Mutations Stem Cells Genome Projects Gene Technology

Question 1

(Refer to June 2011 paper) Plant physiologists attempted to produce papaya plants using tissue culture. They investigated the effects of different concentrations of two plant growth factors on small pieces of the stem tip from a papaya plant. Their results are shown in the table.

Callus is a mass of undifferentiated plant cells. Plantlets are small plants.
Explain the evidence from the table that cells from the stem tip are totipotent. (2)

Answer 1

Gives rise to new plants;

So must be able to develop into different tissues

Question 2

Calculate the ratio of cytokinin : auxin that you would recommend to grow papaya plants by this method

Answer 2

5:1

Question 3

Papaya plants reproduce sexually by means of seeds
Papaya plants grown from seeds r very variable in their yield

explain why

Answer 3

Crossing over during meiosis and the random fertilisation of gametes

Question 4

Explain the advantage of growing papaya plants from tissue culture rather than from Seeds

Answer 4

They will b genetically identical

Question 5

Totipotent

Answer 5

Can differentiate into any type of body cell

Question 6

Pluripotent cells found in ..

Can differentiate into …

Answer 6

Embryos and can differentiate into almost any type of cell

Question 7

Multi-potent and unipotent

Answer 7

Found in mature mammals

Multipotent = differentiate into a limited number of cells e.g. bone marrow - wbc , rbc,

Unipotent - can only differentiate into one type of cell , cardiomyocytes

Question 8

Ips cells

Answer 8

Created from adult unipotent cells
Treated w transcription factors to switch on genes that induce pluripotency

Advantages : don’t cause embryonic destruction 
Self renewal (can divide indefinitely to give a limited supply)
Used in medical treatment instead of embryonic cells

Question 9

Multipotent cells are found in …

Answer 9

Multipotent cells are found in mature mammals

Question 10

Totipotent cells can develop into

Answer 10

Totipotent cells can develop into pluripotent cells in embryos

Question 11

Totipotent cells exist for..

Answer 11

Totipotent cells exist for limited time in embryonic development

Question 12

Pluripotent cells can b used to

Answer 12

Treat human disorders

Question 13

Stages of regulation by oestrogen

Answer 13

Oestrogen enters the cell thru the phospholipid bilayer

Oestrogen binds to receptors on transcription factors in the cytoplasm

Binding of oestrogen causes the transcription factors to change shape and form a receptor-hormone complex

The receptor-hormone complex enters the nucleus

The receptor-hormone complex binds to the promotor region of the dna

Transcription is initiated

Question 14

What is a mutation

Answer 14

A change to the base sequence of DNA

Question 15

describe what happens In a translocation mutation

Answer 15

A sequence of bases is moved from one location in the genome to another

Question 16

Explain why a mutation in a polypeptide that makes of an enzyme could affect the enzymes function

Answer 16

The mutation may result in a change to the shape of the enzymes active site
this may stop substrates from being able to bind to the active site
leaving the enzyme unable to catalyse the reaction

Question 17

What is a hereditary mutation

Answer 17

Mutation thats Passed on to an individual’s offspring as a result of a mutation in the gametes

Question 18

Do Mutations always affect the protein coded for by the gene explain your answer

Answer 18

No because the genetic code is degenerate this means that not all mutations will result in a change to the amino acid sequence of a protein

Question 19

2-aminopurine is a base analog That can substitute for both adenine and guanine during DNA replication

explain why this base is a mutagenic agent

Answer 19

This base can pair with both thymine and cytosine which could cause a substitution mutation in the new DNA during DNA replication

Question 20

Mustard gas is an alkylating agent Explain how exposure to mustard gas may affect the sequence if amino acids in a particular polypeptide

Answer 20

Alkylating agents such as mustard gas can add an alkyl group to guanine, changing the structure so that it pairs w thymine instead of c which may result in a change in the amino acid sequence of a polypeptide

Question 21

When might a mutation occur spontaneously

Answer 21

During dna replication

Question 22

Whats a mutagenic Agent

Answer 22

sumn that causes an increase in the number of mutations

Question 23

Mutagenic agents examples

Answer 23

Ionising radiation
Uv radiation
Base analogs
Alkylating agents

Question 24

P53 is a tumour suppressor gene mutations in P53 are found in over half of all cancers

suggest how p53 normally functions

suggest how mutations in P53 could lead to cancer

Answer 24

A mutation in p53 could inactive the gene
the protein it codes for wont be produced
this will cause cells to start dividing uncontrollably eventually leading to cancer

Question 25

A woman has found a lump in her breast
her doctor tells her that she has breast cancer and left it spread to her liver the woman is 49 years old and is having oestrogen-containing HRT to treat symptoms of the menopause
explain why taking HRT may have contributed to the woman developing breast cancer

Answer 25

HRT increases oestrogenic levels in the body
An increase in exposure to oestrogen over an extended period of time is thought to increase the risk of developing breast cancer