Molecular Biology

Which ONE of the following IS NOT a structural gene in the lac operon? (EXAM MCQ) **

a) lacB

b) lacA

c) lacY

d) lacZ

lacB (The structural genes are lacZ, lacY, and lacA — lacB is not one of them.)

The bacterial chromosome is (EXAM MCQ)

a) Always a single circular piece of DNA

b) Contained in the nucleus of the cell

c) Linear and/or circular DNA

d) Replicated in a conservative manner

Always a single circular piece of DNA

In terms of the initiation of mRNA synthesis, which ONE of the following statements is FALSE? (EXAM MCQ)

a) Involves the binding of ribosome small subunit to the Shine-Delgarno sequence

b) Involves the binding of RNA polymerase to a promoter sequence

c) Is enhanced in prokaryotes by the presence of sigma-factors

d) Results in the formation of a transcription bubble

Involves the binding of ribosome small subunit to the Shine-Delgarno sequence (This refers to translation, not the initiation of mRNA synthesis.)

Prokaryotic translation is terminated when (EXAM MCQ) *

a) When a stop codon enters the ribosome A site

b) When the RNA polymerase releases sigma factor

c) When the ribosome spontaneously disassembles

d) When a hairpin loop forms in the RNA followed by a run of U residues

When a stop codon enters the ribosome A site

In terms of the DNA replication fork, select the ONE FALSE statement from the list below (EXAM MCQ)

a) The leading strand is replicated continuously towards the replication fork in the

5'—>3' direction

b) A replication fork moves away from the site of origin

c) The lagging strand grows towards the replication fork

d) DNA helicase unwinds the DNA strand at the replication fork

The lagging strand grows towards the replication fork

(It grows away from the replication fork in short fragments.)

What is the function of the primase enzyme? (EXAM MCQ) *

a) RNA template generation

b) Fills in nucleotides between Okazaki fragments

c) Breaks hydrogen bonds of a DNA double helix

d) Inserts nucleotides in a 5'—>3' direction

RNA template generation

(Primase synthesizes a short RNA primer.)

Which subunit of the RNA polymerase holoenzyme is essential for promoter recognition? (EXAM MCQ) *

a) α subunit

b) β subunit

c) β' subunit

d) σ (sigma) subunit

σ (sigma) subunit

Which of the following is a START codon? (EXAM MCQ)

a) GGC

b) UUA

c) CUG

d) AUG

AUG

Which ONE of the following RNA molecules is NOT involved in protein translation? (EXAM MCQ) *

a) messenger RNA (mRNA)

b) transfer RNA (tRNA)

c) ribosomal RNA (rRNA)

d) long non-coding RNA (lncRNA)

long non-coding RNA (lncRNA)

Shot-gun sequencing is a method (EXAM MCQ)

a) Employed in DNA sequencing projects where an ordered map of the DNA is initially

created and the sequence referred back to the ordered map for compilation

b) Employed to determine the sequences of proteins

c) Employed in proteomics projects to determine the protein content of a sample.

d) Employed in DNA sequencing projects where multiple DNA fragments are sequenced and

information is recompiled aided by computer analysis

Employed in DNA sequencing projects where multiple DNA fragments are sequenced and information is recompiled aided by computer analysis

Genomics involves determination of (EXAM MCQ)*

a) Protein content of a cell or sample

b) DNA content of a cell or sample

c) DNA sequences from a cell or sample

d) Metabolite content of a cell or sample

DNA sequences from a cell or sample

Eukaryotic messenger RNAs are characterized by (EXAM MCQ)

a) The addition of a polyA tail at its 5 'end

b) Being polycistronic

c) The removal of introns in a process known as splicing prior to translation

d) Being translated as they are being synthesized E. Starting all with the AUG codon

The removal of introns in a process known as splicing prior to translation

What is the approximate size of the human genome?(EXAM MCQ)

a) 3.2 million base pairs (bp)

b) 100,000 base pairs (bp)

c) 3.2 billion base pairs (bp)

d) 1 trillion base pairs (bp)

3.2 billion base pairs (bp)

What is a heritable (germline) mutation?(EXAM MCQ)*

a) Mutations in somatic cells

b) Mutations in RNA

c) Mutations in egg or sperm cells

d) Mutations in bone marrow cells

Mutations in egg or sperm cells

Which of the following is an accurate definition of a tumour suppressor gene?(EXAM MCQ) *

a) Genes that drive meiosis

b) Genes that drive mitosis

c) Genes that normally arrest cell division

d) Genes that block transcription

Genes that normally arrest cell division

In terms of the bacterial chromosome, which ONE of the following statements is FALSE? (EXAM MCQ)

a) Chromosome is always linear

b) Contained in the cell's nucleoid

c) Contains little repetitive DNA

d) Undergoes supercoiling

Chromosome is always linear

In terms of PCR primer design, which one of the following recommendations would you advise in order to limit primer dimer formation? (EXAM MCQ)

a) Design primers with base repeats e.g. ATATATAT

b) Design primers with runs of bases e.g. GGGGGGGG

c) Design primers that avoid complementarity of bases at the 3' ends of primers

d) Design primers with multiple G/C rich 3' ends

Design primers that avoid complementarity of bases at the 3' ends of primers

Which of the following statements regarding the process of transcription is FALSE? (EXAM MCQ)

a) Compared to DNA replication, only a short molecule is produced

b) Adds uracil bases instead of thymine

c) RNA polymerase can start transcription without the need for a primer

d) Proof reading occurs during transcription

Proof reading occurs during transcription

If an antisense DNA strand reads 3'-ATGCGCCAT-5', what is the RNA strand sequence? (EXAM MCQ)

a) 3'-UACGCGGUA-5'

b) 5'-TACGCGGTA-3'

c) 3'-TACGCGGTA-5'

d) 5'-UACGCGGUA-3'

5'-UACGCGGUA-3'

In terms of transcription factors (TFs), which ONE of the following statements is FALSE? (EXAM MCQ)

a) TFs are proteins that bind to DNA sequences

b) Can change the local DNA conformation

c) Only increase the levels of transcription

d) Interact with RNA polymerase

Only increase the levels of transcription

Rho factors bind to RNA molecules at what sites? (EXAM MCQ)

a) Rut sites

b) Shine-Delgarno sites

c) Promoters

d) TATA boxes

Rut sites

A silent mutation occurs when (EXAM MCQ)

a) The mutation is repaired by the DNA repair mechanisms before it undergoes transcription

b) A codon in a gene is altered by base substitutions, but there is no change in the amino acid sequence of the protein

c) The antisense strand of the DNA is transcribed instead of the sense strand

d) base substitutions alter a codon to become a STOP codon

A codon in a gene is altered by base substitutions, but there is no change in the amino acid sequence of the protein

What role does the 3' end of the 16S ribosomal RNA molecule play in translation initiation? (EXAM MCQ)

a) Forms peptide bond between amino acids

b) Binds to a specific site on mRNA molecule

c) Binds to initiator tRNA

d) Involved in the dissociation of ribosome complex

Binds to a specific site on mRNA molecule

What was the conclusion of the Meselson-Stahl Experiment? (EXAM MCQ)

a) DNA replication was dispersive

b) DNA replication was conservative

c) DNA replication was semi-conservative

d) DNA replication was semi-dispersive

DNA replication was semi-conservative (Discovered that DNA strands can separate and provide the template for two new strands)

Polycistronic messenger RNA refers to (EXAM MCQ)

a) a mRNA that contains introns and exons

b) a mRNA that needs to undergo splicing before translation

c) a mRNA which encodes two or more proteins

d) a mRNA that is produced in eukaryotes only

a mRNA which encodes two or more proteins

In terms of the RNA interference (RNAi) pathway, which ONE of the following IS NOT part of the RNAi pathway?(EXAM MCQ)

a) Drosha

b) Dicer

c) Argonaute proteins

d) Sigma factors

Sigma factors

Where is the site of protein-DNA interactions?(EXAM MCQ)

a) Minor groove of DNA

b) Major groove of DNA

c) Exons

d) Introns

Major groove of DNA

What is the function of the helicase enzyme?(EXAM MCQ)

a) RNA template generation

b) Fills in nucleotides between Okazaki fragments

c) Breaks hydrogen bonds of a DNA double helix

d) Inserts nucleotides in a 5'—>3' direction

Breaks hydrogen bonds of a DNA double helix

What are Okazaki fragments?(EXAM MCQ)

a) They are the fragments of DNA synthesized on the leading strand in DNA replication

b) They are the fragments of DNA generated by PCR

c) They are the fragments of DNA synthesized on the lagging strand in DNA replication

d) DNA fragments generated produced by the action of DNA ligase

They are the fragments of DNA synthesized on the lagging strand in DNA replication

Which ONE of the following IS NOT part of the translation initiation complex?(EXAM MCQ)

a) mRNA template

b) 30S ribosome subunit

c) tRNA carrying N-formyl-methionine

d) Elongation factors

Elongation factors

Which of the following is a STOP codon? (EXAM MCQ)

a) GGC

b) UAG

c) CUG

d) AUG

UAG

The ribosomal binding site is also known as the (EXAM MCQ)

a) Start codon

b) Rut site

c) Shine-Dalgarno sequence

d) Kozak sequence

Shine-Dalgarno sequence

In terms of the human genome, which ONE of the following statements is FALSE (EXAM MCQ)

a) 3.2 billion base pairs in size

b) Approximately 97% of the genome is non-coding

c) Largest gene is 2.3 million base pairs in size

d) Larger genome than the common wheat plant

Larger genome than the common wheat plant

A restriction enzyme (EXAM MCQ)

a) Binds to DNA and hydrolyses the phosphodiester bonds in both strands

b) Binds to the ends of DNA and joins them together

c) Removes single bases from the ends of DNA

d) Is an enzyme involved in the final stages of cell division

Binds to DNA and hydrolyses the phosphodiester bonds in both strands

In a polymerase chain reaction (PCR), what is the main advantage of Taq polymerase? (EXAM MCQ)

a) Retains activity at high temperatures

b) Does not add the wrong nucleotides during amplification

c) Can amplify long fragments

d) Cannot withstand high temperature used to denature DNA

Retains activity at high temperatures

Which ONE of the following IS NOT a characteristic of prokaryotic chromosomes?

a) Many prokaryotes contain a single circular chromosome

b) Condensed in the nucleoid via DNA supercoiling

c) Contain little repetitive DNA

d) Contain multiple linear chromosomes

Contain multiple linear chromosomes

Which type of bond links nucleotides together in a DNA strand?

Phosphodiester bond

Central Dogma

DNA-(transcription)-RNA-(translation)-protein

Transcription

DNA/Gene is copied mRNA is the copy used to build a protein

Translation

mRNA is used as intermediate instruction code to build a protein

What feature of DNA allows it to have directionality?

The 5' phosphate and 3' hydroxyl ends

How are the two strands in a DNA double helix arranged?

Antiparallel

Gene

The sequence of nucleotides within a portion of DNA that codes for a peptide or a functional RNA.

Genome

The complete set of DNA (genetic material) in an organism.

Operon

Group of genes that are located adjacent to one another in the genome.

Open reading frame (ORF)

The length of DNA which is transcribed into RNA

What do operons produce?

A single polycistronic mRNA (mRNA which encodes two or more proteins)

Exons

Coding sequence - "Stuck" together during splicing and part of mature mRNA molecule used for translation

Introns

Non-coding sections of transcript that are spliced out of the mature mRNA

Describe the gene structure of prokaryotes

mainly comprises the operon-based gene clusters (no introns)

Describe the gene structure of eukaryotes

open reading frame is disturbed by the presence of introns

Do interns interrupt the reading frame of eukaryotes or prokaryotes?

Eukaryotes

Describe the prokaryotic chromosome

Single, circular, contains essential genes

Describe the eukaryotic chromosome

Multiple, linear, condensed into a membrane bound nucleus

Where do translation and transcription occur in prokaryotes?

cytoplasm (occur simultaneously)

Where do translation and transcription occur in eukaryotes?

Transcription in the nucleus translation in the cytoplasm

Are prokaryotes haploid or diploid?

Haploid

Are eukaryotes haploid or diploid?

Diploid

Which genome is more efficient - prokaryotes or eukaryotes?

Prokaryotes (contain little repetitive DNA, eukaryotes have large amounts of noncoding and repetitive DNA)

Which direction does DNA polymerase synthesize a new strand?

5' to 3'

Why can nucleic acids only be synthesized in the 5' to 3' direction?

Because DNA polymerase adds nucleotides to the 3' OH group

What was a major achievement of the Human Genome Project in 2001?

Completion of approximately 92% of the human genome sequence

What is a contig in genomics?

A set of overlapping DNA sequences representing a consensus region

What percent of the human genome is estimated to be intergenic DNA?

About 62%

Which term refers to DNA regions between genes that often have no known function?

Intergenic regions

What is the purpose of bioinformatics in genomics?

To analyze and manage large biological datasets

Which scientist duo first proposed the semiconservative model of DNA replication?

Watson and Crick

Which structure was used to separate DNA strands during the Meselson-Stahl experiment?

Cesium chloride (CsCi) gradient centrifugation

Why was 15N used in the Meselson-Stahl experiment?

To distinguish old DNA strands from newly synthesized ones

How big is the average human gene?

3000 base pairs

How big is the biggest gene in the human genome?

2.3 million base pairs

How much of the human genome is non-coding?

97%

What percentage the human genome is identical to chimps?

98%

How many genes are in the human genome?

46000

Describe semiconservative DNA replication

daughter duplex are produced from one parental & one newly synthesized strand (two strands each containing one bit of old DNA and one bit of new)

Describe conservative DNA replication

2 original strands stay together after serving as templates for 2 new strands that also stay together (two strands at the end - one contains only old DNA, the other only new DNA)

Describe dispersive DNA replication

integrity of both parental strands disrupted - new duplex strands made of old & new DNA (neither the parental strands nor the parental duplex is preserved)

Where does replication begin?

origin of replication

What type of sequence is associated with sites of origin?

AT rich sequences

What happens at the origin of replication?

DNA binding proteins bind to initiate replication which allows for the recruitment of helicase and replication moves out bidriectionally

What is the number of human origins

40000-80000

What is the number of E. Coli origins

1

Why do humans need more origins of replication than other more simple organisms?

If there was only one origin of replication in the human genome replication would take too long

What type of bonds connect nitrogenous bases

hydrogen bonds

What is a replication fork

the Y-shaped structure that forms when the DNA double helix is unwound during replication, where new DNA strands are synthesized on each of the separated single strands

Where does replication terminate?

The point opposite the circle from the origin (replication is bidirectional)

What does DNA helicase do?

Enzyme that separates the two strands of nucleotides by breaking hydrogen bonds between complementary base pairs - "unzipping" the DNA strand.

What enzyme unzips DNA?

DNA helicase

What is an SSB?

single stranded binding protein

What is the function of SSBs?

attach to each strand to hold them apart and prevent them from base pairing and reforming a double helix during replication.

What is the function of DNA polymerase?

to add nucleotides to the end of a growing DNA strand (synthesises new DNA strand)

What enzyme synthesises DNA?

DNA polymerase

Can DNA polymerase initiate DNA strand formation?

No - needs a primer

What type of molecules are primers?

RNA

How are RNA primers synthesised?

Primase

What does primase do?

Synthesizes RNA primer

How do primers start the process of DNA replication?

They serve as binding sites for DNA Polymerase

How would you describe the continuity of the replication process?

Semi discontinuous

How would you describe the continuity of the lagging strand?

Discontinuous

How would you describe the continuity of the leading strand?

Continuous