Gene Expression - Chapter 20

Question 1

What is mutation

Answer 1

Any change in the structure of quantity of DNA

Question 2

What is a substitution mutation and what are their effects?

Answer 2

Substitution-when one base is swapped for another
-Can lead to a stop codon so protein is truncated(different protein)
-Formation of a different amino acid
-Different codon but for the same amino acid

Question 3

What is a duplication mutation and what are its effects?

Answer 3

One or more bases are repeated and therefore produces a frameshift.

Question 4

What is an insertion and deletion mutation and what are its effects?

Answer 4

where one or more nucleotide pairs are inserted or deleted from the sequence. This type of mutation alters the sequence of nucleotides after the insertion/deletion point known as a frameshift.

Question 5

What are inversion mutations and what are its effects?

Answer 5

A group of bases become separated from the DNA sequence and then rejoin at the same position but in the reverse order.
This therefore affects the amino acid that is produced.

Question 6

What are translocation mutations and what are its effects?

Answer 6

A group of bases become separated from the DNA sequence on one chromosome and are inserted into the DNA sequence on another chromosome.
This can often lead to significant effects on the phenotype.

Question 7

What are some causes of mutations(mutagenic agents)

Answer 7

High energy ionising radiation e.g alpha rays, gamma rays
UV light
Chemical mutagens e.g nitrogen dioxide, alcohol, tar in tobacco
Spontaneous errors in DNA Replication

Question 8

What is a stem cell and where can they be found?

Answer 8

A cell that can differentiate, able to self renew(replace themselves)and become any type of human cell
Found in embryo, placenta, umbilical cord stem cells,

Question 9

What are totipotent cells?

Answer 9

Cells that can differentiate and mature into any type of human cell in the body
Found in the embryo
They only translate part of their DNA which allows them to specialise

Question 10

What are the differences between pluripotent, multipotent and unipotent stem cells?

Answer 10

Pluripotent- found in embryo and can differentiate almost into any type of cell(except embryonic)
Mulitpotent-found in adults and can only differentiate into limited number of specialised cells
Unipotent- found in adults and can only differentiate into one type of cell

Question 11

What are induced pluripotent stem cells?

Answer 11

a type of pluripotent cell that is produced from unipotent stem cells
Similar to embryonic stem cells as they can divide limitlessly and can be used to repair damaged tissues

Question 12

How does oestrogen control transcription?

Answer 12

Oestrogen is lipid soluble so can diffuse through phospholipid bilayer
Binds to promoter region on DNA and changes its shape- activating it and stimulating transcription by the binding of RNA Polymerase

Question 13

What are epigenetics?

Answer 13

Epigenetics involves heritable changes in gene function, without changes to the base sequence of DNA.

Question 14

How can you decrease transcription

Answer 14

Condense the DNA-histone complex
Either by decreased acetylation or increased DNA methylation

Question 15

How does decreased acetylation affect transcription?

Answer 15

Increases positive charge on the histones
DNA binds more tightly
Transcriptional factors cannot bind to DNA/promoter region
Gene switched off
Reversible change

Question 16

How does increased methylation affect transcription?

Answer 16

Methyl group attaches to cytosine base on DNA
Prevents transcriptional factors binding by attracting proteins that condense the DNA-histone complex
Irreversible change

Question 17

How does siRNA affect translation?

Answer 17

Binds to mRNA via complementary base pairing
Cuts mRNA strand into smaller pieces
Thus cannot be translated into polypeptides so gene isn’t expressed

Question 18

What are the two types of tumour and what are the main differences?

Answer 18

Benign tumour-non cancerous tumour(cells doesn’t metastasise)
Malignant tumour- tumour that spreads to different parts of the body and is cancerous
Malignant- cancerous(cells metastasise), grows quickly, cells are unspecialised
Benign- grow slowly, isn’t as harmful, cells are specialised

Question 19

What are the role of proto-onco genes?

Answer 19

They stimulate cells to divide by producing proteins that stimulate cell division, allow the checkpoints of the cell cycle to be passed, and can cause cancer if mutated

Question 20

How do oncogenes cause cancer?

Answer 20

Formed from mutated proto-oncogenes and result are permanently switched on resulting in cell division that is uncontrolled.
It does this by permanently activating a cell surface receptor so that cell division is switched on the absence of a growth factor
Codes for a growth factor that is produced in excessive amounts which causes uncontrolled cell division

Question 21

What is the role of a tumour suppressor gene?

Answer 21

Codes for proteins that slows down cell division, repairs DNA and programmes apoptosis(cell death)

Question 22

How does abnormal methylation of tumour suppressor gene affect cell division

Answer 22

Hypermethylation of tumour suppressor gene affects the promoter region
Tumour suppressor gene becoming inactivated
Transcription of the promoter region of tumour suppressor gene is silenced
Inactivation leads to increased cell division and formation of tumour

Question 23

How does oestrogen cause breast cancer?

Answer 23

Oestrogen binds to the promoter region on DNA which activates the genes promoting cell division, leading to tumour formation and uncontrolled cell division