B20 Gene Expression

Question 1

What is a mutation

Answer 1

An alteration to the DNA base sequence. Often arise spontaneously during DNA replication

Question 2

What are addition and deletion mutations

Answer 2

Where 1 or more nucleotides (bases) are either inserted/deleted from the DNA sequence

Question 3

What is a substitution mutation

Answer 3

Where 1 nucleotide (bases) in the DNA sequence is replaced by another

Question 4

What is a duplication mutation

Answer 4

Where 1 or more nucleotides (bases) duplicate and repeat

Question 5

What is an inversion mutation

Answer 5

Where a group of nucleotides (bases) become separated from the DNA sequence, then rejoin in the reverse order i.e. they have flipped

Question 6

What is a translocation mutation

Answer 6

Where a group of nucleotides (bases) become separated from the DNA sequence, and are then inserted into the DNA of a different chromosome

Question 7

Which mutations are most likely to have a significant impact and why

Answer 7

Insertion, deletion, duplication, translocation

Because they produce a frameshift, meaning the entire amino acid sequence produced will be different

Question 8

Which mutations are less likely to have a significant impact and why?

Answer 8

Substitution, inversion

Because they only alter 1 or very few triplets, the amino acid sequence might not be affected due to the degenerate nature of the genetic code

Question 9

Is a mutation resulting in a change to the amino acid sequence always harmful

Answer 9

No

May be neutral if the resulting change in protein has no effect on the organism.

Also may be beneficial, which is the basis for evolution and natural selection.

Question 10

What is a mutagenic agent

Answer 10

Factors that increase the rate of gene mutation

Question 11

Give examples of mutagenic agents

Answer 11

Chemical mutagens such as: alcohol and benzene.

Ionising radiation such as UV and x-ray

Question 12

What is the genome

Answer 12

The complete set of genetic information contained in the cells of an organism

Question 13

What is genome sequencing

Answer 13

Identifying the DNA base sequence of an individual. This allows us to determine the amino acid sequence of the polypeptides coded for by that DNA

Question 14

What is the proteome

Answer 14

The complete set of proteins that can be produced by a cell

Question 15

Can we directly translate the genome into the proteome

Answer 15

In simple organisms, yes.

In complex organisms, du to the presence of non-coding DNA and regulatory genes, it is much harder to obtain the proteome

Question 16

Give an application of sequencing the proteome in simple organisms

Answer 16

Identifying potential antigens for use in vaccine production

Question 17

Give some applications of genome sequencing

Answer 17

• comparing genomes between species to determine evolutionary relationships
• genetic matching
• personalised medicine
• synthetic biology

Question 18

How have sequencing methods changed over time

Answer 18

Used to be a manual process, however now it has become automated. A reaction mixture is created and after the process is complete, a machine reads the base sequence

Question 19

What is a stem cell

Answer 19

Undifferentiated cells, that can divide indefinitely and turn into other specific cell types

Question 20

Name 3 types of stem cell

Answer 20

Totipotent

Pluripotent

Multipotent

Question 21

Define a totipotent stem cell

Answer 21

Can develop into any cell type including the placenta and embryo

Question 22

Define a pluripotent stem cell

Answer 22

Can develop into any cell type excluding the placenta and embryo

Question 23

Define a multipotent stem cell

Answer 23

Can only develop into any cell few different types of cell

Question 24

What happens to totipotent cells during embryonic development

Answer 24

Certain parts of the DNA are selectively translated so that only some genes are ‘switched on’, in order to differentiate the cell into a specific type and form the tissues that make up the foetus

Question 25

Give a unique feature of pluripotent cells and the use of this feature

Answer 25

They can divide in unlimited numbers, and can therefore be used to repair or replace damaged tissue

Question 26

What is a unipotent cell? Give an example

Answer 26

A cell that can only develop into 1 type of cell. This happens at the end of specialisation when the cell can only propagate its own type. An example is cardiomyocytes (heart cells)

Question 27

Which types of stem cells are found in embryos

Answer 27

Totipotent and pluripotent Multipotent and unipotent cells are only found in mature mammals

Question 28

Give some uses of stem cells

Answer 28

Medical therapies e.g. bone marrow transplants, treating blood disorders. Drug testing on artificially grown tissues. Research e.g. on formation of organs and embryos.

Question 29

How are induced pluripotent stem cells produced

Answer 29

From mature, fully specialised (somatic) cells. The cell regains capacity to differentiate through the use of proteins, in particular transcription factors.

Question 30

How are induced pluripotent stem cells produced

Answer 30

From mature, fully specialised (somatic) cells. The cell regains capacity to differentiate through the use of proteins, in particular transcription factors.

Question 31

What is a transcription factor

Answer 31

A protein that controls the transcription of genes so that only certain parts of the DNA are expressed, e.g. in order to allow a cell to specialise.

Question 32

How do transcription factors work

Answer 32

1. Move from cytoplasm into nucleus 2. Bind to promoter region upstream of target gene 3. Makes it easier or more difficult for RNA polymerase to bind to gene. This increases or decreases transcription rate.

Question 33

Give an example of a hormone that affects transcription and explain how it works

Answer 33

1. Steroid hormone oestrogen diffuses through cell membrane 2. Forms hormone-receptor complex with ER alpha receptor in the cytoplasm 3. Complex enters the nucleus and acts as transcription factor to facilitate binding of RNA polymerase

Question 34

What is meant by epigenetics

Answer 34

A heritable change in gene function without change to the base sequence of DNA

Question 35

How does increased methylation of DNA affect gene transcription?

Answer 35

Involves addition of a CH3 group to cytosine bases which are next to guanine. Prevents transcription factors from binding. Therefore gene transcription is suppressed.

Question 36

How does decreased acetylation of histones affect gene transcription

Answer 36

Positively-charged histones are positively charged bind to negatively-charged DNA. Decreasing acetylation increases positive charge of histones. Binning becomes too tight and prevents transcription factors from accessing the DNA. Therefore gene transcription is suppressed.

Question 37

How might epigenetic changes affect humans

Answer 37

They can cause disease, either by over activating a gene’s function (such as in cancer) or by suppressing it.

Question 38

Give an application of epigenetics

Answer 38

Treatments of various diseases. Development of ways to reverse epigenetic changes.

Question 39

Describe the process of RNA interference, including the organisms in which it occurs

Answer 39

RNA molecules act to inhibit gene expression, usually by destroying mRNA so that it cannot be translated. Occurs in eukaryotes and some prokaryotes.

Question 40

Give some characteristics of benign tumour

Answer 40

- slow growth - defined by a clear boundary due to cell adhesion molecules - cells retain function and normal shape - don’t spreads easily - easy to treat

Question 41

Give some characteristics of malignant tumours

Answer 41

Rapid, uncontrollable growth Ill-defined boundary ( finger-like projections) Cells do not retain function and often die Spreads quickly and easily (metastasis) Difficult to treat

Question 42

Describe the role of tumour-suppressor genes

Answer 42

Code for proteins that control cell division; in particular, stopping the cell cycle when damage is detected. They are also involved in programming apoptosis i.e ‘self destruction’ of the cell

Question 43

Explain how tumour-suppressor genes can be involved in developing cancer

Answer 43

A mutation in the gene could code for a non functional protein. Increased methylation or decreased acetylation could prevent transcription. Cells will divide uncontrollably resulting in a tumour

Question 44

Describe the role of proto-oncogenes

Answer 44

Control cell division; in particular, code for proteins that stimulate cell division

Question 45

Explain how proto-oncogenes can be involved in developing cancer

Answer 45

Mutation in the gene could turn into a permanently activated oncogene. Decreased methylation or increased acetylation can cause excess transcription. This results in uncontrolled cell division and formation of a tumour.

Question 46

Explain how abnormal methylation of genes can cause cancer

Answer 46

Hyper-methylation of tumour-suppressor genes or oncogenes can impair their function and cause the cell to divide uncontrollably.

Question 47

Explain how oestrogen can be involved in developing breast cancer

Answer 47

We already know oestrogen is an activator of RNA polymerase. Therefore in areas of high oestrogen concentration, such as adipose tissue in the breasts, cell division can become uncontrolled