(20) Mutations and Gene Expressions

Question 1

define mutation

Answer 1

a change to the base (nucleotide) sequence of DNA

Question 2

what is a substitution mutation

Answer 2

one or more bases are swapped for another

Question 3

what is a deletion mutation

Answer 3

one or more bases are removed

Question 4

what is an addition mutation

Answer 4

one or more bases are added

Question 5

what is a duplication mutation

Answer 5

one or more bases are repeated

Question 6

what is an inversion mutation

Answer 6

a sequence of bases is reversed

Question 7

what is a translocation mutation

Answer 7

a sequence or bases is removed from one location in the genome to another (can be movement within the same chromosome or to a different chromosome)

Question 8

what are mutagenic agent s

Answer 8

increase the rate of dna being misread during replication eg UV radiation, ionising radiation, chemicals and some viruses

Question 9

what are the 2 types of genes that control cell division

Answer 9

photo oncogenes and tumour suppressor genes

Question 10

what do tumour suppressor genes do

Answer 10

slow cell division by producing proteins that stop cells dividing or cause them to self destruct (apoptosis)

Question 11

what happens if a mutation occurs in a tumour suppressor cells

Answer 11

the protein isn’t produced so the cells divide uncontrollably resulting in a tumour

Question 12

what do proto oncogenes do

Answer 12

stimulate cell division by producing proteins that make cells divide

Question 13

what happens if a mutation occurs in a proto oncogene

Answer 13

the gene can become overactive which stimulates the cells to divide uncontrollably resulting in a tumour

Question 14

what is a malignant tumour

Answer 14

cancer- grow rapidly and invade and destroy surrounding tissue. cells can break off and spread to other parts of the body in the bloodstream or lymphatic system

Question 15

what are benign tumours

Answer 15

not cancer- grow slower than malignant tumours and are often covered in fibrous tissue that stops cells invading other tissues. often harmless but can cause blockages and pressure on other organs

Question 16

how do tumour cells look and function differently to normal cells

Answer 16

1. irregular shape
2. nucleus is larger and darker than in normal cells
3. don’t produce proteins needed to function adequately
4. different surface antigens
5. don’t respond to growth regulating processes
6. divide by mitosis more frequently

Question 17

what is methylation of dna for

Answer 17

method of regulating gene expression- can control whether or not a gene is transcribed and translated

Question 18

what is abnormal methylation

Answer 18

hypermethylation- happens too much

hypomethylation- happens too little

Question 19

how can abnormal methylation cause cancer

Answer 19

tumour suppressor genes can be hypermethylated meaning genes aren’t transcribed and the proteins they produce to slow cell division aren’t made

proto-oncogenes can be hypomethylated and that increases the production of proteins that encourages cell division

Question 20

3 theories that suggest why increased exposure to oestrogen can increase the risk of breast cancer

Answer 20

1) can stimulate certain breast cells to divide which increases the chance of mutations
2) if cells then do become cancerous their replication could be further assisted by oestrogen
3) other research suggests oestrogen introduces mutations directly into the dna of certain breast cells

Question 21

what is a totipotent stem cell

Answer 21

stem cells that can mature into any type of body cell (only found in the first few divisions of an embryo)

Question 22

what are pluripotent stem cells

Answer 22

stem cells in an embryo that can still specialise into any body cell but lose the ability to become the stem cells that make up the placenta

Question 23

what are multipotent stem cells

Answer 23

able to differentiate into a few different types of cell eg both red and white blood cells can be formed from multipotent cells in bone marrow

Question 24

what are unipotent stem cells

Answer 24

can only differntiate into one type of cell

Question 25

how do stem cells become specialised

Answer 25

all stem cells contain the same genes but not all of them are expressed. under the right conditions, some are expressed.
mrna is only transcribed from specific genes which can be translated to proteins which determine the cell structure and processes. these changes are hard to reverse and so the cell stays specialised

Question 26

what are cardiomyocytes

Answer 26

heart muscle cells that make up a lot of the tissue in our hearts

Question 27

what is SCID (severe combined immunodeficiency)

Answer 27

a genetic disorder affecting the immune system- WBC’s are defective so they are ssuceptible to infection can be treated with a bone marrow transplant

Question 28

one pro and one con of adult stem cells from bone marrow

Answer 28

pro: can be obtained in a relatively simple operation with little risk
con: aren’t as flexible as embryonic stem cells (multipotent not pluripotent)

Question 29

pro and con of embryonic stem cells

Answer 29

pro: can divide an unlimited amount of times and develop into all body cells (pluripotent)
con: ethical issues of embryos and after 4-5 days the stem cells are removed and embryo destroyed

Question 30

what are induced pluripotent stem cells (iPS)

Answer 30

created by scientists in a lab and involves reprogramming specialised adult body cells to become pluripotent. the adult cells are made to express a series of transcription factors by infecting the adult body cells with a modified virus

Question 31

pros of iPS cells

Answer 31

potential to be as flexible as embryonic stem cells but obtained from adult tissue so less ethical issues
could be made from patients own cells so wouldn’t be rejected

Question 32

how are activators and repressors (both transccription factors) different

Answer 32

activators stimulate the rate of transcription (help RNA polymerase bind to the start of the target gene)
repressors inhibit the rate of transcription by binding to the target gene so rna polymerase can’t

Question 33

how does oestrogen initiate the transcription of target genes

Answer 33

binds to the transcription factor forming an oestrogen-oestrogen receptor complex, this moves from cytoplasm to nucleus where it binds to dna sites at the start of the target gene this helps rna bind to the target gene

Question 34

what is RNA interference (RNAi)

Answer 34

a small double stranded RNA stops mRNA from target genes being translated into protein.

Question 35

how do epigenetic marks affect eukaryotes

Answer 35

they determine whether a gene is switched on or off by attachment or removal of chemical groups (epigenetic marks) and these alter how easy it is for enzymes needed for transcription to interact with and transcribe dna

Question 36

how does increased methylation of dna switch a gene off

Answer 36

a methyl group attaches to the dna coding for a gene at a CpG site (cytosine, phosphodiester bond, guanine) and this changes the dna structure so the enzymes and proteins can’t interact with the gene and so it is not expressed

Question 37

how does decreased acetylation of histones switch genes off

Answer 37

when histones are acetylated the chromatin is less condensed so transcriptional machinery can access the dna but when acetyl groups are removed the chromatin becomes highly condensed so genes can’t be transcribed

Question 38

what is a framshift

Answer 38

when a base or multiple bases is inserted, removed or duplicated into the genome. means that triplet codes downstream from the mutation experience a mutation