Prokaryote Genetics

Question 1

where does transcription occur?

Answer 1

in the cytoplasm

Question 2

how does it differ from eukaryote genetics?

Answer 2

no separation of DNA, transcription and translation are coupled

Question 3

how does prokaryote translation timing differ in prokaryotes?

Answer 3

translation begins when the mRNA is still being synthesised

Question 4

what is the order of a prokaryote gene?

Answer 4

promoter, transcription start site, RNA coding sequence, termination site and terminator gene

Question 5

how is the DNA packaged?

Answer 5

one or more circular chromosomes and plasmids

Question 6

how is the DNA coiled?

Answer 6

circular chromosomal DNA coiled into looped domains and then further supercoiled into looped DNA

Question 7

what is the leading strand replicated with?

Answer 7

DNA polymerase III

Question 8

what is the lagging strand replicated with?

Answer 8

DNA polymerase I

Question 9

what is another function of DNA polymerase I?

Answer 9

removes the RNA primer from the DNA strand

Question 10

what does topoisomerase 4 do?

Answer 10

disconnects the 2 strands

Question 11

why are repressor proteins needed?

Answer 11

as genes are usually switched on by default

Question 12

what promotor elements are on prokaryote genes?

Answer 12

-35 and -10 promotor sections

Question 13

what are promotor sections?

Answer 13

parts of the DNA that the polymerase directly binds to

Question 14

what is a pribnow box?

Answer 14

-10 element

Question 15

what enzyme is used for transcription?

Answer 15

RNA polymerase

Question 16

what is a holoenzyme?

Answer 16

a compound formed by the combination of an enzyme and its coenzyme

Question 17

what is RNA polymerase made up of?

Answer 17

5 subunits and a sigma factor

Question 18

how is an open complex formed?

Answer 18

the sigma factor binds to the -10 and -35 promotor elements which forms a transcription bubble

Question 19

how is the bubble able to continue down the strand?

Answer 19

when a short mRNA strand is produced, the sigma factor is released

Question 20

what are the two types of stop signals?

Answer 20

rho-independent and rho-dependant

Question 21

how does rho-independent signals work?

Answer 21

hairpin loop in the DNA is formed which is followed by U bases causing a weaker bond between the U and the A bases so the strand dissociates

Question 22

how is the hairpin loop formed?

Answer 22

signal region contains a section that is repeated a few bps away in the inverted sequence, followed by U bases

Question 23

how does rho-dependant signals work?

Answer 23

rho factor binds to the end of the mRNA chain and catches up to the RNA polymerase, knocking it off via the torpedo effect

Question 24

what are the things needed for prokaryotic translation?

Answer 24

mRNA strand, ribosomes, initiation factors, tRNA

Question 25

what ribosomes are used in prokaryotes?

Answer 25

70s, with 50s and 30s subunits

Question 26

where and why does the ribosome bind to the DNA?

Answer 26

binds at the shine-delgarno sequence, due to a portion of the 16s rRNA on the small subunit being complementary

Question 27

what promotes the binding of the 16s rRNA?

Answer 27

IF3

Question 28

how does the initiator tRNA then bind to the strand?

Answer 28

IF2 promotes the binding of the tRNA to the mRNA strand

Question 29

what is the final step in attachment?

Answer 29

IF2 and IF3 are released and the 50s subunit attaches

Question 30

how does elongation occur?

Answer 30

tRNA binds to the complementary codon, then the next anticodon binds at the entry site causing a peptide bond to form, and the ribosome moves along the strand

Question 31

what are the 3 different release factors?

Answer 31

RF1 and RF2 and RF3

Question 32

how do prokaryotes control gene expression?

Answer 32

genes grouped together in operons which are controlled using a single promotor region

Question 33

how might operons be inhibited?

Answer 33

repressor can bind to an operator region to physically block the movement of polymerase

Question 34

how might operons be activated?

Answer 34

activators can bind next to the DNA polymerase and increase the rate of translation

Question 35

what is an inducible operon?

Answer 35

operons that are usually switched off and can be switched on by an inducer

Question 36

what is a repressible operon?

Answer 36

operons that are usually switched on and can be switched off using a corepressor

Question 37

what does the lacZ gene code for?

Answer 37

beta galactosidease

Question 38

what does lacY gene code for?

Answer 38

beta galactosidase permease

Question 39

what does the lacA gene code for?

Answer 39

beta galactosidase transacetylase

Question 40

what does the lacI gene code for?

Answer 40

lactose repressor

Question 41

what does beta galactosidase do?

Answer 41

converts lactose to glucose and galactose

Question 42

what does beta galactosidase permease do?

Answer 42

membrane bound protein that pumps lactose into a cell

Question 43

what does beta galactosidase transacetylase do?

Answer 43

enzyme that transfers acetyl group from acetyl co-A to beta galactosides

Question 44

what does lactose repressor do?

Answer 44

represses expression of lactose metabolising genes

Question 45

what causes negative expression of lac operon?

Answer 45

absence of lactose represses expression

Question 46

what causes positive expression of the lac operon?

Answer 46

absence of glucose activates the expression

Question 47

how does the absence of lactose help the cell to save energy?

Answer 47

does not transcribe enzymes that do not need to be present

Question 48

how does the presence of lactose allow transcription?

Answer 48

allolactose binds to the repressor and stops it from preventing translation

Question 49

how does the absence of glucose activate transcription of the lac operon?

Answer 49

CAP and cAMP binds to the CAP binding site and facilities the binding of RNA polymerase

Question 50

what happens when there is no glucose and no lactose?

Answer 50

no transcription due to CAP being active and bound to the DNA and lac repressor acts as a roadblock