Topic 7 -Microbial Genetics I & II

Question 1

What is genetics?

Answer 1

study of what genes are, how they carry information, how info is processed, and how genes are replicated

Question 2

What is a genome?

Answer 2

all of the genetic material in a cell (chromosomes/mitochondria/chloroplasts/plasmids)

Question 3

What is genomics?

Answer 3

molecular study of genomes

Question 4

What is a chromosome?

Answer 4

structure that carries hereditary info, contains many genes. Can be circular (bacterial) or linear (humans)

Question 5

What is a gene?

Answer 5

region of DNA that carries a function or produces a functional product (protein or RNA)

Question 6

What is a genotype?

Answer 6

genetic makeup of an organism (e.g. all the genes)

Question 7

What is a phenotype?

Answer 7

external manifestation of genotype or expression of genes (e.g. blue eyes)

Question 8

Name the 3 basics categories of genes

Answer 8

1. structural genes (code for proteins)
2. RNA (code for)
3. regulatory genes (control gene expression)

Question 9

A bit about bacterial chromosomes

Answer 9

Haploid

single, circular

Question 10

A bit about eukaryote chromosomes

Answer 10

multiple & linear

Diploid

Question 11

Describe the structure of DNA

Answer 11

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

Question 12

Describe DNA replication

Answer 12

5’=>3’ direction

1. enzymes unwind parental double helix
2. proteins stabilise unwound parental DNA
3. leading strand is synthesised continuously by DNA polymerase
4. Lagging strand is synthesised discontinuously. RNA polymerase synthesises short primer, DNA polymerase extends
5. DNA polymerase digests RNA primer and replaces it w/ DNA
6. DNA ligase joins discontinuous ends of lagging strand

Question 13

DNA replication is….?

Answer 13

semiconservative.

Each chromosome ends up w/ 1 new & 1 old strand

Question 14

Describe the structure of RNA and name the 3 different types

Answer 14

Ribose sugar & phosphate backbone
4 nucelotides - A, U, C & G
3 types:
mRNA (messenger)
tRNA (transfer)
rRna (ribosomal)

Question 15

Describe the process of DNA transcription

Answer 15

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

Question 16

What is a codon?

Answer 16

Groups of 3 nucleotides (e.g. AUG, UUG)

Question 17

Describe the process of DNA translation

Answer 17

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.

Question 18

Central dogma of molecular biology?

Answer 18

DNA=>RNA=>PROTEIN

Question 19

What is an operon?

Answer 19

a set of genes; all of which are regulated as a single unit.

Consists of a promotor, operator and structural genes coding for proteins

Question 20

What are constitutive and regulative enzymes?

Answer 20

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)

Question 21

Briefly describe the regulation of an operon

Answer 21

repressor active; operon off. Repressor binds to operator region, blocking transcription.

repressor inactive; operon on. Inducer binds to repressor, inactivating it, allowing transcription.

Question 22

What is a point mutation?

Answer 22

base substitution or missense mutation

Question 23

What is a nonsense mutation?

Answer 23

changes a normal codon into a stop codon

Question 24

What is a frameshift mutation?

Answer 24

insertation or deletion of 1 or more nucleotide pairs

Question 25

What is a silent mutation?

Answer 25

alters a base but does not change the amino acid

Question 26

What is a back-mutation?

Answer 26

A mutated gene reverses to its original base composition

Question 27

name the 2 kinds of mutation repair

Answer 27

Light repair or excision repair

Question 28

What is a mutagen? Give examples

Answer 28

a physical or chemical agent that increases the mutation rate above the spontaneous level. E.g. X-rays, base analogs

Question 29

What is the purpose of the AMES test?

Answer 29

to detect if a compound is mutagenic (carcinogenic)

Question 30

Outline the procedure of the AMES test

Answer 30

1. Indicator organism (mutant strain of salmonella) has lost ability to synthesise histidine, is added to experimental sample 2. This culture is added to a histidine lacking media and incubated. This mutation is highly susceptible to back-mutation 3. exposing cells of this mutant to a mutagen will produce revertants able to make histidine, which can be detected & counted

Question 31

What is horizontal gene transfer? Name the 3 mechanisms

Answer 31

``` transfer of genes b/w cells of the same generation. 3 recombination mechanisms are: 1. Transformation 2. Conjugation 3. Transduction ```

Question 32

What is vertical gene transfer?

Answer 32

Occurs during repro: b/w (down the) generations of cells

Question 33

Describe genetic recombination

Answer 33

occurs when an organism acquires & expresses genes that originated in another organism

Question 34

Describe genetic transformation

Answer 34

chromosome fragments from lysed cell are accpeted by recipient cell; genes on DNA fragment are then acquired by recipient. Donor & recipient may be unrelated.

Question 35

Describe genetic conjugation

Answer 35

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

Question 36

Describe genetic transduction

Answer 36

Think virus reproduction!!!!! | Bacteriophage (virus that targets bacteria) serves as carrier of DNA from donor cell to recipient cell

Question 37

Describe what a plasmid is

Answer 37

small, circular DNA material found in cytoplasm. self-replicating, can move to new cells

Question 38

Name the 5 different kinds of plasmids & their functions

Answer 38

1. Conjugative plasmid: carries genes for sex pili & transfer of plasmid 2. Dissimilation plasmids: encode enzymes for catabolism of unusual compounds 3. R factors: encode antibiotic resistant genes 4. Virulence genes: pathogens 5. Bacteriocin genes: kill competing bacteria

Question 39

Describe what a transposon is

Answer 39

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