This document discusses the structure and function of genetic material in microbes. It covers the basics of DNA and RNA structure, DNA replication, transcription, translation, the genetic code, and mechanisms of genetic transfer in bacteria. DNA is made of nucleotides with a phosphate, sugar, and nitrogenous base. It takes the form of a double helix. Bacterial DNA replication occurs via a replication fork that uses the parental DNA strands as templates. Transcription converts DNA into mRNA which is then translated into proteins. Mutation, transformation, conjugation, and transduction allow for genetic variation in bacteria.

1. MICROBIAL
GENETICS
PREPARED BY
WELFREDO YU,JR.

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
• A-T
• G-C

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

5. DNA REPLICATION
Bacteria have closed, circular DNA
Genome: genetic material in an organism
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

6. DNA REPLICATION-OCCURS AT
THE REPLICATION FORK
5’ to 3 ‘
DNA helicase-unzips + parental DNA strand
that is used as a template
• Leading stand (5’ to 3’-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)

7. REPLICATION FORK

8. PROTEIN SYNTHESIS
DNA------- mRNA------ protein
transcription translation
Central Dogma
of Molecular Genetics

9. TRANSCRIPTION
One strand of DNA used as a template to
make a complimentary strand of mRNA
Promoter/RNA polymerase/termination
site/5’ to 3’
Ways in which RNA & DNA differ:
• RNA is ss
• RNA sugar is ribose
• Base pairing-A-U

10. TRANSCRIPTION

11. 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)

12. GENETIC CODE
DNA: triplet code
mRNA: codon (complimentary to triplet code of DNA)
tRNA: anticodon (complimentary to codon)

13. 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

14. GENETIC CODE

15. 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 (protein synthesis occurs here)
tRNA=transfers amino acids to ribosomes
for protein synthesis)

20. MUTATIONS
Changes in base sequence of DNA/lethal and inheritable
Can be:
• Harmful
• Lethal
• Helpful
• Silent

21. NORMAL DNA/MISSENSE
MUTATION

22. NONSENSE
MUTATION/FRAMESHIFT
MUTATION

23. 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 1 bacteria to
another via a pilus
• Transduction: DNA transferred from 1 bacteria to
another by a virus

24. TRANSDUCTION BY A
BACTERIOPHAGE

25. TRANSFORMATION

26. CONJUGATION IN E.
COLI

27. CONJUGATION
CONTINUED…

28. CONJUGATION
CONTINUED…