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 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 genetics.gsk.com/graphics/ dna-big.gif ) DNA is double stranded, but RNA is single stranded. However, RNA can base-pair with itself to create double stranded regions. DNA RNA tRNA

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

12 3 kinds of RNA Tobin and Duschek, Asking About Life; 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

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 (-CH 3 ) 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.