Q: A tRNA molecule has the anticodon $$5'\text{-}GAA-3'. $$Which mRNA codon will it recognize, and what amino acid will it carry?

mRNA codon $$5'\text{-}CUU-3'$$, carrying leucine

Question 1

Which of the following best describes the central dogma of molecular biology, and what enzymes are responsible for each step?

Accepted Answer

DNA is transcribed into RNA by RNA polymerase, and RNA is translated into protein by ribosomes.

Question 2

Which of the following is an exception to the central dogma, and how does it modify the flow of genetic information?

Accepted Answer

Reverse transcription, where RNA is used as a template to synthesize DNA by reverse transcriptase: $$RNA \rightarrow DNA$$

Question 3

Given the following DNA template strand: $$3'	ext{-}TACGGTACG-5'$$, what is the corresponding mRNA sequence produced during transcription?

Accepted Answer

$$5'	ext{-}AUGCCAUGC-3'$$

Question 4

A DNA sequence is mutated from $$5'	ext{-}ATG\,GAA\,TGA\,CCT-3' to$$ $$5'	ext{-}ATG\,GAA\,TAA\,CCT-3'. $$What type of mutation has occurred, and what is the likely effect on the protein?

Accepted Answer

Nonsense mutation; a premature stop codon is introduced.

Question 5

Why is the genetic code described as redundant, unambiguous, and nearly universal?

Accepted Answer

Multiple codons can specify the same amino acid, each codon specifies only one amino acid, and the code is used by almost all organisms.

Question 6

During eukaryotic mRNA processing, which of the following modifications occur, and what is their significance?

Accepted Answer

Addition of a 5' cap, splicing of introns, and addition of a poly(A) tail; these modifications protect mRNA and facilitate translation.

Question 7

A tRNA molecule has the anticodon $$5'	ext{-}GAA-3'. $$Which mRNA codon will it recognize, and what amino acid will it carry?

Accepted Answer

mRNA codon $$5'	ext{-}CUU-3'$$, carrying leucine

Question 8

Which of the following best explains why there are fewer tRNAs and aminoacyl-tRNA synthetases (ARSs) than codons?

Accepted Answer

The wobble hypothesis allows some tRNAs to pair with more than one codon.

Question 9

Which of the following is a key difference between transcription in bacteria and eukaryotes?

Accepted Answer

Bacterial transcription occurs in the cytoplasm and does not involve RNA processing, while eukaryotic transcription occurs in the nucleus and involves capping, splicing, and polyadenylation.

Question 10

Which of the following best describes the lytic cycle of a virus?

Accepted Answer

The virus immediately replicates, assembles new virions, and lyses the host cell to release progeny.

Question 11

Which of the following best explains why bacteria primarily rely on transcriptional regulation of gene expression?

Accepted Answer

Transcriptional regulation is energy efficient, allowing bacteria to quickly respond to environmental changes by controlling mRNA synthesis.

Question 12

A mutation in the lac operon causes the lac repressor protein to be unable to bind the operator. What is the likely consequence for lac operon expression in the absence of lactose?

Accepted Answer

The lac operon will be constitutively expressed, even without lactose.

Question 13

Which of the following is a mechanism by which chromatin remodeling can increase transcriptional output in eukaryotes?

Accepted Answer

Acetylation of histone tails, which loosens chromatin structure and allows transcription factors to access DNA.

Question 14

How does alternative splicing contribute to protein diversity in eukaryotic cells?

Accepted Answer

By allowing a single gene to produce multiple mRNA variants, which are translated into different proteins.

Question 15

Which of the following best describes the role of ubiquitin and the proteasome in protein degradation?

Accepted Answer

Ubiquitin tags proteins for degradation, and the proteasome recognizes and degrades these tagged proteins.

Question 16

In DNA cloning, what is the primary function of restriction enzymes?

Accepted Answer

To cut DNA at specific sequences, generating fragments with sticky or blunt ends.

Question 17

Which of the following is NOT a required component of a PCR reaction?

Accepted Answer

DNA ligase

Question 18

How do ddNTPs function in Sanger sequencing?

Accepted Answer

They terminate DNA synthesis when incorporated, allowing determination of the DNA sequence.

Question 19

Which of the following provides evidence for genetic equivalence in plants and animals?

Accepted Answer

The ability to clone an entire organism from a single differentiated cell, as seen in Dolly the sheep.

Gene Expression, Regulation, Viruses, Biotechnology, and Development: Study Notes

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