DNA Structure and Function

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Questions and Answers

What did Hershey and Chase conclude about the genetic material of phage T2?

Phage DNA and proteins both carry genetic information.

Proteins are the genetic material.

DNA, not proteins, functions as genetic material. (correct)

RNA serves as the genetic material.

What is the role of DNA polymerases during DNA replication?

To repair proteins post-replication.

To synthesize RNA.

To initiate replication at the origin of DNA.

To proofread new DNA and replace incorrect nucleotides. (correct)

Which of the following is an example of a harmful chemical agent that can cause DNA damage?

Electrolytes

Cigarette smoke (correct)

Protein supplements

Vitamin C

What is the purpose of mismatch repair enzymes in DNA replication?

To correct errors in base pairing. Signup and view all the answers

Which statement accurately describes the entry of phage DNA into bacterial cells during infection?

Only phage DNA enters the bacterial cell, while proteins remain outside. Signup and view all the answers

What is the primary function of telomeres in eukaryotic chromosomes?

To protect against gene loss during replication Signup and view all the answers

Which statement best describes heterochromatin?

It is highly condensed and often found in regions such as centromeres. Signup and view all the answers

What role does telomerase play in aging and cancer cells?

It maintains the length of telomeres, allowing cells to continue dividing. Signup and view all the answers

How do prokaryotic chromosomes differ from eukaryotic chromosomes?

Prokaryotic chromosomes are circular and lack histones. Signup and view all the answers

What occurs during the transformation process described by Griffith?

Harmless strain bacteria become pathogenic through gene assimilation. Signup and view all the answers

What is the significance of chemical modifications to histones?

They influence the organization and expression of chromatin. Signup and view all the answers

What is a primary consequence of DNA polymerase limitations in eukaryotic cells?

Shortening of linear DNA molecules after replication Signup and view all the answers

What are bacteriophages?

Viruses that specifically infect bacteria Signup and view all the answers

What is the relationship between telomere shortening and aging?

Shortening of telomeres accelerates aging processes. Signup and view all the answers

What was the main conclusion from Avery, McCarty, and MacLeod's experiments?

DNA is the substance responsible for transformation in bacteria. Signup and view all the answers

Why do chromosomes occupy restricted regions within the nucleus?

To organize genetic material efficiently Signup and view all the answers

How is DNA organized in eukaryotic cells during interphase?

Predominantly in loosely packed euchromatin Signup and view all the answers

Which type of chromatin is primarily associated with limited gene expression?

Heterochromatin Signup and view all the answers

What occurs to chromosomes prior to mitosis?

They are primarily in a highly condensed state. Signup and view all the answers

Which enzyme is responsible for joining Okazaki fragments during DNA replication?

DNA ligase Signup and view all the answers

What is the direction of elongation for a new DNA strand during replication?

5' to 3' Signup and view all the answers

Which model of DNA replication suggests that each daughter molecule consists of one old strand and one new strand?

Semiconservative model Signup and view all the answers

What type of DNA damage is repaired by nucleotide excision repair?

Thymine dimers and bulky adducts Signup and view all the answers

What is the role of helicases in DNA replication?

Untwist the double helix Signup and view all the answers

What does Chargaff's rule state about base pairing in DNA?

A = T, G = C Signup and view all the answers

Which components make up the backbone of the DNA molecule?

Sugar and phosphate Signup and view all the answers

What are Okazaki fragments?

Short segments of DNA produced during lagging strand synthesis Signup and view all the answers

In DNA replication, which enzyme synthesizes RNA primers?

Primase Signup and view all the answers

What special property is characteristic of DNA polymerases during replication?

They add nucleotides only to the 3' end of a growing strand. Signup and view all the answers

What did Watson and Crick conclude about the structure of DNA?

DNA has a double-helical structure. Signup and view all the answers

What phenomenon enables DNA replication to be semiconservative?

Antiparallel structure Signup and view all the answers

What are single-strand binding proteins' role in DNA replication?

To stabilize single-stranded DNA Signup and view all the answers

What is the total length of a primer introduced in DNA replication?

5-10 nucleotides Signup and view all the answers

Study Notes

DNA Structure

DNA, the substance of inheritance, is a double helix, comprised of two outer sugar-phosphate backbones, with nitrogenous bases paired in the molecule's interior.
The double helix model was introduced by Watson and Crick in 1953, using X-ray images captured by Rosalind Franklin and Maurice Wilkins, and insights from Erwin Chargaff's work.
The helical structure of DNA was deduced by interpreting the X-ray diffraction pattern of DNA.

Base Pairing

The model proposed by Watson and Crick suggests specific base pairings: Adenine (A) with Thymine (T), and Guanine (G) with Cytosine (C).
This pairing explains Chargaff's rules (A = T; G = C) and suggests a possible copying mechanism for the genetic material.
The base pairings, although specific, don't result in a uniform width of the double helix, due to the differences in size and shape of the bases.

DNA Replication

The double helix structure is essential for DNA replication, as each strand acts as a template to build a new complementary strand.
DNA polymerases add nucleotides to the free 3' end of a growing DNA strand.
Replication happens in the 5' to 3' direction, but the two strands are antiparallel, leading to different replication mechanisms for the leading and lagging strands.

Semiconservative Replication

The semiconservative model of DNA replication proposes that each new molecule will have one old strand and one newly made strand.
This model was validated by the Meselson-Stahl experiment, which used heavy (N15) and light (N14) isotopes of nitrogen to trace the parental DNA strands during replication.

Replication Process

DNA replication begins at specific sites called origins of replication, where two DNA strands are separated, creating a replication "bubble".
The "bubble" expands as two replication forks move in opposite directions, unzipping the DNA helix.
Enzymes involved in DNA replication include:
- Helicases: Untwist the double helix.
- Single-strand binding proteins: Stabilize single-stranded DNA.
- Topoisomerase: Relieves overwinding ahead of replication forks.
- Primase: Synthesizes an RNA primer, which provides a starting point for DNA polymerases.
- DNA polymerases: Add nucleotides to the new DNA strand, using the parental strand as a template.
- DNA ligase: Joins Okazaki fragments, short segments of DNA produced during discontinuous replication of the lagging strand.

DNA Repair

DNA can be damaged by harmful physical agents or undergo spontaneous changes.
DNA repair mechanisms, like nucleotide excision repair, use enzymes to cut out damaged stretches of DNA and replace them with new, correctly sequenced nucleotides.
Proofreading and repairing DNA during replication ensures a low error rate.

Evolutionary Significance

Mutations in DNA sequences can become permanent, passed on to future generations, contributing to genetic variations.
This genetic variation serves as a source for natural selection, driving evolution.

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Description

Explore the fascinating world of DNA in this quiz, focusing on its double helix structure, base pairing mechanisms, and the intricacies of DNA replication. Understand how Watson and Crick, along with Franklin and Chargaff, contributed to this landmark discovery in genetics. Test your knowledge on how these elements work together to store and transmit genetic information.