Regulation of Gene Expression

Question 1

how can bacteria control their metabolism?

Answer 1

1. enzyme regulation - short term, enzymes are active or inactive
2. gene regulation - long term, controls what genes get expressed and which dont, controls the synthesis of RNA using the operon concept

Question 2

what are the components of an operon?

Answer 2

1. promoter- where RNA polymerase binds
2. regulatory gene - makes repressors
3. operator - where a repressor binds to inhibit protein synthesis
4. genes - the genes the RNA poly. will create a polypeptide from

Question 3

what is an operon?

Answer 3

a cluster of 3+ genes on a DNA strand that control RNA transcription, only appears in prokaryotes

Question 4

what are the two forms of operon gene expression?

Answer 4

1. lac operon - repressible - positive
2. trp operon - inducible - negative

Question 5

what is negative gene regulation?

Answer 5

-operons are turned off by the repressor
-the state of the repressor dictates if the model is repressible or inducible

Question 6

what is a repressible operon?

Answer 6

-transcription is normally ON, can be turned OFF when needed
-ex. e. coli make Trp if none is present, and the created Trp then turns off the Trp operon [w/ repressor] because Trp is now present

Question 7

what is an inducible operon?

Answer 7

-transcription is normally OFF, can be turned ON in the presence of specific molecules
-ex. lac operon is only active when lactose can bind to the repressor to remove it so the bacteria can make lactose digesting enzymes

Question 8

what is the difference between negative and positive gene regulation?

Answer 8

negative = repressor turns off operon
positive = operons are turned on, promotes gene expression

Question 9

what is CAP / cAMP?

Answer 9

CAP - catabolite activator protein
cAMP - cyclic AMP
cAMP binds to CAP, CAP binds to DNA and enhances transcription

Question 10

how do glucose levels influence the lac operon?

Answer 10

-if glucose is absent, cAMP accumulates in cell, which binds to CAP and enables transcription of lactose [assuming lactose is present]
-lactose inactivates the repressor, and the absence of glucose enables transcription

Question 11

what are the 5 levels of gene expression in eukaryotes?

Answer 11

1. pre-transcriptional control
2. transcriptional control
3. post transcriptional control
4. translational control
5. post translational control

Question 12

what is pre-transcriptional control?

Answer 12

-regulation of what genes are / arent expressed, DNA methylation can inactivate gene transcription in certain regions such as the 2nd X chromosome in females
-acetylation of histone proteins promotes transcription

Question 13

what is transcriptional control?

Answer 13

-regulatory proteins that inhibit/promote transcription by making DNA less/more able to bind to RNA polymerase
-enhancers, control elements, and transcription factors

Question 14

what is post transcriptional control?

Answer 14

-the blocking or stimulating of gene expression by changing the splicing order of exons
-the changing of the lifespan of mRNA by attaching 5’ caps and poly a tails to mRNA

Question 15

what is translational control?

Answer 15

-affects on ribosome attachment during translation
-regulatory proteins can attach to untranslated regions on the 5’ or 3’ ends of mRNA

Question 16

what is post translational control?

Answer 16

-involves ubiquitin and proteasomes (protein complexes that can degrade proteins)
-cleaving, 3d shaping, and phosphorylation of synthesized polypeptides

Question 17

what creates cancer cells?

Answer 17

cancer cells are created when a normal cell escapes the regulations on division and growth

Question 18

what are proto oncogenes?

Answer 18

normal, safe genes that code for growth factors (stimulate normal cell growth & division)

Question 19

what are oncogenes?

Answer 19

cancer causing genes, a mutated/changed version of a proto oncogene

Question 20

what are tumor suppressor genes?

Answer 20

genes that control or inhibit abnormal cell division

Question 21

how do tumor suppressor genes and proto oncogenes cause cancer?

Answer 21

-due to mutations, the proto oncogenes can become oncogenes
-tumor suppressing genes can be turned off, oncogenes can get turned on

Question 22

what is the difference between a structural and regulatory gene?

Answer 22

structural - genes that code for proteins needed for cell structure or function
regulatory - genes that code for proteins that turn other genes on or off