Unit 3.5.7 - Gene Expression

Question 1

Where do specialised cells originally come from?

Answer 1

Stem cells

Question 2

What are stem cells?

Answer 2

Unspecialised cells that can develop into other types of cells.

Question 3

What is meant by stem cells are self renewal?

Answer 3

They are capable of dividing to produce more stem cells.

Question 4

Name two places you would find stem cells in multi cellular organisms?

Answer 4

In the embryo and in some adult tissue like bone marrow.

Question 5

What are totipotent stem cells?

Answer 5

Stem cells that can mature into any other type of cell.

Question 6

What are multipotent stem cells?

Answer 6

Stem cells that can develop into a few types of cells.

Question 7

How do stem cells become specialised generally?

Answer 7

They only transcribe and translate part of their DNA because certain genes are turned off.

Question 8

During transcription and translation how do stem cells become specialised in three steps?

Answer 8

1. Genes that are expressed get transcribed into mRNA which is then translated into proteins.
2. These proteins modify the cell and determine the cell structure and control cell processes.
3. These changes caused by these proteins causes the cell to become specialised.

Question 9

Once the stem cells become specialised why does it stay specialised?

Answer 9

The changes are hard to reverse.

Question 10

Where are stem cells found in mature plants?

Answer 10

In the meristems.

Question 11

Where are the meristems?

Answer 11

Areas where the plant is still growing like in the root and shoots.

Question 12

Are plants stem cells multipotent or totipotent?

Answer 12

Totipotent

Question 13

What type of cloning is tissue culture?

Answer 13

Invitro

Question 14

What is tissue culture?

Answer 14

Growing a plant tissue artificially.

Question 15

Describe in four steps how you carry out tissue cultures?

Answer 15

1. A single totipotent stem cell is taken from the meristem.
2. The cell is placed in some growth medium that contains nutrients and growth factors.
3. The plant’s stem will grow and divide into a mess of unspecialised cells.
4. If the conditions are suitable the cells will mature into specialised cells.

Question 16

What two diseases to stem cell therapies currently exist for?

Answer 16

Diseases affecting the blood and the immune system.

Question 17

How can bone marrow transplant be used to treat diseases of the blood in two steps?

Answer 17

1. Bone marrow transplants replaces the faulty bone marrow in patients with abnormal blood cells.
2. The stem cells used divide and specialise to produce healthy blood cells.

Question 18

Why can stem cells be used to replace damaged tissues?

Answer 18

They can divide into specialised cell types and replace damaged tissues.

Question 19

What are the two potential sources for stem cells?

Answer 19

Adult stem cells and embryonic stem cells.

Question 20

Are adult stem cells or embryonic stem cells more flexible and why?

Answer 20

Embryonic stem cells because they are totipotent.

Question 21

How are embryonic stem cells collected?

Answer 21

Embryos are grown in a lab using IVF, once the embryos are 4 - 5 days old stems cells are removed and the rest of the embryo is destroyed.

Question 22

What are three reasons for using embryonic stem cells?

Answer 22

1. stem cells can be obtained from unfertilised embryos so the embryo wouldn’t survive past a few days.
2. They are totipotent.
3. Using them for treating diseases could save lives or improve a person’s quality of life.

Question 23

What are two reasons against using embryonic stem cells?

Answer 23

1. There are adult stem cells so why use them.

2. Results in the destruction of an embryo which could have grown into a human being.

Question 24

Even though all the cells in an organism carry the same gene why do the structure and function of the cells vary?

Answer 24

Not all the genes in the cell are expressed.

Question 25

What is the transcription of genes controlled by?

Answer 25

Transcription factors.

Question 26

How do transcription factors bind to the promoters?

Answer 26

They move from the cytoplasm to the nucleus, bind to specific DNA sites called promoters near the target gene and they control expression there.

Question 27

How do transcription factors control expression?

Answer 27

They control the rate of transcription.

Question 28

What are two broad types of transcription factors?

Answer 28

activators and repressors.

Question 29

How do activators change the rate of transcription?

Answer 29

They increase it by helping RNA polymerase to bind.

Question 30

How do repressors change the rate of transcription?

Answer 30

Decrease the rate of transcription by stopping RNA polymerase from binding.

Question 31

Name one common molecule that binds to a transcription factor in the body.

Answer 31

Oestrogen

Question 32

How does oestrogen affect transcription in 3 steps?

Answer 32

1. It binds to transcription factors called oestrogen receptors forming an oestrogen - oestrogen receptor complex 2. The complex moves from the cytoplasm into the nucleus where it binds to specific DNA sites near the target gene where it acts as an activator or repressor 3. Whether the complex acts as a activator or repressor depends on the cell and the target gene

Question 33

Why do the levels of oestrogen affect the rate of transcription?

Answer 33

It can form complexes with transcription factors which act as repressors or activators

Question 34

What type of RNA can also affect gene expression?

Answer 34

siRNA

Question 35

What does siRNA stand for?

Answer 35

Small interfering RNA

Question 36

What does siena look like?

Answer 36

Short molecules of double stranded RNA that is complementary to the specific target genes and the mRNA thats formed from it

Question 37

What does siRNA interfere with to affect gene expression?

Answer 37

Transcription and translation

Question 38

What is the mechanism called that siRNA affects translation through?

Answer 38

RNA interference

Question 39

What are the three steps in RNA interference?

Answer 39

1. In the cytoplasm siRNA and associated proteins bind to the target mRNA 2. The proteins cut up the mRNA into sections so it can no longer be translated 3. So the siRNA prevents the expression of the specific gene as its proteins can no longer be made during translation

Question 40

How does siRNA have the potential for treating genetic disorders?

Answer 40

By stopping a known harmful gene from being expressed