D1.1 DNA Replication | Quizlet

Define DNA replication

The process of producing an exact copy of DNA with identical base sequences.

State the function of DNA replication

To pass genetic information during reproduction and to support growth and repair by creating new cells.

Explain complementary base pairing

Adenine pairs with Thymine; Cytosine pairs with Guanine via hydrogen bonds.

State the meaning of semiconservative replication

Each new DNA molecule contains one original (parent) strand and one newly synthesized strand.

State the role of helicase

Breaks hydrogen bonds between DNA strands, separating the parent strands.

State the role of DNA polymerase

DNA polymerase is an essential enzyme responsible for synthesizing new strands of DNA during DNA replication. Its main roles include:

• Adding nucleotides: It matches free nucleotides with their complementary bases on the original (template) strand (A with T, C with G), forming the new strand in a 5’ to 3’ direction.

• Proofreading: It checks for and corrects most errors during replication, ensuring high fidelity.

• Repair: Some DNA polymerases are involved in repairing damaged DNA.

Describe the direction of DNA synthesis

New nucleotides are added only to the 3' end; replication proceeds in the 5' to 3' direction.

Define replication fork

The Y-shaped region where the DNA strands are separated for replication.

Distinguish leading and lagging strand

Leading strand is synthesized continuously toward the fork; lagging strand is synthesized in fragments away from the fork.

Define Okazaki fragments

Short DNA fragments synthesized discontinuously on the lagging strand.

State the role of primase

Lays down RNA primers to signal where DNA polymerase should start replication.

State the role of DNA polymerase III

Adds new nucleotides in the 5' to 3' direction and proofreads for errors.

State the role of DNA polymerase I

Removes RNA primers and replaces them with DNA nucleotides.

State the role of DNA ligase

Joins Okazaki fragments by forming phosphodiester bonds between nucleotides.

Define PCR (Polymerase Chain Reaction)

A technique to amplify DNA by creating many copies of a DNA sequence.

Explain why heat is used in PCR

Heat replaces helicase by breaking hydrogen bonds between DNA strands.

State the role of primers in PCR

Short DNA sequences that indicate where replication should begin.

State the role of Taq polymerase in PCR

Heat-resistant DNA polymerase that synthesizes DNA during PCR.

Explain why Taq polymerase is used in PCR

It resists denaturation at high temperatures used to separate DNA strands.

Define gel electrophoresis

Technique to separate DNA fragments by size using an electric field in a porous gel.

Explain the movement of DNA in gel electrophoresis

Negatively charged DNA moves toward the positive electrode; shorter fragments travel further.

Define reverse transcription

The process of converting RNA into complementary DNA (cDNA).

Explain how PCR is used in virus detection

Steps of PCR in Virus Detection

1. Sample Collection
   A sample is taken from a patient (e.g., nasal swab, saliva, or blood), which may contain viral RNA or DNA.

2. RNA Viruses: Reverse Transcription (RT-PCR)
   If the virus is RNA-based (like SARS-CoV-2), the RNA is converted into complementary DNA (cDNA) using the enzyme reverse transcriptase.

3. Amplification (PCR Cycles)
   The cDNA or viral DNA is amplified through repeated cycles involving:

   • Denaturation: DNA strands are separated by heating.

   • Annealing: Short primers bind to specific viral gene sequences.

   • Extension: DNA polymerase extends the primers, copying the target viral DNA.

4. Detection

   • In conventional PCR, amplified DNA is visualized using gel electrophoresis.

   • In real-time PCR (qPCR), fluorescent dyes or probes allow quantification of the viral DNA as it is amplified.

Define short tandem repeats (STRs)

Repeating sequences of bases in DNA, varying in number between individuals.

Explain how STRs are used in paternity testing

DNA samples are amplified and separated; child's bands must match bands from the mother and one father.

State the directionality of DNA strands

DNA strands are antiparallel; one runs 5' to 3', the other 3' to 5'.

Explain proofreading by DNA polymerase III

Detects and replaces incorrectly paired nucleotides during DNA replication.

Describe the base pairing rule in DNA

Adenine pairs with thymine via two hydrogen bonds; cytosine pairs with guanine via three hydrogen bonds.

State why complementary base pairing is essential in DNA replication

It ensures that the new strand is an exact copy of the template strand.

Describe the structure of a nucleotide

A nucleotide consists of a phosphate group, deoxyribose sugar, and a nitrogenous base.

Explain the role of hydrogen bonds in DNA structure

They hold the complementary nitrogenous bases together, stabilizing the double helix.

Define anti-parallel in DNA strands

DNA strands run in opposite directions: one 5' to 3', the other 3' to 5'.

Name the sugar in DNA nucleotides

Deoxyribose.

Name the four nitrogenous bases in DNA

Adenine, thymine, cytosine, guanine.

Explain why replication must occur before cell division

To ensure that each daughter cell receives an identical set of DNA.

List the steps in DNA replication

Unwinding, strand separation, primer addition, elongation, primer removal, ligation.

Describe the role of single-stranded binding proteins

They stabilize unwound DNA strands and prevent them from re-annealing.

Explain the function of topoisomerase

Relieves tension ahead of the replication fork by cutting and rejoining DNA strands.

Define RNA primer

A short sequence of RNA nucleotides that provides a starting point for DNA synthesis.

State why RNA primers are used in DNA replication

DNA polymerase cannot start synthesis without an existing nucleotide chain.

Differentiate DNA polymerase I and III

Polymerase III adds nucleotides; polymerase I replaces RNA primers with DNA.

Describe phosphodiester bond formation

A covalent bond between the phosphate of one nucleotide and the sugar of the next.

Identify the enzyme responsible for joining Okazaki fragments

DNA ligase.

Explain the need for Okazaki fragments on the lagging strand

DNA synthesis can only occur 5' to 3', requiring fragments to be built away from the fork.

Describe the function of PCR

Amplifies DNA by cycling through denaturation, annealing, and extension phases.

List components needed for PCR

DNA sample, primers, Taq polymerase, free nucleotides, buffer solution.

State the purpose of a primer in PCR

Marks the starting point for DNA synthesis.

Define denaturation in PCR

Heating the DNA to break hydrogen bonds and separate the strands.

Define annealing in PCR

Cooling to allow primers to bind to the single-stranded DNA.

Define extension in PCR

DNA polymerase adds nucleotides to build new DNA strands.

State one real-world application of PCR

Disease diagnosis, forensic analysis, or paternity testing.

Define STR (short tandem repeat) analysis

Comparing variable numbers of repeating DNA sequences for identification.

Describe how STRs differ among individuals

Individuals have different numbers of repeats at specific loci.

State how STRs are used in forensic science

To match DNA profiles from crime scenes to suspects.

Explain how gel electrophoresis helps in paternity testing

It compares banding patterns from child, mother, and possible fathers.

Describe how DNA polymerase III ensures accuracy

It has proofreading activity that corrects mismatched base pairs.

Explain what happens if DNA replication errors are not corrected

It can result in mutations, which may cause genetic disorders or cancer.

Name the organism from which Taq polymerase is derived

Thermus aquaticus.

Describe the environmental condition where Taq lives

Hot environments like hydrothermal vents.

Define mutation

A change in the DNA sequence.

Explain why DNA ligase is essential in DNA replication

It seals the gaps between Okazaki fragments on the lagging strand.

State one benefit of mutations

Source of genetic variation for evolution.

State one disadvantage of mutations

May result in nonfunctional proteins or disease.