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 mm sized cell.
Area of cell containing the DNA: nucleoid.

6. Synthesis of each DNA strand is 5’ 3’
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 5’to 3’ synthesis, lagging strand must repeatedly top and start; needs an RNA primer each time.

8. When you’re 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.

10. 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

11. About RNA-2 2) RNA contains ribose instead of deoxyribose
3) RNA contains uracil instead of thymine.
deoxyribose.htm

12. 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
Tobin and Duschek, Asking About Life;

13. 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.

14. 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.