Final Exam- Gene Expression/Regulation

Question 1

constitutive genes

Answer 1

always expressed

Question 2

regulated genes

Answer 2

inducible and repressible

Question 3

polycistronic mRNA

Answer 3

multiple genes encoded by one mRNA

Question 4

E. coli lac operon

Answer 4

(promo-I)promo-O-Z-Y-A

identified by inducing a nonsense mutation in the upstream genes

Question 5

lacZ
lacY
lacA
lacI

Answer 5

B-galactosidase
permease
transacetylase
repressor

Question 6

allolactose

Answer 6

lactose is converted to allolactose which serves as an inducer

Question 7

bacterial conjugation

Answer 7

unidirectional gene transfer (F plasmid) from F+ to F-
produces merodiploids
integration and excision is rare, but can take host chromo with plasmid

Question 8

regulation of lac operon

Answer 8

I binds to O, repressing
if lactose is present, allolactose binds repressor, freeing operon which is transcribed
if no glucose, CAP-cAMP complex binds to CAP site adjacent to promoter, aiding in RNA pol binding
binding sites by DNase activity

Question 9

trp operon

Answer 9

promo-O-leader(w/ attenuator)-EDCBA

Question 10

trpR

Answer 10

forms aporepressor protein

binding with Trp forms repressor which binds to O, preventing txn

Question 11

attenuation of trp operon

Answer 11

hairpin loops of leader region
1&2: pause (contains trp codons) (allows for loading ribosome)
2&3: antitermination (pairs if ribosome stalls at trp codons in 1)
3&4: termination (if no antitermination loop, this forms causing RNA pol to dissociate)
never fully off

Question 12

gene regulation

Answer 12

transcriptional control
processing conrol
transport control
translational control by ribosome selection
mRNA degradation control
protein degradation control

Question 13

proteins of txn

Answer 13

general txn factors GTF
activators
coactivators
repressors

Question 14

GTFs

Answer 14

allow basal txn, but dont influence rate

Question 15

activators

Answer 15

2 domains: DNA binding and activation domains
distinct DNA binding motifs (helix-turn-helix, zinc finger, and leucine zipper)
activation domain stimulates txn

Question 16

repressor mechanisms

Answer 16

competitve DNA binding (bind where activator needs to bind)
masking the activation surface (domain on activator bound)
direct interaction with GTFs
recruitment of repressive chromatin remodeling complexes
recruitment of HDAC

Question 17

GAL regulation in yeast

Answer 17

GAL1, 7, 10, 5 required for galactose metabolism
GAL4 codes for activator
Gal80p is repressor in absence of galactose

Question 18

no galactose

Answer 18

Gal80p (repressor) binds Gal4p activation domain; no txn

Question 19

+galactose, -glucose

Answer 19

Gal3p converts galactose to inducer, inducer binds to Gal80p, causing it to move on Gal4p, exposing activation domain and allowing txn

Question 20

+galactose, +glucose

Answer 20

Mig1p represses in presence of glucose

Question 21

txn regulation by polypeptide hormone

Answer 21

polypeptide hormone binds to receptor on plasma membrane, activating signal transduction pathway, eliciting cell response

Question 22

txn regulation by steroid hormones

Answer 22

steroid diffuses across membrane, binds and activates steroid hormone receptor, binds to genome and alters expression

Question 23

glucocorticoid induced activation

Answer 23

glucocorticoid binds receptor, HSP90 leaves, proteins dimerize, binds to Glucocorticoid Response Element, upregulating txn

Question 24

combinatorial gene regulation

Answer 24

more genes than regulators
multiple activators/repressors for each gene
different combinations for each

Question 25

chromatin mediated

Answer 25

by nucleosomes

Question 26

repression by nucleosomes

Answer 26

transcriptionally active genes are more sensitive to DNaseI; regions around gene=hypersensitive histone can outcompete TBP to bind with TATA; TBP can prevent histone deposition; enhancer binding proteins can prevent histone binding

Question 27

chromatin remodeling

Answer 27

``` HATs-Histone Acetyl Transferases -acetylates histone tails -causes loss of H1 and decondensation of 30nm fiber -increased promoter accessibility HDACs-Histone DeACetylases -removes acetyl groups ```

Question 28

ATP dependent remodeling

Answer 28

slide, resructure, remove, transfer nucleosomes by hydrolysis of ATP SWI/SNF- switch from MATA to MATa -sucrose nonfermenting (same gene)

Question 29

gene silencing (position effect)

Answer 29

telomere packaging with rap1, sir2, 3, 4 sir2=HDAC; will continue to pack down genome H3 methylation blocks spreading

Question 30

gene silencing (DNA methylation)

Answer 30

CG repeats | 5mC

Question 31

genomic imprinting

Answer 31

Igf2 from maternal chromo not transcribed bc CTCF binds to insulator and represses; H19 transcribed paternal chromo has methylated H19 and insulator, no CTCF, Igf2 transcribed, H19 not

Question 32

alternative splicing/polyadenylation

Answer 32

produces two different gene products from one section of genome like operon, but not can be transcribed to different points at which it is polyadenylated alternative splicing translated into precursor polypeptides, cleaved