Control Of Gene Expression: Eukaryotes

Question 1

Chromosomal protein alterations?

Answer 1

DNA → packed with history proteins into nuclessomes
DNA is inaccessible to RNA polymerase and transcription factors
Histones → have “tails” with t+ve charged AA attracted to negatively charged DNA

Question 2

Define acetyl ‘ation

Answer 2

Allows transcription
To tails
Adds acetal group which changes charges & opens up the nucleosome to allow access to RNA polymerase
Positively charged histore tails

Question 3

Define beacetylation?

Answer 3

Inhibits transcription
It gene is to be switched off
History deacetylase enzyme con remove acetal groups to inhibit access to RNA polymerase

Question 4

Define Epigenetic’s ?

Answer 4

Study of heritable changes in gene expression that occur without changes in the DNA sequence
Histone acetylation → set early in embryo function

Question 5

What is histone deacetylation determined by?

Answer 5

DNA methylation →
Methyl group is covalently added to 5’ carbon of cytosine forming 5 - methyl cytosine
Catalysed by DNA methyltransferase

Question 6

When does methylation occur and where?

Answer 6

Usually occur in a C & G doublet called Cp G islands → often in promoter regions
Diagonally opposite cytosines on the 2 strands of double helix are methylated

Question 7

Can methylation patterns be inherited?

Answer 7

Yes mitosis ‘

Usually inherited when DNA replicates prior tomitosis
Maintenance methylate catalyses formation of 5 - methyl cytosine in new strand.
Prior to mitosis → much of methylatan pattern removed by demethylases.
Some is still inherited → previous gen can affect future gen

Question 8

What are affects of DNA methylation?

Answer 8

Methyl groups in promoter region attract history deaceylases → transcription repression
Methylated genes otter inacté

Question 9

X-chromosome inactivation

Answer 9

Females → potential to prod x2 protein from genes on ne chromosome

Question 10

Define regulator sequence?

Answer 10

Different genes need to be regulated so must have same in promoters
A single regulator proteins → regulate expression
E.g.) activate 3 genes A, b,c - combat stress drought
Brought stress activates transcription of single regulator protein gene
The regulator protein binds to regulator sequencein promoters of genes AB C to stimulate transcription
Genes → A, BIC prod diff proteins participating in the drought stress response in coordinated way

Question 11

How dues transcriptional initiation work in pro &Euk ?

Answer 11

Pro→ RNA polymerases binds to directly recognitori sequence on promoter (pribnow box)
EUK → general transcription factors bind to recognition in sequence on promoter ( TATA box)
RNA polymerases binds to general transcription factors assembled on the chromosomes

Question 12

Define specific transcription factors?

Answer 12

Bind to regulatory protein binding sequences/ regulatory elements just upstream.
Can either be activators / REPRessors.
STF → bind to protein complex called mediator which facilitates the interaction with the basal transcription apparatus

Question 13

What are enhancers /silencers?

Answer 13

Enhancer sequence → bind to additional activators
Silencer sequence → bind to additional repressors ‘
Additional regulatory protein binding sequences are thousands of base pairs from the transcriptional start site
In order for such enhancers/silencers to interact with basal transcription apparatus → DNA bends bringing distant regulatory sequence into close proximity to promoter

Question 14

Define introns?

Answer 14

Non-coding sequence within a gene which separates the protein coding “exon”
Introns are transcribed but removed before final mRNA leaves the nucleus
DNA → introns, exons
Pre-mrna → interns, exons
mRNA → exons

Question 15

What is spliceosome?

Answer 15

An RNA splicing machine
Small nuclear ribonucleoprotein particles ( snrnps) cut pre-mrna release introns and splice exons together
Processing part 2_
* G - cap = added at 5’ end (G TP) protects it from being digested by ribonuclease and facilitate ribosomes binding
* poly A tail added at 3’ end assists in export from nucleus and stabilises the mRNA

Question 16

Trans port control / mRNA stability control?

Question 17

What are Micro RNA’s?

Answer 17

Micro RNA’s (mi RNA) → post transcriptional regulators of gene expression

Coded by DNA
RNA transcripts have a sequence which allows them to fold back on themselves by base pairings to form double stranded hairpins
Recognized by dicer proteins
→ cut by DIC ER to form 22 short bp double strand ed fragments
1 strand → incorporated into RNA - induced silencing complex (RISC)
Guided to target mRNA by complementary base pairings
Causes target mRNA degradation & inhibits translation

Question 18

What is posttranslation aspects of protein synthesis?

Answer 18

Eukaryotic cells
→ polypeptide may be moved from synthesis site to an organelle or out of the cell
Often modified with more chemical bonds
AA sequence also contains signal sequence → “address label”

Question 19

What is destinations for newly translated polypeptides in EUK cells.

Answer 19

As polypeptide chai is made, information contained in its AA sequence may target the protein to a organelle
Father modifications en occur in ER or transfer to Golgi
PROTEOLYSIS: cutting of the polypeptide chain
GLYCOSYLATION: addi lion of sugars to the protein to form glycoproteins
PHOSPHORYLATION: additions of phosphate groups to proteus

Question 20

How are reporter genes made?

Answer 20

Step 1: isolate the promoter gene of plant cab
Step 2: choose a reporter
Step 3: isolate the coding sequence of E. Coil
Step 4, join promoter to Gus coding sequence to create recombinant reporter construct
Step 5: generically engineer a transgenic plant containing the reporter construct
Target plant contains → reporter construct as well as original gene
Whenever original transcribed so is report here
If we con detect Gus also las expert