Download - Dna
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DNA Structure & Function
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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.
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• Genotypic = Replication. Store &transmit info.• Phenotypic = Gene expression. Control devlp of
phenotype.• Evolutionary = Mutation. Changes produce
variations.
Fx…..preserving, copying and transmitting information.
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Chromosomes composed of 2 macmol. i. Protein. ii. Nucleic acids DNA(d) and
RNA(s)
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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
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Pentose sugars
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Structure of nucleotides
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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
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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.
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More nucleotides can be added, building up a long polynucleotide chain.
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The stability of the double helix is due to the large number of covalent, H+ and hydrophobic bonds.
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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
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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.
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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.