Organization of the gene, Transcription, & Translation

Question 1

Which of the following is the primary outcome of transcription?

Answer 1

Synthesizing RNA from DNA

The central dogma of biology explains the flow of genetic material as moving from DNA to RNA to protein. Transcription is the process of synthesizing RNA from DNA.

Question 2

In which organelle does DNA transcription occur in eukaryotes?

Answer 2

Nucleus

DNA transcription is the process of synthesizing RNA from DNA. This takes place entirely within the nucleus of eukaryotes.

Question 3

Which of the following is the mechanism by which RNA polymerase adds a nucleotide to RNA?

Answer 3

Formation of a phosphodiester bond between the 3’ hydroxyl group on the RNA chain and the phosphate group of the nucleotide

RNA is synthesized in the 5’→3’ direction. Nucleotides are added to the 3’ end of a growing chain, with the formation of a phosphodiester bond between the 3’ hydroxyl group on the RNA chain and the phosphate group of the nucleotide.

Question 4

Which base is present in RNA but not DNA?

Answer 4

Uracil

Question 5

Where in the cell are poly-A tails added to mRNA sequences?

Answer 5

Nucleus

Post-transcriptional modification is the alteration of RNA after transcription. These modifications include the addition of a poly-A tail and a 5’-cap, as well as splicing and ubiquitination.

Question 6

Which of the following processes will mark an mRNA for destruction?

Answer 6

Ubiquitination

Ubiquitination is a post-transcriptional modification that can flag mRNA strands for destruction.

Question 7

Site activators bind to which of the following?

Answer 7

Enhancer

Enhancers are DNA sequences that promote gene transcription. They are bound and activated by site activators and can be located upstream or downstream from a gene.

Question 8

TATAAT and CAAT boxes comprise which of the following DNA regions?

Answer 8

Promoter

Promoter regions involve DNA made of repeating sequences of TATAAT or CAAT that are bound by transcription factors and RNA polymerase II. These sequences control gene expression and are found near the beginning of a gene (10-35 bp upstream).

Question 9

Which of the following binds to the promoter region?

Answer 9

RNA polymerase II

RNA polymerase II is a eukaryotic DNA polymerase that binds to the promoter region of DNA to initiate transcription of a gene.

Question 10

Which sequence will be expressed and leave the nucleus after transcription?

Answer 10

Exons

Exons are the components of transcribed mRNA that will comprise mature mRNA. Exons are the only sequences involved in DNA transcription that will leave the nucleus.

Mnemonic: EXons are EXpressed; INtrons stay IN the nucleus.

Question 11

Which of the following is found at the 3’ end of the synthesized mRNA strand?

Answer 11

Multiple adenosine bases (Poly A tail)

Poly-A tails are sequences of multiple adenosine bases added onto the 3’ end of mRNA. It signals for the addition of the AAUAAA sequence to be added to mRNA to direct proper cleavage of the molecule.

Question 12

Which of the following is bound by repressors and inhibits gene transcription?

Answer 12

Sequence found on an intron

Silencers are sequences of DNA that are bound by repressors and suppress transcription of their associated gene. These sequences are found on introns or far away from a gene and will be removed from the final mRNA sequence.

Question 13

Which of the following is the correct list of components that make up mature mRNA?

Answer 13

3’ poly-A tail, a 5’ methylguanine cap, and exon sequences

There are 3 components to mature mRNA: a 3’ poly-A tail, a 5’ methylguanine cap, and exon sequences. Mature mRNA will leave the nucleus where translation into a polypeptide will occur.

Question 14

Amino acids bind to which of the following sequences on tRNA?

Answer 14

CCA

Amino acids bind to the CCA sequence on the 3’ end of tRNA.

Mnemonic: CCA = Can Carry Amino acids.

Question 15

Which of the following structures allows tRNA to bind to the ribosome?

Answer 15

t-arm

The T-arm of tRNA allows for attachment with the ribosome during translation. The T-arm contains uridine, cytidine, and ribothymidine residues that are unique to this structure.

Question 16

Which structure binds to the enzyme responsible for adding an amino acid to tRNA?

Answer 16

D-Arm

The D-arm of tRNA contains dihydrouridine residues that bind to aminoacyl tRNA synthetase.

Aminoacyl tRNA synthetase is an enzyme that uses an ATP to add an amino acid to the CCA end of tRNA, a process known as “charging.”

Question 17

Which of the following components of tRNA determines which amino acid will be added to a polypeptide during translation?

Answer 17

Anticodon

The anticodon loop contains a trinucleotide sequence that correlates with an mRNA codon. Matching these codons and anticodons determines which amino acids will be added to the polypeptide chain during translation.

Key Takeaway:
The anticodon is a trinucleotide sequence found on tRNA that binds to a complementary mRNA codon.
This sequence determines the amino acid that will be added to the growing polypeptide chain during translation.

Question 18

Which of the following describes the concept of redundancy in the context of DNA translation?

Answer 18

Multiple codons with different base sequences from the anticodon can code for the same amino acid.

Redundancy of codons refers to the mechanism by which multiple codons with different base sequences from the anticodon can code for the same amino acid.

This is possible due to the wobble pairing. That is, the third base in codon sequences of a tRNA anticodon can differ from the anticodon while still coding for the same amino acid. This mechanism is protective against mutations that could lead to potential errors in translation.

[Choice C]: Codons coding for the same amino acids across species is known as the “universality” of codon sequences.

Key Takeaway:
The redundancy of codons describes how multiple codons can code for the same amino acid.
Redundancy is possible due to the wobble position in codons.

Question 19

Redundancy allows for which of the following mutations to occur safely in translation?

Answer 19

Silent

Codon redundancy describes how codons can code for the same amino acid despite having a different base in the 3rd, or wobble, position of the tRNA anticodon.

This allows different bases in the wobble position to persist, resulting in silent mutations that have no effect on the amino acid added during translation.

Question 20

Which of the following molecules provides the energy to allow for tRNA charging?

Answer 20

ATP

Aminoacyl tRNA synthetase is the enzyme responsible for loading amino acids onto the CCA sequence of tRNA. This process is called charging and requires an ATP to take place.

Question 21

In eukaryotes, the first ribosomal subunit to assemble during initiation is the _____ subunit which requires energy derived from _____.

Answer 21

40s ; GTP

Initiation is the first step in DNA translation and involves the assembly of ribosomal subunits. The 40s subunit is assembled first using energy derived from hydrolysis of a GTP molecule.

Question 22

The 30s ribosomal subunit can identify where to bind on the mRNA strand by locating which of the following?

Answer 22

Shine-Dalgarno sequence

The Shine-Dalgarno sequence is located ~7 bases upstream of the start codon on mRNA in prokaryotes. The 30s ribosomal subunit locates this sequence and uses it to identify where to bind on the mRNA to assemble a full 70s ribosome.

Question 23

Which of the following are the correct sizes of eukaryotic ribosomal subunits and a fully assembled ribosome?

Answer 23

D

In eukaryotes, the small 40s subunit and the large 60s subunit assemble around the mRNA to create a full 80s ribosome. In prokaryotes, the subunits are 30s and 50s, which assemble into a 70s ribosome.

Key Takeaway:
The subunits and ribosome in eukaryotes have even numbers: 40s, 60s, and 80s.
The subunits and ribosome in prokaryotes have odd numbers: 30s, 50s, and 70s.

Question 24

Which of the following is the start codon?

Answer 24

AUG

The AUG codon codes for methionine and is the first codon of mRNA translated by a ribosome. It is therefore known as the start codon.

Question 25

Which of the following is true of fMET?

Answer 25

It signals the presence of bacteria in human tissues

fMET is a derivative of methionine found only in prokaryotes used to initiate protein synthesis. In humans, fMET can be recognized and bound by polymorphonuclear cells that subsequently recruit leukocytes to the site.

Question 26

Which ribosomal site contains the growing polypeptide chain?

Answer 26

P-site

The P site is the second site within the ribosome that contains the growing polypeptide chain. After the amino acid of the new tRNA in the A site has formed a peptide bond, the tRNA, along with the entire polypeptide chain attached, will move from the A site to the P site.

The sites APE stand for Aminoacyl, Peptidyl, and Exit.

Question 27

Which of the following molecules is the energy source involved in initiation, elongation, and termination of a polypeptide chain?

Answer 27

GTP

During translation, enzymes derive energy from the hydrolysis of GTP to perform initiation, elongation, and termination of polypeptide chains.

Question 28

A mutation that adds the codon UAG into a gene sequence will have what effect?

Answer 28

Nonsense mutation

UAG is a stop codon found at the end of an mRNA sequence that signals the termination of a polypeptide chain.

If a stop codon is placed in the middle of an mRNA sequence due to a mutation, it will lead to premature termination of the polypeptide chain. This is known as a nonsense mutation.

Mnemonic: The three stop codons can be remembered with the following phrases:
U Go Away (UGA)
U Are Away (UAA)
U Are Gone (UAG)
[Choice A]: Missense mutations occur when a mutation causes a different amino acid to be placed into a polypeptide chain.

Key Takeaway:
Aberrant insertion of a stop codon leads to premature termination of the polypeptide chain.
This is known as a nonsense mutation.

Question 29

Where does post-translational modification primarily occur?

Answer 29

Golgi apperatus

Post-translational modification involves additions, reductions, and alterations to polypeptide chains after synthesis. The majority of modification occurs in the Golgi apparatus. Some modification also occurs in the cytoplasm and the endoplasmic reticulum.

Key Takeaway:
The majority of post-translational modification occurs in the Golgi apparatus.

Question 30

DNA transcription ceases when RNA polymerase reaches the signal.

Answer 30

termination

Question 31

(DNA/RNA) polymerase unwinds the DNA double helix at the initiation of transcription.

Answer 31

RNA polymerase

Question 32

A hybrid is a small segment where messenger RNA is still hydrogen-bonded to template DNA during the elongation phase of DNA transcription.

Answer 32

DNA-RNA hybrid

Question 33

are RNA complexes that must remove introns and combine exons in order to change the pre-messenger RNA into functional messenger RNA.

Answer 33

Splicesomes

Question 34

Transcription factors bind to a unique DNA sequence termed the , which signals to initiate DNA transcription.

Answer 34

promoter

Question 35

The promoting factor is a protein complex that is required to allow the cell to move from the G2 phase to the M phase.

Answer 35

M-phase

Question 36

kinases are regulatory proteins that regulate the transition to the S phase of the cell cycle and whose concentrations remain constant.

Answer 36

Cyclin-dependent kinases

Question 37

Most cells contain a checkpoint at the phase of the cell cycle, often termed the restriction point.

Answer 37

G1 phase

Question 38

are regulatory proteins that regulate the transition to the S phase of the cell cycle and whose concentrations increase and decrease with the cell cycle.

Answer 38

Cyclins