DNA Replication – Process Lecture 17 1. Forms of DNA Helices 2 DNA Replication Template DNA (parent…
Dna
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Transcript of 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.