DNA contains the genetic material of organisms in the form of nucleotides arranged in a double helix structure. The double helix is composed of two strands of nucleotides linked by hydrogen bonds between complementary nucleotide bases. DNA stores and transmits genetic information from one generation to the next through replication and cell division. It controls the development of an organism's phenotype through gene expression and can produce variations through mutation that lead to evolution over time.

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 TGA ATT 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.