Topic 7 -Microbial Genetics I & II Flashcards
What is genetics?
study of what genes are, how they carry information, how info is processed, and how genes are replicated
What is a genome?
all of the genetic material in a cell (chromosomes/mitochondria/chloroplasts/plasmids)
What is genomics?
molecular study of genomes
What is a chromosome?
structure that carries hereditary info, contains many genes. Can be circular (bacterial) or linear (humans)
What is a gene?
region of DNA that carries a function or produces a functional product (protein or RNA)
What is a genotype?
genetic makeup of an organism (e.g. all the genes)
What is a phenotype?
external manifestation of genotype or expression of genes (e.g. blue eyes)
Name the 3 basics categories of genes
- structural genes (code for proteins)
- RNA (code for)
- regulatory genes (control gene expression)
A bit about bacterial chromosomes
Haploid
single, circular
A bit about eukaryote chromosomes
multiple & linear
Diploid
Describe the structure of DNA
Two stranded helix basic unit is called a nucleotide, each consisting of: 5/3 carbon sugar (deoxyribose) phosphate group Nitrogenous base: A, C, T or G
Describe DNA replication
5’=>3’ direction
- enzymes unwind parental double helix
- proteins stabilise unwound parental DNA
- leading strand is synthesised continuously by DNA polymerase
- Lagging strand is synthesised discontinuously. RNA polymerase synthesises short primer, DNA polymerase extends
- DNA polymerase digests RNA primer and replaces it w/ DNA
- DNA ligase joins discontinuous ends of lagging strand
DNA replication is….?
semiconservative.
Each chromosome ends up w/ 1 new & 1 old strand
Describe the structure of RNA and name the 3 different types
Ribose sugar & phosphate backbone 4 nucelotides - A, U, C & G 3 types: mRNA (messenger) tRNA (transfer) rRna (ribosomal)
Describe the process of DNA transcription
DNA is transcribed to make RNA (m, r or t)
5’=>3’ direction
1. RNA polymerase binds to promotor, DNA unwinds
2. RNA is synthesised by complementary base pairing of free nucleotides w/ nucleotide bases on template DNA strand
3. Site of synthesis moves along DNA; DNA that has been transcribed rewinds.
4. Transcription stops when it reaches terminator
5. RNA & RNA polymerase are released and helix reforms
What is a codon?
Groups of 3 nucleotides (e.g. AUG, UUG)
Describe the process of DNA translation
tRNA carrying 1st aa is paired w/ start codon on mRNA. Then tRNA carrying 2nd aa etc etc. This continues for each codon creating peptide bonds and releasing the previous tRNA until stop codon is reached. This releases & forms a new polypeptide
Consult textbook/lecture notes diagram.
Central dogma of molecular biology?
DNA=>RNA=>PROTEIN
What is an operon?
a set of genes; all of which are regulated as a single unit.
Consists of a promotor, operator and structural genes coding for proteins
What are constitutive and regulative enzymes?
Constitutive -expressed at fixed rate
Regulative -only expressed as needed. Can be repressible (inhibit gene expression, mediated by repressors) or inducible (transcription turned on. mediated by inducers)
Briefly describe the regulation of an operon
repressor active; operon off. Repressor binds to operator region, blocking transcription.
repressor inactive; operon on. Inducer binds to repressor, inactivating it, allowing transcription.
What is a point mutation?
base substitution or missense mutation
What is a nonsense mutation?
changes a normal codon into a stop codon
What is a frameshift mutation?
insertation or deletion of 1 or more nucleotide pairs
What is a silent mutation?
alters a base but does not change the amino acid
What is a back-mutation?
A mutated gene reverses to its original base composition
name the 2 kinds of mutation repair
Light repair or excision repair
What is a mutagen? Give examples
a physical or chemical agent that increases the mutation rate above the spontaneous level.
E.g. X-rays, base analogs
What is the purpose of the AMES test?
to detect if a compound is mutagenic (carcinogenic)
Outline the procedure of the AMES test
- Indicator organism (mutant strain of salmonella) has lost ability to synthesise histidine, is added to experimental sample
- This culture is added to a histidine lacking media and incubated. This mutation is highly susceptible to back-mutation
- exposing cells of this mutant to a mutagen will produce revertants able to make histidine, which can be detected & counted
What is horizontal gene transfer? Name the 3 mechanisms
transfer of genes b/w cells of the same generation. 3 recombination mechanisms are: 1. Transformation 2. Conjugation 3. Transduction
What is vertical gene transfer?
Occurs during repro: b/w (down the) generations of cells
Describe genetic recombination
occurs when an organism acquires & expresses genes that originated in another organism
Describe genetic transformation
chromosome fragments from lysed cell are accpeted by recipient cell; genes on DNA fragment are then acquired by recipient.
Donor & recipient may be unrelated.
Describe genetic conjugation
Plasmid mediated -self replicating circular DNA
requires:
cell to cell contact (pillus)
recipient doesn’t already have a plasmid
Recipient receives a copy, so both donor/recipient have the plasmid
Describe genetic transduction
Think virus reproduction!!!!!
Bacteriophage (virus that targets bacteria) serves as carrier of DNA from donor cell to recipient cell
Describe what a plasmid is
small, circular DNA material found in cytoplasm. self-replicating, can move to new cells
Name the 5 different kinds of plasmids & their functions
- Conjugative plasmid: carries genes for sex pili & transfer of plasmid
- Dissimilation plasmids: encode enzymes for catabolism of unusual compounds
- R factors: encode antibiotic resistant genes
- Virulence genes: pathogens
- Bacteriocin genes: kill competing bacteria
Describe what a transposon is
Small segments of DNA that can move from one region of a DNA molecule to another.
Carry transposase gene, encode a recombinase allowing cutting/resealing DNA
Can excise out of DNA & recombine at another location
