Molecular genetics of bacteria

1
Molecular genetics of bacteria

• Emphasis ways that bacteria differ from
  eukaryotes
• DNA structure and function definitions.
• DNA replication
• Transcription and translation
• Gene regulation and regulation of metabolism
• Genetic exchange among bacteria

2
DNA structure

• double helix
• Sugar-phosphate backbone
• A-T, C-G base pairs
• bases on inside, H- bonded
• strands anti-parallel

3
Review of directionality in DNA
4
DNA source of cellular information

• Information flow DNA?RNA ?protein
• also DNA ?DNA
• Segments of DNA with specific information genes.
• Structure of DNA highly related to function
• Information coded in sequence of bases
• Complementary strands means that when each is
  copied, two identical molecules are made.

5
DNA in prokaryotes

• Most bacteria have a single, circular, molecule
  of DNA
• Some have more than one, some have linear DNA
• Packaged w/ histone-like proteins, coiled tightly
  in loops, attached to membrane
• 1.6 mm of DNA in a 0.002 mm sized cell.
• Area of cell containing the DNA nucleoid.

6
DNA replication

• Origin of DNA replication particular site on DNA
  where copying of the DNA always starts.
• Replication is bidirectional
• In each direction, there is a replication fork.
• Bacterial DNA is circular, so there is one Origin
  and one terminus
• Synthesis of each DNA strand is 5 ?3
• Replication is semi-conservative
• New DNA molecules made of one old, one new strand.

7
DNA replication figures
Because of requirement for 5to 3 synthesis,
lagging strand must repeatedly top and start
needs an RNA primer each time.
8
When youre small, you need to be stingy and quick

• Look for many ways that bacteria can save energy
  and respond quickly to changes in environment.
• E. coli needs 30 minutes to replicate its DNA,
  but only 20 minutes to divide into two. How? It
  gets a head start.

9
Genotype vs. Phenotype, bacterial style

• Genotype the genetic make-up of an organism.
• Phenotype the genetic information expressed by
  the organism.
• Eukaryotes difference is often due to masking of
  recessive alleles by dominant ones
• In bacteria, which are generally monoploid,
  phenotype is determined by which genes are being
  expressed at the present time in response to
  environmental conditions.

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About RNA
1) DNA is double stranded, but RNA is single
stranded. However, RNA can base-pair with itself
to create double stranded regions.
RNA
DNA
tRNA
genetics.gsk.com/graphics/ dna-big.gif
http//www.fhi-berlin.mpg.de/th/JG/RNA.jpg http//
www.santafe.edu/images/rna.gif
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About RNA-2
2) RNA contains ribose instead of deoxyribose 3)
RNA contains uracil instead of thymine.
www.layevangelism.com/.../ deoxyribose.htm
http//www.rothamsted.bbsrc.ac.uk/notebook/courses
/guide/images/uracil.gif
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3 kinds of RNA
mRNA a copy of the gene is translated to make
protein. tRNA smallest RNA, does actual decoding.
rRNA 3 sizes that, along with proteins, make up
a ribosome.
tRNA
rRNA
http//www.cu.lu/labext/rcms/cppe/traducti/tjpeg/t
rna.jpeg Tobin and Duschek, Asking About Life
http//www.tokyo-ed.ac.jp/genet/mutation/nort.gif
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Some enzymes of molecular biology

• DNA polymerases
• Synthesize DNA operate in 5?3 direction only
• RNA polymerases
• Synthesize RNA by copying DNA
• DNA ligase
• Enzyme that connects adjacent 3-OH and 5
  phosphate
• Exonuclease
• Enzyme that cuts bases from the end of a strand
• Endonuclease
• Makes internal cuts in a DNA or RNA molecule
• Restriction endonuclease cuts at a specific
  internal sequence.

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Methylation

• Many organisms add methyl groups (-CH3) to DNA,
  especially to cytosine.
• One of several reasons is self-protection from
  restriction endonucleases
• Enzymes recognize sequences of nucleotides that
  occur at random and cut the DNA
• Viral DNA injected into cytoplasm of bacteria is
  destroyed, protecting the bacterium.
• Methylation protects bacterial DNA from cutting
  by its own restriction enzymes.