4 RNA polymerases RNA processing Splicing of pre-mrna Introns Vs exons tRNA Protein synthesis Post-transitional modifications Chaperone protein

Question 1

RNA polymerases have no proofreading function in ____ (prokaryotes/eukaryotes).

Answer 1

Eukaryotes

Question 2

A gardener finds a cap mushroom and decides to eat it. Later, liver failure develops. How did this happen?

Answer 2

The mushrooms likely contain α-amanitin, which inhibits RNA polymerase II and causes severe hepatotoxicity

Question 3

In eukaryotes, ____ makes tRNA, ____ makes mRNA, and ____ makes rRNA
RNA polymerase

Answer 3

III; II; I

Question 4

Of the RNA types, ____ is the largest RNA, ____ is the most abundant RNA, and ____ is the smallest RNA.

Answer 4

mRNA; rRNA; tRNA (massive, rampant, and tiny, respectively)

Question 5

In prokaryotes, which enzyme makes rRNA, mRNA, and tRNA?

Answer 5

RNA polymerase (one single multisubunit complex)

Question 6

Where does RNA polymerase II open DNA?

Answer 6

At the promoter site

Question 7

What is rifampin’s mechanism of action?

Answer 7

Inhibition of RNA polymerase in prokaryotes

Question 8

What is actinomycin D’s mechanism of action?

Answer 8

Inhibition of RNA polymerase in both prokaryotes and eukaryotes

Question 9

Where does eukaryotic RNA processing occur?

Answer 9

In the nucleus

Question 10

Which three modifications take place during eukaryotic RNA processing?

Answer 10

Capping on the 5′ end, polyadenylation on the 3′ end, and splicing out of introns

Question 11

Approximately how many adenosine monophosphates are added to the 3′ end of mRNA during polyadenylation?

Answer 11

200

Question 12

What is the term for the initial (unprocessed) RNA transcript in eukaryotes?

Answer 12

Heterogeneous nuclear RNA (hnRNA)

Question 13

What function does the sequence AAUAAA serve in eukaryotes?

Answer 13

Polyadenylation signal

Question 14

Poly-A polymerase ____ (does/does not) require a template.

Answer 14

Does not

Question 15

A science experiment is done to add the 7-methylguanosine cap. Where does this occur in the cell?

Answer 15

In the nucleus—it is added to the 5′ end of the hnRNA

Question 16

What is the role of cytoplasmic P-bodies in RNA processing?

Answer 16

Location of mRNA quality control—accomplished using exonucleases, decapping enzymes, and micro-RNAs

Question 17

What binds to a primary mRNA transcript and forms a spliceosome?

Answer 17

Small nuclear ribonucleoprotein particles (snRNPs) and other proteins

Question 18

snRNPs form a lariat-shaped loop in order to do what?

Answer 18

Isolate an intron for removal

Question 19

A patient presents with a malar “butterfly” rash and renal disease. What antibodies does her disease make?

Answer 19

She has lupus, associated with spliceosomal snRNP antibodies (anti-Smith); mixed connective tissue disease (MCTD) has anti-U1 RNP antibodies

Question 20

____ (Exons/Introns) contain the genetic information to code for protein.

Answer 20

Exons (exons exit and are expressed)

Question 21

What is the name for the intervening noncoding segments of DNA within a gene?

Answer 21

Introns (introns are intervening sequences and stay in the nucleus)

Question 22

β-thalassemia mutations can result from ____, a process that combines exons to make unique proteins in different tissues.

Answer 22

Alternative splicing, which, in this case, yields a pathologic protein

Question 23

What mechanism allows the same gene to encode for multiple proteins?

Answer 23

Alternative splicing

Question 24

A patient’s cancer cells undergo genetic analysis. What splicing-related phenomenon may be implicated in the tumor’s initial oncogenesis?

Answer 24

Abnormal splicing variants

Question 25

What part of a tRNA lies opposite from its 3′ aminoacyl end?

Answer 25

The anticodon end

Question 26

Which three-nucleotide sequence do all eukaryotic and prokaryotic tRNAs have at their 3′-ends?

Answer 26

CCA (Can Carry Amino acids)

Question 27

• Where on a tRNA does the amino acid that will be incorporated into the protein bind?

Answer 27

The 3′ end

Question 28

Does charging a tRNA molecule with an amino acid require energy?

Answer 28

Yes, as ATP is hydrolyzed in the process

Question 29

If a tRNA had a methionine bound to it, what would the sequence of the codon it binds read, in 5′-to-3′ order? And the anticodon?

Answer 29

Codon = AUG; anticodon = CAU

Question 30

• What are the substrates of the reaction that is catalyzed by aminoacyl-tRNA synthetase (the “matchmaker”)?

Answer 30

The uncharged tRNA and the appropriate amino acid, ATP

Question 31

What does aminoacyl-tRNA synthetase do?

Answer 31

It scrutinizes the amino acid before and after it binds to tRNA, hydrolyzing the bond if an incorrect amino acid is present

Question 32

Which sequence is necessary for tRNA-ribosome binding?

Answer 32

Thymine, pseudouridine, cytosine (TΨC), found on the T-arm

Question 33

What is the purpose of the D-arm?

Answer 33

Ensures identification by the correct aminoacyl-tRNA synthetase

Question 34

What hypothesis states that only the first two positions of a triplet codon on mRNA have a precise pairing with the tRNA anticodon?

Answer 34

Wobble hypothesis

Question 35

The wobble hypothesis primarily explains the ____ (unambiguous/degeneracy/universal/commaless) nature of the genetic code.

Answer 35

Degeneracy

Question 36

What are the two subunits of the eukaryotic ribosome called?

Answer 36

The 60S subunit and the 40S subunit—40S + 60S leads to 80S (Eukaryotic = Even)

Question 37

____ (Eukaryotes/Prokaryotes) have ribosomes with 50S and 30S subunits.

Answer 37

Prokaryotes; 30S + 50S leads to 70S (prOkaryotes are Odd)

Question 38

A scientist studying protein synthesis wants to block initiator methionine tRNA. He makes an inhibitor blocking the A site. Will this work?

Answer 38

No, as the initiator methionine tRNA does not bind at the A site (it is the sole exception; all other aminoacyl-tRNA combinations bind here)

Question 39

At the start of protein synthesis, what process occurs at the same time as the hydrolysis of methionine’s bond with its tRNA?

Answer 39

The formation of a peptide bond between methionine and the second amino acid in the polypeptide

Question 40

When referring the “P site” of a ribosome, what does the “P” stand for?

Answer 40

Peptide—the P site accommodates the growing polypeptide chain

Question 41

Which molecules are responsible for assembling the 40S subunit with the initiator tRNA?

Answer 41

Eukaryotic initiation factors (IFs)

Question 42

In what direction relative to the mRNA does the ribosome shift after the formation of a peptidyl bond?

Answer 42

Toward the 3′ end

Question 43

When the ribosome shifts after the formation of a peptidyl bond, to what position does the tRNA with the growing peptide chain go?

Answer 43

The P site (translocation)

Question 44

What molecule provides the energy for the binding of tRNA to the ribosome/mRNA complex?

Answer 44

Guanosine triphosphate (GTP tRNA = Gripping)

Question 45

What molecule provides the energy for the translocation of the ribosome along the mRNA?

Answer 45

Guanosine triphosphate (GTP tRNA = Going places)

Question 46

When the ribosome shifts after the formation of a peptidyl bond, where is the uncharged tRNA found?

Answer 46

• In the E position (holds Empty tRNA as it Exits

Question 47

In protein synthesis, what are the three steps of protein elongation?

Answer 47

Aminoacyl-tRNA binding to A site, transfer of growing peptide chain to amino acid at the A site by the ribsome, and, finally, translocation

Question 48

A patient takes an antibiotic that blocks the prokaryotic 30S subunit from assembling. How does it interfere with protein synthesis?

Answer 48

It inhibits formation of the initiation complex, causing misreading of mRNA

Question 49

• A patient with a MRSA infection takes an antibiotic that inhibits translocation by binding the 50S subunit. Does this affect human cells?

Answer 49

No—the 50S subunit is prokaryotic, so human cells are minimally targeted by this drug

Question 50

In termination, what recognizes the stop codon and frees the completed protein from the ribosome?

Answer 50

Release factor

Question 51

What is an example of protein trimming after translation?

Answer 51

Removing N- or C-terminal propeptides from a zymogen to yield a mature protein (example: conversion of trypsinogen into trypsin)

Question 52

A scientist wants to write about covalent alterations. Name six kinds of posttranslational protein modifications that are involved.

Answer 52

Phosphorylation, glycosylation, hydroxylation, methylation, acetylation, and ubiquitination

Question 53

• What is a chaperone protein?

Answer 53

An intracellular protein that is involved in facilitating and/or maintaining protein folding

Question 54

A scientist studies Hsp60, a protein expressed in yeast to prevent misfolding at high temperatures. How are these proteins classified?

Answer 54

Heat shock proteins̬class of chaperone proteins that facilitate and maintain proper protein folding)