Unit 8: Gene expression and DNA technology

Question 1

What is a gene mutation?

Answer 1

changes in sequence of nucleotide bases in DNA

Question 2

What genes control the rate of cell division?

Answer 2

Proto-oncgenes

Tumour suppressor genes

Question 3

What is the function of a Proto-oncogene

Answer 3

genes that code for proteins that stimulate cell division

Question 4

What is the function of Tumour suppressor genes?

Answer 4

genes code for proteins that slow cell devision

Question 5

What can happen if mutations occur in proto-oncogenes and tumour suppressor genes?

Answer 5

mutations can lead to rapid uncontrolled cell division (by mitosis) leading to the development of a tumour

Question 6

How do mutations in proto-oncogenes occur?

Answer 6

a mutated version called a oncogene stimulates cells to divide too quickly

resulting in tapid uncontrollable cell division

Question 7

How do mutations in Tumour suppressor genes occur?

Answer 7

a mutation leads to the tumour suppressor protein not being made of being non functional*

results in rapid uncontrollable cell division

Question 8

What is cancer?

Answer 8

a group of diseases caused by alterations in the genes that regulate mitosis and the cell cycle

Question 9

What is a tumour?

Answer 9

masses of dividing cells

Question 10

What are the two types if tumours

Answer 10

Benign

Malignant

Question 11

Describe a benign tumour

Answer 11

• grow slower than malignant
• non cancerous, they dont spread to other tissues bc the tumour is enclosed by fibrous tissue
• cells remain differentiated (specialised)
• nucleus has a normal appearance

Question 12

Describe a Malignant Tumour

Answer 12

• grow faster than benign
• cancerous cells break off and spread to other parts of the body bc tumour isn’t enclosed
• cells become undifferentiated (not specialised)
• nucleus is larger and darker

Question 13

What are stem cells?

Answer 13

undifferentiated cells that can divide by mitosis and differentiate into different types of cells

Question 14

What are Totipotent stem cells?

Answer 14

occur for a limited time in early manmalian embryos

can differentiate into any type of cell

Question 15

What are pluripotent stem cells?

Answer 15

• found in embryos and develop from totipotent stem cells
• can differentiate into almost any type of cell
• cant produce cells of embryonic tissue

Question 16

What ate the two embryonic stem cells

Answer 16

Totipotent

Pluripotent

Question 17

What are multi-potent stem cells?

Answer 17

adult stem cells

found in mature aminals

differentiate into few limited types of specialised cells

Question 18

What are unipotent stem cells?

Answer 18

found in mature animals

can only differentiate into one type of cell

Question 19

What are induced pluripotent stem cells (iPS)?

Answer 19

type of pluripotent cell produced from unipotent stem cells

appropriate transcription factors make the unipotent cell pluripotent

Question 20

What is the function of iPS cells?

Answer 20

develop into a wide range of different types of tissue which could be used to treat people with certain diseases

Question 21

What is the function of a transcription factors?

Answer 21

proteins that bring about expressions of some genes and inhibit other genes so that these cells differentiate a particular cell

Question 22

Describe the role of oestrogen and gene expression

Answer 22

• oestrogen is lipid soluble and diffuses across the cell membrane
• oestrogen specifically bind to a receptor protein that is part of a transcription factor
• transcription factor enters nucleus
• binding change of shape of TF and allows it to bind to promoter sequence of a gene
• allows RNA polymerase to attach to gene and catalyse transcription
• mRNA then subscribed then translated into a protein

Question 23

how can oestrogen lead to cancer?

Answer 23

In some tissues oestrogen increases the expressions of genes

so high concentrations can increase uncontrollable cell division

Question 24

How does Tamoxifen treat some breast cancer?

Answer 24

it is converted into endoxifen which is a molecule of a similar structure to oestrogen

It competes with oestrogen for biding to an oestrogen receptor

Question 25

what is siRNA?

Answer 25

short double stranded sections of RNA Usually 20 to 25 base pairs long

Question 26

what is the function of siRNA?

Answer 26

Regulates gene expression by **causing mRNA to be broken down after transcription** thus **preventing translation**

Question 27

How does siRNA prevent translation?

Answer 27

- double stranded RNA is hydrolysed into short molecules - RNA becomes single stranded siRNA - siRNA binds to an enzyme that hydrolyses mRNA - it then binds to a specific molecule of mRNA by complementary base pairing and guides to hydrolytic enzyme to a target molecule of mRNA - The enzyme hydrolyses the mRNA this prevents the translation

Question 28

What is epigenetics?

Answer 28

change in **gene function** without changes in the base sequence DNA **heritable**

Question 29

What causes epigenetics?

Answer 29

aspects if the environment e.g stress diet

Question 30

What are. two epigenetic changes?

Answer 30

increased methylation of DNA decreased acetylation of associated histones

Question 31

How does increased methylation occur?

Answer 31

- **methyl group attaches** to the DNA sequence of a gene - attaches to CpG site - prevents binding of transcription factors to promoter sequence so gene isn’t expressed - thus preventing transcription

Question 32

How does acetylation increase transcription?

Answer 32

histones are **more acetylated** meaning the **chromatin is less condense** so transcription is more likely as genes are more accessible to transcription factors

Question 33

How does acetylation decrease transcription?

Answer 33

histones are less acetylated so the chromatin is more condensed This inhibits transcription as genes are not accessible to transcription factors

Question 34

how can epigenetic changes lead to disease?

Answer 34

By causing abnormal activation/inhibition of genes

Question 35

How can cancer develop from hypermethylation?

Answer 35

**too much** methylation of tumour suppressor genes so they are not transcribed the proteins that slow down cell division are not produces causing rapid cell division

Question 36

How can Hypomethylation cause cancer?

Answer 36

**too little** methylation of proto-oncogenes so **they’re continually transcribed** this increases production of proteins involved in stimulating cell division causing rapid cell division and to development

Question 37

What are the function of restriction endonucleases?

Answer 37

**hydrolyse phosphodiester bonds** in DNA/RNA producing smaller fragments

Question 38

Where do restriction enzymes hydrolyse DNA/RNA?

Answer 38

at specific base sequences AKA **recognition sequences**

Question 39

How are sticky ends made

Answer 39

when restriction enzymes hydrolyse DNA at different **locations other then the recognition sites**

Question 40

How are blunt ends made?

Answer 40

When restriction enzymes hydrolyse DNA at the same position in both strands

Question 41

What is the **function** of sticky ends?

Answer 41

enable DNA to be **joined or spliced** onto a different piece of DNA **more easily** because complementary base pairing occurs between sticky ends

Question 42

What is gel electrophoresis?

Answer 42

Separates DNA/RNA fragments by size - small fragments will travel faster/further thru the gel when an electric charge is applied

Question 43

Where do fragments move in gel electrophoresis?

Answer 43

Negatively charged DNA fragments move **towards positively charged terminals**

Question 44

Outline gel electrophoresis

Answer 44

- DNA samples placed in well at top of gel - DNA fragments in the each sample separate according to size - fragments are then transferred to a nylon membrane then radioactively labelled probes are added - nylon membrane is placed on X-ray and position of radioactivity labelled fragments are revealed as dark bands **(autoradiography)**