module 6 - 19.2 regulation of transcription and translation (1)

Question 1

what is gene expression?

Answer 1

involves flow of genetic information from its origin in the nucleus to the ribosomes where polypeptides or proteins are synthesised

Question 2

where does transcription occur?

Answer 2

nucleus of a cell

Question 3

what is transcription?

Answer 3

involves formation of mRNA that carries a complementary DNA message to the ribosomes in the cytoplasm

Question 4

where does translation occur?

Answer 4

ribosomes in cytoplasm of a cell

Question 5

what is translation?

Answer 5

involves translation of mRNA message into specific sequence of amino acids to form a polypeptide or protein

Question 6

how is gene expression controlled at the transcriptional phase?

Answer 6

transcription is prevented so mRNA is not synthesised

Question 7

how is gene expression controlled at the post transcriptional phase?

Answer 7

the mRNA is controlled after it has been synthesised

Question 8

how is gene expression controlled at the translational phase?

Answer 8

process of translation is prevented

Question 9

how is gene expression controlled at the post translational phase?

Answer 9

the polypeptide is modified after it has been synthesised

Question 10

what to proteins and transcriptional factors do?

Answer 10

• they activate the gene
• they are specific molecules that move from the cytoplasm and the nucleus

Question 11

what do all transcriptional factors contain?

Answer 11

all contain DNA-binding domains which attach to specific sequences of DNA adjacent to the genes they regulate

Question 12

what are the 2 classes of transcriptional factors?

Answer 12

• activators
• repressors

Question 13

what are activators?

Answer 13

speed up the rate of transcription as they facilitate the binding of RNA polymerase to the start of the target gene and activate transcription

Question 14

what are activators needed for?

Answer 14

needed for RNA polymerase to attach to the start of the target gene on the DNA chain

Question 15

what are repressors?

Answer 15

they slow down the rate of transcription by binding themselves to the start of the target gene
- prevents RNA polymerase from binding

Question 16

what happens when a gene is not being expressed?

Answer 16

the site on the transcriptional factor that binds to the specific nucleotide sequence in the DNA is blocked by a repressor molecule

Question 17

how are transcriptional factors regulated?

Answer 17

• regulate signals produced by other molecules
• hormones activate transcriptional factors and so stimulate transcription

Question 18

how does oestrogen affect the process of transcription?

Answer 18

• they affect specific genes which control cell growth by affecting transcription
• oestrogen is lipid soluble so diffuses easily through phosophlipid bilayer
• once inside, oestrpgen combines with an oestrogen receptor, forms oestrogen-receptor complex

Question 19

what are the 2 oestrogen receptors?

Answer 19

• oestrogen receptor alpha
• oestrogen receptor beta

Question 20

what does oestrogen receptor alpha act as?

Answer 20

an activator allowing the RNA to do its job

Question 21

what happens when oestrogen binds to the oestrogen-receptor alpha complex?

Answer 21

• shape of DNA binding site on transcriptional factor changes and thus activates it
• activated transcriptional factor can then correctly employ its DNA-binding domains to attach to a specific sequence of DNA to regulated gene

Question 22

what does oestrogen receptor beta act as?

Answer 22

a repressor, blocking the action of RNA polymerase

Question 23

what does ER beta act as?

Answer 23

acts as a dominant inhibitor of ER alpha transcriptional activity in cells that express both receptors

Question 24

how can oestrogens and their metabolic products initiate tumour growth?

Answer 24

1. binding of an oestrogen to its ER stimulates cell division and DNA replication of mammary cells
2. oestrogen metabolism can produce genotoxic and mutagenic products
   - both processes disrupt cell cycle, apoptosis and DNA repair

Question 25

what so most biologically RNAs contain?

Answer 25

self complementary sequences that allow parts of RNA to fold and pair with itself to form a double helix

Question 26

once an mRNA strand has been synthesised, can gene expression still be prevented?

Answer 26

yes - can still be prevented by breaking down the mRNA before its genetic code can be translated into a polypeptide (post transcriptional control)

Question 27

what is RNA interference?

Answer 27

• biological process where RNA molecules inhibit gene expression caused by destruction of specific mRNA molecules
• interference of the mRNA (RNAi)

Question 28

what is RNAi caused by?

Answer 28

2 distinct groups of short RNA
- small interfering RNA (siRNA)
- microRNA (miRNA)

Question 29

how is normal RNA and siRNA different?

Answer 29

• RNA - single stranded
• siRNA - double stranded, has the ability to interfere with expression of specific genes

Question 30

how does siRNA affect translation?

Answer 30

through a process called post transcriptional RNA interference

Question 31

what are the 2 types of DNA affected by transcriptional factors?

Answer 31

• promoter DNA
• enhancer DNA

Question 32

what is promoter DNA?

Answer 32

• a region of DNA that initiates transcription of a particular gene
• located near transcription start sites of genes on the same strand and upstream on DNA

Question 33

what is enhancer DNA?

Answer 33

short region of DNA, bound by proteins and stimulates/represses transcription