1.7 - Genes and Their Expression

Question 1

% of genes that code for proteins

Answer 1

1%

Question 2

% of non-coding regulatory regions and genes

Answer 2

80%

Question 3

what is a gene?

Answer 3

DNA sequence that is the template that encodes information for a functional product made of RNA or protein

Question 4

how is RNA. critical player in gene expression? (3)

Answer 4

1. key information molecule
2. important regulator of gene expression
3. critical in synthesis of protein

Question 5

first step in which gene expression can be controlled

Answer 5

transcription

Question 6

key structures of prokaryotic gene (3)

Answer 6

1. promoter region
2. transcriptional start site
3. transcriptional terminator site
   (not same as start/stop codons)

Question 7

promoters

Answer 7

sequence of DNA upstream from gene where RNA polymerase binds to synthesise RNA transcript

Question 8

location of promoter sequence

Answer 8

sequence comes before gene itself, direct RNA polymerase to which strand of DNA they should bind to/ transcribe gene

Question 9

conserved regions of promoter in E.coli (2)

Answer 9

1. -35 consensus sequence
2. -10 consensus sequence (pribnow box)

Question 10

effect of deviators from consensus sequence

Answer 10

impairs binding of RNA polymerase to promoter, effects gene expression

Question 11

operators

Answer 11

structural features specific to prokaryotes

Question 12

location of operators

Answer 12

either within (between consensus regions) the promotor, or between promoter and gene

Question 13

role of operators

Answer 13

binding sequence in which a repressor protein can bind (can physically stop RNA polymerase binding)

Question 14

termination sequence (2)

Answer 14

1. creates a hairpin structure that matches, causing stalling of RNA polymerase
2. combined with an AT-rich region (aids the stalling)

Question 15

monocistronic gene

Answer 15

one gene between promoter and termination site, resulting in one mRNA being transcribed and one protein translated

Question 16

polycistronic genes

Answer 16

in bacteria, can have multiple genes between one promoter and termination site, producing one mRNA transcript but multiple proteins from the mRNA

Question 17

role of polycistronic genes in bacteria

Answer 17

allow for coordinated expression of multiple genes in same pathway (often enzymatic pathways)

Question 18

example of role of polycistronic genes in bacteria tryptophan synthesis (2)

Answer 18

1. when bacteria need to synthesise tryptophan, multiple enzymes required for it’s metabolism
2. to ensure all enzymes expressed to synthesise tryptophan, all genes regulated by same promoter and produce single mRNA

Question 19

type II genes

Answer 19

eukaryotic genes transcribed by RNA polymerase II

Question 20

TATA box

Answer 20

sequence involved in positioning RNA polymerase correctly at promoter (similar to -10 consensus sequence or pribnow box in bacteria)

Question 21

TATA box location

Answer 21

sequence about 25 bp upstream of transcription start site (sequence = TATAAAA)

Question 22

which type of genes have TATA box?

Answer 22

most genes transcribed by RNA polymerase II have TATA box

Question 23

location of further upstream control elements (eukaryotes)

Answer 23

in space beyond TATA box (50-200bp) from transcriptional start site

Question 24

upstream control elements with common sequences (eukaryotes) (2)

Answer 24

1. CAAT box with sequence:
   - GGCCAATCT
2. GC box with sequence:
   - GGGCGG

Question 25

role of upstream control elements with common sequences in eukaryotes (CAAT box/GC box)

Answer 25

most eukaryotic genes have one, acts as sites in which general transcription factors can bind

Question 26

general transcription factors

Answer 26

proteins that help with recruitment and positioning of RNA polymerase II

Question 27

similar element to operators in bacteria in eukaryotes

Answer 27

regulators

Question 28

effects of regulators in eukaryotes (2)

Answer 28

1. enhancers can promote gene expression 2. silencers can inhibit gene expression

Question 29

enhancer/silencer competition

Answer 29

sometimes both sequences occupy same space, compete with each-other to control gene expression

Question 30

difference in location of regulators compared to operators (2)

Answer 30

1. regulators - can be hundreds to thousands of nucleotides away from gene 2. operators - next to or within promoters

Question 31

how are regulators trans-acting?

Answer 31

(in eukaryotes) regulators far away from promoter

Question 32

how are operators cis-acting?

Answer 32

(in bacteria) operators right next to promoter

Question 33

how do upstream control elements interact with regulators significantly upstream?

Answer 33

upstream control elements binds general transcription factors which recruit mediator complex which can then interact with proteins binding to the regulators significantly upstream along DNA

Question 34

how can specialised proteins increase association of DNA with a regulator (like enhancer/silencer)

Answer 34

specialised proteins can hold eukaryotic chromosomal DNA in loops, increasing association with regulator

Question 35

where is lots of chromatin located in a chromosome?

Answer 35

telomere and centromere (chromatin condensation can vary along length of chromosome)

Question 36

why are there very little genes at the telomere and centromere?

Answer 36

lots of chromatin, not efficient to keep unwinding to allow for gene expression, could compromise chromosome integrity

Question 37

where are genes normally found in the chromosome?

Answer 37

euchromatin

Question 38

insulator role

Answer 38

cis-acting elements, ensure genes and/or other chromosomal structures don't interfere with gene exprssion

Question 39

insulator effect on enhancers and neighbouring genes (2)

Answer 39

1. can block enhancers from working 2. can block neighbouring genes from interacting with promoters

Question 40

insulator effect on heterochromatin

Answer 40

can act as barrier against heterochromatin encroaching into euchromatin and repressing gene expression

Question 41

exons

Answer 41

part of gene that code for amino acid sequence for proteins

Question 42

introns

Answer 42

part of gene that do not code for proteins and are. between exons, can play important regulatory roles

Question 43

do bacteria have introns and exons?

Answer 43

no, coding region of bacterial genes generally uninterrupted

Question 44

bacteria UP element

Answer 44

upstream element rich in thymine, helps strengthen promoter region

Question 45

activators (prokaryotes)

Answer 45

other sites, normally upstream of promoter that can enhance and stabilise RNA polymerase binding,