3C- Controlling Gene Expression

Question 1

promotor sequences

Answer 1

Specific region on the DNA to which transcription factors bind to stimulate transcription

Question 2

enhancer sequences

Answer 2

specific region of DNA to which transcription factors bind and regulate the activity of the DNA by changing the structure of the chromatin= open\closed chromatin structure

Question 3

open chromatin structure

Answer 3

active Gene expression

Question 4

closed chromatin structure

Answer 4

Gene inactivity

Question 5

transcription factors (2)

Answer 5

• protein that binds to the DNA in the nucleus and affects the process of transcribing DNA to RNA
• allowing different genes to be expressed or repressed

Question 6

Describe Epigenetic modification (3)

Answer 6

• changes that affect gene expression
• example: DNA methylation, histone modification
• involved in differentiation

Question 7

DNA methylation (6)

Answer 7

• gene switched off
• methyl groups are placed on DNA by a DNA methyltransferase enzyme
• they are added to base of cytosine or adenine
• methyl group changes the arrangement of the DNA molecule and prevents transcription from taking place
• modifies the structure of histones
• always silences a gene or sequence of genes

Question 8

DNA demethylation (3)

Answer 8

• genes switched on
• removal of methyl groups
• allows genes to become active again so they can be transcribed

Question 9

Explain how epigenetic changes affect the activation of genes in daughter cells (3)

Answer 9

• genes are deactivated or activated in stem cells
• because of DNA methylation/histone binding
• therefore the same genes will be activated in the daughter cells

Question 10

histones (3)

Answer 10

• positively charged proteins
• DNA helices wind around the histones to form chromatin
• the histones determine the structure of the chromatin

Question 11

heterochromatin

Answer 11

• when chromatin is densely coiled and condensed around histones and the genes are not available to be copied to make proteins

Question 12

Histone acetylation (4)

Answer 12

• acetyl group is added to lysine in histone
• this opens up the structure and activates the chromatin
• allows genes in that area to be transcribed
• removing an acetyl group causes heterochromatin

Question 13

Histone methylation (3)

Answer 13

• methyl group is added to lysine in histone
• depending on position of lysine, methylation causes either inactivation or activation of DNA region
• silences genes, such as one of the X chromosomes in every female

Question 14

non-coding RNA (ncRNA) (7)

Answer 14

• transcribed but not used (does not code for proteins)
• do not leave nucleus
• bind to DNA, inactivates (hides) the DNA
• affects transcription of DNA code
• modifies chromatin structure or modifies the products of transcription
• genes and whole chromosomes can be silenced by ncRNA
• also responsible for deactivating one of the X chromosomes in females (in order to maintain the balance of gene products in males and females)

Question 15

steps in controlling gene expression (3)

Answer 15

1. Transcriptional Control
   - transcription factors (proteins bind to DNA sequences, enhancer, silencer
   - Epigenetics (DNA methylation, demethylation, histone modification
   - non-coding RNA
2. Post Transcriptional Control
   - RNA splicing (Intron/Exon)
3. Post Translational Control
   - proteins modified in Golgi

Question 16

introns

Answer 16

segments of a DNA or RNA molecule containing information which does not code for proteins or a peptide sequence

Question 17

exons (2)

Answer 17

• parts of gene that code (expressed)

segments of a DNA or RNA molecule containing information that codes for a protein or peptide sequence

Question 18

post-translational control (2)

Answer 18

• modifications of proteins after they have been synthesized

- proteins modified in golgi

Question 19

How a cell differentiates? (5)
How a cell gains function?
How cell changes structure?

Answer 19

• there is a chemical stimulus which causes DNA methylation/gene expression change
• genes are activated or deactivated
• activated genes will produce mRNA
• mRNA translated into protein
• protein permanently modifies cell

Question 20

RNA splicing (3)

Answer 20

• this modification to the pre-mRNA always involves the removal of the introns and some of the exons
• enzyme complexes known as spliceosomes join togeter the exons that are to be transcribed and produce the mature, functional mRNA
• the spliceosomes may join the same exons in a variety of ways

Question 21

result of RNA splicing (4)

Answer 21

• a single gene may now produce several versions of functional mRNA which is transcribed from the same section of DNA
• these different versions of mRNA code for different arrangements of amino acids, which produce different polypeptide chains, and therefore different proteins
• ultimately this can result in a single gene producing several different phenotypes
• this is one way that the genotype can produce more proteins than there are genes