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Biochemistry Exam 1 - PT3

Terms in this set (23)

the central dogma of molecular biology:
1. describes how macromolecules are divided into four major classes
2. describes how DNA sequence information is converted to RNA sequence information, which is converted to protein sequence information
3. describes how DNA sequences are translated into mRNA molecules
4. describes how DNA is replicated through an RNA intermediate
5. describes how RNA is transcribed into protein
2. describes how DNA sequence information is converted to RNA sequence information, which is converted to protein sequence information
both proteins and lipids spontaneously form ogranized structures in solution. what chemical driving force plays a large role in this process?
1. amphiphatic effect
2. electrostatics
3. hydrogen bonding
4. hydrophobic effect
5. dipole-dipole interactions
4. hydrophobic effect
at pH 9:
1. the solution has less hydroxide ion than at neutral pH
2. the solution has 100x the hydronium ion as at neutral pH
3. the solution has 1/100 as much hydronium ion as at neutral pH
4. the solution is neutral
5. the solution is acidic
3. the solution has 1/100 as much hydronium ion as at neutral pH
which of the following statements about proteins is FALSE?
1. proteins are polymers of amino acids
2. the interior of a protein is hydrophilic
3. proteins usually contain secondary structure elements
4. many enzymes are proteins
5. the exterior of proteins is mostly covered by polar and charged residues
2. the interior of a protein is hydrophilic
predict the charge of the polypeptide shown below (from N- to C-terminus) at the physiological pH (pH=7.4)
1. a net charge of +1
2. a net charge of +3
3. a net charge of -1
4. a net charge of zero
5. a net charge of -3
3. a net charge of -1
Alpha helices:
1. contain amino acid residues with any possible phi and psi torsion angles
2. display their constituent amino acid side chains (R groups) only at one face
3. exhibit regular patterns of backbone hydrogen bonding
4. always pair with beta strands
5. have an upper limit of 3 residues
3. exhibit regular patterns of backbone hydrogen bonding
a peptide bond:
1. can adopt any possible phi and psi torsion angles in a protein
2. forms when two cysteine residues react
3. forms a plane with six atoms from two amino acids
4. forms when water is added to two amino acids
5. is very unstable in aqueous solution
3. forms a plane with six atoms from two amino acids
the solution to the Leventhal paradox describes:
1. our inability to understand protein folding
2. the ability of proteins to fold reversibly
3. that tertiary structure is unrelated to amino acid primary structure
4. how proteins fold by a defined folding pathway with intermediates
5. that most proteins are unfolded in a cell
4. how proteins fold by a defined folding pathway with intermediates
in a gel-filtration experiment
1. proteins are separated based on native size and shape
2. proteins are separated based on charge
3. proteins are separated based on binding to a ligand
4. proteins are separated using antibody complexes
5. none of the above
1. proteins are separated based on native size and shape
the purification of an enzyme results in a homogenous sample with 500 units of activity. the crude, starting material contained 10,000 units of activity. the purified enzyme sample had a mass of 10 mg, while the starting material consisted of 10 grams of total protein. choose the BEST answer that describes the progress of this purification
1. yield of enzyme was 0.1%
2. yield of enzyme was 5%
3. yield of enzyme was 5000 units/mg
4. specific activity of the purified enzyme was 50 units/gram
5. specific activity cannot be calculated from the data provided
2. yield of enzyme was 5%
what is the main reason one adds sodium dodecyl sulfate to a protein sample prior to running it on a SDS-PAGE gel?
1. to stabilize the protein
2. to break the protein down
3. to give the protein an overall negative charge
4. to align the protein within the gel
5. to control the pH of the protein sample
3. to give the protein an overall negative charge
the free energy change (delta G) provides information about the chemical reaction. which of the following statements about free-energy change is TRUE?
1. only exergonic reactions have free energy
2. the standard free-energy change in a chemical reaction is the inverse of the equilibrium constant
3. the free-energy change determines the rate of a reaction under standard conditions
4. the free-energy change of a reaction depends on the mechanism of the reaction
5. at equilibrium the free-energy change of a reaction is equal to zero
5. at equilibrium the free-energy change of a reaction is equal to zero
which statement about an enzyme's active site is FALSE?
1. it possesses a unique chemical microenvironment
2. specificity is due to the three dimensional structure of the enzyme
3. it promotes formation of the transition state
4. it interacts with substrate through multiple weak interactions
5. residues of the active site are close in amino acid sequence
5. residues of the active site are close in amino acid sequence
in the sequential mode of allostery:
1. the enzyme exists in only the T- or R- state, no intermediate states are allowed
2. there is no effect of ligand binding on the other unbound subunits
3. all subunits will change conformation at once
4. the binding of one subunit will affect the affinity and alter the conformation of the neighboring subunits
5. only positive cooperativity can be explained
4. the binding of one subunit will affect the affinity and alter the conformation of the neighboring subunits
the interaction between an enzyme and substrate at the active site:
1. is irreversable
2. is described by the turnover number, kcat
3. is best described by the "lock and key" model
4. promotes the formation of the transition state
5. occurs through several covalent bonds
4. promotes the formation of the transition state
the derivation of the Michealis-Menton equation includes several key assumptions. one assumption is that the activity of the enzyme is measured early in time to obtain the initial velocity of the reaction. what is the reason for this assumption?
1. it makes the enzyme assay easier because we only measure enzyme activity for a short time
2. it allows us to ignore the reverse reaction of P->S
3. it simplifies determining both the forward and reverse rate constants
4. it allows us to monitor the reverse reaction
5. it allows up to assume that the michealis constant (KM) and substrate dissociation constant (Kd) are nearly identical
2. it allows us to ignore the reverse reaction of P->S
which of the following is CORRECT about the turnover number (kcat):
1. it is determined at conditions where the enzyme is not saturated with substrate
2. kcat=k-1/k1
3. it indicates the rate at which an enzyme catalyzes a particular reaction
4. it describes the efficiency of selecting and converting the substrate to product
5. it is equal to the concentration of substrate at which all the enzyme active sites are occupied
3. it indicates the rate at which an enzyme catalyzes a particular reaction
noncompetitive inhibition of an enzyme has which of the following characteristics?
1. Vmax is unchanged, but KM is increased
2. inhibition can be overcome by increasing substrate concentration
3. Vmax is decreased, but KM is unchanged
4. the ratio of KM/Vmax remains constant
5. Vmax and KM are both decreased
3. Vmax is decreased, but KM is unchanged
which description below BEST describes the Lineweaver-Burk (double-reciprocal) plots of enzyme reactions with and without a competitive inhibitor?
1. the lines are parallel
2. the lines intersect on the X axis
3. the lines intersect on the Y axis
4. the Vmax is increased
5. A lineweaver-burk cannot be used to analyze competitive inhibition
3. the lines intersect on the Y axis
the catalytic serme (Ser195) in chymotrypsin is NOT?
1. a general acid
2. an electrophile
3. located in the active site
4. a component of the oxyanion hole
5. a nucleophile
2. an electrophile
a fetus needs to obtain oxygen from its mother. what property of hemoglobin allows this to occur?
1. fetal hemoglobin has more subunits than adult hemoglobin
2. the fetus has more 2,3-BPG than then adult
3. fetal hemoglobin has a higher affinity for O2 than the adult hemoglobin
4. fetal Hb shifts the O2 binding curve to higher oxygen concentrations (to the right) in the fractional saturation vs pO2 binding plot
5. fetal hemoglobin is not cooperative
3. fetal hemoglobin has a higher affinity for O2 than the adult hemoglobin
what is the result of 2,3 biphosphoglycerate (BPG) binding to hemoglobin?
1. it prevents O2 from dissociating
2. it stabilizes the T state of hemoglobin
3. it allosterically enhances the reaction of CO2 with terminal amino groups
4. it increases the sensitivity to changes in pH
5. it produces an anionic pocket for binding heterotrophic regulators
b. it stabilizes the T state of hemoglobin
the Bohr effect helps regulate oxygen binding to hemoglobin. which of the following statements BEST describes the Bohr effect?
1. increasing the pressure of CO2 results in the release of O2, from oxyhemoglobin
2. binding of 2,3-biphosphoglycerate (2,3-BPG) and lowering the pH increases the R state of hemoglobin
3. lowering the pH and increasing the partial pressure of CO2 enhances the release of O2 from oxyhemoglobin
4. increasing the pH and partial pressure of O2 results in stabilization of the T state of hemoglobin
5. all of the above statements describe aspects of the Bohr effect
3. lowering the pH and increasing the partial pressure of CO2 enhances the release of O2 from oxyhemoglobin
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