Bacterial Genome

Bacterial Genome

Genome (of a cell/virus) is its entire genetic complement (inc. genes and sequences that connect all genes together)
1. All animals, plants and bacteria use DNA to carry their genetic info. Some viruses use RNA, either ss/ds DNA or RNA
  1. DNA Bases A=T and C=G (not equal in ss viruses)
    1. Most prokaryotes contain one ds circular DNA. Some have more than 1 (e.g. Vibrio Cholerae). Some are linear
      1. Chromosomes are localized in a a region called the Nucleiod
        Chromosomal DNA is folded into loops 50,000-10,000 bps long, held in place by protein and RNA, then folded into a compact mass.
        Stretched out DNA would measure 1.6mm
2. The human DNA encodes about 30,000 genes
Plasmind... a small circular molecule of DNA
1. Exists independently of the chromosome
2. Can be as small as 1-2 Kb or over 100Kb.There can be one or over 300 copies of each plasmid
3. They code for their own replication and usually have one or more traits
4. Genes that are carried on the plasmid are NOT essential for normal metabolism
5. Fertility (F) Factors
  1. Carry instructions for conjugation, allowing genes to transfer from one bacteria to another
6. Resistance (R) Factors
  1. genes that give resistance to antibiotics for heavy metals. important in medicine as they are why antibiotics stop working to treat infections
    1. Due to the spread of R-factor plasmids many antibiotics can't be used
      1. 98% of s.aureus strains are resistant to penicilin
7. Bacteriocin Factors
  1. carry genes for toxins that kill other bacteria and allow a bacteria to kill the competition
8. Virulence Factors
  1. carry genes fro structures, enzymes and toxins that enable a bacteria to become pathogenic and cause disease
    1. Shigella has 230 Kb virulence plasmid that allows it to attach & invade the human gut and cause dysentry
      1. can also be found in salmonella and E.coli sp
9. Degradative Factors
  1. carry genes for the breakdown of chemicals (e.g. oils, xylene) can be useful economically & enviromentally
10. Cryptic Plasmids
  1. Function is unknown
Genome Organisation
1. Not all DNA codes for protein. some is just for space between genes
  1. Genes can run left-right or right-left
2. Coding & Non-coding
  1. DNA has 2 strands coding and non-coding strand
    1. Coding Strand matches the sequence of the mRNA. It has the sequence that matches the bases that code the protein and makes sense when we read it
    2. Non-coding strand is copied by RNA Polymerase (also known as the template strand)
3. RNA Polymerase can initiate a new RNA strand
  1. DNA Polymerase can not start a new strand, they need a primer, a starting point they can then extend from a 3'end
4. Organisation of Prokaryotic Genes
  1. DNA is transcribed into mRNA by RNA Polymerase (enzyme_
    1. The promoter sequence, upstream of the start of the RNA coding seqeunce is where RNA Polymerase interacts to begin transcription
      1. The promoter consists of 2 sequences. One if found 35 bases before the start of the mRNA and one is found 10 bases before the start.
        Referred to as -35 and -10 promoter sequences
        -35 consensus consequence TTGACA
        -10 consensus consequence TATAAT
        TTGACA ----17+/- ---- TATAAT
        Beyond the promoter is the first base that RNA Polymerase turns into mRNA
        Can only be found experimentally
        mRNA...in bacteria messages can be polycistronic (one mRNA encodes for several proteins)
        Eukaryotes do not do this. One mRNA encodes for ONLY one protein
5. Transcription
  1. 1. RNA Polymerase attaches itself to the DNA strand (before the promoter)
    1. 2. Recognises the promoter and unzips the DNA
      1. 3. Sigma Factor is released from the RNA Polymerase
  2. CodIng regions are EXONS. Non-coding regions are INTRONS
6. Translation
  1. Ribosome (rRNA & Porteins) translate mRNA into protein
    1. In Prokaryotes ribosomes bind to mRNA at a sequence known as Shine Dalgarmo Sequence
      1. Shine Dalgarmo Sequence (a piece of mRNA that is complementary to the 3'end of the 16S RNA of the (ribosome)
      2. AGGAGG is the consensus sequence ad is 4-7 bases 5' of the start codon
        In prokaryotes this is not always AUG (Methionine)
        Ribosomes read the mRNA and specific tRNA molecules incorporate the correct amino acid into the group peptide chain
        Each tNA has a anti-codon that aches the codon in the mRNA
        there is one start codon: AUG (fmet)
        There are 3 stop codons: UAA UGA UAG
Not all DNA is genes coding for proteins
1. Some DNA is intragenic - has no known function (might just be a spacer DNA between genes)
2. There are other structures that can be found in prokaryotic DNA- phages, transposons and intergrons
In TRANSFORMATION, a recipient cell takes up DNA from the enviroment
1. Discovered by Fredrick Griffith (1928)

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	Created by bukkyawox over 11 years ago