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 Genetic engineering

2 DNA structure double helix Sugar-phosphate backbone 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 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

7 DNA replication DNA strands come apart at “origin” Synthesis on each DNA strand is 5’  3’ Replication forks move bi-directionally Replication is semi- conservative

8 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.

9 DNA replication figures Because of requirement for 5’to 3’ synthesis, lagging strand must repeatedly top and start; needs an RNA primer each time.

10 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.

11 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.

12 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

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

14 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