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What are the four bases that form the building blocks for DNA?

Adenine (A), Thymine (T), Guanine (G), and Cytosine (C).

Explain the work of Chargaff and colleagues and its importance to DNA structure.

Chargaff discovered that in DNA, the amount of adenine equals thymine, and the amount of guanine equals cytosine. This established the base pairing rules which are fundamental to DNA structure.

How are the Chargaff rules satisfied in DNA structure?

Chargaff's rules are satisfied because adenine pairs with thymine (A-T) and guanine pairs with cytosine (G-C), thereby allowing for consistent base pairing.

What type of bonds link nucleotides in a DNA chain?

Phosphodiester bonds link the nucleotides together in a DNA chain.

What forces keep the strands of the double-helix together?

Hydrogen bonds between the base pairs and hydrophobic interactions between the stacked bases contribute to the stability of the double helix.

How many hydrogen bonds are involved in A-T and G-C base pairing?

A-T base pairing involves 2 hydrogen bonds, while G-C base pairing involves 3 hydrogen bonds.

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

The two strands of a DNA molecule are antiparallel, meaning one strand runs in the 5' to 3' direction while the other runs in the 3' to 5' direction.

How can you calculate the percentage/amount of any nucleotide if the amount of one is known?

Using Chargaff's rules, if you know the percentage of one nucleotide, you can deduce the percentages of the others (e.g., if A=30%, then T=30%, G and C must each be 20% to total 100%).

What factors can be calculated based on the knowledge of DNA structure?

The number of hydrogen bonds, the number of helix turns, the total number of bases (nucleotides), base pairs, phosphodiester bonds, and the number of purines versus pyrimidines.

Describe the three proposed models for DNA replication.

The three models are: the conservative model, the semi-conservative model, and the dispersive model.

How did Meselson and Stahl prove that DNA replicates semi-conservatively?

They used isotopic labeling to show that each daughter DNA molecule consisted of one old (parent) strand and one new strand.

What are the three steps in DNA replication?

1. Initiation, 2. Elongation, 3. Termination.

What is a replication bubble and how does it form?

A replication bubble forms when DNA is unwound by helicase, resulting in two replication forks that move in opposite directions.

What roles do the following enzymes/proteins play in DNA replication: DNA helicase, DNA polymerase III, DNA polymerase I, DNA primase, DNA ligase, and single-stranded binding proteins?

• DNA helicase: unwinds the DNA double helix.
• DNA polymerase III: synthesizes new DNA strands.
• DNA polymerase I: replaces RNA primers with DNA.
• DNA primase: synthesizes RNA primers.
• DNA ligase: joins Okazaki fragments.
• Single-stranded binding proteins: stabilize unwound DNA strands.

What is the role and function of the RNA primer in DNA replication?

The RNA primer provides a starting point with a free 3'-OH group for DNA polymerase to begin synthesis.

What are Okazaki fragments and their role in DNA replication?

Okazaki fragments are short sequences of DNA synthesized on the lagging strand during DNA replication.

How are leading and lagging strands synthesized during DNA replication?

The leading strand is synthesized continuously in the same direction as the replication fork, while the lagging strand is synthesized in short, discontinuous segments (Okazaki fragments).

In what direction does chain elongation occur during DNA replication?

Chain elongation occurs in the 5' to 3' direction.

What is the role of the sliding clamp during DNA replication?

The sliding clamp holds DNA polymerase in place on the DNA strand, enhancing the enzyme's processivity and ensuring efficient replication.

Define telomeres and describe their significance.

Telomeres are repetitive nucleotide sequences at the ends of chromosomes that protect them from deterioration; they play a crucial role in cellular aging and stability.

What are the different forms of DNA repair?

DNA repair mechanisms include: excision repair, double-strand break repair, and mismatch repair.