L3 - DNA transcription & gene expression

Question 1

Types of RNA molecules

Answer 1

mRNA - transfers messages between DNA inside nucleus, to a protein

tRNA : transfers AA to ribosome which is lying on mRNA

rRNA - ribosomal - component of the ribosome

Question 2

Peptidyl transferase

Answer 2

Enzyme that catalayzes the formation of peptide bonds
Eg RNA molecules
Since they act as enzymes : ribozymes
Nb : tRNA molecule will have an AA added to 3’ end

Question 3

How do we make RNA ?

Answer 3

From RNA polymerase

Question 4

Different types of RNA polymerase

Answer 4

Type :
1 synthesises rRNA

2 NB : synthesises all mRNA

3 synthesiseS all tRNA & rRNA

TIP :
first is the worst
SeConD is the best
Third is tRNA

Question 5

Rna polymerase can & can’t

Answer 5

Can : bring first two nucleotides together in contrast to DNA polymerase

CaNNOT : create a sequence ; base etc can only copy

Question 6

DNA transcription

Promoters :

Answer 6

Tell RNA polymerase exactly where & what to copy

Question 7

DNA transcription in prokaryotes is simple bcos

Answer 7

RNA polymerase binds to the promoter
DNA unravels
Simple

Question 8

DNA transcription harder in eukaryotes
Process
Lecture images v good for this

Answer 8

• Transcriptional factors : proteins that aid transcription
• 1st binds to TATA BOX
• that binds to promoter

Perhaps Tata box becomes promoter

• complex of proteins now recruite RNA polymerase 2
• unravelling of DNA can occur

promoter tells a molecule where transcription begins

Question 9

Transcriptional factors features what activity HINT do they contain ?

Answer 9

Helicase activity - unwinds DNA
Kinase activity - add phosphate groups
This ACTIVÂTES RNA polymerase

Question 10

DNA transcription in this way is v BAD
- how do we improve the efficiency of this process??

• stop transcription occurring ?

Answer 10

• use other TF that are more cell specific?
• use ENHANCER sequence - another TF

Stop:

• Add methyl groups to the DNA
• stops TF binding
• thus transcription can’t occur

Question 11

Nucleosome

Answer 11

Basic unit of DNA packaging in eukaryotes

Consists of lengths of DNA wrapped around histone proteins

Question 12

Chromatin is made of:

Answer 12

DNA & proteins.

Question 13

Histone modifications are needed why? Referred to as chromatic remodelling

Answer 13

• to permit transcription
• DNA is too tightly packed s & must be loosed a little if TF are to bind to it!!
• histone acetyl trasferase - loosens DNA
  How?
  Reduces positive charge of histone thus reducing the attraction to the neg DNA
• histone deacetyl … does opposite

Question 14

Modifications to eukaryote mRNA

Prior to translation but after transcription??? Yes correct !! Check - 3 steps -1 process;

Answer 14

Prior to translation but after transcription
Eg pre cursor RNA - conversion to mature RNA :

• Add 5’ cap (essential for attaching mRNA to a ribosome.)
• Add 3’ poly A tail ( assists mRNA attaching to ribosome but not essential
  Poly A tail is NB as it grooms transport RNA out of nucleus & stabilises it
• Splicing

Question 15

protein synthesis: transcription and translation

Answer 15

CPG BOOKS

YOU KNOW IT XXX