Transcription: Making mRNA

Question 1

The code on DNA must be…

Answer 1

Transcribed into mRNA before mRNA can be translated into protein

Question 2

mRNA Synthesis, 4 Major Steps

Answer 2

1. Initiation
2. Elongation
3. Termination
4. mRNA modification

Question 3

Where does transcription occur in eukaryotes?

Answer 3

In the nucleus

Question 4

Initiation, general explanation

Answer 4

• Transcription begins at a “Promoter”

Question 5

What is a “Promoter”?

Answer 5

A sequence of DNA that marks the beginning of transcription

Question 6

Prokaryotes, Promoter

Answer 6

• RNA binds to a regular Promoter where RNA polymerase attaches and initiates transcription
• No TATA box

Question 7

Eukaryotes, Promoter

Answer 7

• TATA box marks the beginning of Transcription as part of the Promoter

Question 8

Step 1 of Eukaryotic Initiation

Answer 8

Transcription factors bind to DNA at the TATA box

Question 9

Step 2 of Eukaryotic Initiation

Answer 9

RNA Polymerase II binds to the TATA box

Question 10

Step 3 of Eukaryotic Initiation

Answer 10

• More transcription factors are added
• Creates a transcription initiation complex

Question 11

Step 4 of Eukaryotic Initiation

Answer 11

Transcription begins

Question 12

What is a factor?

Answer 12

Small assisting proteins which we don’t need to name

Question 13

Elongation, simple definition

Answer 13

Lengthening RNA

Question 14

Elongation Step1

Answer 14

DNA is unwound to form a transcription bubble

Question 15

Elongation Step 2

Answer 15

RNA polymerase synthesizes mRNA in the 5’ to 3’ direction on the DNA template

Question 16

Termination Step 1

Answer 16

RNA Polymerase II reaches a transcription termination site from the stop codon

Question 17

Termination Step 2

Answer 17

Transcription stops

Question 18

Termination Step 3

Answer 18

mRNA dissociates from the template

Question 19

Termination Step 4

Answer 19

DNA rewinds

Question 20

Termination Step 5

Answer 20

mRNA is released by polymerase

Question 21

mRNA Modification Step 1

Answer 21

• 5’ CAP is placed on the 5’ end of mRNA

Question 22

Functions of 5’ CAP

Answer 22

• Protects mRNA from nucleases and phosphates
• Attachment signal for ribosomes

Question 23

mRNA Modification Step 2

Answer 23

Poly-A Tail is placed on 3’ end of mRNA

Question 24

Functions of Poly-A Tail

Answer 24

• Protects 3’ end from degradation
• Helps ribosomal attachment
• Helps with exporting mRNA out of nucleus

Question 25

mRNA modification Step 3

Answer 25

Introns are spliced out

Question 26

What are introns?

Answer 26

Non-coding sequences that are transcribed but not translated

Question 27

What are exons?

Answer 27

Sequences of mRNA that are important and are translated into protein

Question 28

How do you know what areas are to be spliced out?

Answer 28

They are marked off by “GU-AG”

Question 29

What are splicing factors?

Answer 29

Act as markers so a splicing zone can be created

Question 30

What is a spliceosome?

Answer 30

It pinches and cuts out the introns

Question 31

What are the two exceptional circumstances in splicing?

Answer 31

• Incorrect Splicing
• Alternate Splicing

Question 31

Incorrect Splicing

Answer 31

• Splicing may be inaccurate
• Creates mRNA that is not translated or wrong segments are translated
• Could lead to defective proteins

Question 32

Alternate Splicing

Answer 32

• Deliberate
• By varying areas of splicing more than one possible protein can be made from one gene

Question 33

Example of Incorrect Splicing

Answer 33

In humans: Beta-Thalassemia
- Causes errors in hemoglobin