Biology Lab: DNA Structure and Replication

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Questions and Answers

What are the two types of nitrogen-containing bases found in DNA?

Purines and Pyrimidines (correct)
Purines and Pyrazines
Amino acids and Peptides
Ketones and Aldehydes

What is the main function of the phosphate group in a nucleotide?

To bind with the nitrogen-containing bases
To provide energy for DNA replication
To stabilize the double helix structure
To form the backbone of the DNA molecule (correct)

What is the direction of the nucleotide strands in a DNA molecule?

Parallel and complementary
Antiparallel and identical
Parallel and identical
Antiparallel and complementary (correct)

What is the direction of strand elongation during DNA replication?

5' to 3' (B) Signup and view all the answers

What type of bonds hold the nucleotide strands together in a DNA molecule?

Hydrogen bonds (C) Signup and view all the answers

What is the name of the model that describes the structure of DNA as a double helix?

Watson-Crick Model (D) Signup and view all the answers

Which of the following is NOT a basic requirement for DNA replication?

RNA polymerase (B) Signup and view all the answers

What is the function of primase during DNA replication?

To synthesize RNA primers (D) Signup and view all the answers

What is the term for the process of replication where the new DNA molecules contain one old strand and one new strand?

Semi-conservative (B) Signup and view all the answers

Which of the following statements is TRUE regarding DNA replication?

The energy for DNA synthesis comes from the removal of the two phosphates of the incoming nucleotide. (B) Signup and view all the answers

What does the term "semi-conservative replication" refer to in the context of DNA replication?

Each daughter DNA molecule contains one strand from the parent DNA molecule and one newly synthesized strand. (B) Signup and view all the answers

What is the role of the "old" DNA strand in DNA replication?

The "old" DNA strand serves as a template for the synthesis of the new strand. (D) Signup and view all the answers

Why is the direction of DNA synthesis always 5' to 3'?

The enzymes involved in DNA synthesis can only add nucleotides to the 3' end of a growing DNA strand. (D) Signup and view all the answers

What is the significance of the fact that DNA is synthesized in a 5' to 3' direction?

It ensures that the genetic information is copied accurately from the template strand. (D) Signup and view all the answers

What is the initial step in the DNA replication process?

Formation of the origin of replication (D) Signup and view all the answers

Which enzyme is primarily responsible for synthesizing new DNA strands during replication?

DNA polymerase (B) Signup and view all the answers

Which of the following correctly describes the elongation phase of DNA replication?

DNA polymerase synthesizes new strands. (D) Signup and view all the answers

What occurs during the termination phase of DNA replication?

Replication forks meet and DNA synthesis is completed. (B) Signup and view all the answers

Which statement about the origin of replication is accurate?

It is the starting point for replicating DNA strands. (C) Signup and view all the answers

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Study Notes

DNA Overview

Deoxyribonucleic Acid (DNA) is a nucleic acid located in the nucleus.
DNA is a polymer composed of nucleotides, each containing:
- A deoxyribose sugar (5-carbon sugar)
- A phosphate group
- A nitrogenous base

Nitrogenous Bases

Four nitrogenous bases in DNA:
- Purines: Adenine (A), Guanine (G)
- Pyrimidines: Thymine (T), Cytosine (C)

Structure of DNA

DNA is structured as a double helix, with two nucleotide strands.
Strands run in antiparallel directions, meaning they orient differently.
Hydrogen bonds form between bases: A pairs with T, C pairs with G.
The "ladder" structure consists of a sugar-phosphate backbone and base pairs as rungs.
During replication, the parent strand acts as a template for producing daughter DNA strands.

DNA Replication Process

Replication is semi-conservative; each new DNA molecule contains one old strand and one new strand.
Replication occurs in the 5' to 3' direction.
Energy for synthesis derives from the removal of two phosphates from incoming nucleotides.
Replication features:
- Initiation occurs at specific origins.
- Bidirectional movement is typical during synthesis.
- Strands elongate in a 5' to 3' direction and are semi-discontinuous.

Requirements for DNA Replication

Requires several key components:
- Templates from both strands of parental DNA.
- Nucleotides: dATP, dTTP, dGTP, dCTP.
- Enzymes: DNA polymerase, helicase, primase, ligase.
- RNA primer for initiating synthesis.
- Single-strand binding proteins (SSB) for stabilization.
Proofreading occurs as an error control measure during replication.

Leading and Lagging Strands

The leading strand is synthesized continuously in the same direction as the replication fork.
The lagging strand is synthesized discontinuously, moving away from the replication fork, forming short segments known as Okazaki fragments.

Steps of DNA Replication

DNA replication in prokaryotes begins at a single origin and travels bidirectionally around the circular DNA molecule.
Three primary steps in replication:
- Initiation: The process begins at the origin of replication.
- Elongation: DNA polymerase synthesizes new DNA strands.
- Termination: The replication process concludes once the entire molecule is copied.