Question 1

Look at the data in the figure below. One amino acid location is indicated by an arrow. Why is the amino acid at that location invariant among the three sequences?

Accepted Answer

This is the F8 histidine. It i

Question 2

Which of the following accounts for some of the specificity of the K+ channel?

Accepted Answer

A)  The radius of solvated Na+ is smaller than the radius of solvated K+. 
B)  The number of $\beta$-strands that make up the channel. 
C)  The orientation of backbone carbonyl oxygen atoms in the channel. 
D)  Alternating positive and negative amino acids in the channel pore. 
A)  The radius of solvated Na+ is smaller than the radius of solvated K+. 
B)  The number of $\beta$-strands that make up the channel. 
C)  The orientation of backbone carbonyl oxygen atoms in the channel. 
D)  Alternating positive and negative amino acids in the channel pore.

Question 3

The E. coli maltoporin protein is a homotrimeric porin complex. A related protein is found in another bacterial species that does not form trimers but rather functions as a monomer. A comparison of the amino acid composition of a maltoporin subunit and the new porin showed similar ratios of hydrophobic/hydrophilic amino acids for the two proteins. Explain how this can be the case.

Accepted Answer

The porins are embedded in the membrane.

Question 4

A passive transporter is discovered that can transport both galactose and glucose. The pore of the transporter can accommodate a single sugar at a time. If the extracellular concentrations of galactose and glucose are 0.2 and 3.6 mM, respectively, and the intracellular concentrations are 0.39 and 2.6 mM, respectively, which sugar is most likely to enter the cell through the transporter? Provide two reasons for your answer.

Accepted Answer

Glucose is most likely to enter the cell

Question 5

There are two main structural differences between a typical $\alpha$-helix and the helix formed by gramicidin A. Describe the two structural differences and choose which structural characteristic is more important in the function of gramicidin A. Explain your choice.

Accepted Answer

A typical @#LAT-DLM&-helix is left handed and has

Question 6

Explain the relationship between P50 of oxygen binding and Kd for oxygen binding to myoglobin.

Accepted Answer

P50 is the amount of oxygen bound when h

Question 7

Thin filaments __________, but thick filaments do/are not.

Accepted Answer

A)  contain myosin 
B)  are directly attached to the Z disk 
C)  are part of the sarcomere 
D)  are part of the A band 
A)  contain myosin 
B)  are directly attached to the Z disk 
C)  are part of the sarcomere 
D)  are part of the A band

Question 8

The estrogen receptor is an example of a

Accepted Answer

A)  metabolic enzyme. 
B)  transport protein. 
C)  genomic caretaker protein. 
D)  cell signaling protein. 
A)  metabolic enzyme. 
B)  transport protein. 
C)  genomic caretaker protein. 
D)  cell signaling protein.

Question 9

Which of the following is NOT a characteristic of an enzyme active site?

Accepted Answer

A)  It has a three-dimensional shape. 
B)  It plays a role in increasing the energy of activation of the reaction being catalyzed. 
C)  It is a unique chemical environment. 
D)  It is where the substrate of the reaction can be found. 
A)  It has a three-dimensional shape. 
B)  It plays a role in increasing the energy of activation of the reaction being catalyzed. 
C)  It is a unique chemical environment. 
D)  It is where the substrate of the reaction can be found.

Question 10

Label the structures marked in this diagram of a sarcomere.

Accepted Answer

A is a thi

Question 11

If SERCA is not functioning in a myoblast, which of the following may occur?

Accepted Answer

A)  Myosin will not undergo the conformational change that results in the power stroke. 
B)  Myosin will not be able to bind to the thin filament. 
C)  The myofibrils can shorten but not lengthen. 
D)  The myofibrils can lengthen but not shorten. 
A)  Myosin will not undergo the conformational change that results in the power stroke. 
B)  Myosin will not be able to bind to the thin filament. 
C)  The myofibrils can shorten but not lengthen. 
D)  The myofibrils can lengthen but not shorten.

Question 12

In studying a transporter, it is found that no external energy input is needed to facilitate the movement of a neutral compound through the transporter. The translocation rate of the compound reaches a plateau at high levels of compound. It is a(n)

Accepted Answer

A)  passive transport channel. 
B)  passive transport carrier. 
C)  active transport channel. 
D)  active transport carrier. 
A)  passive transport channel. 
B)  passive transport carrier. 
C)  active transport channel. 
D)  active transport carrier.

Question 13

The $\beta$ subunit of adult hemoglobin has higher sequence similarity to than to __________.

Accepted Answer

A)  fetal $\varepsilon$ subunit; myoglobin 
B)  myoglobin; fetal $\varepsilon$ subunit 
C)  adult $\alpha$1 subunit; fetal $\varepsilon$ subunit 
D)  myoglobin; adult $\alpha$1 subunit 
A)  fetal $\varepsilon$ subunit; myoglobin 
B)  myoglobin; fetal $\varepsilon$ subunit 
C)  adult $\alpha$1 subunit; fetal $\varepsilon$ subunit 
D)  myoglobin; adult $\alpha$1 subunit

Question 14

Which of the following pairs are paralogous genes?

Accepted Answer

A)  chicken myoglobin; human hemoglobin $\alpha$ subunit 
B)  chicken hemoglobin $\alpha$ subunit; chicken hemoglobin $\beta$ subunit 
C)  human hemoglobin $\alpha$ subunit; chicken hemoglobin $\beta$ subunit 
D)  chicken hemoglobin $\alpha$ subunit; human myoglobin 
A)  chicken myoglobin; human hemoglobin $\alpha$ subunit 
B)  chicken hemoglobin $\alpha$ subunit; chicken hemoglobin $\beta$ subunit 
C)  human hemoglobin $\alpha$ subunit; chicken hemoglobin $\beta$ subunit 
D)  chicken hemoglobin $\alpha$ subunit; human myoglobin

Question 15

In both myoglobin and hemoglobin, O2 reversibly binds to a(n) atom contained in a porphyrin ring that is tightly bound to the protein.

Accepted Answer

A)  calcium 
B)  iron 
C)  magnesium 
D)  manganese 
A)  calcium 
B)  iron 
C)  magnesium 
D)  manganese

Question 16

The selectivity of aquaporin for H2O relies on all EXCEPT which of the following?

Accepted Answer

A)  hydrogen bonding to Asn 
B)  a 2.8 Å constriction point within the protein 
C)  inverted $\alpha$-helix dipoles 
D)  electrostatic repulsion from Asn 
A)  hydrogen bonding to Asn 
B)  a 2.8 Å constriction point within the protein 
C)  inverted $\alpha$-helix dipoles 
D)  electrostatic repulsion from Asn

Question 17

Which of the following is NOT an ABC transporter?

Accepted Answer

A)  cystic fibrosis transmembrane conductance regulator protein 
B)  SERCA 
C)  multidrug resistance protein 
D)  maltose transporter from E. coli 
A)  cystic fibrosis transmembrane conductance regulator protein 
B)  SERCA 
C)  multidrug resistance protein 
D)  maltose transporter from E. coli

Question 18

Which is true of the K+ channel but NOT of an aquaporin?

Accepted Answer

A)  Selectivity is achieved through interactions with backbone NH groups. 
B)  It contains $\alpha$-helices. 
C)  It is an active transporter. 
D)  Selectivity is assisted through inverted $\alpha$-helix dipoles. 
A)  Selectivity is achieved through interactions with backbone NH groups. 
B)  It contains $\alpha$-helices. 
C)  It is an active transporter. 
D)  Selectivity is assisted through inverted $\alpha$-helix dipoles.

Question 19

Which of the following is a genomic caretaker protein?

Accepted Answer

A)  topoisomerase 
B)  insulin 
C)  myoglobin 
D)  tubulin 
A)  topoisomerase 
B)  insulin 
C)  myoglobin 
D)  tubulin

Question 20

A newly discovered transporter protein is being investigated using an assay to determine whether transport has occurred in the cells. A nonhydrolyzable form of ATP is added to the cells, and it is found that transport is reduced. Explain these results.

Accepted Answer

The transporter protein must b

Exam 6: Protein Function

Look at the data in the figure below. One amino acid location is indicated by an arrow. Why is the amino acid at that location invariant among the three sequences?

Which of the following accounts for some of the specificity of the K+ channel?

There are two main structural differences between a typical α\alphaα -helix and the helix formed by gramicidin A. Describe the two structural differences and choose which structural characteristic is more important in the function of gramicidin A. Explain your choice.

Explain the relationship between P50 of oxygen binding and Kd for oxygen binding to myoglobin.

Thin filaments __________, but thick filaments do/are not.

The estrogen receptor is an example of a

Which of the following is NOT a characteristic of an enzyme active site?

Label the structures marked in this diagram of a sarcomere.

If SERCA is not functioning in a myoblast, which of the following may occur?

In studying a transporter, it is found that no external energy input is needed to facilitate the movement of a neutral compound through the transporter. The translocation rate of the compound reaches a plateau at high levels of compound. It is a(n)

The β\betaβ subunit of adult hemoglobin has higher sequence similarity to than to __________.

Which of the following pairs are paralogous genes?

In both myoglobin and hemoglobin, O2 reversibly binds to a(n) atom contained in a porphyrin ring that is tightly bound to the protein.

The selectivity of aquaporin for H2O relies on all EXCEPT which of the following?

Which of the following is NOT an ABC transporter?

Which is true of the K+ channel but NOT of an aquaporin?

Which of the following is a genomic caretaker protein?

A newly discovered transporter protein is being investigated using an assay to determine whether transport has occurred in the cells. A nonhydrolyzable form of ATP is added to the cells, and it is found that transport is reduced. Explain these results.

Principles of Biochemistry

Physical Biochemistry: Energy Conversion, Water, and Membranes

Nucleic Acid Structure and Function

Protein Structure

Methods in Protein Biochemistry

Enzyme Mechanisms

Cell Signaling Systems

Glycolysis: a Paradigm of Metabolic Regulation

The Citrate Cycle

Oxidative Phosphorylation

Photosynthesis

Carbohydrate Structure and Function

Carbohydrate Metabolism

Lipid Structure and Function

Lipid Metabolism

Amino Acid Metabolism

Nucleotide Metabolism

Metabolic Integration

DNA Replication, Repair, and Recombination

RNA Synthesis, Processing, and Gene Silencing

Protein Synthesis, Posttranslational Modification, and Transport

Gene Regulation

Filters

Which of the following accounts for some of the specificity of the K⁺channel?

There are two main structural differences between a typical $\alpha$ -helix and the helix formed by gramicidin A. Describe the two structural differences and choose which structural characteristic is more important in the function of gramicidin A. Explain your choice.

Explain the relationship between P₅₀ of oxygen binding and K_d for oxygen binding to myoglobin.

The $\beta$ subunit of adult hemoglobin has higher sequence similarity to than to __________.

In both myoglobin and hemoglobin, O₂ reversibly binds to a(n) atom contained in a porphyrin ring that is tightly bound to the protein.

The selectivity of aquaporin for H₂O relies on all EXCEPT which of the following?

Which is true of the K⁺channel but NOT of an aquaporin?