Topic 8 - Mutations and Gene Expression

Question 1

when does mutation occur

Answer 1

dna replication

Question 2

what is a duplication mutation

Answer 2

one or more bases are repeated
always causes a frame shift

Question 3

what is an inversion mutation

Answer 3

a sequence of bases is reversed

Question 4

what is translocation mutation

Answer 4

• a sequence of bases is moved from one location in the genome to another
• could be within a same chromosome or a different one

Question 5

how can mutagenic agents increase the rate of mutations

Answer 5

• acting as a base - chemicals callled base analogs can substitute for a base during dna replication, changing the sequence
• altering bases - some chemicals can delete or alter bases
• changing th structure of DNA - Some types of radiation can change the structure of DNA which causes problems during replication

Question 6

what are stem cells

Answer 6

undifferentiated cells with the potential to differentiate into a variety of the specialised cell types of the organism

Question 7

where are stem cells found in humans

Answer 7

embryo
stem cells

Question 8

what are totipotent stem cells

Answer 8

• stem cells that can differentiate into any type of body cell including the placenta
• they are only present in the first few cell divisions of an embryo

Question 9

what are pluripotent stem cells

Answer 9

• stem cells that can specialise into any cell in the body but cannot make up the placenta

Question 10

what are unipotent stem cells

Answer 10

• stem cells that can only differentiate into one type of cell

Question 11

what are multipotent stem cells

Answer 11

• stem cells that can differentiate into a few different types of cells

Question 12

how do stem cells become specialised

Answer 12

• mRNA is only transcribed for specific genes
• the mRNA is then translated into proteins
• These proteins modify the cell - they determine the cell structure and control cell processes
• changes to the cell produced by the proteins cause the cell to become specialised
• these changes are difficult to reverse

Question 13

what is an example of a unipotent stem cells

Answer 13

cardiomyocytes

Question 14

what are cardiomyocytes

Answer 14

• heart muscle cells that make up the tissue in our hearts
• some scientists think that old or damaged cardiomyocytes can be replaced by new cardiomyocytes derived from a small supply of unipotent stem cells in the heart

Question 15

how are stem cells used to treat disease

Answer 15

• bone marrow transplant
• stem cells divide and specialise into healthy cells

Question 16

what type of stem cells are in bone marrow

Answer 16

multipotent

Question 17

how are embryonic stem cells extracted

Answer 17

• embryos created in a lab using IVF - egg cell is fertilised outside thw womb
• once the embryos are 4-5 days old stem cells are removed from them and the rest of the embryo is destroyed
• embryonic stem cells can divide an unlimited number of times and develop into all types of body cells - pluripotent

Question 18

what are induced pluripotent stem cells

Answer 18

• reprogramming specialised adult body cells so they become pluripotent
• the adult cells are made to express a series of transcription factors that are associated with pluripotent stem cells
• one of the ways that these can be introduced is by infecting them with a modified virus

Question 19

why do organisms carry the same genes but the structure and function of cells varies

Answer 19

• different genes are expressed
• different proteins are made
• these proteins modify the cell
• they determine cell processes and structure

Question 20

what is transcription controlled by

Answer 20

transcription factors

Question 21

how do activator transcription factors work

Answer 21

• in eukaryotes, transcription factors move from the cytoplasm to the nucleus
• in the nucelus they bind to specific DNA sites near the start of their target genes - the genes they control the expression of
• some transcription factors called activators stimulate or increase the transcription, e.g. help RNA polymerase bind to the start of the target genes

Question 22

how do repressor transcription factors work

Answer 22

• decrease the rate of transription
• they bind to the start of the target gene
• preventing RNA polymerase from binding, stopping transcription

Question 23

how does oestrogen initiate transcription of a target cell

Answer 23

• oestrogen is a steroid hormone that binds to a oestrogen receptor forming an oestrogen-oestrogen receptor complex
• the complex moves from the cytoplasm into the nucleus where it binds to specific DNA sites near the start of the target gene
• the complex can act as an activator of transcription

Question 24

what is RNA interference

Answer 24

• inhibits the translation of mRNA
• Molecules involved are called siRNA (small interfering RNA) and miRNA (microRNA)

Question 25

what is the epigenome

Answer 25

* histones are covered in chemical 'tags' * tags are the epigenome * they determine the shape of the histone-DNA complex

Question 26

what is epigenetics

Answer 26

* heritable changes in gene funcion * without changes to the base sequence of DNA * these changes are caused by changes in the environment that inhibit transcription

Question 27

what do histones do

Answer 27

help the DNA condense into chromatids

Question 28

what is one way of epigenetic control with methyl

Answer 28

* increased mathylation of DNA * a methyl group is attched to the DNA coding for a gene * the group always attaches where the cytosine and gumanine are next to each other * increased methylation changes the DNA structure so the histones wrap tightly around tha DNA * RNA polymerase cannot bind to the promoter for transcription

Question 29

what is one method of epigenetic control with acetyl

Answer 29

* decreased acetylation of histones * when an acetyl group is removed there is an increased positive charge on the histones * this makes them more strongly atatched to the phosphate in the DNA nucleotide * increases DNA and histine attraction * RNA polymerase cannot bind to the promoter * transcription cannot occur

Question 30

how could drugs be used to treat disease caused by epigenetics

Answer 30

* changes are reversible, making thwm a good target for new drugs * these drugs counteract the changes causes by the disease * e.g. a drug to stop DNA methylation * **problems** - changes take place in alot of cells so drugs need to be specific

Question 31

what is a tumour

Answer 31

* a mass of abnormal cells due to uncontrollable cell division

Question 32

what are malignant tumours

Answer 32

* cancerous * grow rapidly and invade and destroy surrounding tissues * cells can break off and spread to other parts of the body in the blood stream or lymphatic system

Question 33

what are benign tumours

Answer 33

* not cancerous * grow slower then malignant tumours and are often covered in fibrous tissue that stops them from invading other tissues * can cause blockages and put pressure on organs * can become malignant

Question 34

what are the 2 types of genes that control cell division

Answer 34

* proto oncogens * tumour supressors

Question 35

what happens if tumour suppressors are inactive

Answer 35

* proteins involved in cell death are not produced * causes uncontrolled cell division * resulting in a tumour

Question 36

what happens if proto oncogens are increased

Answer 36

* the gene will become over active * producting more proteins to make cells divide * causes uncontrollable cell division * resulting in a tumour

Question 37

how are tumour cells different to normal cells

Answer 37

* irregular shape * dont produce all proteins needed * different antigens * divide more frequently

Question 38

how does abnormal methylation of tumour supressors cause tumour growth

Answer 38

* when a tumour suppressor gene is methylated too much the histones wrap tighly around it so RNA polymerase cannot bind to the promoter so the gene is not transcribed * it cannot produce its proteins which means less cell death * more uncontrollable cell division

Question 39

how does decrease methylation of proto oncogens cause tumours

Answer 39

* increases production of protein which encourages cell division * uncontrollable cell division

Question 40

how does increased oestrogen contribute to breast cancer

Answer 40

* The cancer cells within the tumours have oestrogen receptors * oestrogen binds to the receptors * the complex moves from the cytoplasm to the nucleus and binds to the promoter of the gene * the gene is transcribed