6.1.1 control of gene expression

Question 1

what is transcriptional control?

Answer 1

genes being switched on and off

Question 2

what is post-transcriptional control?

Answer 2

mRNA editing, e.g. alternative splicing

Question 3

what is post-translational control?

Answer 3

protein activation

Question 4

transcriptional control
what are the 2 types of chromatin?

Answer 4

1) heterochromatin - tightly wound DNA causes chromosomes to be visible in cell division, transcription of genes can’t occur as RNA polymerase can’t reach genes
2) euchromatin - loosely wound DNA present during interphase. genes can be freely transcribed.

Question 5

transcriptional control
histone modification

Answer 5

• histones are positively charged, DNA is negatively charged
  1) acetylation and phosphorylation reduces the positive charge on histone, causing DNA to coil less tightly so genes can be transcribed as RNA polymerase can reach them.
  2) methylation causes histones to be more hydrophobic, causing them to bind more tightly to each other making DNA coil more tightly and therefore genes can’t be transcribed

Question 6

what is the lac operon?

Answer 6

group of genes that do similar things

Question 7

what are transcription factors?

Answer 7

• proteins that binds to sections of DNA to switch genes on or off
• they activate or repress genes

Question 8

what are TFs made by?

Answer 8

regulatory genes

Question 9

what 2 genes digest lactose?

Answer 9

1) B- galactosidase
2) Lactose permease

Question 10

what does beta galactosidase do?

Answer 10

hydrolyses lactose into galactose and glucose

Question 11

what does lactose permease?

Answer 11

a transport protein that becomes embedded into the E.coli membrane to transport more lactose into the cell.

Question 12

describe the lac operon without lactose

Answer 12

1. LacI produces the TF (the depressor protein)
2. the repressor protein joins to the operator region
3. partially covering the promoter region
4. RNA polymerase can’t bind to promoter region
5. so LacZ and Y cant be transcribed

Question 13

describe the lac operon when lactose is present.

Answer 13

1) lactose acts as an induced
2) lactose binds to the repressor protein, stopping it from binding to the operator region
3) as the shape is changed
4) therefore RNA polymerase can bind to promoter region and transcribe LacZ and Y
5) after binding to cAMP

Question 14

describe in detail what happens during post-transcriptional control (exons and introns) - gene splicing

Answer 14

• DNA split into segments of DNA called introns and exons
• exons are sequences of DNA for genes that can be expressed (coding DNA)
• introns are sequences of DNA that can’t be expressed (non-coding DNA)
• introns are spliced out of the sequence so only exons remain

Question 15

what is alternative splicing?

Answer 15

• different exons are included or excluded from final mRNA,
• increasing the amount of proteins that can be produced from 1 organism

Question 16

describe post-translational gene regulation in depth

Answer 16

• after proteins are produced by translation they can be activated by molecules (e.g. sugars/hormones) to become functional
• folding and shortening of proteins
• some of these molecules bind to cell membrane to trigger production of cAMP > used to alter the 3D shape of proteins by changing active site