Molecular Genetics

In which direction is the complementary strand synthesized?

A. 3’ to 5’

B. 5’ to 3’

B

• DNA polymerase synthesizes DNA in the 5’ to 3’ direction, meaning that it adds nucleotides to the 3’ end of an existing strand

How does histone acetylation affect DNA transcription?

A. increase

B. decrease

C. either

D. no effect

A

• adding acetyl groups neutralizes the positive charges on histone proteins, reducing the electrostatic attraction b/w the positively charged histones and the negatively charged DNA

Why does histone deacetylation decrease transcription levels?

A. blocks RNA polymerase from binding to DNA

B. increases the negative charge of DNA

C. makes histones more positively charged

C

• deacetylation makes histones more positively charged, increasing the electrostatic attraction b/w histone proteins and DNA

• this tightly packed chromatin is inaccessible to RNA polymerase, ultimately decreasing transcription levels

How does histone methylation affect transcription levels?

A. increase

B. decrease

C. either

D. no effect

C

• histone methylation can upregulate or down regulate transcription levels depending on which amino acids are methylated and how many groups are added

What would be the mRNA transcript if the template strand reads 3' TACA 5'?

A. 5’ AUGU 3’

B. 5’ ATGT 3’

C. 5’ UGUA 3’

D. 3’ ATGT 5’

A

• template = noncoding or antisense

• numbers are opposite, letters read left to right

  or

• numbers are the same, letters read right to left

• the mRNA transcript and DNA template strand are antiparallel, so the mRNA is synthesized in the opposite direction to the template DNA strand

  • template is read from 3’ to 5’, the mRNA is synthesized and read from 5’ to 3’

What is an operon?

A. a gene that controls the expression of multiple other genes

B. a group of related genes under the control of one promoter site

C. a region that codes primarily for transcription factors

D. a single gene under the influence of multiple promoter sites

B

To which region of an operon do activators bind?

A. operator regions

B. promoter regions

B

Which of the following best describes the lac operon?

A. inducible operon

B. repressible operon

A

• it is inactive until it is induced to become active

What does cAMP bind to regulate the lac operon?

A. CAP

B. lac repressor protein

C. operator

A

• cAMP binds to CAP

• the cAMP-CAP complex binds upstream of the promoter region and increases the expression of the lac operon

How does the lac repressor protein prevent transcription?

A. binding to the operator

B. binding to the promoter site

C. deactivating CAP

D. increasing glucose levels

A

• repressors bind to the operators

• lac repressor protein binds to the operator and prevents RNA polymerase from transcribing the lac genes

What do the structural genes in the trp operon code for?

A. trp peptidase

B. trp repressor protein

C. tryptophan

D. tryptophan synthetase

D

• the structure genes in the trp operon code for tryptophan synthetase which is an enzyme involved int he synthesis of tryptophan in bacteria

Which of the following best describes the primary benefit of alternative splicing?

A. allows for chromosomes to cross over during prophase I

B. allows for the production of multiple proteins from one gene

C. prevents eukaryotic post-transcriptional modifications

D. prevents mutations from damaging the genetic code

B

• alternative splicing allows for the production of multiple mRNA transcripts from a single pre-mRNA

• this increases genetic diversity w/o increasing the size of the genome

How do miRNA molecules silence gene expression?

A. alternative splicing

B. complementary base pairing with mRNA

C. conversion of mRNA to DNA

D. exonuclease activity

B

• miRNA are small RNA molecules that silence gene expression post-transcriptionally

• they base pair with mRNA, resulting in sequences that cannot be translated

Which of the following terms best describes the phenomenon that multiple codons can code for the same amino acid?

A. degeneracy

B. regeneration

C. relevance

D. semi-conservative

A

All of the following coding strand sequences correspond to an mRNA product that contains a stop codon EXCEPT one. Which one is the EXCEPTION?

A. 5’ TAA 3’

B. 5’ TGG 3’

C. 5’ TAG 3’

D. 5’ TGA 3’

B

• 5’ TGG 3’ in the coding strand corresponds with 5’ UGG 3’ in the mRNA transcript for an amino acid, not a stop codon

(just replace the T’s with U’s)

What catalyzes the peptide bond between the polypeptide chain and incoming amino acid on the aminoacyl-tRNA?

A. aminoacyl-tRNA synthetase

B. the mRNA

C. the ribosome

D. the tRNA

C

Where is the growing polypeptide chain transferred to during the formation of a new peptide bond?

A. A site

B. P site

C. E site

A

• the growing polypeptide chain is initially help at the P site by the tRNA

• when a new tRNA with an amino acid binds to the A site, the polypeptide chain is transferred from the tRNA at the P site to the tRNA at the A site, forming a new peptide bond

What happens when the ribosome reaches a stop codon?

A. a 3’ poly-A tail is added

B. a peptide bond is formed b/w the previous amino acid and the stop codon

C. a release factor enters the A site

D. the final amino acid enters the A site

C

• termination occurs once the ribsosome reaches the stop codon

• this signals a release factor to enter the A site, which causes the finished polypeptide to be released from the ribosome

Which of the following is NOT a common source of genetic mutations?

A. chemical damage

B. DNA polymerase errors

C. infectious disease

D. radiation

E. recombination during prophase

C

What term describes the protein subunit that makes up a viral coat?

A. capsid

B. capsomere

C. envelope

D. glycoprotein

B

• viral coats are made up of a series of protein subunits called capsomeres

• capsomeres come together to form a protective coat called the capsid

Which of the following is a viral element derived from the host's plasma membrane?

A. capsid

B. cell wall

C. envelope

D. genome

C

What is a bacteriophage?

A. a bacteria that consumes viruses

B. a type of F plasmid

C. a virus in the lytic cycle

D. a virus that infects bacteria

D

Given the coding (sense) DNA sequence below, what would be the expected mRNA transcript?

5' TAG ATC AAG 3'

A. 5’ TAC TAC AAG 3’

B. 5’ UAG AUC AAG 3’

C. 5’ UAG 3’

D. 5’ CUU GAU CUA 3’

B

• coding = sense

• the mRNA transcript is nearly identical to the coding strand, but DNA contains thymine, which is replaced by uracil in RNA

• so same order of numbers and letting but U instead of T

Which process uses topoisomerases?

A. transcription

B. histone methylation

C. translation

D. post-transcriptional modifications

E. RNA replication

A

Which structural feature in certain regulatory proteins enables them to bind to DNA through specific interactions with base pairs?

A. 5’ cap

B. alpha helix

C. disulfide bridge

D. transmembrane domain

E. helix-turn-helix

E

• regulatory proteins use structural features called DNA-binding motifs to bind to DNA

  4 main types of motifs:

• zinc finger

• helix-turn-helix

• homeodomain

• leucine zipper

How do bacteriophages contribute to bacterial genetic diversity?

A. transduction

B. F plasmid

C. vertical gene transfer

D. pilus conjugation

E. transformation

A

• in the process of infecting one bacterium, bacteriophages can pick up bacterial DNA and transfer it to a new host after replication, adding the the new bacterium’s gene pool

  • this is transduction

Which of the following processes can a competent bacteria perform?

A. transfer genes out of the bacteria via transduction

B. transfer genes out of the bacteria via transformation

C. transfer genes into the bacteria via transduction

D. transfer genes into the bacteria via transformation

D

• if a bacterium is competent, it can receive genes via transformation, the uptake of naked DNA from the environment

• transduction does not require competent bacteria to deliver or receive bacterial viruses

• competent bacteria import foreign DNA, rather than moving it out

Which best indicates that a bacterial colony is developing antibiotic resistance?

A. more bacteria contain R-factors

B. increased protein synthesis

C. more bacteria possess an F-plasmid

D. decreased bacterial membrane permeability

A

• R-factors are plasmids that contain antibiotic-resistance genes

Which of the following describes a virus that has infected a bacterial cell and integrated into the host's genome?

A. episome

B. vector

C. prophage

D. capsid

E. plasmid

C

• a prophage describes a bacteriophage once it has inserted its genetic material into the genome of the host cell

Which of the following mRNA transcripts, if mutated, would most likely result in a longer-than-expected protein product?

A. 5’ AUG 3’

B. 5’ UAA 3’

C. 5’ UGT 3’

D. 5’ CCC 3’

E. 5’ AUU 3’

B

• UAA is a stop codon

• if any of the stop codons undergo a mutation, an amino acid could be introduced into the protein chain instead of terminating translation

Where does rRNA synthesis take place within a eukaryotic cell?

A. nucleosome

B. nucleolus

C. rough ER

D. cytosol

E. smooth ER

B

All of the following are part of mRNA processing EXCEPT one. Which is the EXCEPTION?

A. phosphorylation of 3’ end

B. addition of a 5’ guanine cap

C. attachment of poly-A tail

D. RNA splicing

E. regulation via miRNA

A

During the process of translation, what results in the release of the completed polypeptide?

A. the ribosome reaches a termination anticodon

B. depletion of amino acids

C. the ribosome reaches the 5’ end of the mRNA

D. depletion of tRNAs

E. the ribosome reaches a termination codon

E

All of the following statements regarding viruses are true EXCEPT one. What is the EXCEPTION?

A. viruses are a classification of infectious cells

B. HIV, influenza, and the common cold are diseases caused by viruses

C. viruses are packages of nucleic acid surrounded by a protein coat

D. bacteriophages can transfer bacterial DNA b/w different hosts

A

• viruses rely entirely on a host cell for their functions, while living cells do not, so they are not “alive”

A researcher injects an unedited human gene encoding for insulin production into a bacterium and a fungus. The fungus produces a noticeable amount of insulin, while the bacterium does not. Which of the following reasons best explains why the bacterium cannot express the gene?

A. eukaryotic genes possess both introns and exons

B. bacteria cannot integrate foreign DNA into their genomes

C. bacterial plasmids must be single-stranded

D. prokaryotic RNA polymerase cannot read eukaryotic DNA

E prokaryotic ribosomes cannot translate eukaryotic mRNA

A

• b/c prokaryotes cannot splice out introns, the translation of unedited eukaryotic genes may result in inaccurate expression

All of the following are involved in protein synthesis EXCEPT one. Which is the EXCEPTION?

A. alpha helix formation

B. glycine

C. peptide bond formation

D. rRNA

E. zinc finger

E

• zinc gingers are a type of DNA-binding motif that allow regulatory proteins to control transcription by binding to specific DNA regulatory sequences

All of the following contribute to DNA mutations EXCEPT one. What is the EXCEPTION?

A. radiation

B. spliceosomes

C. replication errors

D. transposons

E. chemical damage

B

• spliceosomes are large complexes of snRNAs and proteins that catalyze the removal of introns from mRNA transcripts

• they act upon mRNA, not DNA

Which of the following factors limits the number of cell divisions in a cell line?

A. acetylation of histones

B. activation of a terminator sequence

C. activation of silencers

D. genetic drift

E. telomere shortening

E

• as telomeres shrink during replication cycles, the uncopied area will eventually reach important, coding regions of DNA

• damage to coding areas induces apoptosis, ending the cell line

All of the following statements about viral replication are true EXCEPT one. Which is the EXCEPTION?

A. in the lysogenic cycle, the virus remains dormant in the host cell until triggered

B. the virus sheds its plasma membrane upon entering a host cell

C. viral genomes and proteins are synthesized using host cell machinery

D. in the lytic cycle, the virus will destroy the host cell

E. the viral genome may have RNA or DNA as its starting point for replication

B

• a virus does not have a plasma membrane, no well well, and no organelles

Which of the following best describes transposons?

A. movable DNA segments

B. channels b/w connecting cells

C. appendages connecting bacteria during horizontal gene transfer

D. complexes that splice exons

E. transmembrane cellular channels

A

Which of the following statements about human DNA is true?

A. DNA is exclusively found in the nucleus

B. all cells in the human body express the same genes

C. the human genome contains approximately 33,000 genes

D. human DNA contains more non-coding regions than coding regions

E. DNA contains uracil in place of thymine

D