Gene expression

Question 1

Gene expression

Answer 1

DNA template (codes for all proteins that can be made) - then to mRNA - then into protein.

Question 2

How many genes in a human?

Answer 2

Approx 21,000

Question 3

What is the mechanism that changes a gene into mRNA?

Answer 3

Transcription

Question 4

What is the mechanism that changes mRNA into Proteins?

Answer 4

Translation

Question 5

How many mRNA molecules in human?

Answer 5

Approx 196,000

Question 6

How many proteins in a human?

Answer 6

> 300,000

Question 7

What are the modifications that take place after proteins are made?

Answer 7

Post-translational modifications

Question 8

Does translation and transcription take a lot of effort?

Answer 8

Adding a functional process to every human gene in genome a huge percentage of genes involved in translation and transcription.

Question 9

Why do cells look different in different areas?

Answer 9

Even though all cells contain same DNA, gene expression is very tightly controlled. Only certain genes expressed in certain proteins.

Question 10

Where is the DNA found in the cell?

Answer 10

In the nucleus

Question 11

Where does transcription take place in the cell?

Answer 11

In the nucleus

Question 12

Where does translation take place in the cell?

Answer 12

In the cytoplasm - More specifically in the RER but ribosomes.

Question 13

Histones

Answer 13

DNA wrapped around these large protein molecules.

Question 14

What is the structure of a DNA molecule

Answer 14

Double helix. Base pairs in the middle. Sugar and phosphate group runs on ladder.

Question 15

What are the 4 base pairs?

Answer 15

Guanine
Adenine
Cytosine
Thymine

A-T
G-C

Question 16

What is a codon?

Answer 16

Three base pairs in a row. This is a signal for adding a specific amino acid during protein expression.

Question 17

What is a poly A tail?

Answer 17

A base repeated at end potentially defines how stable mRNA is, how long will be there.

Question 18

Chromatin

Answer 18

Tiny space so when combined with histones and proteins. Helps decide wether gene will be transcribed or not.

Question 19

Euchromatin

Answer 19

Open structure of chromatin - more likely to be transcribed. DNase1 sensitive, hyperacetylated, phosphorylated and not methylated allowing transcription to proceed.

Question 20

Heterochromatin

Answer 20

Closed structure of chromatin - less likely to allow transcription.

Question 21

RNA Polymerase

Answer 21

Large protein structure that is made to then go back into nucleus and transcribe DNA.
Polymerase 2 most common.

Question 22

Huntington’s disease gene

Answer 22

One of the largest genes. 169408 bases, 67 exons.

Question 23

How do we know when a gene has started or ended?

Answer 23

Promoter shows when it has started. STOP codon or poly A tail shows the end.

Question 24

Does the whole gene get made in to mRNA?

Answer 24

No. It does not transcribe the promoter. There will be a start codon 5’UTR and a STOP codon 3’UTR

Question 25

Do introns and exons both get transcribed into mRNA?

Answer 25

Yes but Introns do not stay. There is exon splicing in the nucleus. This mature mRNA with be transported from nucleus to cytoplasm.

Question 26

How does transcription start?

Answer 26

Specific Protein will bind to promoter at the right time. 'Make more protein'.

Question 27

TF.. and TBP

Answer 27

Come to recognise promoter together.

Question 28

What does the promoter site on a gene look like?

Answer 28

Can be Distal promoter region. Proximal promoter region (-200 to -50 bp before, CCAAT Box at -75bp). Core promoter region (BRE and TATA Box at -25bp) There will be a TF complex. INR then transcription.

Question 29

Are sequences in promoter for all genes in general?

Answer 29

No. All promoters have general (ubiquitous) transcription factors as well as tissue-specific to precisely control gene expression.

Question 30

How many transcription factors are there?

Answer 30

100's. Grouped together by structure.

Question 31

Are there any other elements that can affect transcription rather than just the promoter site?

Answer 31

Yes. Enhancers - Positively Regulate transcription - can be a long way away - hard to find. Silencers - Negatively regulate transcription. Boundary elements - Block spreading of influence of agents such as enhancers or silencers. Response elements - Sensitive to specific external stimuli such as glucocorticoids.

Question 32

Why is splicing important? How is it related to the small number of bases available?

Answer 32

Can use the same gene in many different ways and to create many different proteins.

Question 33

How do you find out which part of a gene expresses for certain things?

Answer 33

Compare the gene to the mature mRNA. As anything missing would be the intron. Only exons are left, meaning that this part is what expresses what you are looking at.

Question 34

What is at the beginning and end of an intron?

Answer 34

GT at beginning. AG at the end. always. Around these slightly varies.

Question 35

What is the implication of splicing where there is not AG?

Answer 35

It would not know to stop transcribing.

Question 36

What happens in translation?

Answer 36

In ER. Complimentary t(transfer)RNA with one end as an amino acid and other end as an anti codon. These match to the codons on mRNA and determine order of amino acids = protein.

Question 37

Redundancy RNA

Answer 37

All amino acids are given a single letter code to show what the codon encodes for. Some amino acids can be made through multiple codons.

Question 38

What is different when DNA is being encoded into RNA ?

Answer 38

It puts a U instead of a T

Question 39

What is the START codon for translation?

Answer 39

ATG (Methionine)

Question 40

What is the STOP codon?

Answer 40

TAA, TAG, TGA

Question 41

Post translational modification

Answer 41

Bonds between amino acids. Phosphorylation - switching protein on or off. Modified in ER by enzymes. Removal of signal peptide, addition of carbohydrates, folding, disulfide bonds formation. Only properly modified proteins transported from ER to final destination.