6.1.2: Regulation of gene expression Flashcards Preview

Biology A2: 6.1 > 6.1.2: Regulation of gene expression > Flashcards

Flashcards in 6.1.2: Regulation of gene expression Deck (30):
1

What does the bacterium E.coli metabolise as a respiratory substrate?

-The bacterium E.coli normally metabolises glucose as a respiratory substrate.
-However, if glucose is absent and the disaccharide lactose is present, lactose induces the production of two enzymes.

2

Which two enzymes are produced when glucose is absent?

-Lactose permease, which allows lactose to enter the bacterial cell.
-beta-galactosidase, which hydrolyses lactose to glucose and galactose.

3

What does the lac operon consist of?

A length of DNA about 6000 base pairs long containing an operator region lacO next to the structural genes lacZ and lacY that code for enzymes beta-galactosidase and lactose permease, respectively.

4

Next to the operator region, lacO, is the promoter region, P, what is the purpose of the promoter region?

The enzyme RNA polymerase binds to the promoter region to begin transcription of the structural genes lacZ and lacY.

5

A small distance away from the operator region is the regulatory gene, I. What is it's function?

-The regulatory gene codes for a repressor protein (LacI).

6

What happens when the regulatory gene is expressed?

-The repressor protein produced binds to the operator, preventing RNA polymerase from binding to the promoter region.
-The repressor protein therefore prevents the genes lacZ and lacY from being transcribed, so the enzymes for lactose metabolism are not made.
-The genes are 'off'.

7

When lactose is added to the culture medium, once all the glucose has been used, lactose molecules induce the enzymes needed to break it down. How?

-Molecules of lactose bind to the LacI repressor protein molecules; this alters the shape of the LacI repressor protein, preventing it from binding to the operator.
-The RNA polymerase enzyme can then bind to the promoter region and begin transcribing the structural genes into mRNA that will then be translated into the two enzymes.

8

What are transcription factors?

Proteins, or short non-coding pieces of RNA, that act within the cell's nucleus to control which genes in a cell are turned on or off.

9

What do transcription factors do?

-Transcription factors slide along a part of the DNA molecule, seeking and binding to their specific promoter regions.
-They may then aid or inhibit the attachment of RNA polymerase to the DNA, and activate or suppress the gene.

10

Why are transcription factors important in eukaryotes?

Transcription factors are essential for the regulation of gene expression in eukaryotes, making sure that different genes in different types of cells are activated or suppressed.

11

Some transcription factors are also involved in regulating the cell cycle. How?

Tumor suppressor genes and proto-oncogenes help regulate cell division via transcription factors.

12

What do tumor suppressor genes cause?

Mutations to these genes can lead to uncontrolled cell division or cancer.

13

What proportion of genes in the human genome encode transcription factors?

8%

14

Many genes have their promoter regions some distance away, along the unwound length of DNA. How are they spatially not too far away?

Because of how the DNA can bend.

15

What are introns and exons?

-Within a gene there are non-coding regions of DNA called introns, which are not expressed.
-they separate the coding or expressed regions, which are called exons.

16

Describe the process of the splicing of primary mRNA. (three steps)

-The DNA of gene, both introns and exons, are transcribed. The resulting mRNA is called primary mRNA.
-Primary mRNA is then edited and the RNA introns are removed.
-The remaining mRNA exons are joined together.

17

Which enzymes are involved in the editing and splicing process.

Endonuclease enzymes,

18

Describe how introns can differ from each other.

Some introns may themselves encode proteins, and some may become short non-coding lengths of RNA involved in gene regulation.

19

How can some genes encode more than one protein.

-Some genes can be spliced in different ways.
-A length of DNA with introns and exons can, according to how it is spliced, encode more than one protein.

20

Post-translation regulation of gene expression involves the activation of proteins. How are many enzymes activated?

Many enzymes are activated by being phosphorylated.

21

Which enzyme catalyses the formation of cAMP from ATP?

Adenyl cyclase.

22

What is cyclic AMP

An important second messenger involved in the activation of proteins.

23

Describe the steps in which cAMP activates enzymes and may also stimulate transcription.
Step 1:

A signalling molecule, such as the protein hormone glucagon, binds to a receptor on the plasma membrane of the target cell.

24

Describe the steps in which cAMP activates enzymes and may also stimulate transcription.
Step 1: A signalling molecule, such as the protein hormone glucagon, binds to a receptor on the plasma membrane of the target cell.
Step 2:

This activates a transmembrane protein which then activates a G protein.

25

Describe the steps in which cAMP activates enzymes and may also stimulate transcription.
Step 2: This activates a transmembrane protein which then activates a G protein.
Step 3:

The activated G protein activates adenyl cyclase enzymes.

26

Describe the steps in which cAMP activates enzymes and may also stimulate transcription.
Step 3: The activated G protein activates adenyl cyclase enzymes.
Step 4:

Activated adenyl cyclase enzymes catalyse the formation of many molecules of cAMP and ATP.

27

Describe the steps in which cAMP activates enzymes and may also stimulate transcription.
Step 4: Activated adenyl cyclase enzymes catalyse the formation of many molecules of cAMP and ATP.
Step 5:

cAMP activates PKA (protein kinase A)

28

Describe the steps in which cAMP activates enzymes and may also stimulate transcription.
Step 5: cAMP activates PKA (protein kinase A)
Step 6:

Activated PKA catalyses the phosphorylation of various proteins, hydrolysing ATP in the process. This phosphorylation activates many enzymes in the cytoplasm, for example those that convert glycogen to glucose.

29

Describe the steps in which cAMP activates enzymes and may also stimulate transcription.
Step 6:Activated PKA catalyses the phosphorylation of various proteins, hydrolysing ATP in the process. This phosphorylation activates many enzymes in the cytoplasm, for example those that convert glycogen to glucose.
Step 7:

PKA may phosphorylate another protein (CREB, cAMP response element binding)

30

Describe the steps in which cAMP activates enzymes and may also stimulate transcription.
Step 7: PKA may phosphorylate another protein (CREB, cAMP response element binding)
Step 8:

This then enters the nucleus and acts as transcription factor, to regulate transcription.