Brief Introduction to Bacterial genetics.ppt

A brief introduction about bacterial genetics

1. Bacterial genetics
Dr. Muhammad Adnan Sabir Mughal
Lecturer; Department of Pathobiology & Biomedical Sciences,
MNS University of Agriculture, Multan

2. Structure and Function of Genetic
Material
DNA & RNA
DNA=deoxyribonucleic acid
RNA=ribonucleic acid
Basic building blocks:
Nucleotides
Phosphate group
Pentose sugar
Nitrogenous base

3. Structure of DNA
Double stranded (double helix)
Chains of nucleotides
5’ to 3’ (strands are anti-parallel)
Complimentary base pairing
PurineA-T (Adenine=Thymine)
PyramidineG-C (Guanine-Cytosine)

4. DNA Structure
Phosphate-P
Sugar-blue
Bases-ATGC

5. Hydrogen bonds-hold base pairs together
5’ end-means P comes off 5th carbon of
deoxyribose sugar
3’means P comes of 3 rd carbon of
deoxyribose sugar
Ways in which RNA & DNA differ:
RNA is ss
RNA sugar is ribose
Base pairing-A-U

6. Genetic Code
DNA: triplet code
mRNA: codon (complimentary to triplet
code of DNA)
tRNA: anticodon (complimentary to
codon)

7. Genetic Code
Codons: code for the production of a
specific amino acid
20 amino acids
3 base code
Degenerative: more than 1 codon codes
for an amino acid
Universal: in all living organisms

8. Genetic Code

9. DNA Replication
Bacteria have both Linear and circular
DNA (plasmid)
E. coli
4 Million base pairs
1 mm long (over 1000 times larger that
actual bacterial cell)
DNA takes up around 10% of cell
volume

10. DNA Replication-occurs at the
replication fork (Transcription)
5’ to 3 ‘
DNA helicase-unzips + parental DNA strand
that is used as a template
Leading stand (3’ to 5’-continuous)
*DNA polymerase-joins growing DNA strand
after nucleotides are aligned (complimentary)
Lagging strand (5’ to 3’-not continuous)
*RNA polymerase (makes short RNA
primer)
*DNA polymerase (extends RNA primer
then digests RNA primer and replaces it
with DNA)
*DNA ligase (seals Okazaki fragments-the
newly formed DNA fragments)

11. Replication Fork

12. Central Dogma of Molecular Genetics
DNA-------mRNA------protein
translation

13. Transcription
One strand of DNA used as a template to
make a complimentary strand of mRNA
Promoter/RNA polymerase/termination
site/5’ to 3’

14. Transcription (From DNA to mRNA)

15. Types of RNA
Three types:
mRNA: messenger RNA
Contains 3 bases ( codon)
rRNA: ribosomal RNA
Comprises the 70 S ribosome
tRNA: transfer RNA
Transfers amino acids to ribosomes
for protein synthesis
Contains the anticodon (3 base
sequence that is complimentary to
codon on mRNA)

16. Translation
Three parts:
Initiation-start codon (AUG)
Elongation-ribosome moves along mRNA
Termination: stop codon
reached/polypeptide released and new
protein forms
rRNA=subunits that form the 70 S ribosomes
tRNA=transfers respective amino acids to
ribosomes for protein synthesis)

21. Mutations
Changes in base sequence of DNA/lethal
and inheritable
Can be:
Harmful
Lethal
Helpful
Silent

22. Normal DNA/Missense Mutation
Missense-just one different amino acid
formed-single base substitution.

23. Nonsense Mutation/Frameshift
Mutation
Nonsense mutation-base substitution in the
middle of the mRNA results in the
formation of the stop codon/protein
synthesis stopped
Frameshift-1 or a few nucleotides are
deleted or inserted-alters 3by3 transitional
reading frame/produces inactive protein
Base substitutions and frameshift
mutations occur spontaneously or by
chemicals in the environment

25. Genetic Transfer in Bacteria
Genetic transfer-results in genetic variation
Genetic variation-needed for evolution
Three ways:
Transformation: genes transferred from one
bacterium to another as “naked” DNA
Conjugation: plasmids transferred from one
bacteria to another via a pilus
Transduction: DNA transferred from one bacteria
to another by a virus (Bacteriophages)

26. Transduction by a Bacteriophage

27. Transformation

28. Conjugation in E. coli

29. Conjugation continued…

30. Conjugation continued…

31. Comparison Prokaryote, eukaryote,Archae