure affect water reabsorption in the kidneys

Answer 13

Increasing blood pressure should increase flow of fluid through the kidney system and decrease, rather than increase, water reabsorption.

Question 14

what determines blood pressure

Answer 14

cardiac output and resistance to blood flow

Cardiac output (stroke volume x heart rate) determines the amount of blood pumped into the system by the heart per unit time.

The resistance to blood flow is primarily determined by sphincters that regulate how much blood is allowed to flow through a certain area of the body

Thus blood pressure equals total peripheral resistance times cardiac output, a relationship analogous to Ohm’s law for electrical circuits.

Question 15

vasoconstriction vs dilation

+ their relationship w heat

Answer 15

Vasoconstriction, the narrowing of a vessel, restricts blood flow to an organ and can increase blood pressure
– involved in heat conservation bc decreased blood within constricted vasculature restricts the amount of heat that is allowed to escape into the environment

Vs. Vasodilation increases blood flow to both the muscle during exercise and the skin during blushing.
– involved in heat loss bc presence of increased blood within dilated vasculature in cutaneous tissue allows heat to escape from the surface of the body into the environment

Question 16

how does sperm move

Answer 16

sperm motility requires large amounts of ATP as evidenced by the high concentration of mitochondria in the sperm midpiece.

Question 17

major liver functions

gall bladder function

Answer 17

detoxification of poisons

production of bile, which facilitates fat absorption in the small intestine by breaking large fat droplets into smaller ones

The gall bladder is an organ that stores bile produced by the liver.

Question 18

are mutations heritable

Answer 18

yes

Question 19

how are 3D structures of a protein stabilized

- also, denaturation

Answer 19

by covalent bonds and noncovalent interactions between different regions of the linear peptide

denaturation = disorganization of proteins via heat input or pH change

Question 20

albumin

Answer 20

one of the major plasma proteins that regulate osmolarity of the blood, acting as a marker of where water should flow

An increase in plasma albumin will upset the osmotic balance because the blood will become hypertonic with respect to the tissue. Water will have to flow into the bloodstream from the tissues to reestablish equilibrium.

Vs. a decrease in plasma albumin will create a hypotonic bloodstream, such that water will flow from the blood into the tissues to reestablish equilibrium.

Question 21

one similarity and one diff btwn bacterial and human cells

Answer 21

the ability to produce ATP via ATP synthase is common to both bacterial and human cells. Both types of cells possess a membrane-embedded electron transport chain capable of generating a H+ gradient, which drives synthesis of ATP via ATP synthase. This ATP synthesis takes place on the plasma membrane of bacteria and on the inner mitochondrial membrane in human cells.

In contrast, the chemical composition of prokaryotic and eukaryotic ribosomes, although similar, is distinct enough that several types of antibiotics are able to preferentially target prokaryotic ribosomes over eukaryotic ribosomes.

Question 22

calcitonin

Answer 22

Calcitonin reduces bone resorption. Bone resorption occurs when the level of calcium in the blood plasma is low, but resorption is not needed when the level of calcium is high. Therefore, resorption would be reduced by calcitonin under conditions in which the level of calcium in the plasma is high.

Question 23

how would the loss of the parathyroid gland affect us

Answer 23

Loss of the parathyroid gland would lead to hypocalcemia, a condition of low blood calcium, resulting from the lack of parathyroid hormone.

This would cause increased neuromuscular excitability because of the change in membrane potential, which under normal physiological conditions, is partially kept in balance with extracellular calcium.

Question 24

how do we determine whether one species is separate from another

Answer 24

two species are related if they are able to successfully breed and produce fertile offspring

if their offspring is nonviable or sterile, the two species are considered SEPARATE / UNRELATED

Question 25

The sequence of events in the human menstrual cycle involves close interaction among which organs?

Answer 25

HYPOTHALAMUS – PITUITARY – OVARY

The HYPOTHALAMUS regulates release of hormones involved in menstruation by secreting hormone-releasing factors into the pituitary portal circulation.

Gonadotropic hormones: FSH and LH produced by the PITUITARY gland

Ovarian hormones: estrogen and progesterone; produced in various locations at diff times

Question 26

where is uracil found

Answer 26

in RNA not DNA, thus only found in the nucleus and will be transcribed + subsequently removed in the ribosome

Question 27

endosymbiotic theory

Answer 27

eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like modern-cell mitochondria / chloroplasts

Instead of being digested, the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells, which created a symbiotic relationship.

Question 28

What type or class of chemical messenger traveling in the blood would most probably link the brain with the digestive tract and fat cells in the control of body weight?

A) Hormones
B) Neurotransmitters
C) Digestive enzymes
D) Protein receptors

Answer 28

Hormones - most hormones travel from the endocrine gland in which they were produced, through the blood, to their target tissue

Vs. Neurotransmitters by definition are released at neural synapses

Vs. Digestive enzymes are found in the digestive tract, but they do not travel through the bloodstream.

Vs. Protein receptors interact with chemical messengers but are not the signal themselves.

Question 29

glycogen

Answer 29

form of glucose that is synthesized, stored, and broken down in the liver

Question 30

Tidal volume

Answer 30

maximal amount of air in the lungs after inspiration, including the residual volume it must have after expiration.

Thus, if you have a tidal volume of 800 mL per breath and a residual volume of 150 mL, you are really only breathing in 650 mL per breath.

Question 31

describes the roles of the proteins actin and myosin during muscular contraction

Answer 31

according to the sliding filament model (aka cross linking bridge formation model), bridges between actin and myosin form, break, and re-form, leading to a shortening of muscle sarcomeres.

Question 32

optic cup

Answer 32

The optic cup develops from a bulge on the side of the developing brain, which influences the overlying ectoderm to produce the lens. It is therefore an example of cells inducing neighboring cells to differentiate.

Question 33

what hormone triggers ovulation

Answer 33

surge of concentration of the luteinizing hormone

Question 34

how does dehydration affect the kidneys

Answer 34

severe dehydration greatly reduces the volume of filtrate moving through the nephrons of the kidney

If fluid volume is too drastically reduced, the kidney will be unable to effectively do its job of filtering and maintaining homeostasis within bodily fluids.

Question 35

superantigens

Answer 35

Superantigens bypass a processing step normally performed by antigen-presenting cells, and also differ from normal antigens by binding to T cells outside the standard antigen binding site.

Because this unique type of binding activates approximately 20% of the T lymphocytes, as opposed to 1 in 100,000 T cells activated by conventional antigenic stimulation, superantigens are considered nonspecific stimulators

Negative effects of nonspecific stimulation by superantigens occur because the activation of so many T cells causes the release of massive levels of cytokines.

Question 36

bile

Answer 36

made in liver and stored in gallbladder for release during digestion

The bile salts are amphipathic

• • interact w lipids to form an emulsion
• • interact w aqueous solution in the gut and its digestive enzymes, thus leading to the breakdown of the lipids

Question 37

how do post translational modifications alter histones

Answer 37

recall that histones are positively charged, which allow them to interact / regulate the condensing of the negatively charged nucleic acids found in DNA

Posttranslational modifications that alter the charge on histone proteins affect their ability to condense DNA.

Question 38

identify the characteristic that differentiates growing, developing long bones from adult bones

Answer 38

Long bones grow via endochondral ossification, which requires cartilaginous growth plates at the ends of long bones, that thicken as cartilage and later become ossified. Dividing bone cells and haversion canals can be present in fully ossified adult bones.

Haversion canals: any of the minute tubes which form a network in bone and contain blood vessels.