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A Level Biology > Unit 8 > Flashcards

Unit 8 Flashcards

1
Q

Gene mutation

A

-A change in the base sequences of DNA (on chromosomes).
-Can arise spontaneously during DNA replication (interphase).

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2
Q

Mutagenic agent

A

A factor that increases rate of mutation.

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3
Q

How a gene mutation can lead to a non-functional protein?

A

-Changes sequence of base triplets in DNA so changes sequence of codons on mRNA.
-So changes sequence of amino acids in the encoded polypeptide.
-So changes position of hydrogen/ionic/disulphide bonds between amino acids.
-SO changes tertiary structure of protein.
-Enzymes- active site changes shape so substrate can no longer bind, enzyme- substrate complex can’t form.

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4
Q

Types of mutations

A

-Substitution
-Addition
-Deletion
-Duplication
-Inversion
-Translocation

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5
Q

Gene mutation- doesn’t affect the amino acids order

A

-Some substitutions change only 1 triplet code/codon which could still code for the same amino acid.
-Genetic code is degenerate.
-Some occur in introns which do not code for amino acids as they are removed during splicing.

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6
Q

Why a change in amino acid sequence isn’t always harmful?

A

-May not change tertiary structure of protein
-May positively change the properties of the protein, giving the organism a selective advantage.

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7
Q

Frameshift

A

-Occurs when mutations change the number of nucleotides/ bases by a number not divisible by 3.
-This shifts the way the genetic code is read, so all the DNA triplets/ mRNA codons downstream from the mutation change.

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8
Q

Mutations- shorter polypeptides

A

-Deletion or translocation- triplet missing so amino acids missing.
-Sub, add, deletion, duplication, inversion, translocation- premature stop triplet so amino acids missing at end of polypeptide.

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9
Q

Stem cells

A

Undifferentiated cells capable of:
-Dividing by mitosis to replace themselves indefinitely.
-Differentiating into other types of cells.

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10
Q

How are stem cells specialised?

A

-Stimuli lead to activation of some genes.
-So mRNA is transcribed only from these genes and then translated to form proteins.
-These proteins modify cells permanently and determine cell structure/function.

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11
Q

Totipotent cells

A

-Occur for a limited time in early mammalian embryos.
-Can divide and differentiate into any type of body cell.

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12
Q

Pluripotent

A

-Found in mammalian embryos.
-Can divide and differentiate into most cell types.

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13
Q

Multipotent

A

-Found in mature mammals
-Can divide and differentiate into a limited number of cell types.

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14
Q

Unipotent

A

-Found in mature mammals.
-Can divide and differentiate into just one cell type.
-Cardiomyotes.

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15
Q

Stem cells- treatment of human disorders

A

-Transplanted into patients to divide in unlimited numbers.
-Then differentiate into required healthy cells to replace damaged/ faulty cells.

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16
Q

Examples of stem cells for treatment

A

-Potential treatment of type 1 diabetes by creating healthy islet cells that produce insulin.
-Bone marrow stem cell transplant for sickle cell disease/ blood cancers.
-Destroy patients bone marrow before treatment- no faulty cells produced.
-Transplant stem cells from healthy person- divide and differentiate into healthy cells.

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17
Q

Induced pluripotent stem cells

A

-Obtain adult somatic cells (non-pluripotent or fibroblasts) from patient.
-Add specific protein transcription factors associated with pluripotency to cells so they express genes associated with pluripotency (reprogramming).
-Transcription factors attach to promoter regions of DNA, stimulating or inhibiting transcription.
-Culture cells to allow them to divide by mitosis.

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18
Q

Use of stem cells in treating human disorders

A

For
-Can divide and differentiate into required healthy cells, so could relieve human suffering by saving lives and improving quality of life.
-Embryos are often left over from IVF and would otherwise be destroyed.
-iPS cells unlikely to be rejected by patient’s immune system as made with patient’s own cells.
-iPS cells can be made without destruction of embryo and adult can give permission.
Against
-Ethical issues with embryonic stem cells as obtaining them requires destruction of an embryo and potential life- embryo can’t consent.
-Immune system could reject cells and immunosuppressant drugs are required.
-Cells could divide out of control leading to formation of tumours/ cancer.

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19
Q

Transcription factors

A

-Proteins which regulate transcription of specific target genes in eukaryotes.
-By binding to a specific DNA base sequence on a promoter region.

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20
Q

How transcription can be regulated by TF?

A

-TF moves from cytoplasm to nucleus.
-Bind to DNA at a specific DNA base sequence on a promoter region.
-Stimulates or inhibits transcription (production of mRNA) of target gene by helping or preventing RNA polymerase binding.

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21
Q

How oestrogen affects transcription

A

-Oestrogen is a lipid-soluble steroid hormone so diffuses into cell across phospholipid bilayer.
-In cytoplasm, oestrogen binds to its receptor, an inactive TF, forming an oestrogen-receptor complex.
-Changes shape of the inactive TF forming an active TF.
-The complex diffuses from cytoplasm into the nucleus.
-Binds to a specific DNA base sequence on the promoter region of the target gene.
-Stimulating transcription of target genes forming mRNA by helping RNA polymerase bind.

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22
Q

Why does oestrogen only affect target cells

A

Other cells do not have oestrogen receptors.

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23
Q

Epigenetics

A
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24
Q

Epigenome

A
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25
Epigenetic control of gene expression in eukaryotes
26
Methylation- inhibit transcription
27
Acetylation- inhibit transcription
28
Epigenetics- disease development and treatment
29
RNA interference (RNAi)
-Inhibition of translation of mRNA produced from target genes, by RNA molecules. -This inhibits expression of a target gene.
30
Regulation of translation by RNA interference
-Small interfering RNA (siRNA) or micro-RNA (miRNA) is incorporated into a protein, forming an RNA-induced silencing complex (RISC). -siRNA synthesised as double-stranded RNA- 1 strand incorporated. -miRNA synthesised as a double-stranded hairpin bend of RNA- both strands incorporated -Single stranded miRNA/ siRNA within RISC binds to target mRNA with a complementary base sequence. -This leads to hydrolysis of mRNA into fragments which are then degraded, prevents ribosomes binding. -Reducing/ preventing translation of target mRNA into protein.
31
How do tumours and cancers form?
-Mutations in DNA/ genes controlling mitosis can lead to uncontrolled cell division. -Tumour formed if this results in mass of abnormal cells. -Malignant tumour- cancerous, can spread of metastasis -Benign tumour- non-cancerous
32
Benign tumours
-Grow slowly. -Cells are well differentiated -Cells have normal, regular nuclei -Well defined borders and often surrounded by a capsule so do not invade surrounding tissue. -Do not spread by metastasis- cell adhesion molecules stick cells together. -Can normally be removed by surgery and they rarely return.
33
Malignant tumours
-Grow faster -Cells poorly differentiated -Cells have irregular, larger/ darker nuclei. -Poorly defined borders and not encapsulated so can invade surrounding tissues. -Spread by metastasis- cells break off and spread to other parts of the body- forms secondary tumours. -Can normally be removed by surgery combined with radiotherapy/ chemotherapy but often return.
34
Tumour suppressor genes
Code for proteins that: -Inhibit/ slow cell cycle. -Causes self-destruction (apoptosis) of potential tumour cells.
35
Role of tumour suppressor genes in development of tumours
-Mutation in DNA base sequence- production of non-functional protein. -By leading to change in amino acid sequence which changes protein tertiary structure. -Decreased histone acetyltion, increased DNA methylation- prevents production of protein. -By preventing binding of RNA polymerase to promoter region, inhibiting transcription. -Both lead to uncontrolled cell division- cell division cannot be slowed.
36
Proto-oncogenes
Code for proteins that stimulate cell division Oncogene is mutated proto-oncogene
37
Role of oncogenes in development of tumours
-Mutation in DNA base sequence- overproduction of protein or permanently activated protein. -By leading to change in amino acid sequence which changes protein tertiary structure. -Decreased DNA methylation or increased histone acetylation- increases production of protein. -By stimulating binding of RNA polymerase to promoter region, stimulating transcription. -Both lead to uncontrollable cell division- cell division cannot stop.
38
Why do tumours require mutations in both alleles of tumour suppressor gene but only one allele of an oncogene?
-One functional allele of a tumour suppressor gene can produce enough protein to slow the cell cycle or cause apoptosis of potential tumour cells- cell division is controlled. -One mutated oncogene allele can produce enough protein to lead to rapid/ uncontrolled cell division.
39
Epigenetics in cancer treatment
40
Role of increased oestrogen conc in development of some breast cancers.
-Some breast cancers have oestrogen receptors, which are inactive TF. -If oestrogen conc is increased, more oestrogen binds to oestrogen receptors forming O-R complexes which are active TF. -These bind to promoter regions of genes that code for proteins stimulating cell division. -This increases transcription/ expression of these genes, increasing rate of cell division.
41
Similar structure to oestrogen- treat oestrogen receptor-positive breast cancers
-Drugs bind to oestrogen receptors (inactive TF), preventing binding of oestrogen. -So no/ fewer TF bind to promoter region of genes that stimulate cell cycle.
42
Genome
Complete set of genes in a cell
43
Proteome
Full range of proteins that a cell can produce.
44
Genome sequencing
-Identifying the DNA base sequence of an organism's genome. -So amino acid squence of proteins that derive from an organism's genetic code can be dtermined.
45
How determining genome of pathogen allows vaccines to be developed?
-Could identify the pathogen's proteome. -Could identify potential antigens to use in the vaccine.
46
Application of genome sequencing
-Identification of genes/ alleles associated with genetic diseases/ cancers. -New targeted drugs/ gene therapy developed. -Screen patients, allowing early prevention/ personalised medicine. -Identification of species and evolutionary relationships.
47
Why can't genome be directly translated into proteome
-Presence of non-coding DNA. -Presence of regulatory genes.
48
How are sequencing methos changing?
-They have become automated. -They are continuously updated.
49
Recombinant DNA technology
Transfer of DNA fragments from one organism or species to another
50
Why transferred DNA can be translated within cells of recipient (transgenic) organism?
-Genetic code is universal -Transcription and translation mechanisms are universal
51
DNA fragments using restriction enzymes
-Restriction enzymes cut DNA at specific base 'recognition sequences' either side of the desired gene. -Shape of recognition site complementary to active site. -Many cut in staggered fashion forming 'sticky ends' (single stranded overhang).
52
DNA fragments from mRNA
-Isolate mRNA from a cell that readily synthesises the protein coded for by the desired gene. -Mix mRNA with DNA nucleotides and reverse transcriptase- reverse transcriptase uses mRNA as a template to synthesise a single strand of complementary DNA (cDNA). -DNA polymerase can form a second strand of DNA using cDNA as a template.
53
Advantages of obtaining genes from mRNA rather than directly form the DNA removed from cells
-Much more mRNA in cells making the protein than DNA- easily extracted -In mRNA, introns have been removed by splicing whereas DNA contains introns. -So can be transcribed and translated by prokaryotes who can't remove introns by splicing.
54
Fragments of DNA using a gene machine
-Synthesises fragments of DNA quickly and accurately from scratch without need for a DNA template. -Amino acid sequence of protein determined, allowing base sequence to be established. -These do not contain introns so can be transcribed and translated by prokaryotes.
55
In vitro to amplify DNA fragments
-Outside living organism -Polymerase Chain reaction- PCR
56
In vivo to amplify DNA fragments
-Inside living organism -Culturing transformed host cells
57
PCR
-Mixture heated to 95C. -This seperates DNA strands. -Breaking hydrogen bonds between bases. -Mixture cooled to 55C. -This allows primers to bind to DNA fragment template strand. -By forming hydrogen bonds between complementary bases. Mixture heated to 72C. -Nucleotides align next to complementary exposed bases. -DNA polymerase joins adjacent DNA nucleotides, forming phosphodiester bonds.
58
Role of primers in PCR
-Primers are short, single stranded DNA fragments. -Complementary to DNA base sequence at edges of region to be copied/ start of desired gene. -Allowing DNA polymerase to bind to start synthesis- can only add nucleotides onto pre-existing 3' end. -Two different primers (forward and reverse) are required as end bases are different.
59
Why does DNA replication eventually stop in PCR?
Limited number of primers and nucleotides which are eventually used up.
60
Amplifying DNA fragments in vivo
-Add promoter and terminator regions to DNA fragments. -Insert DNA fragments and marker genes into vector using restriction enzymes and ligases. -Transform host cells by inserting these vectors. -Detect genetically modified (GM)/ transformed cells/ organisms by identifying those containing the marker gene. -Culture these transformed host cells, allowing them to divide and form clones.
61
Why are promoter and terminator regions added to DNA fragments that are used for GM?
Promoter- allow transcription to start by allowing RNA polymerase to bind to DNA, can be selected to ensure gene expression happens only in specific cell types. Terminator- ensure transcription stops at end of a gene, by stopping RNA polymerase.
62
Role of vectors in recombinant DNA technology?
Transfer DNA into host cells/ organisms
63
Role of enzymes in inserting DNA fragments into vectors
-Restriction endonucleases/ enzymes cut vector DNA. -Same enzyme used that cut the gene out so vector DNA and fragments have 'sticky ends' that can join by complementary base pairing. -DNA ligase joins DNA fragment to vector DNA. -Forming phosphodiester bonds between adjacent nucleotides.
64
How host cells are transformed using vectors?
-Plasmids enter cells. -Viruses inject their DNA into cells which is then integrated into host DNA.
65
Explain why marker genes are inserted into vectors
-To allow detection of GM/ transgenic cells/ organisms. -If marker gene codes for antibiotic resistance, cells that survive antibiotic exposure= transformed. -If marker gene codes for fluorescent proteins, cells that fluoresce under UV light= transformed. -As not all cells/ organisms will take up the vector and be transformed.
66
Recombinant DNA technology in medicine
-GM bacteria produce human proteins- more ethically acceptable than using animal proteins and less likely to cause allergic reactions. -GM animals/ plants produce pharmaceutical- cheaper. -Gene therapy
67
Recombinant DNA technology in agriculture
-GM crops resistant to herbicides- only weeds killed when crops sprayed with herbicide. -GM crops resistant to insect attack- reduce use of insecticide. -GM crops with added nutritional value -GM animals with increased growth hormone production.
68
Recombinant DNA technology in industry
-GM bacteria produce enzymes used in industrial processes and food production.
69
Gene therapy
-Introduction of new DNA into cells, often containing healthy/ functional alleles. -To overcome effect of faulty/ non-functional alleles in people with genetic disorders.
70
Issues with gene therapy
-Effect is short lived as modified cells have a limited lifespan- requires regular treatment. -Immune response against GM cells or viruses due to recognition of antigens. -Long term effect not known- side effect- DNA may disrupt genes interfering with gene expression.
71
Humanitarians support recombinant DNA technology
-GM crops increase yields- increased global food production- reduced risk of famine/ malnutrition. -Gene therapy has potential to cure many genetic disorders. -'Pharming' makes medicines available to more people as medicines cheaper.
72
Environmentalists and anti-globalisation activists oppose DNA technology
-Recombinant DNA may be transferred to other plants- potential herbicide resistant 'superweeds'. -Potential effects of food webs- reduce biodiversity. -Large biotech companies may control the technology and own patents.
73
DNA probes
-Short, single stranded pieces of DNA. -With a base sequence complementary to bases on part of a target allele/ region. -Usually labelled with a fluorescent or radioactive tag for identification.
74
Why DNA probes are longer than just a few bases?
-A sequence of a few bases would occur at many places throughout the genome. -Longer sequences are only likely to occur in target allele.
75
DNA hybridisation
-Binding of a single stranded DNA probe to a complementary single strand of DNA. -Forming hydrogen bonds/ base pairs.
76
Genetic screening to locate specific alleles of genes
-Extract DNA and amplify by PCR. -Cut DNA at specific base sequences using restriction enzymes. -Seperate DNA fragments/ alleles using gel electrophoesis. -Transfer to a nylon membrane and treat to form single strands with exposed bases. -Add labelled DNA probes which hybridises/ binds with target alleles- wash to remove unbound probe. -To show bound probe, expose membrane to UV light if a fluorescently labelled probe was used. -Or use autoradiography (expose to X-ray film) if a radioactive probe was used.
77
Gel electrophoresis
-A method used to separate nucleic acid (DNA/RNA) fragments or proteins. -According to length/mass and charge.
78
Gel electrophoresis to seperate DNA fragments
-DNA samples loaded into wells in a porous gel and covered in buffer solution (which conducts electricity). -Electrical current passed through- DNA is negatively charged so moves towards positive electrode. -Shorter DNA fragments travel faster so travel further.
79
How can data from gel electrophoresis be interpreted?
-Run a standard with DNA fragments/ proteins of known lengths under the same conditions. -Compare to position of unknown DNA fragments/ proteins to estimate their size. -Shorter DNA fragments/ proteins travel further/faster.
80
Examples of use of labelled DNA probes
-Screening patients for heritable conditions. -Screening patients for drug responses. -Screening patients for health risks.
81
Role of genetic counsellor
-Explain results of genetic screening, including consequences of a disease. -Discuss treatments available for genetic condition. -Discuss lifestyle choices/ precautions that might reduce risk of a genetic condition developing. -Explain probability of condition/ alleles being passed onto offspring- enable patients to make informed decisions about having children
82
Personalised medicine
-Medicine tailored to an individual's genotype/ DNA. -Increasing effectiveness of treatment.
83
Screening of individuals for genetically conditions and drug responses
For -Some people could be heterozygous/ carriers -Can enable these people to make lifestyle choices to reduce chances of diseases developing, to prevent suffering/ death. -Allows people to make informed decisions about having their own biological children. -Allows use of personalised medicines, increasing effectiveness of treatment. Against -Screening for incurable diseases or diseases that develop later in life may lead to depression. -May cause undue stress id patient does not develop the disease. -Could lead to discrimination by insurance companies/ employers. -Many diseases are rare. -Many are caused by many genes so would need too many probes (expensive).
84
VNTRs
-Variable Number of Tandem Repeats. -Repeating sequences of nucleotides/ bases. -Found within non-coding sections of DNA at many sites throughout an organism's genome.
85
VNTRs use in genetic fingerprinting
-Probability of two individuals having the same VNTRs is very low. -As an organism's genome contains many VNTRs and lengths at each loci differ between individuals.
86
Genetic fingerprinting to analyse DNA fragments
-Extract DNA and amplify by PCR. -Cut DNA at specific base sequences using restriction enzymes. -Seperate DNA fragments/ alleles using gel electrophoesis. -Transfer to a nylon membrane and treat to form single strands with exposed bases. -Add labelled DNA probes which hybridises/ binds with target alleles- wash to remove unbound probe. -To show bound probe, expose membrane to UV light if a fluorescently labelled probe was used. -Or use autoradiography (expose to X-ray film) if a radioactive probe was used.
87
Genetic fingerprinting vs genetic screening
-Both use PCR to amplify DNA sample -Both use electrophoresis to seperate DNA fragments. -Both use labelled DNA probes to visualise specific DNA fragments. -Genetic fingerprinting analyses VNTRs whereas genetic screening analyses specific alleles of a gene.
88
Genetic fingerprinting to determine genetic relationships
-More closely related organisms have more similar VNTRs, so more similarities in genetic fingerprints. -Paternity testing- father should share around 50% of VNTR bands with child.
89
Genetic fingerprinting- determine genetic variability
Differences in VNTRs arise from mutations, so more differences show greater diversity within a population.
90
Use of genetic fingerprinting in forensic science
-Compare genetic fingerprint of suspects to genetic fingerprint of DNA at crime scene. -If many bands match, the suspect was likely present at the crime scene.
91
Use of genetic fingerprinting in medical diagnosis
Some VNTR patterns are associated with an increased risk of certain genetic disorders.
92
Use of genetic fingerprinting in animal and plant breeding
-Shows how closely related 2 individuals are, so that inbreeding can be avoided. -Breed pairs with dissimilar genetic fingerprints.

A Level Biology (11 decks)

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