Lecture 5a - How Can the Sequence of a Gene Code for a Specific Protein - transcription

Question 1

What is the central dogma?

Answer 1

It describes information flow in a cell

RNA -> DNA -> Proteins

Question 2

What are the determining factors of RNA?

Answer 2

2 -OH
Uracil
Short (compared to DNA)
short-lived
single stranded
structural
stems and loops - > RNA is self complementary
Enzymatic
Abundant

Question 3

Why would you use RNA?

Answer 3

1) you can make many forms of mRNA form one gene
2) 2 -OH makes the phosphate become circular, breaking the RNA chain
3) 2 -OH means RNA can form a helix which is stronger then that of DNA

Question 4

What is a gene?

Answer 4

• A length of DNA that codes for RNA + control regions
• basic unit of information

Question 5

What is half of a gene called?

Answer 5

a broken gene

Question 6

What are some non-coding uses of genes?

Answer 6

• mRNA - codes for a protein
• tRNA - assists in making proteins
• rRNA - “ “

Question 7

What is a promoter?

Answer 7

• controls the initiation of transcription
• close to the beginning of the gene at the 5’ end

Question 8

What is the termination site?

Answer 8

transcription terminated here

Question 9

What is the transcription start site (TSS)?

Answer 9

transcription happens from here from the 5’ to the 3’ of the DNA

Question 10

How do promoters function?

Answer 10

• proteins factors bind to specific sequences within the promoter
• these can either enhance or repress the initiation of transcription from the TSS
• if enough positive factors bind then:
  
  • DNA is bent
  • bending separates into single stranded at TSS
  • RNA polymerase can bind at one strand and transcription can begin

Question 11

Give an example of a positive protein factor

Answer 11

TATA
enhanced expression

Question 12

What are proteins that bind to the promoter influenced by?

Answer 12

environmental conditions

Question 13

Describe the process of extension?

Answer 13

• DNA is separated by bending at initiation
• creating a single strand bubble with double stranded at either end
• RNA polymerase opens up DNA - forming a transcription bubble
• transcribes RNA 5’ to 3’ using DNA as a template

The top strand of DNA (the one that will be the same as the RNA) Is called the sense strand

Question 14

Describe the process of stopping transcription

Answer 14

• RNA continues transcribing until it reaches a signal
• the signal is recognised in the RNA
• signals a protein to bind to RNA that cuts the RNA and knocks RNA polymerase off DNA

Question 15

What is the stop signal in eukaryotes?

Answer 15

poly-A-signal

Question 16

What is the role of the poly-A-tail?

Answer 16

• protects RNA
• RNA looses an A every time it is translated, causing degradation in the mRNA