The molecular process of transcription

Question 1

The process o transcription facilitated by

Answer 1

RNA polymerase that uses 1 strand of DNA as a template and matches DNA bases with RNA bases (A-U, C-G) to produce a single stranded RNA

Question 2

The stretch of DNA (gene) that is transcribed into an RNA molecule is called a

Answer 2

Transcription unit

Question 3

Bacteria

Answer 3

have 1 type of RNA polymerase that synthesises not only mRNA bt also pother types of RNA that function in protein synthesis

Question 4

Eukaryotes

Answer 4

-Have 3 types of RNA polymerase numbered, I, II, III. The one used for mRNA synthesis is RNA polymerase II
-Other 2 RNA polymerases transcribe RNA molecules that are not translated into protein

Question 5

The process of transcription [bacteria]

Answer 5

To begin the transcription: RNA pol must be able to recognise start of gene and bind firmly to DNA at this site

Question 6

Way in which RNA pol recognises the transcription start site in eukaryotes and bacteria is different

Answer 6

focusing on bacteria

Question 7

When RNA pol encounters a region on the DNA molecule called a promoter (upstream from the gene)

Answer 7

it latches tightly onto the DNA at this site. The promoter contains a sequence of DNA and it is released after RNA pol has synthesised approx 10 nts of RNA

Question 8

After RNA pol binds to promoter sequence on DNA

Answer 8

The enzyme opens up the double helix immediately in front of it to expose the nts

Question 9

One of the 2 exposed DNA strands then acts as a template for

Answer 9

complementary base-pairing with incoming ribonucleotides to synthesise RNA

Question 10

RNA synthesis then continues in the process of

Answer 10

chain elongation until the RNA pol enzyme encounters another sequence in the DNA, terminator (or stop site)

Question 11

At this point the polymerase

Answer 11

halts and release both the DNA template and the newly made RNA chain

Question 12

RNA pol then re associates with the sigma factor and

Answer 12

searches for another promoter where it can begin the process of transcription again

Question 13

Summary of transcription process in 3 steps

Answer 13

1 binding and initiation
2 elongation
3 termination

Question 14

binding and initiation

Answer 14

-Specific sequences of nucleotides along the DNA mark where transcription of a gene begins
-DNA sequence where RNA polymerase attaches directly to and initiates transcription is known as the promoter
-After RNA pol binds to promoter, DNA strands unwind and RNA polymerase initiates RNA synthesis at the start point on the template strand

Question 16

Elongation

Answer 16

-Polymerase moves downstream, unwinding DNA and elongating RNA transcript in 5’ -> 3’ direction
-DNA strands reform to form double helix behind RNA polymerase

Question 17

Termination

Answer 17

-specific sequences of nucleotides along the DNA mark where transcription of a gene ends
-sequence that signals the end of transcription is called the terminator
-RNA polymerase stops adding nts to RNA strand and RNA molecule released

Question 18

Termination in eukaryotes

Answer 18

mRNA processing events must occur during 3 steps of transcription (before RNA leaves nucleus)

Question 19

Termination in bacteria

Answer 19

No RNA processing required: RNA is ready for immediate translation into protein

Question 20

Initiation step of transcription

Answer 20

Differs between eukaryotes and prokaryotes

Question 21

Bacteria

Answer 21

RNA pol binds directly to promoter to initiate transcription

Question 22

Eukaryotes

Answer 22

-Collection of proteins called transcription factors required
-They mediate the bing of RNA pol II to promoter
-A promoter DNA sequence called a TATA box is crucial for forming the transcription initiation complex
-Then complex moves pol II to start site of gene and it begins to polymerase

Question 23

Transcription in Eukaryotes vs prokaryotes

Answer 23

3 stages of transcription are the same eukaryotic and bacterial cells; initiation, elongation, termination

Question 24

Initiation step slightly different

Answer 24

RNA pol II in eukaryotic cells rely on a series of proteins (called transcription factors) whereas RNA pol in prokaryotic cells rely on the sigma factor to direct RNA polymerase to promoter region of the gene

Question 25

Promoter region of eukaryotic genes contain

Answer 25

aTATA sequence whereas prokaryotic genes do not

Question 26

There is a promoter region (with TATA sequence)

Answer 26

For every individual eukaryotic gene whereas some prokaryotic genes can be expressed (transcribed) under the control of one promoter region = opérons

Question 27

RNA pol II works for the exact same way as RNA pol (bacteria)

Answer 27

Using 1 strand template DNA in gene to read DNA bases and adds corresponding RNA bases polymerising phospherdiester bonds in 5’-3’ direction to produce single stranded mRNA (messenger RNA)