An RNA chain is synthesized in which direction?

5′-to-3′ only

In eukaryotes, which parts of a gene are transcribed into RNA?

introns and exons

How many different aminoacyl-tRNA synthetases do most organisms have?

one for each amino acid

What is false regarding codons in mRNA molecules?

Some codons code for more than one amino acid.

It is thought that, early in the history of life, RNAs not only stored information but acted as catalysts in cells. Which reaction is catalyzed by a ribozyme in present-day cells?

peptide bond formation during translation

Which of the following statements is NOT true about liver cells and kidney cells in the same organism?

They contain different genes.

Which of the following would be the best method for determining which genes are being transcribed in a particular cell type?

RNA sequencing

In eukaryotes, where do transcription regulators bind?

upstream, downstream, or within the genes they control

What is an operon?

a set of genes transcribed as a single mRNA from a single promoter

Which is NOT an example of epigenetic inheritance?

the inheritance of a single point mutation in a gene

Which does NOT affect gene expression at the post-transcriptional level?

DNA methylation

A scientist prepared 1.2 liters of a 250 mM sodium chloride (NaCl) solution. However, after preparing the solution (but not using it), she determines that the experiment setup needs 20% more solution than originally planned. Because it is critical that the solution concentration be exactly 250 mM NaCl, she decides to:1. Increase the volume of the solution to 1.5 liters.
2. Correct the NaCl concentration by calculating the amount of NaCl required to
reach the desired concentration.
Considering that the molecular weight of NaCl is 58.44 g/mol, select the correct answer below:

She needs to add 4.38 g NaCl to the existing solution and then complete the volume to 1.5 liters.

A chemist needs to prepare 350 ml of a 100 mM potassium nitrate (KNO3) solution. However, after preparing the solution, the chemist realizes that the experiment requires the final concentration to be 150 mM. Because it is critical that the solution concentration be exactly 150 mM KNO3, the chemist decides to:
1. Increase the volume of the solution to 0.5 liters.
2. Correct the KNO3 concentration by calculating the amount of KNO3 required to reach the desired concentration.

Considering the molecular weight of KNO3 is 101.10 g/mol, select the correct answer below:

The chemist needs to add 4.08 g KNO3 to the existing solution and then complete the volume to 0.5 liters.

A scientist initially prepared 2.0 liters of a 150 mM potassium chloride (KCl) solution. After reviewing the experiment setup, she realizes that she now needs to increase the solution volume by 30%, maintaining the same concentration of 150 mM. To ensure accuracy:
1. She increases the volume to 2.6 liters.
2. She recalculates the amount of KCl needed to reach the correct concentration
in the new volume.
Given that the molecular weight of KCl is 74.55 g/mol, how much KCl should she add?

She needs to complete the volume to 2.6 liters and then add 6.72 g KCl to the solution.

A chemist prepared 750 ml of a 400 mM magnesium sulfate (MgSO4) solution. Upon realizing that the experiment now requires 20% more solution, the chemist decides to increase the volume while keeping the concentration exactly at 400 mM. The chemist:
1. Increases the volume to 900 ml.
2. Adjusts the amount of MgSO4 required to maintain the proper concentration.
Given that the molecular weight of MgSO4 is 120.37 g/mol, how much more MgSO4 should be added to achieve the target concentration?

8.64 g

A biologist is preparing a 500 ml solution of 0.5 M calcium chloride (CaCl2) for an experiment. Later, she realizes that she needs an additional 40% volume, while the concentration must remain exactly 0.5 M. The solution’s volume is increased to 700 ml. To correct the concentration:
1. The biologist needs to calculate how much more CaCl2 is required.
2. The molecular weight of CaCl2 is 110.98 g/mol.
How much additional CaCl2 should the biologist add to the solution to maintain
the desired concentration?

11.10 g

A technician prepared 1 liter of a 300 mM lithium chloride (LiCl) solution. The experiment calls for an additional 50% volume increase, while the concentration must remain exactly 300 mM. The technician decides to increase the volume to 1.5 liters. To correct the concentration:
1. The technician calculates the amount of LiCl needed to reach the desired
concentration.
2. The molecular weight of LiCl is 42.39 g/mol.
How much more LiCl should be added to the solution?

6.36 g

What is the function of primase in RNA primer synthesis?

It uses ribonucleoside triphosphates to create RNA primers.

How does primase differ from DNA polymerase?

Primase does not require a base-paired 3’ end to start synthesis.

What type of chemical modification commonly results from UV radiation and can
lead to permanent mutations if left unrepaired?

Formation of thymine dimers

Which of the following mutations is caused by the deamination of cytosine?

Cytosine is converted into uracil

If a guanine base undergoes oxidation, what type of mutation can occur if the damage is not repaired?

conversion of guanine into 8-oxoguanine

What happens when 8-oxoguanine is mispaired during DNA replication?

It pairs with adenine, leading to a G:C to T:A transversion

Which of the following is a consequence of the methylation of cytosine in DNA?

Increased likelihood of spontaneous deamination to thymine

How does deamination of adenine lead to mutations if left unrepaired?

Adenine is converted to hypoxanthine, leading to mispairing with cytosine

Which of the following best describes the mutation caused by the oxidation of
thymine?

It causes thymine to form 5-hydroxymethyluracil, which can pair incorrectly
during replication

Which of the following is true regarding the formation of abasic sites (loss of a
base) in DNA?

DNA polymerase inserts random bases opposite the abasic site, leading to mutations

What is the primary function of the excision step in DNA repair?

Removal of the damaged DNA strand

Which enzyme is primarily responsible for the re-synthesis step in DNA repair?

DNA polymerase

What role does DNA ligase play in the DNA repair process?

It seals the nick between the newly synthesized DNA and the existing strand.

Which of the following best describes nucleotide excision repair (NER)?

It repairs damage caused by thymine dimers and other bulky lesions.

What is the primary function of base excision repair (BER)?

It removes and replaces damaged bases like oxidized or deaminated bases.

Which enzyme recognizes and removes the damaged base in base excision repair?

DNA glycosylase

During mismatch repair (MMR), what recognizes the mismatch and distinguishes the newly synthesized strand from the template strand?

MutS and MutL proteins

How does the repair of double-strand breaks by homologous recombination (HR) occur?

It uses the sister chromatid as a template to accurately repair the break.

What is the function of DNA helicase during DNA replication?

It unwinds the DNA double helix.

Which enzyme synthesizes the RNA primer required for DNA replication?

Primase

In what direction does DNA polymerase synthesize new DNA strands?

5’ to 3’ direction

What is the name of the fragments synthesized on the lagging strand during DNA
replication?

Okazaki fragments

Which enzyme is responsible for joining Okazaki fragments together?

DNA ligase

What is the role of single-stranded binding proteins (SSBs) in DNA replication?

They stabilize the single-stranded DNA and prevent reannealing.

Which enzyme relieves the tension ahead of the replication fork by breaking and rejoining the DNA strands?

Topoisomerase

What is the leading strand in DNA replication?

The strand synthesized in the 5’ to 3’ direction toward the replication fork

Which enzyme is primarily responsible for adding new nucleotides to the growing DNA strand during replication?

DNA polymerase

How does replication of the lagging strand differ from replication of the leading strand?

The lagging strand is synthesized in short fragments that are later joined together, while the leading strand is synthesized continuously.

What is the role of the origin of replication in DNA replication?

It is the specific sequence of DNA where replication begins.

What is the main function of telomerase?

It adds repetitive nucleotide sequences to the ends of chromosomes.

Why is telomerase important for the replication of eukaryotic chromosomes?

It extends the 3’ ends of chromosomes, preventing their shortening during
replication.

Which type of cells typically express high levels of telomerase?

Cancer cells

What happens to chromosomes in most somatic cells when telomerase is not
active?

The telomeres shorten with each round of cell division.

Which of the following is a component of the telomerase enzyme?

An RNA template that is complementary to the telomere sequence

What is the correct sequence of information flow according to the central dogma
of molecular biology?

DNA → RNA → Protein

What process describes the conversion of DNA into RNA?

Transcription

Which enzyme is responsible for synthesizing RNA from a DNA template?

RNA polymerase

What is the process by which RNA is translated into a protein?

Translation

Which type of RNA carries the genetic information from DNA to the ribosome for
protein synthesis?

Messenger RNA (mRNA)

Which cellular organelle is the site of protein synthesis?

Ribosome

What is the role of transfer RNA (tRNA) during translation?

It brings amino acids to the ribosome based on the mRNA sequence.

Which of the following best describes the genetic code?

It is universal and redundant, with multiple codons encoding the same amino
acid.

Which codon serves as the start signal for translation in most organisms?

AUG

What is the process by which RNA is converted back into DNA in some viruses?

Reverse transcription

What is the primary function of messenger RNAs (mRNAs)?

They code for proteins.

Which type of RNA forms the core of the ribosome’s structure and catalyzes
protein synthesis?

Ribosomal RNAs (rRNAs)

Which RNA type is primarily involved in regulating gene expression?

MicroRNAs (miRNAs)

What role do transfer RNAs (tRNAs) play in protein synthesis?

They serve as adaptors between mRNA and amino acids.

Which type of RNA provides protection from viruses and proliferating
transposable elements?

Small interfering RNAs (siRNAs)

What is one function of long noncoding RNAs (lncRNAs)?

They act as scaffolds and serve other diverse functions.

Which of the following RNA types is involved in RNA splicing, gene regulation,
and telomere maintenance?

Other noncoding RNAs

Which RNA type does not directly code for proteins but instead serves a
structural and catalytic role in the ribosome?

Ribosomal RNAs (rRNAs)v

Which type of RNA can regulate gene expression by interfering with the
translation of specific mRNAs?

MicroRNAs (miRNAs)

95.Which of the following RNAs is not involved in coding for proteins but plays
important roles in gene regulation, RNA splicing, and other cellular processes?

Other noncoding RNAs

96.Which type of RNA polymerase is responsible for transcribing most rRNA genes?

RNA polymerase I

What does RNA polymerase II primarily transcribe?

Protein-coding genes and miRNA genes

Which of the following is transcribed by RNA polymerase III?

tRNA genes and 5S rRNA gene

Which RNA polymerase is responsible for transcribing noncoding RNAs such as
those involved in the spliceosome?

RNA polymerase II

What is the function of RNA polymerase I in eukaryotic cells?

It transcribes most rRNA genes.

Which polymerase transcribes the genes for many small RNAs, including
tRNA and 5S rRNA?

RNA polymerase III

RNA polymerase II is primarily involved in transcribing genes that encode
what?

Protein-coding genes and small noncoding RNAs

Which polymerase is involved in the transcription of spliceosome-related
genes?

RNA polymerase II

Which type of RNA polymerase is responsible for transcribing tRNA genes?

RNA polymerase III

What is the role of RNA polymerase II in the production of noncoding RNAs?

It transcribes noncoding RNAs such as those for the spliceosome.

Which of the following is a key difference between bacterial and eukaryotic
mRNAs?

Bacterial mRNAs are often polycistronic, encoding multiple proteins.

What is a characteristic of eukaryotic mRNAs that is absent in bacterial
mRNAs?

Presence of a poly-A tail at the 3’ end

How do bacterial mRNAs differ from eukaryotic mRNAs in terms of
post-transcriptional modifications?

Bacterial mRNAs do not have a 5’ cap or a poly-A tail.

Which of the following is true regarding the structure of eukaryotic mRNAs?

Eukaryotic mRNAs have a 5’ cap and a 3’ poly-A tail.

What is the significance of a 5’ cap in eukaryotic mRNAs?

It is required for ribosome binding and initiation of translation.

How are bacterial and eukaryotic mRNAs different in terms of introns and
exons?

Eukaryotic mRNAs typically contain introns that are spliced out before translation.

Where does transcription and translation occur in bacterial cells?

Both occur simultaneously in the cytoplasm

What is the lifespan of bacterial mRNAs compared to eukaryotic mRNAs?

Bacterial mRNAs are typically degraded rapidly, with a short half-life.

In eukaryotic cells, what processing step is involved in converting pre-mRNA to mature mRNA?

Splicing out of introns and joining of exons

What is a polycistronic mRNA?

An mRNA that codes for multiple proteins, typically found in bacteria

What is the first step in the process of translation?

The ribosome assembles at the start codon of mRNA.

Which codon signals the start of translation in most organisms?

AUG

Which of the following molecules brings amino acids to the ribosome during
translation?

Transfer RNA (tRNA)

What happens during the elongation phase of translation?

tRNA anticodons pair with mRNA codons, adding amino acids to the growing peptide chain.

Which of the following is the function of the ribosome during translation?

It catalyzes the formation of peptide bonds between amino acids.

What is the role of the E site on the ribosome?

It binds the tRNA that has released its amino acid and is about to exit the
ribosome.

Which type of bond forms between amino acids during translation?

Peptide bond

What happens when a stop codon is encountered during translation?

The ribosome disassembles, and the polypeptide chain is released.

What is the mechanism of action of tetracycline?

Prevents the binding of aminoacyl-tRNA to the A site of the ribosome

Which antibiotic inhibits bacterial protein synthesis by preventing the transition from initiation to elongation?

Streptomycin

How does chloramphenicol inhibit bacterial protein synthesis?

Blocks peptidyl transferase reaction on ribosomes

Which antibiotic binds to the exit channel of the ribosome and inhibits elongation of the peptide chain?

Erythromycin

What is the target of rifamycin in bacterial cells?

Inhibition of RNA polymerase

What is the function of the trp operon in Escherichia coli?

To regulate the production of tryptophan

How is the trp operon regulated when tryptophan levels are high?

The trp repressor binds to the operator, preventing transcription.

What is the role of tryptophan in the regulation of the trp operon?

It acts as a co-repressor, enabling the trp repressor to bind the operator.

Where does the trp repressor bind when tryptophan levels are high?

The operator region

What happens to the trp operon when tryptophan is scarce in the
environment?

The trp operon is fully transcribed, leading to the synthesis of enzymes for tryptophan production.

What role does RNA polymerase play in the trp operon when tryptophan is
low?

It binds to the promoter and initiates transcription of the trp operon.

What is the role of attenuation in the regulation of the trp operon?

It allows fine-tuning of transcription based on tryptophan levels.

How does the leader peptide sequence affect the trp operon in E. coli?

It forms secondary structures that can terminate transcription prematurely when tryptophan is abundant.

137. What happens when the trp repressor is inactivated?

RNA polymerase binds to the promoter and transcription of the trp operon begins.

What does the trp operon code for?

Enzymes involved in tryptophan biosynthesis

What is the primary function of the lac operon in Escherichia coli?

To regulate the metabolism of lactose

Which gene in the lac operon codes for beta-galactosidase, the enzyme that breaks down lactose?

lacZ

What is the role of the lacI gene in the lac operon?

It encodes the repressor protein that binds to the operator.

What happens when lactose is present in the environment of Escherichia
coli?

Lactose binds to the lac repressor, causing it to release from the operator and allowing transcription of the lac operon.

In the absence of lactose, what happens to the lac operon?

The repressor binds to the operator, blocking transcription

Which molecule acts as an inducer for the lac operon?

Lactose

What happens to the lac operon when both glucose and lactose are present
in the environment?

Transcription of the lac operon is repressed by the presence of glucose through catabolite repression.

What is the role of the CAP-cAMP complex in the regulation of the lac
operon?

It enhances the binding of RNA polymerase to the promoter, increasing transcription in the absence of glucose.

What is the effect of glucose on the lac operon?

It decreases the concentration of cAMP, preventing activation of the lac operon.

Which of the following conditions would result in maximum expression of the lac operon?

No glucose and high lactose

How do the mechanisms of repression differ between the trp operon and the lac operon in Escherichia coli with respect to their interaction with their repressor proteins and environmental signals?

The trp repressor requires a co-repressor (tryptophan) to bind to the operator, while the lac repressor binds to the operator in the absence of lactose and is inactivated when lactose is present.

The DNA sequence shown below includes the beginning of a sequence that codes for a protein. What would be the result of a mutation that changed the underlined bold C to an A?

5'-ATCATGAATGTAGCACGCATTCACATAAGGTTT-3'

M-N-V-A-S-I-H-I-R-F

In a DNA double helix, _____

the two DNA strands run antiparallel

Which of the following sequences can fully base-pair with itself?

5’-GGATATCC-3’

Which of the following best represents the total number of chromosomes found in each of the somatic cells in your body?

46

Which of the following histone proteins does not form part of the octameric core?

H1

What is the most likely explanation for the similarity in the coding sequences
that direct the sequence of amino acids in the enzyme phosphofructokinase between skinks and Komodo dragons, despite variation in the surrounding sequences?

Mutations in coding sequences are more likely to be deleterious to the organism than mutations in noncoding sequences.

Which of the following does not occur before a eukaryotic mRNA is exported from the nucleus?

The ribosome binds to the mRNA.

Why is the lagging strand synthesized discontinuously at the replication fork?

DNA polymerase can polymerize nucleotides only in the 5′-to-3′ direction.

Which chromatin components are not retained when the classic “beads-on-a-string” structure is generated?

30-nm fiber

Which amino acid would you expect a tRNA with the anticodon 5’-CCA-3’ to carry?

tryptophan

Which protein is responsible for the recruitment of splicing factors to the CTD of RNA Polymerase during transcription initiation in eukaryotes?

snRNP

Which of the following correctly identifies the nucleosomal core histones?

H2A, H2B, H3 and H4

The DNA from two different species can often be distinguished by a difference in the:

ratio of A + T to G + C.

DNA replication is considered semiconservative because:

Each daughter DNA molecule consists of one strand from the parent DNA molecule and one new strand.

Which of the following sequences can fully base-pair with itself?

5′-AAGCGCTT-3′

If the genome of a bacterium requires about 20 minutes to replicate, how can the genome of the fruit fly be replicated in only three minutes?

The fruit fly genome contains more origins of replication than the bacterial genome.

Which of the following statements is true?

rRNA contains the catalytic activity that joins amino acids together.

In eukaryotes, but not prokaryotes, ribosomes find the start site of translation by:

scanning along the mRNA from the 5′ end.

The distinct characteristics of different cell types in a multicellular organism are produced mainly by the differential regulation of the:

transcription of genes transcribed by RNA polymerase II.

How are most eukaryotic gene regulatory proteins able to affect transcription when their binding sites are far from the promoter?

By looping out the intervening DNA between their binding site and the promoter

Which amino acid would you expect a tRNA with the anticodon 5′-CUU-3′ to carry?

lysine (lys)

What would be the outcome of the Hershey-Chase experiment if protein (and not DNA) was the carrier of the genetic information?

The infected bacteria would be positive for S35 radioactive labeling, and not P32.

What are the major and minor grooves?

Spaces between the turns of the DNA double helix

The complementary strand for the sequence 5’-GCACTTCG-3’ is:

3’-CGTGAAGC-5’

What happens to genes present in a part of DNA folded into heterochromatin?

They will not be expressed.

DNA replication origin is a segment of DNA that is most likely to be:

Rich in A-T base pairthe

DNA replication is:

semi-conservative

A replication fork is:

an open site in the DNA double helix where DNA replication occurs

The enzyme that digests the primers made by primase is called:

ribonuclease

In their 1953 paper on the double-helical structure of DNA, Watson and Crick famously wrote: “It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material.” What did they mean?

Each strand in a DNA double helix contains all the information needed to produce a complementary partner strand.

When are chromosomes in their most compact form?

during mitosis

Which statement is true about the association of histone proteins and DNA?

Histone proteins have a high proportion of positively charged amino acids, which bind tightly to the negatively charged DNA backbone.

Where is heterochromatin not commonly located?

chromosomal regions carrying genes that encode ribosomal proteins

Consider the process that a cell uses to replicate its double-stranded DNA before undergoing cell division. Which statement describes the DNA in the resulting daughter cells?

The double helix in each daughter cell consists of one parent strand and one newly synthesized strand.

When is homologous recombination, which can flawlessly repair double-strand DNA breaks, most likely to occur?

after the cell’s DNA has been replicated

DNA mismatch repair typically corrects what percentage of replication errors?

99%

Which of the following best defines a mutation?

permanent change in a DNA sequence

What is true of eukaryotic mRNAs?

They are translated after they are exported from the nucleus.

An RNA chain is synthesized in which direction?

5′-to-3′ only.

In eukaryotes, which parts of a gene are transcribed into RNA?

introns and exons.

How many different aminoacyl-tRNA synthetases do most organisms have?

one for each amino acid

It is thought that, early in the history of life, RNAs not only stored information but acted as catalysts in cells. Which reaction is catalyzed by a ribozyme in present-day cells?

peptide bond formation during translation

Which of the following statements is NOT true about liver cells and kidney cells in the same organism?

They contain different genes.

In eukaryotes, where do transcription regulators bind?

RNA sequencing

In eukaryotes, where do transcription regulators bind?

upstream, downstream, or within the genes they control.

What is an operon?

a set of genes transcribed as a single mRNA from a single promoter.

Which is NOT an example of epigenetic inheritance?

the inheritance of a single point mutation in a gene.

Which does NOT affect gene expression at the post-transcriptional level?

DNA methylation.

The chromatin structure of chromosomal centromeric regions is:

heterochromatic.

The nucleotide sequence of one DNA strand of a DNA double helix is:
5ʹ-GGATTTTTGTCCACAATCA-3ʹ
What is the sequence of the complementary strand?

5ʹ-TGATTGTGGACAAAAATCC-3ʹ

In the DNA of certain bacterial cells, 13% of the nucleotides contain adenine. What are the percentages of the other nucleotides?

A = 13%, T = 13%, C = 37%, G = 37%

Which of the following statements are correct?
Each eukaryotic chromosome must contain the following sequence elements:

many origins of replication, two telomeres, one centromere

Which of the following statements are correct?

• The error rate of DNA replication is reduced both by proofreading by DNA polymerase and by DNA mismatch repair.
• in the absence of DNA repair, genes become less stable.

You have a segment of DNA that contains the following sequence:
5’-GGACTAGACAATAGGGACCTAGAGATTCCGAAA-3’ <=Watson
3’-CCTGATCTGTTATCCCTGGATCTCTAAGGCTTT-5’ <=Crick
If you know that the DNA region that is transcribed into RNA from this segment
contains the following sequence:
5’-TTTCGGAATCTCTAGGTCCCTATTGTCTAGTCC-3'
Which of the following choices best describes how transcription occurs?

The Crick strand is the template strand; RNA pol. moves along the 3' to 5' direction of the template strand.

• A and C correspond to the 3’-end and 5’-end of the coding strand, respectively.
• B and D correspond to the 5’-end and 3’-end of the template strand, respectively.
• E corresponds to the 5'-end of the mRNAs being synthesized

false

A = 5'-end of the mRNA,
B = last Ribosome to initiate translation,
C = amino terminal of the emerging polypeptide,
D = polypeptide produced by the first ribosome engaged in translation,
E = 3'-end of the mRNA

A = 3'-end of the mRNA
B = polypeptide produced by the first ribosome engaged in translation,
C = last Ribosome to initiate translation,
D = amino terminal of the emerging polypeptide,
E = 5'-end of the mRNA,