Download Molecular genetics of bacteria

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Molecular genetics of bacteria
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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
Genetic engineering
DNA structure
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• double helix
• Sugar-phosphate
backbone
• bases on inside, H
bonded
• strands antiparallel
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Review of
directionality in
DNA
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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.
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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.
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Plasmids
• Plasmids are small, circular DNA molecules
– Found in the cytoplasm of many bacteria
– Plasmids are not essential for survival of the cell
– They may exist singly or in many copies
– Plasmids have a variety of functions
• Examples: metabolic, resistance, fertility, bacteriocin,
tumor-inducing, cryptic
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DNA replication
• DNA strands come
apart at “origin”
• Synthesis on each DNA
strand is 5’ 3’
• Replication forks move
bi-directionally
• Replication is semiconservative
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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 on each DNA strand is 5’ 3’
• Replication is semi-conservative
– New DNA molecules made of one old, one new strand.
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DNA replication figures
Because of requirement for 5’to
3’ synthesis, lagging strand must
repeatedly top and start; needs an
RNA primer each time.
When you’re small, you need to be
stingy and quick
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• 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.
Genotype vs. Phenotype, bacterial style
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• 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.
tRNA
rRNA: 3 sizes that,
along with proteins,
make up a ribosome.
rRNA
http://www.cu.lu/labext/rcms/cppe/traducti/tjpeg/trna.jpeg;
Tobin and Duschek, Asking About Life; http://www.tokyo-ed.ac.jp/genet/mutation/nort.gif