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AQA A LEVEL Biology > Section 8 Genes > Flashcards

Section 8 Genes Flashcards

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1
Q

What is a stem cell?

A

An unspecialised/ undifferentiated cell with a potential to form any cell within the body

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2
Q

How does a stem cell become a specialised cell?

A

Differentiation

3 changes: Cell shape, number of organelles, new content

Occurs by controlling gene expression

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3
Q

Stem cell in animals/mammals/humans?

A

Totipotent=zygote
Pluripotent=Embryonic stem cells
Multipotent= bone marrow stem cells
Unipotent= Tissues

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4
Q

What are induced pluripotent stem cells?

A

Turning unipotent body cells into pluripotent cells involves activating certain deactivated genes using transcription factors

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5
Q

How can stem cells be used in human therapy?

A

Use stem cells to produce tissues/organs for transplant

Use stem cells to treat irreversible diseases.

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6
Q

Where are the stem cells within a plant cell?

A

In embryo= Zygote /Embryonic stem cells

In adult= meristem cells in stem/shoot/root

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7
Q

What are stem cells used for in plants?

A

Traditionally cuttings were taken from plants and used to grow genetically identical plants

Tissue culture

What is the process

Take cutting from plant or root (called an explant)

Place the explant in a nutrient rich medium so meristem cells divide by mitosis

Produces a mass of meristem (called callus)

Take each meristem cell and grow in plant grow factor medium to promote differentiation and formation of shoot and 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 genes
Activating= protein made
Inhibition gene= protein not made

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9
Q

Examples 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

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10
Q

Examples 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 the 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 the gene function without changes to the base sequence of DNA

Changes may be due to lifestyle, stress, diet

Chromatin is surrounded by an epigenome

Epignenome 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 become inactivated

Chromatin becoming more loose means transcription factors can reach the DNA and the gene will be activated

These changes may be caused 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 transcription factors cannot gain access

Decreased acetylation= removing acetyl groups, increases positive charges on the DNA which condense the DNA histone complex so transcription factors cannot gain access (gene inhibited).

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13
Q

What is cancer?

A

Formation of a malignant tumour

Is caused by uncontrolled cell division (mitosis)

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14
Q

What is 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

Insertion=adding a base, deletion= removing a base

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15
Q

Malignant vs benign tumours?

A

Malignant tumours

Rapid growth (rapidly dividing cells)
Cells are unspecialised 
Cells can spread (Metastatis)
Systemic effects
Requires surgery/ chemotherapy/ radiotherapy
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16
Q

What normally controls cells division (mitosis)?

A

2 genes: proto-oncogene & tumour suppressor 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

17
Q

What is cancer? (CONT.)

A

Caused by mutation of genes that control cell division

Causes of mutation = random or mutagens

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

Mutation of tumour suppressor gene = loss of protein to inhibit cell division

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

19
Q

Epigenetics and cancer?

A

Main example= increased methylation of tumour suppressor genes leads to inhibition of tumour suppressor genes leading to cancer

20
Q

What is genetic engineering?

A

Changing the genetic make-up of an organisms DNA by adding or removing a gene

The DNA becomes Recombinant

The organism becomes genetically modified

21
Q

Why do we genetically engineer animals?

A

To provide better characteristics

To provide more/ better product

22
Q

What are some examples of genetically engineering animals?

A

Additional characteristics

add a gene for disease resistance

Add a gene for growth hormone

Making useful products

23
Q

Why are plants genetically engineered

A

To give them additional (favourable) characteristics

So they can make useful products

24
Q

Examples of genetic engineering in plants?

A

Additional characteristics

Add gene for disease resistance

Add gene for pest resistance

Add gene to promote growth for a higher yield

MAKING USEFUL PRODUCTS

25
Q

Why are bacteria genetically engineered?

A

So they can make useful products

E.G. To make proteins such as Insulin

26
Q

What are the 5 steps of producing human proteins from genetically engineered bacteria?

A
  1. Isolation
  2. Insertion
  3. Transformation
  4. Identification
  5. Growth/cloning
27
Q

What is the first step of producing human proteins from genetically engineered bacteria and what is the process?

A

Isolation

Either by reverse transcriptase or restriction enzyme or gene machine

RT= enzyme found in virus converts RNA to DNA, obtaining mRNA for insulin

 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

What is the second step of producing human proteins from genetically engineered bacteria and what is the process?

A

Insertion

Cut plasmid using the RE 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 to backbone

Recombinant plasmid (carrying human insulin gene)

29
Q

What is the third step of producing human proteins from genetically engineered bacteria and what is the process?

A

Mix recombinant plasmid with bacteria

Add Calcium ions and heat shock

Bacteria will become permeable and take up the recombinant plasmid

Genetically modified bacteria

30
Q

What is the fourth step of producing human proteins from genetically engineered bacteria and what is the process?

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

What is the fifth and final step of producing human proteins (insulin) from genetically engineered bacteria and what is the process?

A

Grow genetically modified bacteria

They will produce the protein

32
Q

What is PCR?

A

Its a polymerase chain reaction

It is used to replicate DNA artificially

Step 1: heat to 95c hydrogen bonds break, double strand seperates, left with 2 template strands

Step 2: cool to 55c, primers bind (short single stranded sections of DNA) to start of each template strand, prevents the templates from rejoining and allows the DNA polymerase to bind and build a new strand.

Step 3: Heat to 72c, DNA nucleotides attach to complementary bases, DNA polymerase joins sugar phosphate backbone of new strands

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 vio method of DNA replication?

A

In-vitro= PCR

In-vivo= using bacteria to replicate DNA

Benefits of in-VITRO= more rapid, less complex

Benefits of in VIVO= more accurate, less chance of contamination

35
Q

What is a DNA probe?

A

A short single stranded section of DNA

Has a specific base sequence so it binds to the complementary genes

Is radioactively/fluorescently labelled

If a gene is present in DNA, DNA probe will bind it and show up be radioactivity

36
Q

What is genetic screening?

A

Analyse an individual’s DNA for the presence of a particular gene

Use DNA probes

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?(LONG 5 stage process)

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
  1. Extraction
     extracting the individual’s DNA
  2. Digestion
     cutting the DNA down into fragments
     use Restriction Enzymes that cut just outside the VNTR (leaves the VNTR of the introns)
  3. Separation
     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
  4. Hybridisation
     add radioactively labelled DNA Probes complementary to the DNA fragments
  5. Development
     add photographic film and take an x-ray to produce the banding pattern picture
38
Q

What is genetic sequencing

A

Determining base sequence of a genome

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 phlyogenetic classification, identify genes that are related to specific diseases

39
Q

What is a proteome?

A

Full set of of proteins produced by a certain genome

AQA A LEVEL Biology (8 decks)

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