1. Molecular Genetics

2. DNA STRUCTURE AND REPLICATION
BUILDING BLOCKS OF DNA: Nucleotides:
5 carbon sugar (deoxyribose)
Nitrogenous base (A, T, C, or G)
Phosphate group

3. NITROGENOUS BASES

4. DNA Structure § Double helix Double stranded Twisted ladder
Sides of ladder consist
of alternating sugar &
phosphate groups
Rungs of ladder − 2
bases
Purine – pyrimidine
A – T
C – G
Hydrogen bonds
hold bases together
H bonds between
A and T 3
C and G
DNA Structure

5. Antiparallel Strands Semiconservative model
One strand 5’ at top & 3’ at bottom
Other strand: 5’ at bottom & 3’ at top
Antiparallel Strands Semiconservative model 5
’ end th
carbon in
deoxyribose 3 rd
Nucleotide

6. P S ROTEIN YNTHESIS DNA • Double stranded Sugar = deoxyribose
Bases = ATCG
Transcription
messenger RNA mRNA
single stranded
sugar = ribose
bases = AUCG
carries code for
making
proteins from
DNA in nucleus
to ribosomes in
cytoplasm
Ribosomes 2
subunits
small
large
% r 60
ibosomal
RNA
(rRNA) 40
% protein
Site of protein synthesis
Amino
acid
tRNA
transfer RNA
carries amino acid to
ribosomes
Anti-codon base pairs
with codon on mRNA
specific
Anti-
codon

7. GENETIC CODE 1 codon = 3 consecutive bases
1 codon codes for 1 amino acid (A.A.)
There are 4 bases (A, T, C, G)
Thus 43 (64) possible combinations of codons
There are 20 amino acids
Code is redundant (2 or more codons code for same amino acid) but not ambiguous (no codon codes for more than 1 amino acid)

8. Amino Acid—Codon Chart

9. PROTEIN SYNTHESIS – OVERVIEW Central Dogma of Biology
DNA (Coding strand)
mRNA
Transcription
Translation (
uses codons in mRNA to
build protein)
Protein

10. base-pairs RNA nucleotides with exposed DNA bases
ROTEIN S
YNTHESIS
– T
RANSCRIPTION
DNA
mRNA
grows in 5’ to 3’ direction
RNA polymerase •
binds to promoter (TATA box)
separates DNA strands
base-pairs RNA nucleotides with exposed DNA bases
stops when reaches terminator

11. RNA Processing occurs in eukaryotic cells Introns removed Exons linked
5’ cap added
Poly-A tail added
Spliceosome
Cut out introns
Slice exons together
Consists of proteins and SnRNPS
Poly-A tail

12. PROTEIN SYNTHESIS – TRANSLATION
Initiation
mRNA binds to
Small ribosomal subunit
Initiator tRNA base pairs with
1st codon
(start codon)
on mRNA
1st amino acid - methionine
Large ribosomal subunit binds
to complex
Initiator tRNA located at P site – peptidyl-tRNA binding site
A site = Aminoacyl-tRNA binding site

13. 2nd tRNA base pairs with 2nd codon on mRNA at A site
Elongation
2nd tRNA base pairs with 2nd codon on mRNA at A site
Peptidyl transferase forms peptide bond between 1st and 2nd amino acids
1st tRNA exits
mRNA shifts position by 1 codon
2nd tRNA now at P site
3rd tRNA base pairs with 3rd codon at A site
process continues until stop codon reaches A site

14. Stop codon (UGA, UAA, UAG) reaches A site
Termination •
Stop codon (UGA, UAA, UAG) reaches A site
Release factor binds to stop codon
Polypeptide hydrolyzed from tRNA at P site
Complex disassembles
mRNA can be used again
Polypeptide released

19. Recombinant DNA