1. Microbial Genetics

2. Genetic material of Esch coli
Single circular DNA
5x base pairs
Codes for 2000 proteins
haploid- single chromosome

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

4. Structure of DNA Double stranded (double helix) Chains of nucleotides
5’ to 3’ (strands are anti-parallel)
Complimentary base pairing
A-T
G-C
A-adenine
T-thymine
G-guanine
C-cytosine

5. DNA Structure Phosphate- P Sugar- blue Bases- AT GC
Hydrogen bonds-hold base pairs together A-T
5’ end-means P comes off 5’ carbon of deoxyribose sugar
3’means P comes of 3’ end of deoxyribose sugar
Hydrogen bonds-hold base pairs together
5’ end-means P comes off 5’ carbon of deoxyribose sugar
3’means P comes of 3’ end of deoxyribose sugar

6. 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

7. 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)
During replication, on parental ds DNA is converted into 2 identical ds daughter molecules…
After DNA helicase unzips DNA strand, free nucleotides present in cytoplasm are matched up to exposed bases on the single stranded parental DNA
Dna polymerase can add nucleotides only to the 3’ end
Okazaki fragments-1000 nucleotides

8. Replication Fork

9. Protein Synthesis DNA------- mRNA------ protein
transcription translation
DNA ribosome
Central Dogma
of Molecular Genetics

10. 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 instead of A-T
mRNA-messenger RNA

11. Transcription

12. Types of RNA Three types: mRNA: messenger RNA rRNA: ribosomal 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)
mRNA-messenger

13. Genetic Code DNA: triplet code---- A T C
mRNA: codon (complimentary to triplet code of DNA) U A G
tRNA: anticodon (complimentary to codon) A T C

14. 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
64 total codons
3 STOP codons uaa,uga,uag
1 start codon (for protein synthesis) aug (also a sense codon that forms aa)

15. Genetic Code

16. Translation Three parts:
Initiation-start codon (AUG)
Elongation-ribosome moves along mRNA
Termination: stop codon (UGA) 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)

21. MUTATIONS Change in base sequence of DNA
Different AA inserted in protein
Altered phenotype

22. Mutations Changes in base sequence of DNA lethal and inheritable
Can be:
Harmful
Lethal
Helpful
Silent
Silent-neutral

23. Normal DNA Missense Mutation—base subsitution
Missense-just one different amino acid formed-caused from a base substitution, single base is replaced with a different one

24. c ) Nonsense Mutation (base subsitution stop codon UGA) d) Frameshift Mutation (base inserted or deleted)
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. Causes of mutations Chemicals Radiations Viruses ---inserted
bonds of wrong bases not AT but AC
Base analogues are taken up – bromouracil instead of thymine
Frame shift mutations----tobacco insert between bases
Radiations
X-rays breaks bonds of ribose phosphate chain,
Free radicals—damage bases,
H bonds of bases are altered by changing outer electrons of bases.
UV—dimers of bases----replication inhibited
Viruses ---inserted

26. Mutation due to transposons
Transfers DNA in same bacteria from one site of chromosome to another or to plasmid
Make copy and insert
where Inserted can cause mutation

27. WHAT ARE TRANSPOSONS? Pieces of DNA Jumping genes Moves within DNA or
Between DNA, Plasmid &Bacteriophage
Replicate n make copy but not indepedently only with DNA
Insertion sequences small transposons
Code for drug resistsnce & enzymes,toxins

28. WHAT ARE PLASMIDS ? Extra chromosomal DS DNA in cytoplasm
Capable of independent replication
Integrate in DNA
Transmissable & non transmissable
Code for antibiotic resistance ,toxins,enzymes

29. 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 to one bacteria to another via a pilus
Transduction: DNA transferred from one bacteria to another by a virus
Transduction-DNA passed from 1 bacteria to another in a bacteriophage (virus) and then incorporated into the host DNA

30. Transformation

31. Transduction by a Bacteriophage

32. Examples of transduction bacteriophage
Botulinism toxin
Corynebacterium toxin
Diptheria toxin
Erythrogenic toxin

33. Conjugation in E. coli F factor-plasmid F+ cell –donor/f- is recipient
Hfr-when plasmid becomes incorporated into chromosome of bacteria, that cell is called a high frequency of recombination cell
During conjugation, hfr cell can transfer chromosomal dna to f-cell

34. Conjugation continued…

35. Conjugation continued…

36. Bacteriophage containing host-cell DNA is involved in which of the following processes?
 Transformation
Conjugation
Transduction
Transcription
Recombination

37. Plasmids is involved in which of the following processes?
 Transformation
Conjugation
Transduction
Transcription
Recombination

38. Mobile genetic elements that code for antibiotic resistance genes in bacteria but are incapable of self-replication are
plasmids
R factor
Temperate RNA phages
Transposons
Virulent DNA phages