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DNA and DNA

replication

Lecture objectives

• Explain the importance of complementarity for

DNA structure and function.

• Explain the basic mechanism of DNA

replication.

• Describe DNA replication in eukaryotes and

prokaryotes.

Nucleotides: Building Blocks of

Nucleic Acids

• Consists of 3

components

1. 5 Carbon

(pentose)

sugar

2. Nitrogenous

base

3. Phosphate

group

Nucleotides: Building Blocks of

Nucleic Acids

• The pentose sugars found in nucleic acids give them their names. Ribonucleic acids (RNA) contain ribose, while deoxyribonucleic acids (DNA) contain deoxyribose.
• The absence of a hydroxyl group at the position thus distinguishes DNA from RNA. In the absence of the hydroxyl group, the sugar is more specifically named 2 - deoxyribose.

THE PHOSPHODIESTER BACKBONE

The Structure of DNA (Watson & Crick Model DNA STRUCTURE DNA : Deoxyribonucleic acid

• consist of two long strands wrapped around each other to form a double-stranded helix with antiparallel strands .

• DNA double helix. DNA STRUCTURE - DOUBLE HELIX

Semiconservative DNA replication

• The parent molecule unwinds, and two new daughter

strands are built based on base-pairing rules

• DNA Replication is “Semi-conservative” (a) The parent molecule has two complementary strands of DNA. Each base is paired by hydrogen bonding with its specific partner, A with T and G with C. (b) The first step in replication is separation of the two DNA strands. (c) Each parental strand now serves as a template that determines the order of nucleotides along a new, complementary strand. (d) The nucleotides are connected to form the sugar-phosphate backbones of the new strands. Each “daughter” DNA molecule consists of one parental strand and one new strand. A C T A G A C T A G A C T A G A C T A G T G A T C T G A T C A C T A G A C T A G T G A T C T G A T C T G A T C T G A T C

The DNA replication: Key players

✓Topoisomerase

✓Helicase

✓Primase

✓Single stranded

binding proteins

DNA replication

Synthesis of lagging strand

DNA replication

Synthesis of lagging strand

DNA replication

Synthesis of lagging strand

DNA replication

Synthesis of lagging strand