DNA Structure and Base Pairing Rules

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Questions and Answers

What prevents tangling and supercoiling during DNA replication?

Topoisomerases (correct)

Single-strand binding proteins

DNA polymerase

RNA primer

In which direction does DNA synthesis always proceed?

Both 3' → 5' and 5' → 3'

5' → 3' (correct)

Depends on the strand type

3' → 5'

Which strand is synthesized continuously toward the replication fork?

Lagging strand

Okazaki fragments

RNA primer strand

Leading strand (correct)

What is the role of DNA ligase in DNA replication?

Links Okazaki fragments Signup and view all the answers

How do prokaryotic DNA replication and eukaryotic DNA replication differ?

Prokaryotes have circular chromosomes, eukaryotes have linear chromosomes Signup and view all the answers

What is synthesized by DNA primase during replication?

RNA primer Signup and view all the answers

What structure is formed where the replication occurs?

Replication bubble Signup and view all the answers

What components make up a nucleotide in DNA?

Phosphate group, deoxyribose sugar, nitrogenous base Signup and view all the answers

What are short fragments on the lagging strand known as?

Okazaki fragments Signup and view all the answers

Which of the following correctly describes the structure of DNA?

Two polynucleotide chains arranged in a coiled double helix Signup and view all the answers

Which process occurs in eukaryotic cells during interphase?

DNA replication Signup and view all the answers

What is the distance between adjacent base pairs in the DNA double helix?

0.34 nanometers Signup and view all the answers

Which protein binds to single-stranded DNA during replication to stabilize it?

Single-strand binding proteins Signup and view all the answers

Which statement about DNA replication is true?

It is semiconservative, involving one original and one new strand Signup and view all the answers

What type of bonding holds the two chains of the DNA helix together?

Hydrogen bonding between complementary base pairs Signup and view all the answers

According to Chargaff's rules, which base pairs are complementary?

Adenine and Thymine; Guanine and Cytosine Signup and view all the answers

Which model of DNA replication describes a scenario where parental and newly synthesized strands are mixed?

Dispersive model Signup and view all the answers

What characteristic of DNA's polynucleotide chains allows for complementary base pairing?

Antiparallel orientation Signup and view all the answers

How does the structure of DNA contribute to its function as a carrier of genetic information?

The specific base pairing rules enable accurate replication of genetic material. Signup and view all the answers

What is the outcome after transferring E. coli from 15N to 14N medium for one generation?

Only hybrid DNA is produced. Signup and view all the answers

Which process describes semiconservative replication?

Each daughter double helix consists of one original strand and one new strand. Signup and view all the answers

What role do DNA helicases play in DNA replication?

They open or unwind the double helix. Signup and view all the answers

Which statement accurately describes the components of hybrid DNA?

Hybrid DNA contains one strand of 15N and one strand of 14N. Signup and view all the answers

How do single-strand binding (SSB) proteins contribute to DNA replication?

They stabilize the unwound single DNA strands. Signup and view all the answers

What enables the determination of DNA molecule locations within a centrifuge tube?

The absorption of UV light at 260 nm. Signup and view all the answers

What is formed after two generations of E. coli in 14N medium starting from 15N?

DNA hybrids and 14N-only DNA will be present. Signup and view all the answers

Which of the following best describes the initiation point of DNA replication?

It begins at specific origins of replication. Signup and view all the answers

In the Meselson-Stahl experiment, what conclusion was drawn about DNA replication?

DNA replication is semiconservative. Signup and view all the answers

Why is it important that each daughter strand of DNA be complementary to the template strand?

It ensures fidelity and proper sequencing. Signup and view all the answers

Study Notes

DNA Structure

DNA is a polymer of nucleotides
Each nucleotide contains a nitrogenous base, a pentose sugar (deoxyribose), and a phosphate group.
Purines include adenine and guanine
Pyrimidines include thymine and cytosine
DNA has a backbone of alternating sugar and phosphate groups joined by phosphodiester linkages.
The 3' carbon of the deoxyribose sugar is attached to the phosphate group and the 5' carbon of the next deoxyribose.
The bases are located in the centre of the DNA molecule.
The two polynucleotide chains run antiparallel.
The DNA double helix is 2.0 nm wide and each turn is 3.4 nm high.
Each pair of bases is 0.34 nm apart.
The sugar-phosphate backbones form the outside of the helix. The bases associate in the centre.

Base Pairing Rules

Hydrogen bonding between base pairs holds the two chains of the helix together.
Adenine (A) forms 2 hydrogen bonds with thymine (T).
Guanine (G) forms 3 hydrogen bonds with cytosine (C).
The sequence of bases in one strand determines the sequence of bases in the other strand (complementary).
This is known as Chargaff's rule (A=T and G=C).

DNA Replication

DNA replication is the process by which DNA makes a copy of itself.
It occurs during interphase, prior to cell division.
DNA replication is semiconservative.
One original strand from the parent molecule and one newly synthesized complementary strand.
DNA replication begins at specific sites on the DNA, called origins of replication.

DNA replication steps and enzymes

DNA helicases open the double helix.
Single-strand binding (SSB) proteins stabilize the single DNA strands.
Topoisomerases prevent tangling and knotting of the DNA.
DNA primase synthesizes RNA primers.
DNA polymerase adds nucleotide subunits to the 3' end of an existing growing polynucleotide strand.
Okazaki fragments are short DNA fragments that are synthesized discontinuously on the lagging strand.
DNA ligase links Okazaki fragments.
DNA synthesis proceeds in the 5' to 3' direction.
Leading strand is synthesized continuously.
Lagging strand is synthesized discontinuously.
DNA replication is bidirectional.

Meselson-Stahl Experiment

E. coli was grown in a medium containing heavy nitrogen (15N).
15N was incorporated into DNA.
E. coli was transferred to a medium containing 14N.
After one or two generations, DNA density supported semiconservative replication.

DNA replication in prokaryotes and eukaryotes

Prokaryotic chromosomes are single, circular. Replication begins at a single origin and proceeds in two directions.
Eukaryotic chromosomes are multiple, linear. Replication begins at multiple origins. Replication occurs as bubbles that expand and fuse.

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Description

This quiz covers the fundamental aspects of DNA structure, including the properties of nucleotides and the double helix formation. Additionally, it discusses the base pairing rules and the significance of hydrogen bonding in maintaining the stability of the DNA molecule.