Topic 2 - chapter 8 'Control of gene expression'

Question 1

housekeeping proteins include…

Answer 1

structural proteins of chromosomes, RNA polymerases, DNA repair enzymes, ribosomal proteins, enzymes involved in glycolysis and other basic metabolic processes, and many of the proteins that form the cytoskeleton

Question 2

haemoglobin genes only expressed in …?

Answer 2

reticulocytes

Question 3

Cells generally express between ? & ? genes out of a possible 25000.

Answer 3

5000 and 15000

Question 4

An example that A Cell Can Change the Expression of Its Genes in Response to External Signals

Answer 4

When liver cell exposed to glucocorticoid hormone - during starvation or intense exercise -> increase prod. of glucose from AA’s & other small molecules

Question 5

T or F - different cell types respond in the same way to same extracellular signals

Answer 5

false - respond in different ways

Question 6

What are The levels of possible control of gene expression

Answer 6

1. transcriptional control
2. RNA processing control
3. RNA transport & localisation control
4. mRNA degradation control
5. translation control
6. protein activity control

Question 7

What are regulatory DNA sequences?

Answer 7

a region required for RNA polymerase to bind to the promoter used to SWITCH GENES ON OR OFF

Question 8

What do regulatory DNA sequences need to work?

Answer 8

proteins called TRANSCRIPTION REGULATORS which bind to DNA

Question 9

simplest bacterium codes for how many transcription regulators?

Answer 9

several hundred

Question 10

Humans code for how many transcription regulators?

Answer 10

several thousand

Question 11

Transcription regulators bind to what? Bonds…?

Answer 11

major groove of a DNA helix
bonds include: hydrogen, ionic, and hydrophobic interactions (individually weak but 20 bonds => protein-DNA highly specific & very strong

Question 12

What are the 3 DNA binding motifs?

Answer 12

homeodomain, the zinc finger, and the leucine zipper

Question 13

Re. DNA-binding motifs; most of the contacts with the DNA bases are made by

Answer 13

alpha helix 3

Question 14

In the homeodomain what contacts what?

Answer 14

asparagine contacts adenine

Question 15

The zinc finger motif is made up of what?

Answer 15

alpha helix & beta sheet bound by zinc (covalently bonded together to allow contact with DNA bases in major groove)

Question 16

Leucine zipper is made up of what?

Answer 16

2 alpha helixes that bind as dimers

Question 17

An example of a bacterial transcription switch?

Answer 17

trp operon

Question 18

What do activators do?

Answer 18

make promoters stronger

Question 19

Re. Lac operon, when conditions are +glucose & +lactose

Answer 19

operon off & CAP not bound

Question 20

Re. Lac operon, when conditions are +glucose & -lactose

Answer 20

operon off, repressor bound & CAP not bound

Question 21

Re. Lac operon, when conditions are -glucose & -lactose

Answer 21

operon off, repressor bound & CAP bound

Question 22

Re. Lac operon, when conditions are -glucose & +lactose

Answer 22

operon ON, no repressor & CAP bound => RNA prod.

Question 23

Eukaryotic activators are bound to what? Describe gene activation at a distance…

Answer 23

enhancers -> looping of DNA to touch mediator & proteins in the vicinity of the promoter incl. RNA polymerase II and general transcription factors

Question 24

How can proteins allow histones to become more accessible?

Answer 24

activator proteins can recruit histone-modifying enzymes & chromatin-remodeling complexes to promoter region of a gene

Question 25

Explain how eukaryotic genes are regulated by combinations of proteins

Answer 25

histone-modifying enzymes, chromatin-remodelling complexes, mediator, general transcription factors, RNA polymerase, bound to promoter, also near TATA box, far away are transcription regulators

Question 26

TATA box is where in relation to start of transcription?

Answer 26

upstream

Question 27

The Expression of Different Genes Can Be Coordinated by a Single Protein. explain...

Answer 27

it's the final number in the combination analogy | glucocorticoid receptor protein with glucocorticoid bound is the last number in the combination

Question 28

How can combinatorial control create different cells types? eg?

Answer 28

key transcription regulators -> nonmuscle cells to myoblasts by activating changes in gene expression typical of differentiating muscle cells. eg. MyoD in fibroblasts of chick embryo -> muscle cells by induced expression of MyoD gene

Question 29

What 3 ways can daughter cells 'remember' what cells they're supposed to be?

Answer 29

``` + ve feedback loops DNA methylation (exclusively on cytosine bases) recognised by maintenance methyltransferase chromatin structure ```

Question 30

How can formation of an entire organ be triggered by a single transcription regulator

Answer 30

Ey - flies & Pax-6 - vertebrates crucial for eye development | control expression of many genes by binding to DNA sequences in their regulatory regions

Question 31

Explain riboswitches...guanine eg...

Answer 31

self-regulating RNA - when guanine is scarce -> RNA polymerase transcribes -> gene for purine biosynthesis turned ON - when guanine is plentiful -> binds to riboswitch -> conformational change -> transcription terminator terminates transcription -> purine gene turned OFF

Question 32

How can The Untranslated Regions of mRNAs Can Control Their Translation?

Answer 32

- translational repressor protein binds to ribosomal binding site -> no protein made - warmer temp of bacteria (Listeria...) - binding of small molecule to riboswitch - complimentary antisense blocks translation

Question 33

What is the role of microRNA (miRNA)?

Answer 33

miRNA matures & forms RISC -> recognises complimentary target mRNA -> degrades

Question 34

What does RNAi do?

Answer 34

target and destroy double-stranded RNA by 1st cleaving via DICER -> fragments called small interfering RNAs (siRNAs) incorporated into RISC -> destruction

Question 35

What is RISC?

Answer 35

RNA-induced silencing complex

Question 36

What else can RNAi be used for by scientists?

Answer 36

allows them to inactivate almost any gene cultured in cells, plants & animals -> function of individual genes - also new approaches in treating human diseases