Objectives Be able to describe the structure of

Objectives • Be able to describe the structure of a nucleotide • Be able to describe the structure of RNA • Be able to describe the structure of DNA

Why is DNA so important? • DNA carries genetic information • It passes on the features of organisms from one generation to the next • The code on DNA determines the sequence of amino acids in a protein – the primary structure

DNA is made up of many nucleotides Pentose (5 carbon) sugar The organic base contains nitrogen

There are 4 different DNA nucleotides, each with a different base- what are the 4 bases? • A- adenine • T- thymine • G- guanine • C-cytosine

How is a mononucleotide formed? The pentose sugar, organic base and phosphate group are all joined by condensation reactions to form a mononucleotide

A condensation reaction between two nucleotides forms a phosphodiester bond Phosphate group of one mononucleotide is joined to the deoxyribose group of another in a condensation reaction

A polynucleotide contains many nucleotides

Zoom in!

How did we discover the structure of DNA? • http: //www. dnaftb. org/19/animation. html Questions: What stands out from Chargaff’s findings? What would be the problem with pairing A-T or C-G? CLICK THROUGH ANIMATION

Base pairing • The bases on the two strands of DNA attach to each other by hydrogen bonds • The hydrogen bonds hold the two strands together • Adenine always pairs with thymine • Guanine always pairs with cytosine

A complementary to T C complementary to G

Base pairing (DNA interactive. Animations- Base Pairing) Hydrogen bonds

A nucleotide showing the positions of the 3 -prime and 5 -prime carbon atoms on the pentose sugar

Antiparallel strands

The double helix Look at the model

Fill in the gaps on the back of your sheet

Why is DNA so stable? • the phosphodiester backbone protects the more chemically reactive organic bases • hydrogen bonds link the base pairs forming bridges. As there are 3 H-bonds between cysteine and guanine, more C-G pairings make the molecule more stable.

Function of DNA Make a note as we go through

Separate strands are joined by hydrogen bonds, these are easily broken to allow stands to separate for DNA replication & protein synthesis

It is extremely large, allowing lots of genetic information to be stored.

Very stable and can be passed from generation to generation (rarely mutates)

Bases are protected by the sugar phosphate backbone- prevents corruption by outside chemical or physical forces

The sequence of DNA bases codes for the primary structure of proteins.

Base pairing allows DNA to replicate and to transfer information to m. RNA

What is the difference between DNA and RNA?

RNA • A polymer • A single, relatively short polynucleotide chain • Pentose sugar is always ribose • Bases are adenine, uracil, guanine and cytosine

The three types of RNA

Research task… m. RNA Which bases is it made up of? Draw/describe the structure What does it do? r. RNA t. RNA