Dr. Gary Andersen, 913-279-2211 Some slides used with permission from Curtis Smith, KCKCC Reference: Chapter 7,8 from (Black, J., 2005). Microbial Genetics. Genomes – the total of the genetic material in a cell.
Gene - The unit of heredity for a given genetic trait. The site on a DNA molecule that carries the code for a certain cell function.
Viruses – 4 or 5 genes, E. coli – 4228 genes, Human ~ 31,000 genes.Basic Units of Genetics
E. coli cell
DNA (deoxyribonucleic acid) is made of subunits called nucleotides. Nucleotides are made of 3 components. These 3 components are linkedtogether with a covalent bond.
E. Coli = 4.6 million nucleotide pairs (~1mm)
Corn = 2.5 billion nucleotide pairs
Human = 3 billion nucleotide pairs (2nm wide by 2 meters long)DNA
Provides a method for introducing a high degree of variety. (unlimited variety of sequences possible)Significance of DNA Structure
Composed of one Nitrogen base, one Deoxyribose, and one Phosphate group
5. DNA has complimentarity
that is A always bonds with T
and G always with C
6. DNA is always antiparallel. The 2 strands of DNA are always oriented in opposite directions. ( 5’ PO3 end – 3’ OH end)
2. tRNA (transfer) carries amino acids to the ribosome during protein synthesis. Also known as the “ANTICODON”
3. mRNA (messenger) - a complimentary strand of RNA equal in size to 1 gene (normally ~1,000 nucleotides). “CODON” - coded info from DNA (bound for the ribosome)C. FUNCTIONS OF RNA
ReplicationTHE CENTRAL DOGMA OF BIOLOGY “Francis Crick – 1956”
Cell Division) = 2 daughter cells
2. Each cell receives 1 parental strand and 1 daughter strand. (semiconservative replication)DNA REPLICATION
GA sp 08
As the two replication forks meet, the two new chromosomes separate—each containing one new and one old strand
DNA exonuclease (POL I) removes any mistaken base pairs.
DNA ligase seals any gaps and joins the 2 strands together.DNA REPLICTIONCONTINUED
ReplicationTHE CENTRAL DOGMA OF BIOLOGY
1st step in gene expression (i.e.protein synthesis).
The cells genetic plan contained in DNA is transcribed into a complimentary base sequence called messenger RNA (mRNA).
The region of DNA that produces or serves as a template for mRNA is called a gene. A gene normally consists of around 1,000 base pairs. It is the smallest segment of DNA that codes for mRNA.B. TRANSCRIPTION
After transcription, the coded information in mRNA is translated into an enzyme (protein).
This process takes place on the ribosome. Note that the ribosome is made of rRNA and protein.C. TRANSLATION
Translation Animation - http://www.wehi.edu.au/wehi-tv/dna/movies/Translation.mov.gz
Chloroamphenicol – (CA) blocks peptide bond formation during elongation.
Tetracycline – TC – blocks the 2nd site on the ribosome during elongation.
Erythromycin EM – blocks translocase during elongation.Translation Blockers
E. TransductionIII. 5 Ways of Creating Genetic Diversity in Bacteria
a. silent mutations - single base substitution in the 3rd base nucleotide position of a codon. This results in NO change in amino acid. Note that the first 2 letters of the genetic code are the most critical.Types of Mutations
nonsense mutations - single base substitutions that yield a stop codon. Note: there are 3 nonsense codons in the genetic code = NO PROTEIN
4. Frame Shift Mutations - the addition or deletion of 1 or more bases. These are due to powerful mutagens; chemical or physical.
1. alkylating agents. Adds alkyl group, CnH(2n+1) Ex. formalin, nitrogen, mustard, and ethylene oxide (reacts with G changing it to bind with T).
2. base analogs. Mimics a nitrogen base. Ex. AZT is a modified sugar that substitutes for T. Ex. 5 - bromouracil binds with A or G.
3. intercalating agents. Inserts into DNA and pushes bases apart. Ex. AFLATOXIN - a chemical produced by peanut and grain molds. The mold is Aspergillus flavus (fungus).
1. nonionizing radiation - Causes the formation of T= T dimers. UV light @ 260 nm.
2. Ionizing radiation - damages DNA by causing the formation of “free radicals” leading to mutations. 3 Ex. X-rays. Gamma rays from radioactive fallout penetrates the body. Alpha rays from inhaled dust containing radioactive fallout.
2. Occurs in Gram - enteric bacteria like E.coli
3. Discovered in 1946 by Joshua Lederberg and Edward Tatum.
4. Plasmids carry genes that are nonessential for the life of bacteria. Ex. gene for pili (sex pilus). Ex. plasmid replication enzymes. Ex. Medical Problem: R-Factor = antibiotic resistance!C. CONJUGATION
a. Requires a sex pilus
b. F + bacteria transmits a copy of the plasmid to F- bacteria. This converts the F- cell into an F + cell. Medical Problem: The R factor (antibiotic resistance) on the F factor is transmitted! http://www.cat.cc.md.us/courses/bio141/lecguide/unit4/genetics/recombination/conjugation/f.htmlConjugation continued
a. Hfr- bacterial plasmid integrates into the chromosome.
b. Medical Problem:Hfr antibiotic resistance genes are passed during binary fission (every time the cell divides). Therefore, antibiotic resistance spreads very rapidly!
c. When Hfr mate with F – bacteria, only the bacterial genes cross NOT plasmid genes. Genetic diversity results in this case due to recombination. http://www.cat.cc.md.us/courses/bio141/lecguide/unit4/genetics/recombination/conjugation/hfr.html
Transposons were discovered in 1950 by Barbara McLintock in corn.
Causes antibiotic resistance in Staph. aureus, the famous methicillin resistant Staphlococcus aureus (MRSA) strain!D. TRANSPOSITION p 285
1. Discovered in 1952 by Zinder & Lederberg.
2. Two kinds of transduction: generalized and specialized.E. TRANSDUCTION
Lambda phage infects E.coli. The phage does not lyse the cell immediately. Instead it integrates into chromosome of the bacteria as a prophage and remains dormant. This is called the LYSOGENIC CYCLE. Phage genes are replicated and passed to all daughter cells until the bacteria is under environmental stress, from lack of nutrients, etc. Then phage gene will excise from the nucleoid and enter the LYTIC CYLE taking one adjacent gene for galactose metabolism.Specialized Transduction
T even phage lambda phage
lytic cycle lysogenic
random packaging specific gal geneComparison of Bacteriophage