topic 8 - gene expression

Question 1

what is a gene mutation and how do they occur

Answer 1

• a gene mutation is the change in the DNA base sequence of a gene
  -they mainly occur during DNA replication
  -they occur spontaneously but the frequency can be increased by mutagenic agents

Question 2

what affect does mutation have no proteins

Answer 2

-a different order of DNA bases changes the amino acid sequence so there is a different primary structure
-this causes hydrogen and ionic bonds to form in different locations resulting in a different tertiary structure
-this different shape results in a different or non-functioning protein

Question 3

what is an addition and a deletion mutation and what impact does it have

Answer 3

-an addition mutation is when one extra base is added to the sequence
-a deletion mutation is the removal of one base from the sequence
-this causes a frame shift in the base triplets that follow
-this could result in a different polypeptide chain being produced which could form a non functioning protein

Question 4

what is a substitution mutation and what impact does it have

Answer 4

-one base is changed for a different base
-this results in only one codon changing
-due to the genetic code being degenerate the codon may still code for the same amino acids

Question 5

what is a duplication mutation and what impact does it have

Answer 5

-one particular base is duplicated at least once in the sequence
-this causes a frame shift and a different sequence of amino acids are coded for

Question 6

what is inversion mutation and what impact does it have

Answer 6

-a section of bases detaches from the dna sequence but when they rejoin they are inverted
-this results in different amino acids being coded for in that region

Question 7

what is translocation mutation and what impact does it have

Answer 7

-a section of bases on one chromosome detaches and attaches onto a different chromosome or a different place on that chromosome

Question 8

define stem cell

Answer 8

a stem cell is an undifferentiated cell that can continuously divide and become specialised

Question 9

explain how a stem cell specialises

Answer 9

-a stimulus causes selective activation of genes
-this means the mRNA is only transcribed from active genes and translated on ribosomes to form a protein
-these proteins modify the cell permanently as they determine its structure and function

Question 10

what are totipotent stem cells

Answer 10

-totipotent stem cells can mature to produce any type of body cells
-they occurs for a limited amount of time in mammalian embryos

Question 11

what are pluripotent stem cells

Answer 11

-they are found in embryos
-they are able to divide into almost all cells except placenta cells
-they can divide into unlimited numbers and are used to treat human disorders

Question 12

what are multipotent stem and unipotent stem cells

Answer 12

-multipotent and unipotent stem cells are found in mature mammals
-multipotent stem cells are able to differentiate into a few different types of cells like red and white blood cells are formed from multipotent cells in the bone marrow
-unipotent stem cells can only differentiate into one type of cell

Question 13

what are induced pluripotent stem cells

Answer 13

-induce pluripotent stem cells can be produced by programming a specialise adult body cell so they become pluripotent
-the adult cells are made to express a series of transcription factors that are normally associated with pluripotent stem cells
-the transcription factors cause the adult body cells to express genes that are associated with pluripotency
-they are useful in medical treatments as there is no immune rejection as they are made of the patient’s own cells and they overcome ethical issues with embryonic stem cells

Question 14

what are benign tumours

Answer 14

-they can grow very large but at a slow rate
-they are non-cancerous as they produce adhesive molecules which causes the cells to stick together to a particular tissue
-they are often surrounded by a capsule so they remain compact and can be removed via surgery
-the impact is often localised

Question 15

what are malignant tumours

Answer 15

-these grow very large and rapidly
-the cells become specialized
-they do not produce the adhesive so they metastasize and break off and spread around the body
-the tumour is not encapsulated so they grow projections and develop its own blood supply

Question 16

what are oncogenes and how do they cause cancer

Answer 16

-oncogenes are a mutated form of proto-oncogene
-proto-oncogenes creates a protein involved in the initiation of DNA replication and mitosis cell division
-oncogenes are permanently activated to stimulate the cells to divide uncontrollably resulting in a tumour

Question 17

what are tumour suppressor genes and how do they cause cancer

Answer 17

-tumour suppressor genes slow cell division by producing proteins that stop cells from dividing or causing them to self destruct
-if a mutation occurs in the DNA sequence of the tumour suppressor gene the protein is not produced
-this causes the cells to divide uncontrollably resulting in a tumour

Question 18

how does abnormal methylation result in cancer

Answer 18

-methylation means adding a methyl group onto something which could cause a gene to be turned off or on
-when tumour suppressor genes become hypermethylated this causes the gene to become inactive so the proteins that slow cell division are not made
-when proto oncogenes are hypomethylated this results in them acting like oncogenes

Question 19

what is a transcription factor

Answer 19

a protein that controls the transcription of genes by binding to a specific region of DNA

Question 20

explain how transcription factors work

Answer 20

-transcription factors are protein molecules
-the transcription factors move from the cytoplasm into the nucleus
-they bind to a specific DNA base on the promoter region of their target gene
-they stimulate or inhibit transcription of mRNA of the target gene by either helping or preventing the DNA polymerase binding

Question 21

explain the role of oestrogen in initiating transcription

Answer 21

-oestrogen is a steroid hormone that can diffuse across the lipid bilayer as it is lipid soluble
-in cytoplasm the oestrogen binds to a receptor on an inactive transcription factor to form a hormone receptor complex
-the inactive transcription factor changes shape which results in an active transcription factor
-the transcription factor diffuses from cytoplasm to nucleus
-it binds to a specific DNA base on the promoter region of the target gene
-it stimulate transcription of genes by helping RNA polymerase bind

Question 22

how does siRNA inhibit translation

Answer 22

-once mRNA has been transcribed it leaves the nucleus to the cytoplasm
-a single strand of siRNA binds to target mRNA containing a base sequence complimentary to its own
-the proteins associated with siRNA cut the mRNA intro fragment so translation is stopped
-

Question 23

how does miRNA inhibit translation

Answer 23

-it binds to a complimentary sequence on the mRNA
-it prevents attachment of mRNA to the ribosome
-so translation is stopped

Question 24

what is epigenetics

Answer 24

the heritable change in gene function without changing the DNA base sequence
these changes result from changes in the environment

Question 25

how does increased methylation affect transcription

Answer 25

-increase methylation of DNA inhibits transcription
-when methyl group groups are added to cytosine bases in DNA
-the nucleosomes pack more tightly together preventing transcription factors from binding so genes are not transcribed

Question 26

how does decreased acetylation affect transcription

Answer 26

-decreased acetylation inhibits transcription
- decreased acetylation of associated histones increases the positive charge of the histones
-the histones bind more tightly to the negatively charged DNA
-this prevents transcription