L19- Gene expression Flashcards
1
Q
trancription
A
copying the code
2
Q
translation
A
changing the language
3
Q
transcription occurs in the
A
nucleus
4
Q
A
5
Q
translation occurs in the
A
cytoplasm
6
Q
a gene
A
is a stretch of DNA found at a specific locus ona. chromsosme, which codes for a protein
- unit of inheritance and transcription
7
Q
DNA synthesis overview
A
- Needs an enzyme: RNA polymerase
- Need activate substrates: NTPs
- Need template: DNA
- 3 stage process:
- Initiation- promoter recognition. Transcription initiation factor. RNA polymerase- reads 3’ to 5’
- Elongation- 5’ to 3’ chain growth
- Termination- sequence dependent
8
Q
RNA synthesis overview (transcription)
A
- Needs an enzyme: RNA polymerase
- Need activate substrates: NTPs
- Need template: DNA
- 3 stage process:
- Initiation- promoter recognition. Transcription initiation factor. RNA polymerase- reads 3’ to 5’
- Elongation- 5’ to 3’ chain growth
- Termination- sequence dependent
9
Q
RNA translation (translation)
A
- Need enzyme: in the ribosome
- Activate substrate: amino acids
- Needs a template- mRNA
- 3 stage process
- Initiation- tRNA and start codon on the mRNA within the ribosome
- Elongation- moevemtn of tRNA from P site to E site. Peptide bond formation between amino acids on the top of the tRNA
- Termination- stop codon- no tRNA carries amino acid for
10
Q
transcription occurs in the
A
nucleus- euchromatin
11
Q
function of transcription
A
Specific gene is read and copied on an individual mRNA
12
Q
transcription requires
A
RNA polymerase, NTPs, DNA template
13
Q
outline initation of transcription
A
- Transcription factor binds to promotor region (e.g. TATATATA – TATA box) which lies upstream of the gene (right at the beginning)
- Promotor and gene that is transcribed = transcription unit
- TF binds from 5’ to 3’ direction- directs direction of transcription
- TF recruit RNA polymerase (does not require primer just template strand)
- Reads Template DNA from 3’ to 5’ direction
- DNA coding strand is not involved with transcription (mRNA strand will be identical, bar having uracil instead of thymine)
- RNA polymerase breaks Hydrogen bonds, creating a transcription bubble, mRNA transcript produced via the addition of complementary nucleotides
- Transcribes RNA in 5’ to 3’ direction
14
Q
elongation in transcription
A
- mRNA elongation occurs from left to right (5’ to 3’) via the addition of new complementary nucleotides
- As RNA polymerase passes along the DNA the hydrogen bonds between the strands reform
15
Q
termination of transcription
A
1) When RNA reaches the termination sequence of the gene, the RNA polymerase detaches from the DNA
2) mRNA is edited (see below) and proceeds out of the nucleus
16
Q
the initation site
A
The site on the DNA from which the first RNA nucleotide is transcribed is called the +1 site- initiation site
17
Q
nucleotides that come before the initiation site are
A
given a negative number and said to be upstream
18
Q
nucleotides that come after the intiiation site are marked with positive numbers and said to be downstream
A
19
Q
RNA processing converts
A
pre-mRNA to mature mRNA
20
Q
3 types of RNA processing
A
- Capping
- Polyadenylation
- Splicing
21
Q
Capping
A
- At 5’ end- addition of a 5’CAP
- 5’ to 5’ linkage
- Protection against degradation
22
Q
polyadenylation
A
- At 3’ end= polyA tail added by polyA polymerase
- Protection against degradation
23
Q
splicing
A
- removes introns- sequence dependent (e.g. 5 to 3’ splice sites on introns)
- Not random- very precise
- Always one more exon than introns
24
Q
translation involves
A
decoding mRNA and using its info to build a polypeptide chain, which will fold to form a protein.
25
location of translation
ribosomes in the cytoplasm- found on the RER
26
ribosomes assemble proteins from
amino acids based on the sequence of the mRNA
27
translation requires
ribosomes and template (mRNA)
28
difference between prokaryote and eukaryote ribosomes
Prokaryotes
**Prokaryotes**
3rRNAs + 56 proteins
30S + 50S subunit
70S ribosome (related to sedimentation)
**Eukaryotes**
4 rRNAs +82 proteins
40S +60S subunits
80S ribosomes
29
how many rRNAs in eukaryotic ribosomes
4
30
subinits in eukaryotic ribosome
40S and 606 = 80s ribosome
31
rRNA
rRNA ribosomal RNA
* \>80% of all RNA
* RNA polymerase I
* Few kinds
* Many copies of each
32
mRNA messenger RNA
* 2% of all RNA
* RNA polymerase II
* 100,000s of kinds
* Few copies of each
33
tRNA
* 15%
* RNA polymerase III
* 100 kinds
* Lots of copies of each
34
other types of RNA
miRNA
noncoding RNA
35
the genetic code
From 4-letter ‘DNA language’ to 20-letter ‘protein-language’
64 possibilities-only need 20
36
triplet code
three bases make an amino acid
e.g. UUU- phenylalaline
37
initiation codon always
AUG- methionine
38
termination codons
UAA
UAG
UGA
--\> dont code for an amino acid
39
triplet code is
degenrative and non overlapping
40
mRNA is read in the
5' to 3' direction
- N to C polypeptide chain extension
41
adaptor molecule in translation
tRNA
42
each tRNA molecule
* tRNA recognises 1 amino acid molecule, which is bonded to the top of the molecule.
43
structure of tRNA
* mostly ss
* some ds regions which forms loops
* forms clover shape
* Located on the bottom of the tRNA is the anticodon (3 nucleotide bases)
* Anticodon pairs up with complementary codon on the mRNA
* amino acid binds to the 3' end
44
anti codon for methyionyl tRNA recongises
mRNA codon 5'AUG
45
some tRNA can recognise
different codons- for the same amino acid
- degenerative nature
- wobble position
e. g.Alanyl tRNA anticodon 5’IGC, recognises the cocoons 5’GCU, 5’GCC, 5’GCA
( I nucleotide binds with different nucleotides e.g. U, C and A)
46
amino acid activation by tRNA
Enzymes which recognise a specific amino acid, a specific tRNA and ATP- causes AA to become attached to tRNA —\> amino acid activation
47
translation process: initiation
1. tRNA attaches to mRNA which is found within a Ribosome – causes 60S subunit to bind
1. Each tRNA recognises 1 amino acid molecule, which is bonded to the top of the molecule.
2. Located on the bottom of the tRNA is the anticodon (3 nucleotide bases)
3. Anticodon pairs up with complementary codon on the mRNA
2. As translation begins the first codon of the mRNA, the Start codon (usually AUG- methionine) attaches to a ribosome
1. .tRNA with complementary amino acid can bind to three parts of the ribosome: A- aminoacyl site, P- peptidyl site and E- exit site
3. tRNA carrying an anticodon complementary to the start codon (carrying a methionine) of the mRNA binds in the P site
48
translation: elongation
1. mRNA then slides along the ribosome to the next codon, where a new tRNA carrying another amino acid will pair with the mRNA codon (A site)
2. The 2 amino acids will join via a peptide bond (peptidyl transferase)
3. 3)The first tRNA molecule will be released by the ribosome (from E site) and the second will slide into the P site
49
translation: termination
1. This process continues until the ribosome meets a stop codon – no tRNA code for a stop codon- therefore translation terminated
2. Ribosome with polypeptide will translocate to the ER to be packaged
50
what does the APE positions in the ribososme look like
