Lecture 2: DNA Replication

Week 1

How are nucleotides polymerized (combined) to form DNA molecules?

A. By forming hydrogen bonds between the phosphate groups and nitrogenous bases.
B. By linking nitrogenous bases directly through peptide bonds.
C. By forming phosphodiester bonds between the 3' hydroxyl group of one nucleotide and the 5' phosphate group of the next.
D. By joining deoxyribose sugars through glycosidic bonds

C. By forming phosphodiester bonds between the 3' hydroxyl group of one nucleotide and the 5' phosphate group of the next.

What does "semi-conservative replication" mean in the context of DNA replication?

A. Each daughter DNA molecule consists of two newly synthesized strands.
B. One of the original DNA strands is degraded, and two new ones are formed.

C. Each daughter DNA molecule consists of one original (parental) strand and one newly synthesized strand.
D. DNA replication occurs only on one strand of the DNA molecule.

C. Each daughter DNA molecule consists of one original (parental) strand and one newly synthesized strand.

What does it mean when DNA is said to be synthesized in the 5' to 3' direction?

A. Nucleotides are added to the 5' phosphate of the growing strand.
B. Nucleotides are added to the 3' hydroxyl end of the growing DNA strand.
C. DNA synthesis starts at the 3' end of the template strand and proceeds to the 5' end.
D. The 5' and 3' ends refer to positions on the nitrogenous base.

B. Nucleotides are added to the 3' hydroxyl end of the growing DNA strand.

What roles do nucleoside triphosphates (NTPs) and primers play in DNA replication?

A. NTPs act as enzymes, and primers signal the end of replication.
B. NTPs are the building blocks of new DNA, and primers provide a starting point for DNA polymerase.
C. NTPs inhibit DNA polymerase activity, and primers are not required.
D. NTPs are only used in RNA synthesis, not DNA replication.

B. NTPs are the building blocks of new DNA, and primers provide a starting point for DNA polymerase.

Which of the following best outlines the components and steps involved in a PCR reaction?

A. Helicase, primers, DNA polymerase, ligase; denaturation, translation, elongation.
B. DNA template, RNA polymerase, tRNAs; initiation, elongation, termination.
C. DNA template, primers, Taq polymerase, dNTPs; denaturation, annealing, extension.
D. mRNA, ribosomes, DNA polymerase; transcription, duplication, repair.

C. DNA template, primers, Taq polymerase, dNTPs; denaturation, annealing, extension.

What is the key feature of dideoxy sequencing that allows determination of DNA sequence?

A. Use of radioactive isotopes that bind to specific bases.
B. Use of dideoxynucleotides (ddNTPs) that terminate DNA synthesis at specific bases.
C. DNA is copied without any enzyme to prevent errors.
D. Use of double-stranded RNA to label each DNA base.

B. Use of dideoxynucleotides (ddNTPs) that terminate DNA synthesis at specific bases.

Which of the following best compares DNA replication in cells with PCR?

A. Both use the same enzymes and occur at body temperature.
B. DNA replication in cells uses helicase and DNA polymerase; PCR uses heat to separate strands and DNA polymerase to synthesize DNA.
C. PCR requires RNA primers and topoisomerase; cells use DNA primers.
D. DNA replication occurs in a test tube; PCR takes place inside the nucle

B. DNA replication in cells uses helicase and DNA polymerase; PCR uses heat to separate strands and DNA polymerase to synthesize DNA.

Which of the following correctly defines the key terms involved in DNA replication?

A. The replication fork is where transcription begins; the leading strand is synthesized in short fragments.
B. The origin of replication is the end of the DNA strand; the lagging strand is synthesized continuously.
C. The origin of replication is the specific starting point of DNA replication; the replication fork is the area where the DNA is unwound, and replication occurs. The leading strand is synthesized continuously, while the lagging strand is synthesized in short fragments.
D. The replication origin is found only in eukaryotes; the fork joins two DNA molecules into one.

C. The origin of replication is the specific starting point of DNA replication; the replication fork is the area where the DNA is unwound, and replication occurs. The leading strand is synthesized continuously, while the lagging strand is synthesized in short fragments.

What type of bond is formed between nucleotides during DNA synthesis?

A. Hydrogen bond
B. Phosphodiester bond
C. Peptide bond
D. Glycosidic bond

B. Phosphodiester bond

Which experiment provided strong evidence for semi-conservative replication?

A. Franklin-Watson experiment
B. Meselson-Stahl experiment
C. Hershey-Chase experiment
D. Griffith's experiment

B. Meselson-Stahl experiment

Why are primers necessary for DNA polymerase?

A. To unwind the DNA
B. To provide a 3’ hydroxyl group to begin synthesis
C. To terminate synthesis
D. To remove nucleotides

B. To provide a 3’ hydroxyl group to begin synthesis

Which of the following is NOT a step in a standard PCR cycle?

A. Denaturation
B. Transcription
C. Annealing
D. Extension

B. Transcription

What makes PCR different from cellular DNA replication in terms of DNA unwinding?

A. Helicase enzyme is used
B. Single-stranded binding proteins are required
C. Heat is used to denature the DNA strands
D. Ligase unwinds the strands

C. Heat is used to denature the DNA strands

What makes a dideoxynucleotide (ddNTP) different from a normal nucleotide?

A. It lacks a nitrogenous base
B. It has two sugar rings
C. It lacks a 3’ hydroxyl group, halting DNA synthesis
D. It contains three phosphate groups

C. It lacks a 3’ hydroxyl group, halting DNA synthesis

Which strand is synthesized in short fragments during DNA replication?

A. Leading strand
B. Lagging strand
C. Template strand
D. Sense strand

B. Lagging strand

Which of the following is a major difference between PCR and DNA replication in cells?

A. Both use RNA primers
B. Both require multiple enzymes
C. PCR uses heat to denature DNA, while cells use helicase
D. PCR requires Okazaki fragments

C. PCR uses heat to denature DNA, while cells use helicase

Which is true about the primers used in PCR?

A. They are made of RNA
B. They are made of DNA
C. They are made of proteins
D. They are not required

B. They are made of DNA

What must be present for DNA polymerase to start adding nucleotides?
A. A helicase
B. A primer with a free 3’ OH group
C. A complete DNA template
D. An Okazaki fragment

B. A primer with a free 3’ OH group

What are Okazaki fragments?
A. Sections of RNA removed from DNA
B. Short DNA segments synthesized on the lagging strand
C. Primers used to start synthesis
D. RNA sequences in the leading strand

B. Short DNA segments synthesized on the lagging strand

Where does DNA replication begin?
A. On any random base
B. At specific replication origin sites
C. At the 3’ end of every gene
D. Wherever helicase binds

B. At specific replication origin sites

How is DNA replication described directionally at the replication fork?
A. Unidirectional only
B. Bidirectional from the origin
C. From the telomeres inward
D. Leading strand first, then lagging strand

B. Bidirectional from the origin

What happens during the annealing step in PCR?
A. DNA strands separate
B. Primers bind to template strands
C. New strands are completed
D. dNTPs are hydrolyzed

B. Primers bind to template strands

Which component is NOT required in a PCR reaction mix?
A. dNTPs
B. RNA primers
C. DNA polymerase
D. DNA template

B. RNA primers

Why are fluorescent tags used in dideoxy sequencing?
A. To prevent binding
B. To degrade unneeded strands
C. To identify the last incorporated base
D. To speed up the reaction

C. To identify the last incorporated base

Why can’t nucleotides be added after a ddNTP is incorporated?
A. DNA polymerase is removed
B. There’s no 3’ OH group to form a bond
C. The template is lost
D. All nucleotides are used up

B. There’s no 3’ OH group to form a bond