PROTEIN SYNTHESIS

DNADNA

RNARNA

ProteinProtein

Scientists call this the:

Central

Dogma of

Biology!

PART 1: DNA STRUCTURE AND REPLICATION

What is DNA?

DNA = Deoxyribonucleic Acid It is the blueprint for life – it is the

molecule which stores genetic information in ALL living things

DNA contains the instructions for making proteins, which control your cells

Nucleic Acids: DNA

DNA is a nucleic acid and is make up of two strands of nucleotides

A nucleotide is a monomer of a nucleic acid and has 3 parts connected with covalent bonds sugar Phosphate group Nitrogen Base

In DNA, the sugar is deoxyribose

DNA’s Nitrogen Bases

There are four possible nitrogen bases

2 are called purines (2 rings) Adenine Guanine

2 are called pyrimidines (1 ring) Thymine Cytosine

A purine always matches up with a pyrimidine this is called complementary base pairing Adenine pairs with thymine (A-T) Guanine pairs with cytosine (G-C)

DNA’s Shape

The nitrogen bases are held together in the middle by a weak hydrogen bond, which causes the ladder to twist

There are 3 between G and C and 2 between A and T.

This causes the DNA to have a Double Helix shape

DNA Replication

Why does DNA need to replicate? Before a cell can divide (through mitosis or

meiosis) its genetic information must be copied for the new cell

This ensures that the new cell is genetically identical to the parent cell, and that it has all of the necessary information to carry on life processes

The structure of the double helix explains how DNA copies itself

DNA Replication

The “parent” molecule has two complementary strands of DNA.

Each is base paired by hydrogen bonding with its specific partner:

A with T

G with C

DNA Replication

The first step in replication is the separation of the two strands. This is done by the enzyme helicase. Helicase unwinds the two strands and then breaks up the hydrogen bonds in the middle.

DNA Replication

Each exposed parental strand now serves as a template that determines the order of the bases along a new complementary strand.

Free floating nucleotides in the nucleus will add on to each exposed strand, forming two new molecules of DNA. This process is performed by the enzyme DNA polymerase. DNA polymerase adds the bases in the correct order, and also “proof-reads” the strands as it makes the new one.

A will pair with a T. T will pair with an A.

G will pair with a C. C will pair with a G.

DNA Replication

The nucleotides are connected to form the sugar-phosphate backbones of the new strands. This is done by the enzyme ligase, which is like a “glue.”

Each daughter DNA molecule consists of one parental strand and one new strand.

This model of replication is called semi-conservative replication. This is due to the fact that each new molecule has one old strand and one new strand. This ensures that each molecule of DNA is accurate.