1. DNA
Structure & Function

2. 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.

3. • Genotypic = Replication. Store &transmit info.
• Phenotypic = Gene expression. Control devlp of
phenotype.
• Evolutionary = Mutation. Changes produce
variations.
Fx…..preserving, copying and transmitting information.

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

5. 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

6. Pentose sugars

7. Structure of nucleotides

10. 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

12. 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.

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

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

17. Double Helix..
Uprights = Sugar phosphate bond, Rungs = Bases (A+T/G+C)
2 strands running in opposite direction (5’ – 3’)
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20. 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 TGAATT TGA>
 These "sentences" are called genes

21. 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.

22. 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.