Chapter 20 Flashcards
(68 cards)
1
Q
Explain what a substitution mutation is
A
a mutation in which a nucleotide in a section of the DNA molecule is replaced by another nucleotide that has a different base
2
Q
What are the possible outcomes of a substitution mutation
A
- the formation of a stop codon which would prevent the protein from carrying out its normal function
- the formation of a codon for a different amino acid which would change the structure and therefore function of polypeptide
- the formation of a different codon but one that produces a codon for the same amino acid as the genetic code is degenerate
3
Q
Explain what a deletion mutation is
A
the loss of a nucleotide base from a DNA sequence
4
Q
What is the consequence of a deletion mutation
A
a frame shift as DNA is read in triplets so the letters are shifted to be read in triplets
- the gene is now read wrong and the amino acids coded for will be different changing the teritiary structure of the polypeptide therefore producing a non-functional protein
5
Q
What is an addition of bases gene mutation
A
when an extra base becomes inserted in the DNA sequence
has similar effects to a deletion mutation
6
Q
What is a duplication of bases mutation
A
one or more bases are repeated
produces a frame shift to the right
7
Q
What is an inversion of bases mutation
A
a group of bases become separated from the DNA sequence and rejoin at the same position but in the inverse order
- effects what amino acids are produced
8
Q
What is a translocation of bases gene mutation
A
- a group of bases becom seperated from the DNA sequence on one chromosome and become inserted into the DNA sequence of another chromosome
- can lead to an abnormal phenotype
9
Q
What are mutagenic agents
A
any agent that induces a mutation
10
Q
What are some examples of a mutagenic agent
A
- High energy ionising radiation
- chemicals
11
Q
What are some benefits of mutations
A
- produce genetic diversity necessary for natural selection and speciation
12
Q
What are some negatives of mutations
A
- can produce harmful effects that produce an organism that is less suited to the environment
- cause cell division causing cancer
13
Q
What are totipotent stem cells
A
- found in early embryo (total potential)
- able to become any cells
- specialise into pluripotent stem cells
14
Q
What are pluripotent stem cells
A
- differentiate into any body cell - found in blastocysts
15
Q
What are multipotent stem cells
A
found in adults - differentiate into a limited number of stem cells e.g. bone marrow stem cells
16
Q
What are unipotent stem cells
A
differentiate into 1 type of cell - made in adult tissue - derived from multipotent
17
Q
What are embryonic stem cells
A
embryos in early development - able to differentiate into any cells
18
Q
What are umbilical cord stem cells
A
- derived from blood - multipotent stem cells
19
Q
What are placental stem cells
A
- develop into specific cell types
20
Q
What are adult stem cells
A
- found in body tissue - multipotent
21
Q
What are the 3 general properties of stem cells
A
- they can divide + renew themeselves over a long period of time
- they are unspecialised
- they can differentiate into other specialised cell types
22
Q
What are induced pluripotent stem cells
A
- a type of pluripotent stem cell that can be produced from almost any adult unipotent somatic cells
- these cells are genetically altered in a lab to make them acquire the characteristics of embryonic stem cells
23
Q
How are induced pluripotent stem cells produced
A
- they are genetically altered in a lab
- this involves inducing genes + using ‘appropriate protein transcription factors’ - genes that are switched on (expressed) are switched off
24
Q
Ethics of stem cell research
A
- embryos are potential human life
25
Give some uses of stem cells in medicine
- bone marrow transplants - already widely used
- drug research - grow artificial tissues + test using these tissues before human testing
- developmental biology - insight into embryonic development
- replacement of lost or damaged tissues
26
What are the basics of gene expression
- genes encode proteins
- genes expressed in a particular cell determine what a cell can do
- protein production begins with transcription and then translation - control of these determine what proteins are present in a cell
27
How is gene expression controlled
- through transcription
- pre-mRNA splicing
- translation
28
What are transcription factors
proteins that control transcription + when transcription occurs
29
How do transcription factors work
- they move from the cytoplasm to the nucleus and bind to specific DNA sequences called promoter
30
What are activators (TF)
- increase the rate of transcription
- aid the binding of RNA polymerase to the start of the gene and activate transcription
31
What are repressors (TF)
- inhibit the rate of transcription
- bind to the start of the target genes preventing RNA polymerase from binding and stopping transcription
32
Describe the process of transcriptional control
- for transcription to begin the gene is expressed by transcription factors (TF) that move into the nucleus
- each TF binds to a specific sequence of DNA in the promoter region
- when it binds, it causes this region of DNA to begin the process of transcription
- mRNA is produced and is translated into a polypeptide
- when the gene isn't expressed the TF that binds to the DNA isn't active
- as the site is inactive it can no longer bind to the DNA and transcription doesn't occur
33
Explain what transcription factors are
transcription factors are specific protein complexes with different subunits that diffuse from the cytoplasm into the nucleus and bind with the DNA to switch on specific genes
34
What is the role of oestrogen in controlling transcription
- transcription can be controlled by molecules in the cell such as oestrogen
- it affects transcription by binding to a TF allowing it to pass through into the nucleus and promote transcription
- the TF-oestrogen complex can act as an activator of transcription
35
How do inhibitor molecules work
- inhibitor molecules block the DNA binding sites on the TF
- prevents the TF binding to the DNA
- prevents transcription from occurring
36
Describe the process of the effect of oestrogen on gene transcription
- oestrogen is a lipid-soluble molecule and therefore diffuses easily through the phospholipid bilayer
- once inside the cytoplasm of the cell, oestrogen binds with a site on a receptor of the TF -they are complimentary
- by binding the oestrogen changes the shape of the DNA binding site on the TF which can now bind to the DNA
- the TF can now enter the nucleus through a nuclear pore and bind to specific base sequences on DNA
- the combination of the TF with DNA stimulates transcription of the gene that makes up the portion of DNA
37
How can gene expression be regulated after transcription
- alternative splicing - produces different mRNA + proteins
- mRNA chopped = NO transcription
- regulating protein activity = remove amino acids or functional groups
38
How can gene expression be regulated at the level of translation
- RNA interference (RNAi)
39
What is RNAi
- RNAi is where small dsRNA molecules stop mRNA being translated into the target protein
- molecules involved are siRNA + microRNA
40
How does RNAi work
- transcription and splicing have occurred
- mRNA leaves the nucleus to associate with the nucleus to associate with the ribosomes for translation
- however, siRNA molecules bind with the mRNA and proteins associated with the siRNA chop it up preventing the mRNA fragments from being translated
- although it affects a different part in the process the outcome is not the same - the protein isn't produced
41
Describe the process of siRNA
- large dsRNA molecules are cut into double-stranded siRNA by enzyme dicer via hydrolysis
- the siRNA is unwound/split into single-stranded molecules
- one siRNA strand associates with an enzyme
- the siRNA guides the enzyme to one type of mRNA molecule by pairing up its bases with the complementary ones on a section of the mRNA molecule
- once in place, the enzyme 'cuts' the mRNA into small sections
- this renders the mRNA useless so translation cannot occur and the protein isn't produces
42
What are microRNAs (miRNA)
- non-coding RNA sequences that regulate gene expression
43
Where do miRNAs come from
- many miRNAs reside in introns
- when transcribed it exists as long, folded double strands known as hairpin loops
- then processed into single strands
- one strand associates with proteins and binds to target mRNA
44
How do miRNAs affect transcription
- miRNAs aren't totally complementary so it is less specific than siRNA
- one strand of the miRNA associates with proteins
- Binds to mRNA in the cytoplasm
- doesn't cut the mRNA but blocks the translation - the blocked mRNA can be degraded
45
Epigenetics
- process where environmental factors can cause heritable changes in gene function without changing the DNA base sequence
46
How does epigenetics work
- alterations to the genome by adding chemical tags that changes the shape of DNA through:
- methylation of the DNA
- acetylation of histones
47
What is chromatin
- when DNA is loosely packed/less condensed
48
What is heterochromatin
- when DNA is tightly packed/condensed
49
Epigenome
- a layer of chemical tags over the DNA
- flexible = can add or remove tags
50
Deacetylated histone
- heterochromatin
- gene is tightly coiled around the histone therefore its inaccessible
51
Acetylated histone
- chromatin
- as acetyl is negatively charged and DNA is negatively charged so they repel each other
52
How does methylation affect the genome
- methyl groups are added directly to the DNA
- methyl is positively charged and DNA is negatively charged so they attracted
53
What happens when methyl groups are attached
- DNA condenses
- not accessible to the TF
- gene isn't expressed as ther is no transcription
54
How is increased methylation of DNA carried out
- preventing binding of TF to the promoter region
- attracting proteins that condense the DNA - histone complex (induces deacetylation)
55
What happens when a gene is silenced
- increased methylation
- decreased acetylation
56
What happens when a gene is expressed
- decreased methylation
- increased acetylation
57
What is cancer
- a group of diseases caused by damage to genes that regulate mitosis and the cell cycle - this causes uncontrollable cell division that can lead to development of a tumour
58
What genes play a role in cancer development
- oncogenes
- tumour suppressor genes
59
What are the features of a malignant tumour
- can grow to a large size
- grow rapidly
- cell nucleus is often larger and appears darker due to an abundance of DNA
- cells becomes de-differentiated
- cells do not produce adhesions so they tend to spread to other regions of the body a process called metastasis (secondary tumours)
- tumours are not surrounded by a capsule and so they grow finger-like projections into the surrounding tissue
- more likely to be life-threatening
- have systemic effects
- removal involves chemo/radiation and surgery
- more frequently reoccur
60
What are the features of benign
- can grow to a large size
- grow very slowly
- the cell nucleus has a relatively normal apperance
- cells are often well differentiated
- cells produce adhesion molecules so they stick together and so they remain within the tissue = primary tumours
- tumours are surrounded by a capsule of dense tissue and so remain as a compact structure
- much less likely to be life-threatening
- tend to have localised effects on the body
- can usually be removed by surgery alone
- rarely reoccur
61
Describe the process of tumour development
- early tumour
- enlarging tumour developing blood and lymphatic vessels
- circulating tumour cells
- tumour cells adhere to blood vessel walls and squeeze through to form distant metastases
- metastasis in lymph node
62
What can tumours be caused by
- abnormal methylation of tumour suppressor genes/oncogenes
- increased oestrogen concentration
63
What are tumour suppressor genes functions
- maintains normal rates of cell division - slows it down to repair errors b telling cells when to apoptose (die)
64
What do proto-oncogenes do
- stimulate a cell to divide when growth factors attach to a protein receptor on its cell-surface membrane
- this activates genes that cause DNA to replicate and the cell to divide
65
How do proto-oncogenes become permanently switched on
- if it mutates into an oncogene it can become permanently activated
66
What are the reasons behind oncogenes forming
- the receptor protein on the cell-surface membrane can be permanently activated so that cell division is switched on even in the absence of growth factors
- the oncogenes may code for a growth factor that is then produced in excessive amounts, again stimulating excessive cell division
67
What are the 2 ways an oncogene can act
- a receptor protein on the cell- surface mem - cell division is switched on without growth factors
- produce a growth factor in excessive amount
68
How does oestrogen effect tumour development
- post-menopausal women have an increased risk of breast cancer as they have increased levels of oestrogen being produced in fat cells of the breast tissue
- this has a knock on effect as breast tumours result in the production of more oestrogen as do white blood cells
