Discussion 3

Question 1

Which statement is TRUE for RNA but not DNA?

RNA uses 2-deoxyribose sugar.

RNA uses uracil as a nitrogenous base.

RNA is created from DNA in a process known as translation.

RNA is the only nucleic acid that can be absorbed in the UV spectrum.

Answer 1

RNA uses uracil as a nitrogenous base.

Question 2

RNA occurs primarily as single stranded molecules that can give rise to _______ structures.

diploid
stem-loop
parallel
tautomeric
haploid

Answer 2

stem-loop

Question 3

Genomic DNA is _____, resulting in the production of _____.

transcribed; mRNA

translated; tRNA

transcribed; protein

translated; protein

translated; rRNA

Answer 3

transcribed; mRNA

Question 4

Polypeptide synthesis proceeds from the _____ to the _____.

entrance site; exit site

50S subunit; 30S subunit

C-terminus; N-terminus

N-terminus; C-terminus

peptidyl site; aminoacyl site

Answer 4

N-terminus; C-terminus

Question 5

a. Name these three types of RNA____________

Answer 5

rRNA, tRNA, mRNA.

Question 6

_____________ moves genetic information from the nucleus to the ribosomes in the cytoplasm. ______________ decodes the genetic message; it matches sequences of three nucleotides to amino acids. __________________is involved in the catalysis of amide bond formation.

Answer 6

mRNA, tRNA, rRNA.

Question 7

In bacteria, riboflavin can inhibit its own synthesis by binding to an mRNA element termed a _____________

Answer 7

riboswitch.

Question 8

RNA interference is a mechanism of post-transcriptional RNA-dependent ______.

chromatin-remodeling

gene silencing

histone methylation

coactivation

apoptosis

Answer 8

gene silencing

Question 9

What is the region immediately adjacent to the starting site for RNA polymerization called?

promoter

enhancer

initiator

consensus sequence

TF binding site

Answer 9

promoter

Question 10

Two amino acids of the standard 20 contain hydroxyl-groups. They are:

cysteine and serine.

cysteine and threonine.

methionine and cysteine.

methionine and serine.

threonine and serine.

Answer 10

threonine and serine.

Question 11

At a pH above its pKa, the phenol group of tyrosine is_______________

Answer 11

deprotonated.

Question 12

A typical protein weighs ________ daltons.

50

500

5000

50,000

Answer 12

50,000

Question 13

Which statement is most TRUE regarding peptide bonds?

They are amide linkages that connect amino acids.

They are flexible linkages that rotate around the sp2 bond in the carbonyl carbon.

They are composed of an electronegative carbonyl group and an electropositive nitrogen atom.

They are weaker than London dispersion forces.

Answer 13

They are amide linkages that connect amino acids.

Question 14

In the tripeptide Lys-Pro-Ile, the C-terminal residue is____________

Answer 14

Ile.

Question 15

The formation of a dipeptide from two amino acids involves

side-chain complementarity.
loss of water.
oxidation of the α-carbon.
reduction of the α-carbon.
base catalysis.

Answer 15

loss of water.

Question 16

Which one of the following statements about peptide bonds is FALSE. Peptide bonds are:

rigid and planar, with partial double-bond character.

charged.

covalent.

involved in forming the primary structure of proteins.

amides.

Answer 16

charged.

Question 17

Which of the following statements BEST describes a prosthetic group?

They are nonpeptide molecules or ions critical to a protein’s structure.

They are short peptide chains attached to a larger protein.

They are nonfunctional components of a protein.

They are the active part of an enzyme.

Answer 17

They are nonpeptide molecules or ions critical to a protein’s structure.

Question 18

Which of the following are methods of denaturing a protein?

pH changes

heat

mechanical agitation

all of the above

Answer 18

all of the above

Question 19

Why do detergents denature proteins?

The primary structure of the protein can cause alterations in the charges of the residues.

The secondary structure can be altered because of disruptions in the hydrogen bonding.

The forces stabilizing the tertiary structure are disrupted, changing the conformation of the protein.

The quaternary structure can be modified because of the deprotonation of prosthetic groups.

Answer 19

The forces stabilizing the tertiary structure are disrupted, changing the conformation of the protein.

Question 20

Two cysteine residues would most likely result in what type of bonding?

hydrogen bond

disulfide bond

dispersion forces

salt bridge

Answer 20

disulfide bond

Question 21

The simplest protein structure is __________ structure.

primary

secondary

tertiary

quarternary

Answer 21

primary

Question 22

The overall charge of the polypeptide His-Tyr-Lys-Met-Ile-Glu at pH 6.9 is ___?

–2

–1

0

+1

+2

Answer 22

0

Question 23

Which level of protein structure is defined as “the hydrogen bonded arrangement of the polypeptide backbone”?

Primary

Secondary

Tertiary

Quaternary

Answer 23

Secondary

Question 24

Why does a decrease in pH alter/disrupt the tertiary structure of an enzyme?

It reduces disulphide bonds.

It promotes proteolytic cleavage of peptide bonds.

It disrupts ion pairs/salt bridges.

It reduces hydrophobic interactions.

It deprotonates prosthetic groups.

Answer 24

It disrupts ion pairs/salt bridges.

Question 25

Zwitterions are _____. amino acids ionic molecules that are racemic ions that bear both negatively and positively charged groups side-chain carboxylate anions delocalized ions

Answer 25

ions that bear both negatively and positively charged groups

Question 26

Which of the 20 standard amino acids is optically inactive? Arg Pro Ile Gly Cys

Answer 26

Gly

Question 27

Which of the following amino acids has a charged polar side chain at pH 7.0? Leu Ala Met Trp Glu

Answer 27

Glu

Question 28

Which of the following amino acids has a sulfur atom in its side chain? Asn Ser Phe Met Tyr

Answer 28

Met

Question 29

At a pH above its pKa, the R-group of Asp is _____. protonated and neutral protonated and positively charged deprotonated and neutral deprotonated and negatively charged none of the above

Answer 29

deprotonated and negatively charged

Question 30

Leucine has a ___________side chain; glutamate has a ____________ side chain.

Answer 30

Non-polar, charged.

Question 31

At physiological pH, all amino acids have at least _____ charged groups. 0 1 2 3 cannot be determined

Answer 31

2

Question 32

a. How many different amino acids can be incorporated into proteins during translation?

Answer 32

20

Question 33

b. Do ribosomes use L or D amino acids for protein synthesis?

Answer 33

L

Question 34

Choose amino acid(s) and amino acid derivative(s) that can act as neurotransmitter. Select all that apply. glycine glutamate γ-aminobutyric acid (GABA) proline valine

Answer 34

glycine glutamate γ-aminobutyric acid (GABA)

Question 35

The peptide AYDG has an N-terminal _________ residue. glycine glutamic acid glutamine aspartic acid alanine

Answer 35

alanine

Question 36

Which of the following tripeptides would be expected to be the most hydrophobic? KYG KYA GYA DYA DYG

Answer 36

GYA

Question 37

The predominant noncovalent interaction seen in α helices and β sheets is _____. electrostatic interaction hydrogen bond dipole–dipole interaction hydrophobic interaction all of the above

Answer 37

hydrogen bond

Question 38

Which of the following amino acids is generally absent from an α helix? Trp Ser Ile Pro none of the above

Answer 38

Pro

Question 39

α helices and β sheets constitute _____ structure. primary secondary tertiary quaternary none of the above

Answer 39

Secondary

Question 40

Which of the following best describes the peptide backbone in a β sheet? coiled compacted highly extended rigid none of the above

Answer 40

highly extended

Question 41

In a protein, the most conformationally restricted amino acid is ______; the least conformationally restricted is ______. Trp, Gly Met, Cys Pro, Gly Ile, Ala Ala, Pro

Answer 41

Pro, Gly