3.5 - Control of gene expression

Question 1

what does it mean when a gene is expressed?

Answer 1

turned on, making protein associated to said gene

Question 2

when do genes expressed and proteins produced vary? (3)

Answer 2

1. cell type
2. developmental stage
3. environmental conditions

Question 3

housekeeping genes

Answer 3

constitutively (constantly) expressed genes, code for proteins performing basic cell functions

Question 4

what is the main way or regulating gene expression?

Answer 4

controlling transcription

Question 5

transcription factors

Answer 5

proteins that bind to DNA, effecting frequency of transcription of specific gene therefore associated protein

Question 6

how is gene expression in bacteria highly efficient?

Answer 6

genes only expressed when/where they’re required

Question 7

promoters (2)

Answer 7

1. genes have upstream control elements in DNA (promoters)
2. in absence of regulation, promoter exhibits basal (base level) level of transcription

Question 8

repressors

Answer 8

binds to promoter blocking RNA polymerase

Question 9

activators

Answer 9

stimulate RNA polymerase binding to promoter (bind slightly upstream from promoter)

Question 10

operons

Answer 10

used in bacterial gene expression, gene cluster and promoter plus additional sequences, function together in regulation

Question 11

2 eukaryotic transcription factor domains (2)

Answer 11

1. DNA-binding domain
2. activation domain

Question 12

DNA-binding domain (2)

Answer 12

1. binds to regulatory sequences
2. transcription factor proteins structures so they can interact with major groove of DNA helix to affect gene transcription

Question 13

activation domain

Answer 13

regulates polymerase through binding other proteins

Question 14

3 main types of eukaryotic transcription factor (3)

Answer 14

1. homeodomain DNA-binding unit
2. zinc finger domains
3. leucine zipper

Question 15

promoter positive and negative regulatory elements (3)

Answer 15

positive:
1. enhancer
negative:
1. silencers
2. insulators

Question 16

enhancer elements (promoter regulatory element) location

Answer 16

typically thousands of base pairs away from transcription start site (different thing to promoter). either upstream (5’), downstream (3’) or within an intron of transcribed sequence

Question 17

silencers and insulators (promoter regulatory elements) role (3)

Answer 17

• distant
• repress transcription
• demarcate (set boundaries) of regulatory unit/prevent the regulatory sequences within affecting adjacent cells

Question 18

how can enhancer function be assayed

Answer 18

by fusing reporter gene (such as green fluorescent protein) to gene of interest

Question 19

enhancer (promoter element) role

Answer 19

bind transcription factors and co-activators that help stabilise transcription machinery making it easier for RNA polymerase to initiate transcription.

Question 20

how does chromatin effect RNA polymerase access to promoters

Answer 20

hinders access to promoters (default repression)

Question 21

what is required for RNA polymerase to access promoter?

Answer 21

chromatin remodelling

Question 22

what is required for even base level of gene expression?

Answer 22

positive regulation mechanisms

Question 23

how is transcription precision maintained in eukaryotes

Answer 23

combinatorial control of many different factors such as enhancers, chromatin remodelling and basal transcription factors

Question 24

examples of transcription factor activation (2)

Answer 24

1. steroid hormone (hydrophobic)
2. hormone (hydrophilic)

Question 25

steroid hormone transcription factor activation (3)

Answer 25

1. hydrophobic 2. pass through cell membrane and bind to receptor in cytoplasm 3. receptors translocate to nucleus, acts as transcription factors to directly regulate gene expression

Question 26

hormone transcription factor activation (3)

Answer 26

1. binds to receptor on cell membrane 2. activates protein kinase 3. kinase phosphorylates specific inactive transcription factor activating it, triggers activation of particular gene

Question 27

heterochromatin

Answer 27

dense, inactive regions of chromosome

Question 28

euchromatin

Answer 28

less dense, active regions of chromosome (allows access to transcriptional machinery)

Question 29

remodelling complexes

Answer 29

condense/recondense chromatin by sliding nucleosomes in chromosome (allows/prevents access to transcriptional machinery)

Question 30

what allows the recruitment of enzymes and transcription factors?

Answer 30

reversible covalent modification, mostly at N-terminus domain (amino) - found near exterior of nucleosome

Question 31

how can histones be modified (3)

Answer 31

1. acetylation 2. phosphorylation 3. methylation (can be heritable - epigenetic)

Question 32

protein synthesis control points in eukaryotes (7)

Answer 32

1. synthesis of primary RNA transcript 2. posttranscriptional modifications of mRNA 3. degradation of mRNA 4. protein synthesis 5. posttranslational modification of protein 6. targeting and transport of protein 7. degradation of protein

Question 33

role of alternative splicing in perception of different sound frequencies (4)

Answer 33

1. sound vibrations activate potassium channels in hair cell membranes 2. need 100s of different channel isoforms (different versions) to respond to different frequencies 3. alternative exons used at 8 regions encode >500 isoforms of channels 4. each responds to different sound frequency

Question 34

microRNA role

Answer 34

RNAs that regulate eukaryotic gene expression by binding to mRNAs

Question 35

how to microRNAs regulate gene expression (3)

Answer 35

1. binds to mRNA 2. larger initial transcript cleaved to yield the mature mRNA, associates with proteins of argonaut family to form complexes 3. microRNA component of complex binds to mRNA (base pair formation), mRNA subsequently degraded (by cleaving it or blocking translation)

Question 36

% human genes regulated by microRNA

Answer 36

60%

Question 37

proteasome

Answer 37

big complex of enzymes, recycles proteins in eukaryotes

Question 38

how do proteasomes degrade/recycle proteins? (2)

Answer 38

1. proteins targeted for breakdown by labelling with ubiquitin 2. resulting amino acids can be re-used in biosynthesis or further broken down to carbon skeletons for other uses

Question 39

stages of protein life cycle (7)

Answer 39

1. transcription initiation 2. posttranscriptional processing 3. RNA stability 4. translational regulation 5. protein modification 6. protein transport 7. protein degradation

Question 40

what phase of protein do drugs mostly target?

Answer 40

complete proteins eg. receptors and enzymes

Question 41

when are most genes expressed in life cycle of a differentiated tissue?

Answer 41

early development

Question 42

how can you induce pluripotent stem cells? (2)

Answer 42

1. isolate (eg skin cell - fibroblast) and grow in culture 2. introduce genes for a cocktail of transcription factors into the cell

Question 43

potential applications for induced pluripotent stem cells? (3)

Answer 43

1. tissue replacement 2. studying diseases 3. drug screening

Question 44

what cells can become any type of cell?

Answer 44

inner mass cells of early embryos