Topic 3: Gene expression in eukaryotes

Question 1

What is gene expression? (1 point)

Answer 1

1. Gene expression – when a gene is used to make gene products e.g. mRNA, protein.

Question 2

What can proteins from gene expression do? (2 things)

Answer 2

These proteins can:

1. permanently modify a cell during development, so that it becomes specialised

OR

2. can be essential to cell function on a day to day basis e.g. haemoglobin in red blood cells

Question 3

What is differential gene expression? (3 points)

Answer 3

1. When different genes are expressed in a cell in an organism,
2. resulting in different mRNA and proteins being produced,
3. which control cell processes or determine cell structure.

Question 4

Key Summary: Explain differential gene expression/how a stem cell becomes a specialised cell
(4 steps)

Answer 4

1. the correct chemical stimulus is required (e.g. hormone but read Q as different stimuli switch on different genes)
2. causes some genes to be ‘switched on’ and other genes to be ‘switched off’ in different cells
3. mRNA is made ONLY from ‘switched on’ genes by transcription and this mRNA is translated to make proteins
   so different proteins made in different cells
4. proteins determine the structure and function of cells, as the different proteins produced permanently modify a cell, resulting in different types of specialised cells being produced

Question 5

What is the epigenome? (1 point)

Answer 5

1. Chemical markers that are attached to DNA or histones

Question 6

Function of the epigenome (1 point)

Answer 6

1. The epigenome REGULATES gene expression by controlling which genes are switched on to produce proteins

Question 7

What are the 2 types of epigenetic changes?

Answer 7

1. DNA methylation

2. Histone modification

Question 8

Key Summary: How can DNA METHYLATION modify the activation of certain genes/modify gene expression/be involved in switching a gene off? (5 steps)

Answer 8

1. methyl groups attach to DNA cytosine bases preventing RNA polymerase binding to DNA
2. gene is switched off
3. no transcription so no mRNA made
4. no translation so no protein made
5. no gene expression

Question 9

Key Summary: How can HISTONE MODIFICATION modify the activation of certain genes/modify gene expression/be involved in switching a gene off/on? (1 point)

In what case is the gene switched OFF? (1 point)

In what case is the gene switched ON? (1 point)

Answer 9

1. methyl or acetyl groups attach to histone tails which affects how tightly DNA is wrapped around histones
2. if DNA is wound tightly, gene is switched OFF, so no mRNA or protein made, gene IS NOT expressed
3. if DNA is wound less tightly, gene is switched ON, so mRNA and protein are made, gene IS expressed

Question 10

How can a gene be switched OFF via DNA methylation? (2 steps)

Answer 10

1. methyl groups attach to cytosine bases of DNA
2. which prevents DNA polymerase binding to DNA.

NOTE: If gene switched off – no transcription, no mRNA, no translation, no protein made, gene not expressed

Question 11

How can a gene be switched OFF via histone modification? (2 steps)

Answer 11

1. methyl or acetyl groups attach to histone tails,
2. so DNA of a gene is wound more tightly around histones.

NOTE: If gene switched off – no transcription, no mRNA, no translation, no protein made, gene not expressed

Question 12

How can a gene be switched OFF via a protein repressor? (3 steps)

Answer 12

1. A protein repressor molecule attaches to the {DNA promoter region/regulator protein/transcription factor}
2. so RNA polymerase cannot bind to DNA.

AND/OR

3. A protein repressor molecule attaches to the regulator protein.

NOTE: If gene switched off – no transcription, no mRNA, no translation, no protein made, gene not expressed

Question 13

How can a gene be switched ON via histone modification? (2 steps)

Answer 13

1. methyl or acetyl groups attach to histone tails,
2. so DNA of a gene is coiled less tightly around histones exposing DNA to be transcribed.

NOTE: if gene switched on - transcription makes mRNA + translation makes protein – gene is expressed

Question 14

How can a gene be switched ON via a {regulator protein/transcription factor}? (3 steps)

Answer 14

1. Gene is uncoiled, exposing DNA to be transcribed.
2. A {regulator protein/transcription factor} attaches to the DNA promoter region on DNA antisense strand.
3. RNA polymerase enzyme can then also bind to promoter region.

NOTE: if gene switched on - transcription makes mRNA + translation makes protein – gene is expressed

Question 15

Key Summary: How can one cell produce a specific protein but another cell cannot?
(3 steps)

Answer 15

1. Differential gene expression causes different cell specialisation
2. Gene for protein is switched off in some cells by DNA methylation or histone modification
3. Gene for protein is switched on in other cells

Question 16

How do cells communicate? (to make a protein)

6 steps

Answer 16

1. One cell can send a message to another cell to tell it which genes to switch on (so direct which proteins are produced)
2. Signal proteins (eg. hormones made by one cell) bind to specific receptors on the cell surface membrane of another cell

THEN

3. A cascade of second messenger proteins is activated
4. Leads to the uncoiling of the DNA around the target gene and the activation of transcription factors
5. Transcription makes mRNA
6. Protein made by translation

Question 17

(When gene expression goes wrong)

What is FOP? (4 points)

Answer 17

1. rare inherited condition caused by a gene mutation
2. growth of bones within muscle or connective tissue
3. ‘freezing’ of all major limb and backbone joints
4. movement very restricted

Question 18

(In people with FOP)

A gene is responsible for creating ______ is not switched of in ______ blood cells.

Answer 18

bones

white

Question 19

(In people with FOP)
When muscle tissue is ________ (i.e. during an injection) white blood cells move to the site of damage and produce a _______ which causes muscle cells to express the genes that a bone cell would normally express.

Answer 19

damaged

protein

Question 20

(In people with FOP)

_______ cells become ______ cells.

Answer 20

muscle

bone

Question 21

In people WITHOUT FOP, genes for producing proteins that produce specialised bone cells are only switched ___ in places where the skeleton/bone develops (eg. growing limbs).

Answer 21

on