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Biochemistry Session 2 - Protein Structure and Function

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Biochemistry Quiz on Biochemistry Session 2 - Protein Structure and Function, created by Kathleen Lonergan on 07/06/2019.
Kathleen Lonergan
Quiz by Kathleen Lonergan, updated more than 1 year ago
Kathleen Lonergan
Created by Kathleen Lonergan almost 5 years ago
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Question 1

Question
There are thousands of protein possibilities within the human body, but their functions tend to fall under broad categories. For example, enzymes are catalysts. What is an example of a protein that would fall under the regulation-signaling-communication category?
Answer
  • Myosin
  • Growth factor
  • Collagen
  • Glucose transporter

Question 2

Question
A protein that normally contains one serine was incorrectly translated from a mutated mRNA strand and now it contains one alanine in its place. No other amino acids in the chain were affected. What could we expect to result?
Answer
  • A minor structural change, no change in function.
  • A major structural change, a significant change in function.
  • No change in structure or function.
  • No structural change, but a significant change in function.

Question 3

Question
Which of the following are true regarding peptide bonds? (Select all that apply)
Answer
  • Peptide bonds are flat.
  • Peptide bonds are nonpolar.
  • Peptide bonds have freedom of rotation and they are not structurally restricted.
  • Peptide bonds have partial double bond character.

Question 4

Question
Which of the following successfully describes the primary structure of a polypeptide chain?
Answer
  • Localized region of structural symmetry.
  • Three dimensional conformation of an entire intact covalently bonded polypeptide chain.
  • Three dimensional interactions of protein subunits in oligomeric protein complexes.
  • The amino acid sequence from N-terminal to C-terminal end of a single covalently linked polypeptide chain.

Question 5

Question
Bovine insulin consists of a primary structure of an A polypeptide chain and a B polypeptide chain. The total structure is being structurally stabilized by cysteines forming reversible covalent linkages. What is the term for this bond?
Answer
  • Disulfide bond
  • Peptide bond
  • Phosphodiester bond
  • Hydrogen bond

Question 6

Question
The alpha helix is one of the most common secondary structures. All peptide bonds in the helical domain are engaged in _____________, contributing to an overall very stable structure.
Answer
  • Intra-chain hydrogen bonding
  • Disulfide bonding
  • Metallic bonding
  • Steric hindrance

Question 7

Question
A beta sheet is a super secondary structure consisting of multiple beta-strands lined up next to one another in flat, planar arrays. Which bond listed below is responsible for the for this structure's conformation and stability?
Answer
  • Hydrogen bonds between amide hydrogens and carbonyl oxygens in adjacent peptide bonds.
  • Peptide bonds between amide hydrogens and carbonyl oxygens in adjacent peptide bonds.
  • Hydrogen bonds from amino acid residue side-chains positioned perpendicular to the plane of the beta-sheet.
  • Peptide bonds from amino acid residue side-chains positioned perpendicular to the plane of the beta-sheet.

Question 8

Question
Myoglobin is a product of combined inter-helix interactions between 7 alpha-helix domains. This is an example of _________ structure.
Answer
  • Primary
  • Secondary
  • Tertiary
  • Quaternary

Question 9

Question
Which of the following inter-subunit interactions are responsible for precisely stabilizing the quaternary structure? (Select all that apply)
Answer
  • Hydrogen bonds
  • Electrostatic interactions
  • Hydrophobic interactions
  • Van der Waal contacts

Question 10

Question
Generally, protein structure orients hydrophobic amino acids to the interior of the protein and hydrophilic amino acids to the exterior. However, exceptions do exist, and hydrophilic amino acids can be found in the interior. What could happen to the protein if water came into contact with the interior hydrophilic amino acids?
Answer
  • Nothing, water binding to the hydrophilic proteins would promote stabilization.
  • Nothing, it is impossible for water to penetrate the interior of a protein.
  • The overall structure could be denatured.
  • The structural conformation would change, but function would be maintained.

Question 11

Question
Where are "the instructions" for folding a protein into its native functional structure?
Answer
  • The amino acid sequence
  • The molten globule
  • The secondary structure
  • The tertiary structure

Question 12

Question
Which of the following is NOT true regarding chaperone assisted protein folding?
Answer
  • Chaperone proteins convert unstable proteins into properly folded proteins.
  • Chaperone proteins can aid in folding unstructured or denatured proteins.
  • Chaperone proteins are found solely near the exit portals of ribosomes.
  • Chaperone proteins can escort partially folded proteins to large protein complexes that will assist in folding newly synthesized chains.

Question 13

Question
A stable protein, RNaseA, is very stable. It is denatured by exposing it to a chaotrophic agent, a disulfide bond reducing agent, and then subjected to elevated heat. At this point, it was no longer functional. However, function returned when environmental conditions were returned to normal. Which of the following is true about the aforementioned reaction? (Select all that apply)
Answer
  • The primary structure of RNaseA was preserved.
  • The primary structure of RNaseA determined its overall structure.
  • The primary structure was irreversibly damaged, but function was preserved.
  • The structure forming process is random.

Question 14

Question
You have been asked to quickly denature a fairly stable protein. You have tried heating it up, dissolving it in an organic solvent, and shaking it. What is another method you could try? (Select all that apply)
Answer
  • Exposing it to hydrochloric acid
  • Exposing it to dithiotheritol
  • Putting it in a cool, dark drawer
  • Heating it to a higher temperature

Question 15

Question
A modified protein with an added acetyl group is denatured. What could we expect to see in terms of functionality?
Answer
  • As this was a minor modification, the protein will still spontaneously refold and maintain function.
  • It cannot renature appropriately and it is garbage.
  • The protein will partially refold spontaneously, but function will be negatively affected.
  • Denatured proteins function more efficiently than original conformations. It will be faster.

Question 16

Question
You have two febrile patients in your clinic. Patient A has had a sustained fever of 104 degrees Fahrenheit for three days. Patient B has had a sustained fever of 101 degrees Fahrenheit for one day. Which of the following statements are correct? (Select all that apply)
Answer
  • Patient A is at serious risk of denaturing their own replication, transcription, and protein synthesis complexes.
  • Patient B is keeping their infection in check by denaturing bacterial proteins.
  • Patient A is at risk of brain damage.
  • Patient B requires immediate medical intervention.

Question 17

Question
Many serious diseases can arise from the accumulation of plaques as a direct result of protein folding missteps. Which of the following is NOT a step that could ultimately lead to the accumulation of aggregates?
Answer
  • Exposed hydrophobic domains of certain proteins.
  • Protein misfolding
  • Protein denaturing
  • Controlled protein degradation

Question 18

Question
The ubiquitinylation system is analagous to what scenario?
Answer
  • Putting an old, broken chair with a clear sign that says "take me" on your curb that you would like the garbage truck to pick up.
  • Building a complicated piece of IKEA furniture.
  • Taking an old, broken chair out of the garbage because one day you'll have the energy to fix it up.
  • Destroying a complicated piece of IKEA furniture with a hammer.

Question 19

Question
If a protein is entering the S26 proteosome, what can you correctly assume? (Select all that apply)
Answer
  • The protein will be degraded into individual peptides.
  • The protein has been brought to the proteosome by a chaperon protein.
  • The protein has been ubiquitinylated.
  • The protein's quaternary structure will be restored with the addition of ATP.

Question 20

Question
Glycosylation of cell surface proteins helps to coordinate a layer of water molecules to act as an external lubricant for the cell. Which of the following examples accurately utilizes this mechanism?
Answer
  • Glycophorin A protecting the external surface of a red blood cell from frictional forces that may be encountered in circulation.
  • The alpha-helix domain of a membrane protein spanning the phospholipid bilayer, stabilizing the protein's position.
  • Glycophorin A protecting the external surface of a red blood cell from an invading bacteria.
  • The alpha-helix domain of a membrane protein spanning the phospholipid bilayer, destabilizing the protein's position and allowing for the increased passage of water out of the cell.

Question 21

Question
Which of the following is NOT true regarding the Na+/K+ ATPase pump?
Answer
  • Generates the electrical potential across membrane surfaces to drive nerve and muscle function.
  • Regulates cell volume and osmotic pressure.
  • Only supports kidney filtration functions, the Na+/K+ ATPase pump is highly specialized.
  • Most energy in the body is spent maintaining sodium and potassium gradients.

Question 22

Question
The Na+/K+ ATPase pump is an active transport system, meaning energy is expended to support its function. Which of the following steps involves the phosphorylation of ATP?
Answer
  • Binding cytoplasmic sodium ions to the protein.
  • The protein changing its conformation to permit potassium ions to bind to the receptor.
  • Binding extracellular potassium ions to the protein.
  • The protein changing its conformation to permit potassium ions to release from the receptor.

Question 23

Question
You have a heart failure patient that has clinically improved after being prescribed digoxin, a digitalis derivative. Which of the following could explain the mechanism of this improvement?
Answer
  • The digoxin has inhibited the Na+/K+ ATPase pump, decreasing the sodium ion concentration needed to pump calcium ions back into the heart tissue. This has led to an increased calcium ion concentration in the cytosol, increasing contractility of the heart.
  • The digoxin has inhibited the Na+/K+ ATPase pump, increasing the sodium ion concentration needed to pump calcium ions back into the heart tissue. This has led to a decreased calcium ion concentration in the cytosol, increasing contractility of the heart.
  • The digoxin has increased the activity of the Na+/K+ ATPase pump, decreasing the sodium ion concentration needed to pump calcium ions back into the heart tissue. This has led to an increased calcium ion concentration in the cytosol, increasing contractility of the heart.
  • The digoxin has increased the activity of the Na+/K+ ATPase pump, increasing the sodium ion concentration needed to pump calcium ions back into the heart tissue. This has led to a decreased calcium ion concentration in the cytosol, increasing contractility of the heart.

Question 24

Question
The lung airway of a healthy human has a balance of sodium and chloride ion transport through the CFTR channel. A cystic fibrosis patient has an absent or defective CFTR channel, leading to what implications? (Select all that apply)
Answer
  • The movement of chloride ions out of the cell will be impaired or nonexistent.
  • Extracellular osmotic water retention and extracellular lubrication will both be reduced.
  • Mucus will chronically build up in the airways.
  • A decrease in salt release in sweat will occur.

Question 25

Question
There are two major CFTR mutations found in cystic fibrosis. Which of the following mechanisms could explain the impaired ion transport process?
Answer
  • An abnormal channel formation, causing altered CFTR structure resulting in poor membrane binding and partial denaturing. The CFTR protein is degraded.
  • A normal channel formation, but promotion of incorrect ubiquitinylation. The CFTR protein is degraded.
  • The formation of a stable ionic bridge across the channel, partially blocking it and repelling chloride ions.
  • The formation of an unstable ionic bridge across the channel, partially blocking it and attracting chloride ions.

Question 26

Question
What is the main function of collagen?
Answer
  • Structural support
  • Vascularization
  • Neural output
  • Formation of red blood cells

Question 27

Question
Which of the following is NOT true regarding the structure of collagen?
Answer
  • Collagen is very tightly packed and stabilized by interchain hydrogen bonding between centrally located glycine peptide bonds.
  • The structural stability is highly dependent on glycosylation.
  • Proline turns the collagen chain back on itself, resulting in a right handed chain.
  • The structure contains repeated sequences of glycine, alanine, proline, and hydroxyproline.

Question 28

Question
Scurvy is a deficiency of vitamin C, resulting in a destabilization of collagen at normal body temperature. Which of the following is the mostly likely reason for this denaturation?
Answer
  • Key proline and lysine residues do not undergo hydroxylation.
  • Key proline and alanine residues do not undergo hydroxylation.
  • Key proline and lysine residues do not undergo phosphorylation.
  • Key proline and alanine residues do not undergo phosphorylation.

Question 29

Question
Which step directly leads to the formation of a pervasive collagen cross-linked matrix (fibril)?
Answer
  • The twisting of collagen fibers around one another, establishing tight H-bonding contacts. The N-terminal end forms a globular trimeric structure.
  • Excretion from the fibroblast cell and processing by an extra-cellular pair of proteases.
  • The formation of complex covalent bonds between lysine residues on adjacent subunits.
  • The formation of disulfide bonds between chains.

Question 30

Question
In osteogenesis imperfecta, point mutations to the COL1A1 and COL1A2 genes can result in unstable collagen fibers. Which of the following could be an explanation for this instability? (Select all that apply)
Answer
  • Exchanging out glycine for any other amino acid.
  • Mutated hydroxylation enzymes.
  • Mutation in processing sequences at the N and C-terminal domains.
  • Substituting bulky amino acids into the collagen structure.

Question 31

Question
Myoglobin primarily stores oxygen, whereas hemoglobin allows for oxygen transport and delivery. What is the main explanation for this variance in function?
Answer
  • Hemoglobin tightly binds to oxygen, allowing it to successfully carry oxygen through the turbulent bloodstream. Myoglobin has a lower affinity.
  • Both myoglobin and hemoglobin have a low affinity for oxygen, but the structure of both enables unequal binding.
  • The structure of myoglobin is significantly altered when bound to oxygen, making it almost impossible to dissociate. Hemoglobin is only slightly altered, allowing for easy dissociation and binding.
  • Myoglobin and hemoglobin are significantly altered when bound to oxygen, but hemoglobin is able to electrochemically react with capillary walls, permitting oxygen release to the tissues.

Question 32

Question
Each hemoglobin subunit can bind to one oxygen molecule. What happens after the first oxygen molecule binds to the first deoxyhemoglobin subunit?
Answer
  • Three other oxygen molecules bind at the same rate of the first molecule.
  • Conformational changes induced by the binding of the first molecule permit much faster binding of the other three.
  • It depends on the amount of atmospheric oxygen available.
  • Conformational changes induced by the binding of the first molecule inhibit faster binding of the other three.

Question 33

Question
As oxygen tension drops in peripheral tissues, hemoglobin tends to switch to which conformation?
Answer
  • Deoxy - 8 salt bridges
  • Deoxy - 6 salt bridges
  • Oxy - 8 salt bridges
  • Oxy - 6 salt bridges

Question 34

Question
Hemoglobin subunits have two primary histidines, a proximal and a distal. What are the functions of the distal histidine? (Select all that apply)
Answer
  • Linking the protein structure to heme dynamics on oxygen binding and release.
  • Promoting angular binding geometry of ligands.
  • Protecting oxygen binding valence of heme iron by sterically blocking the site.
  • Acting as a "sweep" to clear the heme iron of ligands in the deoxy conformation.
  • Blocking the linear association of CO with heme iron at normal environmental levels of oxygen.

Question 35

Question
Which of the following scenarios would heme exhibit the lowest affinity for oxygen?
Answer
  • pH of 7.4, carbon dioxide partial pressure of 0
  • pH of 7.2, carbon dioxide partial pressure of 0
  • pH of 7.4, carbon dioxide partial pressure of 40 torr
  • pH of 7.2, carbon dioxide partial pressure of 40 torr

Question 36

Question
Which of the following promotes oxygen ejection from hemoglobin? (Select all that apply)
Answer
  • Rapoport-Luebering shunt - stabilization of deoxy form of hemoglobin
  • Rapoport-Luebering shunt - stabilization of oxy form of hemoglobin
  • Formation of 6 additional salt-bridges between the beta subunits
  • Formation of 6 additional salt-bridges between the alpha subunits

Question 37

Question
Which of the following is NOT true regarding fetal hemoglobin?
Answer
  • The gamma subunit in fetal hemoglobin has one less histidine than adult beta hemoglobin.
  • Fetal deoxy hemoglobin is less stable than the mother's.
  • Fetal red blood cells have a lower oxygen affinity.
  • There is a net flow of oxygen across the placental barrier.

Question 38

Question
At what age would we expect to see a baby's gamma hemoglobin have a higher percentage than beta hemoglobin?
Answer
  • 1 week of age
  • 1 year of age
  • 8 weeks of age
  • 9 months of age

Question 39

Question
Which of the following accurately describes Hb-S sickle cell anemia? (Select all that apply)
Answer
  • Lysis of red blood cells.
  • Beta chain 6 position glutamate to valine substitution mutation.
  • Beta chain 6 position glutamate to lysine substitution mutation.
  • Anemia through reduced oxygen transport.

Question 40

Question
A peptide bond:
Answer
  • Has a partial double-bond character.
  • Is ionized at physiologic pH.
  • Is stable to heating in strong acids.
  • Is cleaved by agents that denature proteins, such as organic solvents and high concentrations of urea.

Question 41

Question
Which of the following statements about protein structure is correct?
Answer
  • Proteins consisting of one polypeptide can have quaternary structure.
  • The formation of a disulfide bond in a protein requires that the two participating cysteine residues be adjacent to each other in the primary sequence of the protein.
  • The denaturation of proteins always leads to irreversible loss of secondary and tertiary structure.
  • The information required for correct folding of a protein is contained in the specific sequence of amino acids along the polypeptide chain.

Question 42

Question
An 80-year old man present with impairment of higher intellectual function and alterations in mood and behavior. His family reported progressive disorientation and memory loss over the last 6 months. There is no family history of dementia. The patient was tentatively diagnosed with Alzheimer disease. Which one of the following best describes the disease?
Answer
  • It is associated with beta-amyloid - an abnormal protein with an altered amino acid sequence.
  • It results from accumulation of denatured proteins that have random conformations.
  • It is associated with the deposition of neurotoxic amyloid peptide aggregates.
  • It is associated with the accumulation of amyloid precursor protein.

Question 43

Question
Which of the following statements concerning the binding of oxygen by hemoglobin is correct?
Answer
  • The Bohr effect results in a lower affinity for oxygen at higher pH values.
  • Carbon dioxide increases the oxygen affinity of hemoglobin by binding to the C-terminal groups of the polypeptide chains.
  • The oxygen affinity of hemoglobin increases as the percentage saturation increases.
  • Oxyhemoglobin and deoxyhemoglobin have the same affinity for protons (H+).
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