MCAT Biology Flashcards

Question

In eukaryotes, which residues are most prone to phosphorylation?

Answer 1

Serine (S), tyrosine (Y), threonine (T)

Answer 2

Aldesterone is released from the adrenal cortex in response to low blood pressure. Its primary funciton is to increase sodium reabsoprtion in the distal tubule and coelcting duct. Aldosterone upregulates the sodium-potassium pumps along the lining of the nephron, pumping three sodium ions OUT of the nephron lining (and toward the blood) for every two potassium ions it pumps IN (toward the nephron and away from the blood).

Answer 3

Meiosis in noncyclical and terminates in gamete creation (either sperm cells or ova). It happens once. Mitosis is a cyclical process

Answer 4

Single-crossover events affect only the ends of chromosome arms, while double-crossover events can affect segments in the middle of chromosome arms

Answer 5

Skeletal muscle and cardiac muscle

Answer 6

Gap junctions (intercalated discs that connect the cytoplasm of adjacent cardiac muscle cells, allowing ions to pass from cell to cell)

Answer 7

Cardiac muscle and smooth muscle

Answer 8

Somatic nervous system, meaning conscious control

Answer 9

Autonomic nervous system, meaning not voluntary control

Answer 10

Red fibers (slow-twitch fibers) are a type of skeletal muscle. They obtain their color from the presence of abundant reserves of myoglobin, and are also rich in mitochondria. This means that they prefer oxidative metabolism, and therefore are present in large quanitities in muscles that specialize in performing less intense actions over a longer period of time

Answer 11

White fibers (fast-twitch fibers) lack myoglobin and mitochondria and tend to mobilize glycogen for quick bursts of intense action followed by fatigue.

Answer 12

Hydrolysis

Answer 13

Condensation

Answer 14

Beta-oxidation is a process in which fatty acids are broken down into acetyl-CoA, which can be fed into the citric acid cycle (Krebs cycle) similar to the effects of glycolysis and the pyruvate dehydrogenation complex. Beta-oxidation also generate the electron carriers NADH and FADH2. The beta carbon of each fatty acid is oxidized to a carbonyl.

Answer 15

In addition to breaking down fatty acids into acetyl-CoA, beta-oxidation also generates electron carriers NADH and FADH2 which produce energy in teh electron transport chain. The beta carbon of each fatty acid is oxidized to a carbonyl group. It occurs in the mitochondria in eukaryotic cells.

Answer 16

The total number of alleles in a population has to add up to 1: A + a = 1 And the total number of genotypes in the population must also add up to 1: AA + 2Aa + aa = 1 For examples, if the frequency of the recesssive autosomal allele for polydactyly is 1.2% then a=.012 and A=.988. Therefore 2Aa = 2 x 0.988 x 0.012

Answer 17

Microtubules

Answer 18

Free radicals are molecules or atoms that contain on unpaired valence electron. As such, they typically serve as highly reactive oxidizing agents

Answer 19

FADH2 is the reduced form of flavin adenine dinucleotide (FAD) and NAD is the reduced for of nicotinamide adenine dinucleotide (NAD). Since they are reduced (and are carrying electrons) they tend to serve as reducing agents and would not oxidize.

Answer 20

Eukaryotes

Answer 21

Amino acids that make up a protein may include many acidic or basic side chain groups. Those side chains can either release or absorb protons, allowing them to help buffer the blood through action as a Bronsted-Lowry acid or base

Answer 22

Oxygen is reduced to form H2O

Answer 23

The finale major process of aerobicrespiration through which the majority of aerobically-derived ATP is synthesized. The process begins by passing electrons through a ETC. The final electron acceptor is oxygen. This is the only time in eukaryotic aerobic respiration where oxygen is directly required. These reactions take place in specialized proteins where the energy from NADH and FADH2 (molecules formed in glycolysis and the Krebs Cycle/citric acid cycle) is used up, molecule oxygen is reduced into water, and approximately 30-36 ATP are created from ADP and inorganic phosphate.

Answer 24

Complex I is known as NADH dehydrogenase

Answer 25

Complex II is known as succinate dehydrogenase

Answer 26

Cytochrome bc or c

Answer 27

Cytochrome c oxidase

Answer 28

In the ETC, the energy release from the series of electron transfers is used to pump H+ across the membrane. The unequal concentrations of H+ ions across the membrane establishes an electrochemical gradient, leading to chemiosmosis, or the passive diffusion of the protons down their concentration gradient, which is couple to ATP synthase. This proton ovement generates 90% of the ATP syntheiszed during oxidative phosphotylation. The electrons passing through the electron transport chain gradually lose energy until eventually they are donate to O2, which accepts two H+ ions and is transformed into water.

Answer 29

The passive diffusion of protons down their concentration gradients, which is couple to ATP synthase. If proton gradient is disrupted or destroyed, chemiosmosis can become uncouples from the ETC, resulting in little to no ATP generation despite the transfer of electrons carrying on. Many poisons and toxins act by uncoupling the proton gradient from ATP synthase.

Answer 30

Km is the substrate concentration required to reach Vmax/2

Answer 31

Noncompetitive inhibition is when the inhibitor does not compete with the substrate for the active site, but reduces enzyme activity by binding to another site on the enzyme (allosteric inhibition). Vmax is decreased and Km increases

Answer 32

Competitive inhibition is when the inhibitor directly competes with the substrate for the active site on the enzyme. Km increases since it now takes more substrate to ensure half of the active sites are occupied. Vmax does not change

Answer 33

enzyme substrate affinity α 1/Km (higher Km means weaker affinity)

Answer 34

Uncompetitive inhibition is when the inhibitor binds to only the enzyme-substrate complex, and inactivates it. This causes the number of active enzyme-substrate complexes to descrease, thereby decreasing Vmax. Km also decrease to exactly the same degree as Vmax.

Answer 35

If there is a 95% yield for each couping step and the cycle was run x times, (0.95)^x=final % yield

Answer 36

Lacteals are structures in the intestines associated with absorbing fat into the lymphatic system

Answer 37

46 chromosomes, 22 autosomes, and either 2 X chromosomes or one X and one Y chromosome

Answer 38

interphase. Resting phase is also known as Gap 0 (G0).

Answer 39

mitosis or meiosis

Answer 40

The cell prepares for division. Duing this phase growth and DNA replication occur. There are three stages: Gap 1 (G1), synthesis (S), and Gap 2 (G2). Throughout interphase, chromatin is loosely packaged (euchromatin) to allow transcription and replication.

Answer 41

The cell grows

Answer 42

The cell grows

Answer 43

DNA is replicated. S is located between G1 and G2 and allows checkpoints.

Answer 44

G1/S=restriction point, when a cell commits to division. TThe presence of DNA damage or other external factors can cause a cell to fail this checkpoint and not divide. The G2 checkpoint that takes place before cell division similarly checks for DNA damage after DNA replication, and if damage is detected, serves to “pause” cell division until the damage is repaired.

Answer 45

Cell undergoes division (mitosis in non-sex/germ cells). Mitosis proceeds through prophase (where the nuclear membrane disappears, chromosomes condense, and the mitotic spindle forms), metaphase (where chromosomes line up along the metaphase plate), anaphase (where chromosome are pulled apart), and telophase/cytokinesis (where the nuclear envelope and nucleolus reappear and the cell divides). Meiosis occurs in sex/germ cells and turns a diploid (2n) parent cell into 4 haploid (n) daughter cells in a two-stage process, in which crossover between homologous chromosomes and the random allocation of maternal/paternal chromosomes to daughter cells work together to create genetic variability.

Answer 46

1st step of mitosis, nuclear membrane disappears, chromosomes condense, mitotice spindle forms. The DNA condenses such that distinct chromosomes become visible, as sister chromatids (or copies of a given chromosome) join at a region known as the centromere. The kinetochore assembles on the centromere, and is the site where microtubule fibers that extend from the centrosome and form the mitotic spindle attach to pull the sister chromatids apart in later stages of mitosis.

Answer 47

2nd stage of mitosis after prohphase, chromosomes line up along the metaphase plate

Answer 48

3rd stage of mitosis after prophase and metaphase. Chromosomes are pulled apart

Answer 49

4th stage of mitosis after prophase, metaphase, and anaphase. Nuclear envelope and nucleolus reappear and the cell divides.

Answer 50

Meiosis occurs in sex/germ cells and turns a diploid (2n) parent cell into 4 haploid (n) daughter cells in a two-stage process, in which crossover between homologous chromosomes and the random allocation of maternal/paternal chromosomes to daughter cells work together to create genetic variability.

Answer 51

DNA is negatively charged due to its phosphate backbone.

Answer 52

H1, H2A, H2B, H3, H4

Answer 53

The core a histone contains two dimers H2A and H2B and a tetramer of H3 and H4 while H1 serves as a linking unit. Approximately 200 base pairs of DNA can be wound around a histone, and the complex formed by DNA and a histone is known as a nucleosome.

Answer 54

Euchromatin and heterochromatin

Answer 55

Euchromatin is a loose configuration that is difficult to see under light microscopy and allows DNA to be readily transcribed. Throughout interphase (i.e., most of the cell cycle), DNA generally exists as euchromatin.

Answer 56

Heterochromatin is the tightly coiled, dense form of chromatin that is visible during cell division and is present to a lesser extent even during interphase.

Answer 57

Histones are highly alkaline and are positively charged at physiological pH, hich facilitates their interaction with the highly negatively charged phosphate groups on the backbone of DNA. Modifications like acetylation of histones reduce that positive charge, making histones interact with DNA less closely, which in turn facilitates transcriptional activity.

Answer 58

Spindle fibers move chromosomes in mitosis and are made up of microtubules

Answer 59

Cytokinesis is the splitting of the cell into two that occurs after both metaphase and anaphase

Answer 60

prophase, metaphase, anaphase, and telophase

Answer 61

Meiosis is essential for sexual reproduction. It takes place in germ cells (also known as sex cells). Meiosis differs from mitosis in that it has two stages and results in the formation of four daughter cells, each of which has only one copy of each chromosome (haploid, n), in contrast to mitosis, which generates cells with two copies of each chromosome (diploid, 2n) that are essentially identical to their parent cell.

Answer 62

In prophase I of meiosis, homologous chromosomes (i.e., the maternal and paternal copies of a given chromosome) pair up with each other in a process known as synapsis, forming tetrads. While paired up, homologous chromosomes may exchange genetic information in a process known as crossing over. The crossing-over points are known as chiasmata. This process results in recombinant DNA that is another source of variation in sexual reproduction, in addition to the variability inherent to the process.

Answer 63

In metaphase I of meiosis, homologous pairs, which take the form of tetrads, line up at the metaphase plate. The orientation of the homologous pairs is random in terms of which side of the metaphase plate the maternal or paternal copy of a given chromosome in a homologous pair winds up.

Answer 64

In anaphase I of meiosis, the homologous pairs are separated, and one member of each pair is pulled to each side of the cell.

Answer 65

In meiosis II, which operates similarly to mitosis, the sister chromatids are split up into two haploid daughter cells.

Answer 66

Chemoreceptors, including those of the taste buds in the tongue, olfactory receptors in the nose, carotid and aortic bodies, and chemoreceptor trigger zone of the medulla, are neurons involved in sensing molecules dissolved in gases or liquids.

Answer 67

Mechanoreceptors are neurons that respond to mechanical pressure or distortion. Cutaneous mechanoreceptors are responsible for somatosensation, while those embedded in muscles and ligaments are responsible for sensing muscular stretch and load, including in the afferent arm of a number of reflex arcs.

Answer 68

Osmoreceptors (water homeostasis): respond to the osmolarity of blood

Answer 69

Photoreceptors (sight) respond to the visible spectrum of electromagnetic waves

Answer 70

These receptors can also be broadly divided into exteroceptors, which respond to stimuli from the outside world, and interoceptors, which respond to stimuli generated within the body

Answer 71

During mitosis and meiosis II, sister chromatids are separated. mitosis separates sister chromatids to create two diploid daughter cells. Meiosis I separates homologous chromosomes to create haploid daughter cells, each of which divides again, separating sister chromatids in Meiosis II to create two haploid cells.

Answer 72

We want the phylogenetic tree that requires the fewest "events" (mutation, transfer, etc…) to produce the genetic picture.

Answer 73

p+q=1 where p and q are the only two alleles in the population. Squaring the equation yields: (p + q)^2 = 12 → p^2 + 2pq + q^2 = 1. This second equation allows us to connect genotypes and phenotypes, because the p2 and q2 terms correspond to individuals homozygous for p and q, respectively, while the 2pq term gives the frequency of heterozygotes.

Answer 74

Glycolipids act to provide energy and also serve as markers for cellular recognition.

Answer 75

Phospholipids are a structural component of the membrane

Answer 76

The cytoskeleton of one to the cytoskeleton of the other

Answer 77

ketone bodies and glucose

Answer 78

2 haploid cells with 23 chromosomes, each chromosome consisting of 2 sister chromatids.

Answer 79

ΔG° = -RTlnK, For ΔG° to be negatvie ln(K) must be positive so K>1

Answer 80

Southern blotting is a technique used to identify specific DNA sequences.

Answer 81

Western blots are used to identify protein

Answer 82

Northern blots are used to identify RNA sequences

Answer 83

Edman degradation is a technique used to sequence proteins via successive cleaving of terminal amino acid residues

Answer 84

A nucleoside is composed of a nitrogenous base and a five-carbon sugar (ribose or deoxyribose). Adenosine, is such a molecule. For adenosine, the nitrogenous base is adenine, while the five-carbon sugar is ribose (note the presence of both a 2' and a 3' hydroxyl group).

Answer 85

∆G < 0, Keq > 1, and E° > 0