Dna

DNA Structure & Function

Key terms

Genome = complete set of sequences in the genetic material of an org.

Nucleic acids = Macromolecules (large RMM). Chromosomes = Discrete unit of the genome

carrying many genes. NA and protein. Gene = Segment of DNA specifying production of

a polypeptide chain. It codes for a RNA protein.

• Genotypic = Replication. Store &transmit info.• Phenotypic = Gene expression. Control devlp of

phenotype.• Evolutionary = Mutation. Changes produce

variations.

Fx…..preserving, copying and transmitting information.

Chromosomes composed of 2 macmol. i. Protein. ii. Nucleic acids DNA(d) and

RNA(s)

Structure of nucleotides..

A ) 5 carbon pentose sugar ;

RNA = Ribose, DNA = Deoxyribose.

b) A nitrogen containing base;

2 Purines (A,G) 2 Pyrimidines (C,T/U)

RNA = CGAU, DNA = CGAT

c) A phosphate group

Pentose sugars

Structure of nucleotides

Watson and Crick’s model

double helix sugar-phosphate backbone

= sugar is deoxyribose 4 types of nucleotide

base : A, C, G, T : 2 complementary strands

where A = T, C = G in anti parallel fashion– "complementary“ = fitting

together of 2 molecules with hydrogen bonds

Phosphodiester bonds..

A dinucleotide is formed when a condensation reaction occurs between the phosphate group of one nucleotide and pentose of another forming a phosphodiester bridge linking the 2 nucleotides together.

More nucleotides can be added, building up a long polynucleotide chain.

The stability of the double helix is due to the large number of covalent, H+ and hydrophobic bonds.

Double Helix..

Uprights = Sugar phosphate bond, Rungs = Bases (A+T/G+C)2 strands running in opposite direction (5’ – 3’)

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Genetic code These bases always pair up in the same way.

A single strand of DNA is made of letters: ATGCTCGAATAAATG

The letters make words: ATG CTC GAA TAA ATG TGA ATT TGA

The words make sentences: <ATG CTC GAA TAA> <ATG TGA ATT TGA>

These "sentences" are called genes

Genetic code

The instructions in a gene that tell the cell how to make a specific protein. A, T, G, and C.

3 letter word = codon = Triplet code.

Fx of codon = tell the cell how to make proteins

Start and stop codon.

Genetic code contd.. Inside the nucleus, the DNA message is copied onto

RNA. to transmit the message or genetic code. It has 4 subunits A, T, G, C and are arranged in triplet

codes. Eg ATTGCCTAG read from left to right ATT/GCC/TAG. Each triplet code specifies different amino acids.

Eg. ATT = amino acid “X”GCC = amino acid “Y”TAG = amino acid “Z”

This piece of genetic code will instruct the cell to make a protein in which X,Y and Z are joined together in that order.