Unit 8 Gene Mutations

Question 1

Outline gene mutation and when it occurs

Answer 1

A gene mutation is the alteration of a base in the sequence of bases for one gene
- Likely to occur during DNA replication, which is during interphase in the cell cycle.
- Gene mutations occur spontaneously, frequency increased by mutagenic agents.
- Mutations can result in a different amino acid sequence in the encoded polypeptide.
- So there is a change in hydrogen and ionic bonds therefore tertiary structure different

Question 2

Outline 2 examples of mutagenic agents

Answer 2

• High energy and ionising radiation
• Carcinogens alter structure of DNA

Question 3

Outline 2 different types of gene mutations including addition and inversion

Answer 3

ADDITION
Original: TAC TTC AGG TGG
Mutation: TAC ATT CAG GTG G
- Adding one base which is known as frameshift and hamful as altered codons could potentially code for different amino acids
INVERSION
Original: TAC TTC AGG TGG
Mutation: TAC GGA CTT TGG
- Bases detach and rejoin inverted so code back to front, results in different amino acids being coded for in this region

Question 4

Outline 2 different types of gene mutations including duplication and translocation

Answer 4

DUPLICATION
Original: TAC TTC AGG TGG
Mutation: TAC TTT TCA GGT GG
- 1 base duplicated and causes frameshift to right and a different sequence of amino acids are coded for
TRANSLOCATION
- Section of bases on one chromosome detaches and attaches to a different chromosome & causes significant impacts on gene expression

Question 5

Define stem cells and the different types of stem cells

Answer 5

• Stem cells are undifferentiated cells that can continually divide and become specialised
• These are totipotent, pluripotent, multipotent and unipotent stem cells.

Question 6

Describe totipotent stem cells

Answer 6

• These stem cells can divide to produce any type of body cell.
• During development, totipotent cells translate only part of their DNA, resulting in cell specialisation.
• Totipotent cells occur only for a limited time in early mammalian embryos.

Question 7

Describe Pluripotent stem cells

Answer 7

• These stem cells are found in embryos and can become almost any type of cell and can divide in unlimited numbers
• They are used in research with the prospect of being used to treat human disorders

Question 8

Describe multipotent and unipotent stem cells

Answer 8

• Multipotent and unipotent stem cells are found in mature mammals and can divide to form a limited number of different cell types.(BONE MARROW)
• Multipotent cells, such as bone marrow cells, can differentiate into a limited number of cells, whereas unipotent cells can only differentiate into one type of cell.

Question 9

Describe Induced pluripotent stem cells (iPS cells)

Answer 9

• iPS cells are created from adult unipotent cells.
• These cells, which can be from almost any body cell, are altered in the lab to return them to a state of pluripotency.
• Cells divide and then differentiate, done using transcriptional factors
  UNLIKE PLURPOTENT, ADULT CAN GIVE PERMISSION

Question 10

Outline the role of transcriptional factors

Answer 10

• In eukaryotes, transcription of target genes can be stimulated or inhibited when specific transcriptional factors move from the cytoplasm into the nucleus.
• This can turn on/off genes, so only certain proteins are produced in a particular cell.

Question 11

Outline the hormone important in initiating transcription

Answer 11

• Oestrogen is a steroid hormone that can initiate transcription.
• Oestrogen binds to a receptor site on the transcriptional factor.
• Causes it to change shape slightly, and this change in shape makes it complementary and able to bind to the DNA to initiate transcription.

Question 12

Outline what is meant by epigentics

Answer 12

• Epigenetics is the heritable change in gene function, without changing the DNA base sequence.
• These changes are caused by changes in the environment and can inhibit transcription.

Question 13

Outline increased methylation of the DNA to inhibt transcription

Answer 13

• Increased methylation of DNA inhibits transcription.
  DONT- When methyl groups are added to DNA, they attach to the cytosine base.
  DONT- This prevents transcriptional factors from binding and attracts proteins that condense the DNA-histone complex.
• In this way, methylation prevents a section of DNA from being transcribed.
  may lead to cancer as uncontrolled cell division

Question 14

Outline decreased acetylation of associated histones to inhibit transcription

Answer 14

• Decreased acetylation of associated histone proteins on DNA inhibits transcription.
  DONT- If acetyl groups are removed from the DNA then the histones become more positive and are attracted more to the negative phosphate group on DNA.
  DONT- This makes the DNA and histones more strongly associated and harder for the transcription factors to bind.
• may lead to cancer as uncontrolled cell division

Question 15

Outline the relations of epigenetics and disease, especially cancer

Answer 15

• Tumour suppressor genes produce proteins to slow down cell division and cause cell death if DNA copying errors are detected.
• Increased/abnormal methylation of tumour suppressor genes leads to inhibition of
  tumour suppressor genes leading to cancer (uncontrolled cell division)
  = Increased methylation of DNA inhibits transcription
  = Decreased acetylation of histones inhibits transcription

Question 16

Outline how target genes can be inhibited by RNA interference

Answer 16

When an mRNA molecule that has already been transcribed gets destroyed before it is translated to create a polypeptide chain.

• siRNA complementary to mrRNA so binds to complementary sequence of mRNA.
• and cut up the mRNA so it cannot be translated.
• Preventing translation.

Question 17

Outline 3 factors which have an influence on phenotype

Answer 17

• Diet
• Stress
• Toxins

Question 18

things to remember

Answer 18

-produce health x cells, no faulty x cells produced, stem cells divide by mitosis
- sd do/do not overlap, significant difference, large/small sd

Question 19

define epigentics

Answer 19

Heritable changes in gene function
Without changes to the base sequence of DNA