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Microbial Genetics. Chapter 8. Structure and Function of Genetic Material. DNA & RNA DNA deoxyribonucleic acid RNA ribonucleic acid Nucleotides Phosphate group Pentose sugar Nitrogenous base. Structure of DNA. Double stranded (double helix) polymers of nucleotides

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Structure and function of genetic material
Structure and Function of Genetic Material

  • DNA & RNA

  • DNA

    • deoxyribonucleic acid

  • RNA

    • ribonucleic acid

  • Nucleotides

    • Phosphate group

    • Pentose sugar

    • Nitrogenous base


Structure of dna
Structure of DNA

  • Double stranded (double helix)

  • polymers of nucleotides

  • 5’ to 3’ (strands are anti-parallel)

  • Complimentary Base Pairing

    • A - T

    • G - C


Dna replication
DNA Replication

  • Bacteria have only 1 chromosome (ccDNA)

  • E. coli

    • about 4 million base pairs

    • 1 mm long (1000 times longer than the cell)

    • DNA takes up only about 10 % of cells volume


E. coli DNA

1u 1,360u

1ft. 1,360 ft.


Dna replication occurs at the replication fork 5 to 3
DNA Replication occurs at the Replication Fork (5’ to 3’)

  • DNA Helicase

  • 1. Leading Strand ( 5’ to 3’ )

    • DNA Polymerase

  • 2. Lagging Strand ( 5’ to 3’)

    • RNA Polymerase (RNA Primer)

    • DNA Polymerase (extends primer and digests RNA)

    • DNA Ligase

      • Okazaki Fragments


Bidirectional replication
Bidirectional replication 3’)

  • Origin of replication

  • Termination site


Protein synthesis
Protein Synthesis 3’)

  • DNA mRNA Protein

  • Transcription Translation

  • Central Dogma of Molecular Genetics


Transcription
Transcription 3’)

  • One strand of DNA is used as a template to form a complimentary strand of mRNA

  • mRNA ----> messenger RNA


Transcription1
Transcription 3’)

  • 3 ways RNA differs from DNA

  • Promoter

  • RNA Polymerase

  • Termination Site

  • 5’ to 3’


3 types of rna
3 Types of RNA 3’)

  • 1. mRNA

    • Contains the codons

  • 2. rRNA

    • Ribosomes (70S)

  • 3. tRNA

    • Transfer amino acids to the ribosomes for protein synthesis

    • Anti-codon


Genetic code

DNA 3’)

mRNA

tRNA

Triplet code

codons

anticodons

Genetic Code


Genetic code1
Genetic Code 3’)

  • Codons code for a specific amino acid

  • 20 amino acids

  • 3 base code - 4 bases ( A,U,G,C )

  • 64 possible combinations ( 43)

  • Amino acids are coded for by more than one codon

  • Genetic Code is Degenerative

  • Genetic Code is Universal


Translation
Translation 3’)

  • rRNA

    • ribosomal RNA (forms the ribosomes) (70S)

  • tRNA

    • transfer RNA (transfers amino acids to the ribosomes for protein synthesis)

    • anticodon

      • 3 base sequence that is complimentary to the codon on mRNA


Regulation of gene expression
Regulation of Gene Expression 3’)

  • All Genes are not always being expressed

  • Genes turned on all the time - Constitutive

  • Other genes can be regulated:

    • Turned On

    • Turned Off


Lac operon
lac operon 3’)

  • Lac - Lactose (dissacharide)

    • Glucose and Galactose

  • operon - series of structural genes all under the control of a Regulatory Gene

  • lac operon is normally turned off

  • lac operon is an Inducible operon


Tryptophan operon
Tryptophan operon 3’)

  • Tryptophan - amino acid

  • operon - series of structural genes all under the control of a Regulatory Gene

  • Tryptophan operon is normally turned on

  • Tryptophan operon is a repressible operon


Mutations a change in the base sequence of dna
Mutations - 3’)a change in the base sequence of DNA

  • Mutations can be:

  • 1. Harmful

  • 2. Lethal

  • 3. Beneficial

  • 4. Silent (neutral)

    • UUU - Phe

    • UUC - Phe


Types of Mutations 3’)

Normal DNA


Base Substitution Mutation 3’)

C

Missense Mutation


Base Substitution Mutation 3’)

T

Nonsense Mutation


Frame shift mutation
Frame Shift Mutation 3’)

  • ATG CAT GCA TGC ATT TCC TGC TTA AAA

  • 1. Addition Mutation

  • AAT GCA TGC ATG CAT TTT CCT GCT TAA

  • Reading Frame is Shifted

  • 2. Deletion Mutation

  • TGC ATG CAT GCA TTT CCT GCT TAA

  • Reading Frame is Shifted


Genetic transfer in bacteria
Genetic Transfer in Bacteria 3’)

  • Genetic Transfer - results in Genetic Variation

  • Genetic Variation - is needed for Evolution

  • 3 Ways Genetic Transfer can occur in Bacteria

    • 1. Transformation

    • 2. Cunjugation

    • 3. Transduction


Transformation
Transformation 3’)

  • Genes are transferred from one bacterium to another as “naked” DNA

  • Frederick Griffith (1928)


Griffith s experiment
Griffith’s Experiment 3’)

  • 2 Strains of Streptococcus pneumoniae

    • 1. Virulent strain with a capsule - Pneumonia

    • 2. Avirulent strain without a capsule - no disease






Conjugation 3’)

One bacterium passes some DNA (in a plasmid) to another bacterium


Transduction
Transduction 3’)

  • DNA is transferred from one bacterium to another by a virus

  • Bacteriophage

    • virus that only infects bacteria


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