topic 8: control of gene expression

Question 1

why does each type of antibody bind to specific to one protein

Answer 1

sepcific teritary structure
affects variable region
only binds to complementary protein

Question 2

suggest how a mutation can lead to the production of a protein that has 1 amino acid missing

Answer 2

loss of 3 bases (Triplet)

Question 3

suggest how the spread of mutation may have occured

Answer 3

reproduction of individuals between different populations (interbreeding)

Question 4

gene mutation

Answer 4

-gene mutation = change in base sequence of DNA which results in the formation of a new allele

Question 5

causes of gene mutation

Answer 5

-causes of genetic mutation = ionising radiation, spontaneous erroes during interphase, mutagenic agents

-some mutations occur in introns (non-coding) and DNA is degenerate

Question 6

frame shift

Answer 6

-change in hydrogen bonds in secondary structure

-change in ionic bonds between R groups in teritary structure

-protein no longer functions

Question 7

explain why addition mutation can lead to the production of a non-functional protein

Answer 7

-addition mutation = addition of base in sequence of DNA = change in codons downstream

-no longer code for the same amino acid due to frame shift

-change in ionic bondig in teritary structure

-protein is no longer complementary

Question 8

inheret mutations

Answer 8

Gene mutations in body cells can disrupt normal functions like cell division potentially causing cancer

Mutations in gametes can be inherited by offspring

Question 9

effects of subsitution mutations

Answer 9

-occur when one DNA base is rplaced by another within the genetic sequence

-can create one of three stop codons = terminates polypeptide synthsis = non-functional protein

-may create a codon for a different amino acid = change in shape and function

-create condon for same amino acid = degenerate nature of the genetic code

Question 10

inversion mutation

Answer 10

-inversions = a segement of DNA becomes detached and then reattaches in the opposite direction, inverting sequence of codons and amino acid sequence

Question 11

duplication mutation

Answer 11

-duplications = when one or more DNA bases is repeated altering the reading frame of codons causing frame shift to the right

Question 12

translocation mutation

Answer 12

-translocations = segment of DNA is moved from one chromosome to another = lead to cancer and significant changes in the phenotype

Question 13

addition mutation

Answer 13

-addition = extra base inserted in DNA sequence = frame shift to right not the left

Question 14

transcription factors

Answer 14

Transcription factors can stimulate or inhibit the transcription of particular genes 

Transcription factors bind to DNA as they have binding sites complementary to the base sequence in DNA

Trascription factors can be used to turn unipotent cells into induced pluripotent cells

Question 15

epigenetics

Answer 15

-it is possible for peoples DNA to be 100% accurate but different genes can be activated

-inside the nucelus DNA is wrapped around proteins called histones

-less histone proteins = greatest number of active genes (more loosely packed)

-tightly packed arrangement of histones makes it less likely for transcription to take place as it is harder for trasncrption factors and RNA polmyerase to reach

-gene experession is determined by the shape of DNA-histone complexes

-chemical tags on the complex are known as epigenome

=how can the epigneome be changed = diet, stress, smoking etc

Question 16

acetylation of histones

Answer 16

-acetyl group = O=C-CH3

-acetylation of histones determines the trasncription of genes

-increase in acetylation = transcription is stimulated = DNA histone complex loosens

-DNA = negative charge phosphate group

-Histones = positive R group

-acetyl groups bind to R group in histones and when they bind they remove the positive charge = reduces attraction between phosphate backbone and DNA, loosening from the histone

Question 17

methylation of DNA

Answer 17

-increase in methylation inhibitis transcription = causes DNA histone complex to tighten

-methyl group binds to DNA (specifically cytoseine)

-First, the methyl groups attract proteins that encourage the DNA-histone complex to become more tightly packed. This prevents genes from being accessible, inhibiting transcription.

For example, we’ve seen that when acetylation decreases, the DNA-histone complex tightens. Methyl groups attract proteins which remove acetyl groups from the complex, thereby causing it to become more tightly packed.

Question 18

define epigenetics

Answer 18

Epigenetics = heritable changes in gene function without changes to the base sequence of DNA

Question 19

treatments with epigenetics

Answer 19

Uncontrolled cell growth = development of tumor cells

Trasncription of gene that controls cell growth may be inhibited due to increased methylation

Treating diseases using epigenetics:

-create drug that affects enzymes involved in methylation or acetylation

Question 20

adult vs embryonic stem cells

Answer 20

-adult stem cells are multipotent (capable of becoming more than 1 type of specialised cell) whereas embryonic stem cells are pluripotent (capable of becoming almost any type of specialised cells)

-adult stem cells are found in bone marrow while embryonic stem cells are found in human embryos

-embryos are discarded after 4-5 days and come with ethical implications

-adult stem cells have a more limited potency

Question 21

why not all cells need to be tonipotent

Answer 21

-totipotent stem cells are entirely capable to becoming any type of specialised cell

-not all cells need to be totipotent because their location means they only need to be able to produce specific specialised cells

-g stem cells in the bone marrow need to be able to differentiate into white and red blood cells

Question 22

A skin cell can produce the protein keratin but not myosin. Why?

Answer 22

-all cells in our body contain the same set of genes

-however there are different due to different proteins being made and the activation of different genes

-certain genes will be activated while others not related to the function will remain inactive

-only activated genes are transcribed into mRNA which is translated into proteins

Question 23

stem cells

Answer 23

-Stem cells = undifferentiated cells of an organism that become specialised. Used for growth, development and tissue repair

The more a stem cell can differentiate, the greater its potency

Question 24

types of stem cells

Answer 24

-multi = more than one (capable of becoming more than one specialised cell e.g blood cells)

-pluri = entirely capable of becoming almost any type of specialised cell e.g umbillical cord

-uni = capable of becoming one type of specialised cell e.g cardiomyocytes

-toti = capable of becoming any type of cell e.g embyronic stem cell

Question 25

stem cells in medicine

Answer 25

-stem cell transplants are given to patients with leukaemia (a type of cancer which destroys stem cells)

-stem cells can be used for testing the toxicity and side effects of drugs before human testing

-stem cells can be used for studying the development of organisms and identifyin the causes of a disorder

Question 26

induced pluripotent stem cells

Answer 26

-body cells are genetically altered in a lab to make them acquire the characteristics of embryonic stem cells

Unipotent body cell is obtained

The cell is reprogrammed to become pluripotent

Selected genes are induced to switch on

The cells are capable of dividng indefinetly

Question 27

advantages of IPS

Answer 27

-self-renew imdeifently

-differentiate into various cell types

-avoid ethical issues associated with the use of embyronic stem cells

-could provide an ulimited source of stem cells

Question 28

growth of plant tissue cultures

Answer 28

-plants have totipotent cells in the meritsem tissue found in the tips of roots and shoots

-new cells added to the tips of shoots allows it to grow in specific directions this mans that it can grown in certain conditions

Question 29

transcription factors

Answer 29

-transcription factors = proteins that regulate the transcription of genes. They bind to a specific sequence of DNA on promoter region which is upstream of the coding region to be transcribed

-RNA polymerase will detach at the terminator region. None of this can occur without transcription factors

Question 30

stimulation and inhibtiion

Answer 30

-In eukaryotes, transcription of target genes can be stimulated or inhibited when specific transcriptonal factors move from the cytoplasm into the nucelus through nuclear pores

Question 31

action of transcription factors

Answer 31

-Transcription factors bind to complementary sequence of DNA on a promoter region which is upstream of the coding region to be transcribed

-RNA polymerase allows for the synthesis of an mRNA strand and detaches at the terminator region

-the transcription of target genes can be stimulated or inhibited when specific transcriptional factors move from the cytoplasm to the nucleus

-Transcription factors need to be a specific shape, to be complementary to the DNA base nuelotide and bind to the promoter region

Question 32

activated

Answer 32

-hormones like oestrogen act as transcription factors to increase the rate of transcription

-transcription factor binds to promoter region upstream of DNA

Question 33

inactivated

Answer 33

-inactive genes = not expressed

-when a gene is switched of, transcription factors bind to DNA

-prevent transcription process = no synthesis of polypeptides

Question 34

process of transcription

Answer 34

-DNA helicase unwinds the DNA at the target gene by hydrolysing hydrogen bonds complementary base pairs

-free nucelotides bind to the exposed bases on the template strand through complementary base pairing

-adenine and uracil / cyosteine and guanine

-uracil replaced thymine

-RNA polymerase catalyses condensation reaction = formation of phosphodietser bonds between adjacent nucelotides synthesising the sugar-phosphate backbone

-pre-mRNA is then spliced to remove introns before leaving the nuclear pore

Question 35

role of oestrogen

Answer 35

-while oestrogen is best known for their effects on female reproduction, these steroid hormones also have important physiological functions e.g cardiovascular system, immune system etc

-the biological actions of oestrogen are only found in cells expressing oestrogen receptors = depends on the interactons of these receptors with several differennt proteins

-oestrogen receptors act as transcription factors, either activating or inhibiting the expression of a wide array of genes, recptor alpha / receptor b

Question 36

how oestrogen activates DNA transcription

Answer 36

1) oestrogen enters the cell

2) oestrogen then binds with a site on the transcription factors. By binding oestrogen changes the shape of the DNA binding site on the transcription factor by making it complementary to the promoter region of DNA

3) the transcription factor is now able to enter the nucelus and bind to a specific base sequence of DNA

4) the presence of the transcription factor allows RNA polymerase to bind to the DNA

5) transcription of the target gene can now take place

Question 37

oestrogen = lipid soluble

Answer 37

Hormones like oestrogen can switch on a gene and thus start transcription by combining with a receptor site on the transcriptional factor. This activates the DNA binding site by causing it to change

Shape.

Oestrogen = lipid soluble molecule so diffuses easily through phospholipid membrane