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AQA ALEVEL BIOLOGY P1/P2 > 8. GENES > Flashcards

8. GENES Flashcards

1
Q

What is a Stem Cell?

A
  • a unspecialised/undifferentiated cell
  • potential to form different types of cells
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2
Q

How does a stem cell be come a specialised cell?

A
  • differentiation
  • 3 changes: cell shape, number of organelles, new content
  • occurs by controlling gene expression (some gene are activated, other genes are inhibited)
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3
Q

Stem Cell in Animals/Mammals/Humans?

A
  • Totipotent = Zygote
  • Pluripotent = Embryonic Stem Cells
  • Multipotent = Bone Marrow Stem Cell
  • Unipotent = Tissues
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4
Q

What are Induced Pluripotent Stem Cells (iPS Cells)?

A

turning unipotent body cells into pluripotent cells (like embryonic stem cells), involves activating certain deactivated genes using transcription factors

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5
Q

Stem Cell Therapy in Humans?

A
  • 2 uses,
  • use stem cells to produce tissues/organs for transplant
  • use stem cells to treat irreversible diseases e.g. heart disease, type 1 diabetes, paralysis (inject stem cells at site of disorder – will differentiate to become local specialised cells e.g. heart muscle cells, beta cells of pancreas, neurones)
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6
Q

Stem Cell in Plants?

A
  • In embryo = Zygote/Embryonic Stem Cells
  • In adult = Meristem Cells in Stem/Shoot/Root
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7
Q

Uses of Stem Cells from Plants?

A
  • traditionally cuttings were taken from plants (stem/shoot/root) and used to grow genetically identical plants – possible due to presence of meristem cells
  • tissue culture (micro propagation) = large scale application of cuttings
  • process,
  • take cutting from shoot/stem/root (called explant)
  • place explant in nutrient rich medium so meristem cells divide by mitosis
  • produces a mass of meristem cells (called callus)
  • take each meristem cell and grow in plant growth factor medium to promote differentiation and formation of shoot/root
  • transfer plant to soil and greenhouse
  • then transfer to field
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8
Q

What is Controlling Gene Expression?

A
  • either Activating or Inhibiting a Gene
  • activating gene = protein made
  • inhibiting gene = protein not made
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9
Q

Example of activating genes?

A
  • using oestrogen
  • oestrogen can enter a cell by simple diffusion and bind to receptors on the transcriptional factor
  • causes transcriptional factor to change shape
  • so transcriptional factor can now enter nucleus and bind to promoters on the DNA to activate transcription = activated genes (protein to be made)
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10
Q

Example of inhibiting genes?

A
  • using siRNA (small interfering RNA)
  • making siRNA = double stranded RNA cut down into small sections, made single stranded, then attaches to an enzyme
  • siRNA will bind to complementary sections on mRNA = the enzyme will cut the mRNA so translation cannot occur = gene inhibited (protein not made)
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11
Q

What is Epigenetics?

A
  • Heritable changes in gene function without changes to base sequence of DNA
  • Changes may due to lifestyle, stress, diet
  • Chromatin (DNA-Histone Complex) is surrounded by an Epigenome (chemical layer)
  • Epigenome can either cause the Chromatin to become more condensed or more loose
  • Chromatin becoming more condensed means transcription factors cannot reach the DNA and the gene will be inactivated
  • Chromatin becoming more loose means transcription factors can reach the DNA and the gene will be activated
  • These changes may be brought about by Acetylation or Methylation
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12
Q

How does Methylation and Acetylation affect the Genome?

A
  • Increased Methylation = adding methyl groups, this attracts proteins which condense the DNA-Histone Complex so transciption factors cannot gain access (gene inhibited)
  • Decreased Acetylation = removing acetyl groups, increases positive charges on the Histone which increases the attraction to the phosphate groups on DNA which condense the DNA-Histone Complex so transciption factors cannot gain access (gene inhibited)
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13
Q

What is a Gene Mutation?

A
  • a change in the base sequence of DNA
  • 2 types = substitution and insertion/deletion
  • substitution = replace one base for another, changes one triplet code can be silent (new triplet code codes for same AA), mis-sense (codes for a different AA, so protein shape changes slightly), non-sense (codes for a stop codon, so polypeptide chain not produced)
  • insertion = adding a base, deletion = removing a base both insertion/deletion causes frameshift, all the triplet codes after the mutation changes, so normal polypeptide chain/protein not produced
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14
Q

What is Cancer?

A
  • formation of a malignant tumour
  • due to uncontrolled cell division (mitosis)
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15
Q

Malignant vs Benign Tumour?

A

Malignant Tumours, cancerous

  • Rapid Growth (rapidly dividing cells)
  • Cells are unspeicialised
  • Cells can spread (Metastasis)
  • Systemic Effects
  • Requires Surgery/Chemotherapy/Radiotherapy

benign tumour non cancerous

  • grow slowly
  • do not invade other tissues and do not metastasise, unlike malignant tumours
  • can cause damage such as blockages or by exerting pressure on the organ it is growing in or those surrounding it
  • When removed, benign tumours do not usually grow back
  • Inflammation or infection, Injury, Diet = causes
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16
Q

What normally controls Cell Division (mitosis)?

A
  • 2 genes: proto-oncogene & tumour-supressor gene
  • both produce proteins to control cell division
  • proto-oncogene stimulates cell division
  • tumour-suppressor gene inhibits cell division
  • proto-oncogene produces growth factor and receptor protein, when the growth factor binds to receptor protein on cells it stimulates DNA replication that leads to cell division
  • tumour-suppressor gene produces a protein that inhibits cell division
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17
Q

Cancer?

A
  • caused by mutation of genes that control cell division
  • causes of mutation = random or mutagens (chemicals/radiation)
  • mutation of proto-oncogene leads to formation of a oncogene = over production of growth factor or receptor proteins permanently active = over stimulation of cell division (uncontrolled cell division)
  • mutation of tumour-suppressor gene = loss of protein to inhibit cell division (uncontrolled cell division)
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18
Q

Oestrogen and Cancer?

A

Oestrogen leads to activation of genes – high levels of oestrogen can lead to over activation of Proto-Oncogen forming an Oncogene = Cancer (uncontrolled cell division)

19
Q

Epigenetics and Cancer?

A

Main Example = increased methylation of tumour suppressor genes leads to inhibition of tumour suppressor genes leading to cancer (uncontrolled cell division)

20
Q

What is Genetic Engineering?

A
  • changing the genetic make-up of an organism’s DNA by adding or removing a gene
  • the DNA becomes Recombinant
  • the Organism becomes Genetically Modified (Transgenic)
21
Q

Why do we Genetically Engineer Animals?

A
  • to give them additional characteristics
  • so they can make useful products (proteins)
22
Q

Examples of genetic engineering in animals?

A
  • additional characteristics,
  • add gene for disease resistance
  • add gene for growth hormone for growth
  • making useful products,
  • use to produce anti-thrombin = protein used to make blood clot (people with certain genetic disease may not produce), use milk producing animal to produce, add gene for anti-thrombin next to milk producing gene in animal, therefore anti-thrombin protein will be made in the milk (easily extracted)
23
Q

Why do we Genetically Engineer Plants?

A
  • to give them additional characteristics
  • so they can make useful products (proteins)
24
Q

Examples of genetic engineering in plants?

A
  • additional characteristics,
  • add gene for disease resistance
  • add gene for pest resistance
  • add gene for pesticide resistance
  • add gene to promote growth for high yield
  • produce genetically modified tomatoes = prevented from softening therefore remain hardened (easy for storage and transport), involves preventing formation of softening enzyme, a gene is added that is complementary to the the softening enzyme gene, so its mRNA will bind to the mRNA of the softening enzyme preventing translation of the softening enzyme
  • making useful products,
  • use to make golden rice (rice that contains beta-carotene, a pre-cursor to vitamin A to treat malnutrition deficiency)
  • use to make protein raw material for polymers
25
Q

Why do we Genetically Engineer Bacteria?

A

so they can make useful products (proteins)

26
Q

Genetically engineering bacteria?

A
  • to make useful proteins e,g, Insulin
  • normally used animal sources (problems = limited supply, infection risk, immunorejection)
  • involves adding human insulin gene to a plasmid, then inserting this into a bacteria = the bacteria now has the gene/code to produce the human insulin protein

involves 5 steps =

  1. Isolation, 2. Insertion, 3. Transformation, 4. Identification, 5. Growth/Cloning
27
Q

what happens in isolation? in bacteria

A
  • either by Reverse Transcriptase or Restriction Enzyme or Gene Machine
  • RT = enzyme found in virus, converts RNA into DNA, obtain mRNA for insulin, the RT will convert it into cDNA (single stranded complementary DNA), DNA Nucleotides and DNA Polymerase added to make it double stranded
  • RE = enzyme found in bacteria, cuts DNA at certain base sequences (called recognition sites) by breaking bond between sugar and phosphate, can cut straight or staggered, staggered used in GE as it leaves exposed bases called ‘sticky ends’ [cuts staggered at 6 base pair palindromes, were the 6 bases read forward are identical to 6 bases read backward on both strands]
  • GM = build DNA base sequence from know Amino Acid Sequence of the Protein (uses oligosacchairdes)

end result = Isolated Human Insulin Gene

28
Q
  1. Insertion
A
  • cut plasmid using the same Restriction Enzyme from isolation stage
  • leaves complementary sticky ends
  • join human insulin gene with plasmid via the sticky ends
  • use DNA Ligase to join the sugar-phosphate backbone

= Recombinant plasmid (carrying human insulin gene)

29
Q

what happens in transformation?

A
  • mix recombinant plasmid with bacteria
  • add Ca2+ ions and heat shock
  • bacteria will become permeable and take up the recombinant plasmid

= Genetically Modified Bacteria (carrying recombinant plasmid with human insulin gene)

30
Q

what happens in identificarion?

A
  • identify which of the bacteria have taken up the recombinant plasmid and of these which ones have accepted the new gene (human insulin gene)

step 1 = choose a plasmid that carries an Ampicillin Resistance Gene, so when Ampicillin is added only the bacteria that have taken up the recombinant plasmid will survive (as they will have obtained the ampicillin resistance gene)

step 2 = use gene markers (antibiotic resistant, fluorescent, enzyme) to identify which of the remaining bacteria have accepted the human insulin gene, the human insulin gene will be placed in the middle of these gene markers, if the bacteria accepts the human insulin gene they will reject the gene marker & if the bacteria rejects the human insulin gene they will accept the gene marker
- antibiotic resistant = tetracycline resistance gene lost if human insulin gene accepted, so bacteria no longer resistant to tetracycline, add tetracycline by replica plating (on another plate that carries a few of the bacteria from each colony in their same position), the ones that die are the ones that we want, identify on original plate
- fluorescent = fluorescent gene lost if human insulin gene accepted, so identify bacteria showing no fluorescence
- enzyme = enzyme gene lost if human insulin gene accepted, therefore add colourless substrate, where there is no colour change select those bacteria (as enzyme not made to breakdown colourless substrate for colour change)

end result = Genetically Modified Bacteria

31
Q

. Growth/Cloning

A
  • grow genetically modified bacteria (carrying human insulin gene)
  • they will produce the protein (human insulin)
32
Q

What is PCR?

A
  • polymerase chain reaction
  • used to replicate DNA artificially
  • step 1: heat to 95oC, hydrogen bonds break, double strand separates, left with 2 template strands
  • step 2: cool to 55oC, primers bind (short single stranded sections of DNA) to start of each template strand, prevents the templates from rejoining and allows DNA Polymerase to bind to build the new strand
  • step 3: heat to 72oC, DNA nucleotides attach to complementary bases, DNA Polymerase joins sugar-phosphate backbone of the new strands
    = 2 copies of DNA (each made of 1 original strand, 1 new strand)
33
Q

Polymerase Chain Reaction vs Semi-Conservative Replication?

A
  • PCR can only replicate short DNA fragments, SCR can replicate whole DNA
  • PCR use 95oC, SCR uses DNA Helicase
  • PCR uses primers, SCR does not require primers
34
Q

In-vitro vs In-vivo method of DNA Replication?

A
  • In-vitro = PCR
  • In-vivo = using bacteria to replicate DNA (add DNA fragment to the plasmid, then replicate the bacteria to make many copies of DNA fragment)
  • benefits of in-vitro = more rapid, less complex
  • benefits of in-vivo = more accurate (less mutations), less chance of contamination
35
Q

What is a DNA Probe?

A
  • short single stranded section of DNA
  • has a specific base sequence, so it binds to complementary genes
  • is radioactively/fluorescently labelled
  • if gene is present in DNA, DNA probe will bind to it and show up be radioactivity/fluorescence
36
Q

What is Genetic Screening?

A
  • analyse an individual’s DNA for the presence of a particular gene (e.g. mutated allele)
  • use DNA Probes (single stranded section of DNA, complementary to a particular gene, is radioactively labelled)
  • obtain individuals DNA, make it single stranded, add the specific DNA Probe for the gene to be screened for, if the gene is present the DNA Probe will bind, will show up as radioactivity on an X-ray film
37
Q

What is Genetic Fingerprinting?

A
  • used to produce a unique ‘fingerprint’ of an individual’s DNA (produces a specific banding pattern)
  • used in forensics and paternity testing
  • involves analysing the individual’s introns (non-coding DNA)
  • introns contain repetitive sequences called variable number tandem repeats (VNTR)
  • the number and length of the VNTR are unique for each individual organism

involves 5 steps:
1. Extraction, 2. Digestion, 3. Separation, 4. Hybridisation, 5. Development

38
Q

what happens in extraction?

A
  • extracting the individual’s DNA
39
Q
  1. Digestion
A
  • cutting the DNA down into fragments
  • use Restriction Enzymes that cut just outside the VNTR (leaves the VNTR of the introns)
40
Q
  1. Separation
A
  • separate out the DNA fragments by gel electrophoresis
  • add alkali to make the separated fragments single stranded
  • transfer the fragments to a nylon membrane by Southern Blotting
  • add UV light so the DNA fragments set
41
Q
  1. Hybridisation
A
  • add radioactively labelled DNA Probes complementary to the DNA fragments
42
Q
  1. Development in genetic fingerprinting
A
  • add photographic film and take an x-ray to produce the banding pattern picture
43
Q

What is Genome Sequencing?

A
  • determining base sequence of a genome (full set of DNA)
  • uses Whole-Genome Shotgun (WGS) to cut DNA into smaller sections to be sequenced
  • Bioinformatics is the science by which the information is collected and analysed
  • uses = supports phylogenetic classification, identify genes related to diseases
44
Q

What is a Proteome?

A
  • full set of proteins produced by a certain genome

AQA ALEVEL BIOLOGY P1/P2 (8 decks)

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