MCAT Biology and Biochemistry Flashcards
What will be the effect on a proteins afinity for water if an AA is substituted for a more polar AA?
Substituting a more polar amino acid for a nonpolar amino acid will render the protein more hydrophillic (“water-loving”)
Where will a protonation occur on histadines side chain?
When protonating histadine, the pyradine nitrogen gains the proton. This would not trigger a shift in double bonds in the surrounding structure.
What type of reaction happens when a carboxyl group is removed?
Decarboxylase reactions occur when they remove a carboxyl group from a molecule.
What happens to a molecule above and below its pKa value?
Above the pKa (in more basic conditions) the deprotonated form will predominate; and below the pKa (in more acidic conditions) the protonated form will predominate.
What is the charge of testosterone?
Testosterone is a steroid hormone; it is not charged at all, as evidenced by the fact that it can pass through the plasma membrane and is thus nonpolar.
What is the reaction of adding insulin into the bloodstream?
Insulin is a peptide hormone that promotes the cells to eat up glucose, causing the glucose levels to decrease in in the body.
What structure do steroid hormones typically tend to present in?
Non-polar fused -ring structure
In addition to myosin motor proteins, what type of fibers are involved in cytokinesis as the contractile ring complex?
Actin filaments (microfilaments)
What is the effect of adding cholesterol to a phospholipid bilayer?
Cholesterol promotes fluidity at low temperatures and increases stability at high temperatures.
What is happenign to the cell during G0 phase?
G0 is resting phase. There is no cell division occuring at this time.
Bacteria contain what size of ribsomes?
Bacteria contain an 70S ribosome, which is composed of 30S and 50S subunits.
What are negative-sense RNA viruses?
These viruses contain RNA that is complementary to mRNA, which needs to be synthesized by an eynzyme known as RNA replicase (which is caried in the viron).
What AA does the letter L represent?
L = Leucine
What is the composition of viral envelope?
Viral envelopes are primarily made up of phospholipids and glycoproteins that contribute to recognition and interactions with cell receptors.
What happens in terms of protonation state to an amino acid when the pH > pKa?
The group in question will be deprotonated
What is the estimated isoelectric point of histidine if the pKa = 6?
Isoelectric point should be approximately 7.5. Average two most basic pKa values: 6 + 9 / 2 = 7.5
What types of AA’s are typically found on the outer plasma membrane vs inner membrane? (i.e. polar/hydrophillic, non-polar/hydrophobic, basic, acidic, )
Inner membrane: Non-polar hydrophobic AA’s Outer membrane: Polar hydropilic AA’s
What kind of bonding occurs in secondary structure?
Hydrogen bonding
Intermolecular forces between what two species most directly involved in the formation of the alpha helix backbone?
The amine group on one amino acid and the carbonyl group of another
What does a value > 1 for a hill coefficient mean?
Hill cooperativity reflects cooperativity. A cooefficient > 1 indicates a positive cooperativity, meaning that binding at one position or active site causes binding to take place more easily at the remaining active sites.
What is the function of a kinase?
Kinases are responsible for transferring a high-energy phosphate group from a donor molecule (typically ATP) to the substrate.
In what pathways are allosteric enzyme most prevalent?
Allosteric regulation is a ubiquitous phenomenon in the physiology of multicellular eukaryotic organisms. Many metabolic pathways rely on it, in the form of feed-forward regulation, feedback loops and complex multi-factorial systems such as the hormonal regulation of glucose metabolism.
Which amino acids are most likely to be phosphorylated by kinases?
AA’s that contain -OH groups, which include: serine (S), threonine (T), tyrosine (Y).
What is the effect of components of grapefruit juice binding a statin?
Bergamottin, a component in grapefruit juice, covalently binds enzyme CYP3A4, which is responsible for metabolizing certain statins. This inhibits the enzyme and increases the systemic concentration of the statin, which can be dangerous
What is the term for turn over number in enzyme substrate reactions?
Kcat is also known as the turnover. This is the time it takes one enzyme to tunrover a max amount of substrate molecules per unit time. Kcat = Vmax / [Et]
How is catalytic efficiency determined?
Catalytic efficiency is expressed as Kcat / Km. If enzyme concentration is equal among comparative subjects, then Vmax, which is directly proportional to Kcat, can be used to compare efficiency.
What is a cofactor?
Cofactors are organic or inorganic molecules that assist in the function of an enzyme.
What is a zymogen?
Zymogens are inactive precursors of enzymes that require proteolytic cleavage prior to becoming active.
If given mRNA sequence of 5’ - AUGAA - 3’ what is the sense dsDNA sequence that this corresponds with?
5’ - ATGAA - 3’ The sense DNA strand should have the same sequence as the mRNA strand produced, except the DNA strand should contain thymine instead of uracil.
What are the post-transcriptional modifications in eukaryotes?
- 5’ cap (7-methylguanylate cap) - 3’ poly-A-tail - splicing
What DNA enzyme has a “proofreading mechanism”?
DNA polymerase mainly functions to synthesize new DNA strands complementary to a template, but it also is capable of removing mismatched bases and replace them with the correct bases.
Where does paracrine signaling occur?
Paracrine signaling occurs between local cells (not cells of distinct tissues) and only lasts for a short amount of time, which is due to fast degradation of the paracrine ligands.
How many heavy and light chains does one immunoglobin (Ig) subunit contain?
One immunoglobulin (Ig) subunit contains two heavy chains and two light chains.
What type of protein are cadherins classified as? A. Globular proteins. B. Enzymes C. Transmembrane proteins D. Monotopic proteins
Transmembrane proteins. Cadherins are cell adhesion molecules that comprise adheren junctions, which connect cells to each other. So, it makes logical sense that a cadherin would extend through the membrane of a cell into the environment.
What is the function of a dynein protein?
Dyneins carry cargo towards (-) end of microtubules (towards the center), which is called retrograde transport.
How are G proteins activated and inactivated?
G proteins are activated when a GDP molecule is exchanged for GTP (GDP is NOT simply phosphorylated). G proteins are inactivated by the hydrolysis of GTP, which is accomplished via an intrinsic GTPase activity.
What is the goal and what are the parameters for a test cross?
Goal: Discover the genotype of a phenotypically dominant individual. Parameters: Individual with a dominant phenotype is crossed with an individual with the recessive phenotype.
What do diseases with a high penetrance exhibit?
Diseases with high penetrance show a high correlation between individuals that have the disease genotype and individuals who exhibit the signs and symptoms of the disease.
What is incomplete dominance?
Incomplete dominance is a form of inheritance in which neither allele is completely expressed over the other. Ex: The snapdragon flower. The Homozygous snapdragon flower is either all red or all white, while heterozygotes are blended phenotype of pink.
What are saturated phospholipids?
Saturated molecules are those which have no double bonds in their hydrocarbon chains.
Where are phospholipids synthesized in the cell?
Phospholipids, like most lipids, are synthesized at the surface of the smooth endoplasmic reticulum (ER).
What kind of fat (saturated vs unsaturated) would you add to a membrane to increase fluidity?
Unsaturated fats are more flexible and fluid than saturated fats due to the double bond adding a “kink” into the hydrocarbon tail. Unsaturated fats add fluidity to the membrane, and saturated fats add rigidity as they are much less flexible.
What is the name of the process by which long hydrocarbons could be catabolized by the cell?
Beta oxidation is the process by which long chain hydrocarbons are oxidized to acetyl-CoA by enzymes in the mitochondria.
What double bond configuration is observed when two high priority groups attached to an alkene are on the same side?
The double bond will be designated cis (for simple alkenes) or Z (on “zee zame zide”).
When lactose is present, what does allolactose bind to on the lac operon?
When lactose is present, transcription of structural lac genes takes place. Allolactose binds to the repressor, causing it to dissociate from the operator region. Transcription can take place.
Of the following, which are considered to be coding RNAs? I. tRNA
II. siRNA
III. mRNA
IV. miRNA
Messenger RNA (mRNA) is translated, so it is considered coding RNA.
What are the major differences between cDNA and DNA coding for the same gene?
cDNA, or complementary DNA, is DNA that is reverse transcribed from the associated mRNA molecule. The resulting cDNA sequence is very similar to the regular DNA sequence, but lacks introns (since mature mRNA does not contain introns). Therefore, a cDNA sequence will be shorter than the associated DNA sequence, assuming that the DNA sequence does include at least one intron.
Polymerase chain reaction (PCR) requires use of a thermostable DNA polymerase. The use of such a polymerase is especially important due to which step of the PCR cycle?
Denaturation. The DNA polymerase used in PCR is present throughout the cycle, it must be able to withstand such high temperatures without a significant loss of function. The temperature is raised to approximately 95 degrees to facilitate denaturation and separate the two DNA strands.
A cross between organisms with two different phenotypes produces offspring with a third phenotype that is a blending of the parental traits (e.g. white flowers crossed with red flowers yield pink flowers)
This is an example of incomplete dominance
What is the term that describes the following: clinical symptoms (phenotype) are not always present in individuals who have the disease-causing mutation (genotype)?
Incomplete dominance.
In what stage of the cell cycle is chromatin found to be in a dense condensation?
Chromatin is found in this condition when the cell is preparing to undergo mitosis.
At the peak of an action potential, what is the state of ions flowing across the neuronal cell membrane?
At peak action potential, the membrane potential is ~ +40 mV. At this point, Na stops flowing into the cell, voltage-gated K channels open to allow K to flow out of the cell.
What are the myelinating cells in the CNS and the PNS?
Oligodendrocytes myelinate axons in CNS. Schwann cells myelinate axons in PNS.
What is the role of efferent nerves?
Efferent nerves are responsible for carrying out the reflexive action. Example: The patellar reflex is elicited by striking the patellar ligament, which then activates spindle fibers in the muscle. In this case, efferent nerve role is extension of the leg following activation of muscle spindle fibers in the quadricep
What type of glial cell functions as macrophages in the central nervous system?
Microglia work as macrophages in the CNS. They provide an active immune defense by clearing out pathogens from the brain.
What is the neurotransmitter that is released by somatic neurons in order to induce muscle contraction?
Acetylcholine facilitates muscle contraction. Inhibition of acetylcholine results in less of it being available to bind to the receptor in the neuromuscular junction, thereby reducing the ability of the muscle to contract.
A hormone that acts on neighboring cells is best described as what?
A paracrine hormone acts on nerby cells.
Increased secretion of what mineralocorticoid acts on the distal tubules and collecting ducts of the kidney nephron to stimulate sodium retention, potassium secretion and thus water retention?
The mineralocorticoid aldosterone
What type of four ring structured hormone passes directly through plasma membranes of cells and encounters the nucleus where it affects gene transcription, resulting in long lasting physiological effects?
Steroid hormones
What type of neuron would relay a message from a C-fiber nociceptor?
Nociceptor refers to neurons that convey sensations of pain to the central nervous system. So, these are sensory and afferent neurons.
What effect does insulin have on the process of glycogenesis or glycogen synthesis?
Insulin stimulates glycogen or glycogenesis
What is the effects of LH being present in males and females?
In males: LH binds to receptors on Leydig cells, which stimulates testosterone synthesis and secretion. In females: LH causes mature follicles on the ovary to undergo ovulation, which often occurs between days 11 and 21 of the menstrual cycle.
What is the condition of a spinal cord in which the nerves that run inside the vertebral column are damaged, which interupts efferent signals to reach their destination?
Transection of the spinal cord
What do non-overlapping error bars represent?
It suggests that there is a statistically significant difference present between two variables.
In general, what are the abilities of a stem cell (this is a concern for people who undergo chemotherapy and are trying to eliminate cancer stem cells)?
Stem cells have the ability to undergo self-renewal. Cancer stem cells may be responsible for reocurrence after chemotherapy, which implies that they can resist chemo, replicate, and then differentiate.
What is the process of binding complementary nucleotides?
This process is called hybridization
What type of enzyme removes a phosphate from a substrate?
A phosphatase removes phosphates from substrates.
All other things being equal, in what type of solute conditions can we infer that aquaporins, will localize to the plasma membrane to a greater extent? (In hypotonic, isotonic, hypertonic conditions?)
Hypotonic conditions would provide the most beneficial conditions for increasing the concentration of aquaporins in a plama membrane.
What method of passing on genetic information maintains genetic integrity? (meiosis vs mitosis)
Meiosis functions in genetic recombination to create genetic diversity in offspring. Mitosis maintains genetic integrity.
What enzyme is used to alter the configuation of atoms, while keeping the same atomic ingredients?
Isomeraze is an enzyme that will modify a molecule in this way
What are the responses in the body to an insulin injection?
- Halt production of new sugar 2. Begin storing sugar as glycogen 3. Begin building fatty acids into fats for storing energy
What is the function of acylcarnitine translocase?
This enzyme is essential for the catabolism of fatty acids. If there is a deficiency then there will be an abundance of fatty acids in the body and less energy available.
The mitotic spindle is composed of what structures, which are cytoskeletal components.
Mitotic spindle is composed of microtubules, which are made of tubulin.
What is the term for a structure that evolved independently to carry our the same function?
These are called analogous structures
How do humans (males with XY and females with XX) regulate potential gene imbalances?
As the X chromosome carries more genes than Y chromosomes, in order to balance the genetic load with the males, one of a females XX chromosomes is inactivated, which balances the male XY set.
Why are trisomy pregnancies involving multiple copies of the X chromosome not terminated?
Due to the X chromosome carrying the majority of the genetic load for sexual differentiation, vs Y chromosome holding fewer genes, the additional two X chromosomes can simply be shut down via methylation.
Who would be more at risk of inherating MELAS, a mitochondrial disorder that affects many of the body’s systems, the daughter of a male or the son of a female who has the disease?
The son is more likely to inherit the disease, as mitochondrial disorders are inherited maternally.
What does a low recombination frequency suggest about two genes?
A low recombination frequency suggests that the two genes are physically close.
In what stage do homologous chromosomes separate?
Homologous chromosomes separate during meiosis I, which cause the daughter cells generated in this process to be haploid prior to meiosis II.
What may be a result of a dysfunctional synaptonemal complex?
The synaptonemal complex is a protein based linkage that arises during meiosis and connects homologous chromosomes, and if it is dysfunctional then = issues with recombination and synapsis
Heavy smokers often experience SOB, what comound and binding mechanism is most likely responsible for the SOB?
Carbon Monoxide (CO) has a 250 x greater affinity for hemoglobin than Oxygen does. CO is a direct competitive inhibitor.
How does having hemoglobin that are able to bind bicarbonate at the a1b2 interface enable a crocodile to hold their breath for a long time?
When an crocodile binds bicarbonate it stabalizes the “tense” state of hemoglobin and decreases the affinity of that molecule for O2, which then releases O2.
What metal cofactor helps carbonic anhydrase function as a catalyst for the conversion H2O -> CO2? A. Pt B. Fe C. Zn D. Mg
The active site of carbonic anhydrase contains a zinc molecule, which helps it catalyze the reversible reaction between CO2 and H2O.
Hemoglobin’s O2 binding affinity is affected by the pH of it’s environment and CO2 concentration, what conditions of pH and CO2 concentration are conducive for hemoglobin and O2 binding?
Low CO2 levels and high pH levels. (Since CO2 in the plasma lead to formation of carbonic acid, low CO2 leads to basic blood.
How does the binding of one oxygen molecule change the affinity / availability of that hemoglobin?
The binding of one oxygen molecule to a hemoglobin promotes changes in the position of the central iron ion, which facilitates the binding of additional O2 molecules.
Where does glycolysis occur in the cell?
Glycolysis occurs in the cytoplasm.
What are the three enzymes that catalyze the three irreversible steps in glycolysis?
-Hexokinase, phosphofructokinase, pyruvate kinase
How is step 1 of glycolysis regulated?
Step 1 of glycolysis is regulated by the negative feedback loop. When the product of step one is in excess it will inhibit the forward reaction.
What is the term for the reaction that uses water to synthesise a product?
Hydration reaction
What are the products of the Krebs cycle?
Products: ATP, citrate, NADH
In humans, where does gluconeogenesis take place?
Gluconeogenesis mainly takes place in the liver, but also occurs in the kidneys to a smaller extent.
In what phase of the cell cycle would the pentose phosphate pathway be most active?
In the synthesis phase (S), as ribose 5-phosphate is a product of PPP. This plays an important role in nucleic acid synthesis.
What is the meaning of multipotency when it comes to progenitor cells?
Multipotent progenitor cells have the gene activation potential to differentiate into multiple, but limited cell types. Ex: a multi blood stem cell can differentiate into other blood cells, but not to cells of other lineages.
What is the second law of thermodynamics?
A spontaneous reaction or cyclic process must yield a net entropy increase. (AKA: entropy of the universe should be continually rising)
What species has the greatest energetic yield in the Kreb’s Cycle? A. ATP B. GTP C. FADH2 D. NADH
As NADH drops off electrons at COmplex I of the ETC each mol of NADH contributes enough energy to synthesize 2.5 ATP mols.
