Gene Expression

Question 1

define stem cell

Answer 1

undifferentiated cells that continually divide and become specialised

Question 2

different types of stem cells

Answer 2

totipotent-can divide and produce any type of body cell, they occur only for a limited time in early mammalian embryos.

pluripotent-found in embryos (from the inner mass of a blastocyst), can differentiate into any type of cell excluding placenta and embryo.

multipotent- can only differentiate into a limited number of cells, found in mature mammals e.g in bone marrow + only differentiates to different blood cells

unipotent- can only differentiate to form one type of cell, lots of genes are switched off by regulation of transcription factors, found in mature mammals.

Question 3

uses of embryonic stem cells- pluripotent + its benefits

Answer 3

due to their potency, they can be used to research using them to treat human disorders by growing new organs and tissues e.g Parkinson’s disease or spinal cord injuries.
-this saves or improves quality of life for many people, reduces the need for organ donation

Question 4

issues with using embryonic stem cells

Answer 4

-sometimes the treatment doesn’t work, or the stem cells continually divide to create tumours.
-ethical issues: whether it is right to make a therapeutic clone of yourself to get stem cells from embryo then destroy it
fertilised egg- embryo is a potential life being destroyed

Question 5

sources of stem cells

Answer 5

-embryos: contain stem cells that are pluripotent
-umbilical cord blood: contains stem cells that are multipotent
-placenta: multipotent stem cells
-adult stem cells: multipotent, produce different stem cells to repair those within a particular tissue or organ

Question 6

what happens to totipotent cells during embryonic development

Answer 6

certain parts of the DNA are selectively translated so that only some genes are “switched on”,in order to differentiate the cell into a specific type and form the tissues that make up the foetus.

Question 7

unipotent stem cells with example

Answer 7

-a cell that only develops into one type of cell
-happens at the end of specialisation, when the cell can only propagate its own type
-e.g. cardiomyocytes can divide to form other heart muscle cells

Question 8

uses of stem cells

Answer 8

-medical therapies e.g bone marrow transplants, treating blood disorders
-drug testing on artificially grown tissues
-research e.g. the formation of organs and embryos

Question 9

what are induced pluripotent stem cells (iPS cells)

Answer 9

prouced from mature, fully specialised (somatic) adult cells using appropriate protein transcription factors to overcome some of the ethical issues regarding use of embryonic stem cells.
-have pluripotent state that enables the devlelopment of an unlimited source of any type of human cell needed for therapeutic purposes.

Question 10

how are iPS cells produced

Answer 10

-created from adult unipotent cells, which are altered in a lab to return them to state of pluripotency.
-to do this genes that were switched off to make the cell specialised are switched back on by transcriptional factors
-very similiar to pluripotent embryonic stem cells, but does not cause the destruction of an embryo & the adult can giver permission

Question 11

transcription factor

Answer 11

protein that controls the transcription of the gene so that only certain parts of the DNA are expressed -> in order to allow a cell to specialise.

Question 12

difference between activator and repressor

Answer 12

activator-a transcription factor that increases rate of transcription.
repressor- a transcription factor that decreases the rate of trancription.

Question 13

how do transcription factors work

Answer 13

-moves from the cytoplasm into the nucleus
-it binds to the promoter region upstream of target gene
-this makes it easier or more difficult for RNA polymerase to bind to gene. This increases or decreases rate of transcription.

Question 14

role of oestrogen

Answer 14

-oestrogen is a steroid hormone that can initiate transcription
-it diffuses through cell membrane
-it binds to receptor site on transcriptional factor
-when it binds to the transcriptional factor it causes it to change shape slightly
-this change in shape makes it complementary and bind to the DNA to initiate transcription.

Question 15

epigenetics

Answer 15

the heritable change in gene function, without changing the DNA base sequence.

-caused by changes in environment and can inhibit transcription.

Question 16

environmental factors that can affect epigenetics

Answer 16

factors such as diet, stress and toxins can add epigentic (chemical tags) to the DNA and this can control gene expression.

Question 17

epigenome

Answer 17

the single layer of chemical tags on the histone proteins which are associated with DNA
-these determine the shape of the histone-DNA complex and whether the DNA is tightly wound or unwound->help control the transcription of genes
-if DNA is tightly wound, transcription factors cannot bind, therefore the epigenome, due to changes in environment, can inhibit transcription.

Question 18

2 ways epigenetics can control gene expression

Answer 18

-increasing methylation of DNA
-acetylation of histones

Question 19

how does increased methylation of DNA affect gene transcription

Answer 19

-involves adding methyl (CH3) to cytosine bases on DNA using DNA methyl transferase enzymes.
-this alters the DNA structure-condenses the DNA-histone complex, preventing transcriptional factors from binding to it
-gene transcription is inhibited

Question 20

how does increased acetylation of histones affect gene transcription

Answer 20

-negatively charged acetyl groups repel each other, the DNA loosens from the histones making it less condensed-> makes it more accessible for transcriptional factors to bind.

Question 21

how does decreased acetylation of histones affect gene transcription

Answer 21

-decreased acetylation of associated histones on DNA inhibits transcription.->increases the positive charge of histones, so attracted to more phosphate groups on DNA.
-binding becomes too tight and prevents transcription factors from accessing the DNA.
-gene transcription is suppressed.

Question 22

how can epigenetics cause disease

Answer 22

-by overactivating a gene’s function (such as in cancer) or by suppressing it.

Question 23

application of epigenetics

Answer 23

-used for treatment of various diseases
-development of ways to reverse epigenetic changes

Question 24

role of tumour suppressor genes + how it can lead to cancer

Answer 24

-these genes code for proteins that slow down cell division, repair DNA mistakes and cause cell death-apoptosis-if DNA copying errors are detected.
-if a mutation occurs, or due to epigenetics and results in tumour suppressor gene not producing the proteins to carry out this function-cells can grow out of control, mutated cells would not be identified and destroyed which can lead to cancer

Question 25

abnormal methylation

Answer 25

-abnormal methylation of proto-oncogenes and tumour suppressor genes can cause abnormal cell growth and cancers develop:
-hypermethylation of tumour suppressor genes->increased number of methyl groups attached to it, resulting in gene being inactivated and becomes turned off-can cause cells to divide uncontrollably by mitosis and form tumours
-hypomethylation of proto-oncogenes->reduces the number of methyl groups attached, causing them to be permanently switched on-producing proteins that encourage cell division

Question 26

RNA interferance (RNAi)

Answer 26

-small lengths of non-coding RNA, regulate gene expression by affecting translation, prevents mRNA that has already been transcribed from being translated into a protein.
-occurs in eukaryotes and some prokaryotes.

Question 27

two types of RNAi

Answer 27

-short interfering RNA (siRNA): in animals only
-micro RNA (miRNA): in plants and animals

Question 28

process of RNAi

Answer 28

-an enzyme is used to unwind the double stranded siRNA in cytoplasm
-one of the siRNA strands is used, while other degrades (breaks down).
-the siRNA combines with an enzyme->siRNA-enzyme complex
-the siRNA-enzyme complex binds to target mRNA (as it is complementary to the ase sequence in a section).
-the enzyme with siRNA cuts the mRNA into small fragments- so it can no longer be translated

Question 29

cancer

Answer 29

the result of mutations in genes that regulate mitosis
if these genes mutate and non-functioning proteins are made then mitosis is not regulated-resulting in the uncontrollable cell division of cells and creation of tumour.

Question 30

benign tumours

Answer 30

-slow growth
-non cancerous-> defined by a clear boundary due to cell adhesion ( sticking them together)
-cells retain function and normal shape
-don’t spread easily
-easy to treat
-often not life-threatening, depending on tumour location e.g. in brain-alot harder to remove without damaging brain tissue

Question 31

malignant tumour

Answer 31

-rapid, uncontrollable cell division
-cell nucleus becomes large, cell can become unspecialised again
-don’t produce adhesive, metastasis occurs-> spreads quickly and easily
-finger-like projections into surrounding tissue and develop its own blood supply
-can be life-threatening: much harder to remove tumours, recurrance is more likely

Question 32

role of proto-oncogenes + how it can lead to cancer

Answer 32

-proto-oncogenes code for proteins involved in initiation of DNA replication and mitosis cell division when the body needs new cells.
-mutation can occur- producing mutated version-> oncogene: become permanently activated, cells grow out of control, dividing continually leading to formation of tumours

Question 33

how can oestrogen be involved in developing breast cancer

Answer 33

-increased oestrogen concentrations can lead to breast cancer as:
-post-menopause fat cells in breast tissue produce oestrogen instead of in ovaries
-with age, levels of oestrogen present in women’s breast increases
-this can stimulate more breast tissue cells to divide as oestrogen is an activator of RNA polymerase, increasing chance of mutation
-cancer cell replication could be further promoted by oestrogen causing faster tumour growth.