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Bio Ocr A A Level > Module 6 > Flashcards

Module 6 Flashcards

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1
Q

What are transcription factors, where do they bind in prokaryotes or eukaryotes.

A

Proteins that bind to DNA and switch genes on or off by increasing or decreasing the rate of transcription.

Factors that increase the rate of transcription are called activators. Factors that decrease the rate of transcription are caller repressors.

In eukaryotes, transcription factors bind to specific DNA sites at the start of the target genes. In prokaryotes, transcription factors bind to operons (a cluster of structural genes that are transcribed together)

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2
Q

Describe how the lac operon functions

A

E. coli is a bacteria that can respire both glucose and lactose. Genes containing the script for the enzymes needed to respire lactose are found on the lac operon which has 3 structural genes: lacZ, LacY and LacA

Lactose not present:
- regulatory gene called LacI produces the lac repressor (transcription factor) which binds to the operator site.
- Transcription is blocked because RNA polymerase can’t bind to the promoter.

Lactose present
- lactose binds to the repressor, changing its shape and it can’t bind to the operator site.
RNA polymerase continues to transcribe beta-galactosidase and lactose permease.
- beta-galactosidase is used to hydrolyse lactose to glucose and galactose.
- lactose permease is used to facilitate the passage of lactose across the phospholipid bilayer of the cell membrane to allow more lactose to be respired.

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3
Q

Describe the process of splicing

A

Introns (non coding DNA) is removed from primary mRNA leaving only exons (coding DNA). This forms mature mRNA which leaves the nucleus for translation

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4
Q

Describe how cAMP activates protein kinase A

A

PKA enzyme is made up of 4 subunits.
When cAMP isn’t bound, the 4 units are bound together and inactive.
When cAMP binds, it causes a change in the enzymes 3D structure, releasing the active subunits to make pKA active.

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5
Q

Describe the genes that control body plan, where are they found exactly, what part of them are highly conserved?

A

Hox genes code for the body plan.
Similar how genes are found in animals, plants and fungi.
Hox genes have regions called homeobox sequences that are highly conserved throughout evolution
Homeobox sequences code for a part of the protein called the homeodomain (transcription factor) which binds to specific sites on DNA.

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6
Q

Describe the process of apoptosis, how is it controlled. How are these genes affected by stimuli?

A

Apoptosis is programmed cell death, during development, some genes that control apoptosis are switched on and off in certain cells so the correct body plan develops.

  • enzymes in the cell break down important cell components such as proteins in the cytoplasm
  • as the cell contents are broken down, the cell shrinks and breaks
  • Cell fragments are engulfed by phagocytes and digested.

Genes that regulate apoptosis can respond to internal stimuli (DNA damage during the cell cycle) and external stimuli (lack of nutrient availability).

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7
Q

Describe continuous variation, describe the corresponding graph and give examples of continuous variation

A

Individuals varying within a range is continuous.
Bell shaped histogram shape
Eg. Waist circumference

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8
Q

Describe discontinuous variation, describe its corresponding graph and give examples.

A

When there are distinct categories, it’s discontinuous.
It’s a bar graph
Eg. Blood group

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9
Q

Describe what is meant by polygenic and monogenic characteristics

A

Polygenic characteristics are characteristics that are influenced by many genes

Monogenic characteristics are characteristics that are influenced by only one gene.

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10
Q

How can variation be influenced by environment

A

Etiolation: plants grow abnormally long and spindly because they don’t get enough light

Chlorosis: plants don’t produce enough chlorophyll and turn yellow

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11
Q

What are codominant alleles

A

Where both alleles are expressed in the phenotype as neither one is recessive.
E.g sick cell anaemia. People who are carriers of sickle cell will have some normal blood cells and some sickle cell blood cells

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12
Q

Describe how the alleles work for blood group

A

Allele I^O is recessive
Alleles I^A and I^B are codominant

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13
Q

Describe the nature of sex linked characteristics using colour blindness as an example

A

A characteristic that is sex linked has the corresponding allele on the sex chromosome.
The Y chromosome is smaller so can only carry a few diseases so majority of sex linked diseases are X-linked

Colour blindness:
- caused by a faulty allele carried on the X chromosome
- females need 2 copies of the recessive allele to be colourblind unlike the males which only need one copy.
- female colourblindness is rarer than. Ale colourblindness

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14
Q

Describe autosomal genes and how they are arranged.

A

Autosomes are chromosomes that aren’t sex chromosomes.
Autosomal genes are located on the autosomes.
Genes on the same autosome are said to be linked, the closer they are on the autosome, the more they are linked to each other because they are less likely to be split

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15
Q

What is epistasis?

A

Only present in polygenic characteristics. When the allele of one gene masks the expression of another.

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16
Q

What is evolution

A

Change in allele frequency over time

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17
Q

What is natural selection dependent upon?

A

The right selection pressure must be present. Without a selection pressure, natural selection won’t take place

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18
Q

Describe stabilising selection, and it’s graph.

A
  • occurs when the environment is not changing much
  • individuals with alleles at the extreme ems are more likely to die.
  • bell shaped curve in the middle of the graph.
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19
Q

Describe directional selection

A
  • occurs when there is a change in the environment
  • individuals with alleles at the extremeties survive
  • bell shaped curve shifter more to the left or right of the graph axis.
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20
Q

What is genetic drift

A

Environmental factors affecting the amount of alleles in a population using natural selection to. Genetic drift usually has a greater effect in smaller populations
Evolution of human blood groups is an example of genetic drift

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21
Q

What is a genetic bottleneck, give an example

A

An event like a natural disaster that causes a big reduction in population size leading to a reduction in gene pool.
For example, a flood killing all white mice so only black and grey mice remain.

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22
Q

Describe what the founder effect is, give an example of it.

A

It describes what happens when just a few organisms from a population start a new population with only a limited gene pool.

For example, the Amish.

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23
Q

What equation helps you find the frequency of an allele in a population

A

P + Q = 1

p = frequency of dominant allele
q = frequency of recessive allele

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24
Q

What equation can help find the frequency of genotypes in population

A

p^2 + 2pq + q^2 = 1

P2 = frequency of homozygous dominant
2pq = frequency of heterozygous
Q^2 = frequency of homozygous recessive

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25
Q

Give a few examples of where artificial selection for breeding has gone wrong and a few where it’s gone right.

A

Where it’s gone right:
- modern day cattle produce lots of milk
- bread wheat produces lots of grain.

Where it’s gone wrong
- some over bred pedigree dogs have faces that are so scrunched up that they can’t breathe
- high incidence of hereditary deafness in some dogs.

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26
Q

What is speciation

A

Development of a new species, changes in allele frequency means that some organisms can no longer breed together.

27
Q

What is allopatric speciation and how does it come about.

A
  • geographical isolation stops interbreeding between the two populations
  • populations adapt to the new environment
  • allele and phenotype frequency change leading to the development of a new species.
28
Q

What is sympatric speciation

A

A mutation can occur without geographical isolation that leads to a different number of chromosomes being present in the mutated organism. That separates it from the original population so it can’t reproduce with the other organisms. It can start its own species if it can reproduce asexually.

29
Q

What techniques can be used to study genes

A

Polymerase chain reaction
Gel electrophoresis
Cutting DNA with restriction enzymes.

30
Q

Describe the process of PCR

A
  1. A reaction mixture is set up. It contains: DNA sample, free nucleotides, primers (short pieces of DNA that are complimentary to the bases at the start of the DNA sample), and DNA polymerase (enzyme that creates new DNA strands by making phosphodiester bonds)
  2. DNA mixture is heated to 95*c to break the hydrogen bonds between strands of DNA.
  3. Mixture is cooled to between 50-65*c so the primers can anneal to the strands.
  4. Reaction mixture heated to 72*c so DNA polymerase can line up with free DNA nucleotides alongside the template strand and take part in complimentary base pairing.
  5. 2 new copies of the fragment are made.
31
Q

Describe the process of electrophoresis (same for DNA and RNA)

A
  1. Get a gel tray with wells on one end, they must be closest to the negative electrode. Put this inside a gel box.
  2. Add buffer so the surface of the gel is covered in buffer.
  3. Add equal amounts of DNA and loading dye to each well using a clean micropipette. Record which DNA is in each well
  4. Put the lid on the box and attach the leads and apply voltage.
  5. DNA which is negatively charged moves towards the positive electrode. Small DNA fragments move further and faster. Leave running for 30 mins.
  6. Remove gel tray and tip off excess buffer. Cover the surface of the gel with staining solution, tip off excess and rinse again with water.
32
Q

Describe how restriction enzymes work

A

They recognise specific palindromic sequences (recognition sites) and cut and digest at these areas. They. Can leave either sticky or blunt ends. The bases are separated using a hydrolysis reaction.

33
Q

Describe what DNA profiling is

A

Analysing short tandem repeats using electrophoresis produces a DNA profile. STR’s are repeats of non-coding sequences.
1. Isolate DNA and use PCR to amplify DNA
2. Run the products of PCR on electrophoresis and compare.

34
Q

Describe how genetic engineering is carried out

A
  1. DNA fragment with desired gene is obtained.
  2. DNA fragment is insterted into a vector forming recombinant DNA.
  3. Vector transfers gene to bacteria for reproduction.
35
Q

How does gene therapy work

A
  • alter alleles inside cells to cure genetic disorders
  • if a disease is caused by 2 recessive alleles, add a working dominant allele
  • if a disease is caused by a dominant allele, stick some DNA into the middle of that allele to make it useless
  • insert the allele into the cell via vectors. Eg. Liposomes, viruses or plasmids.
36
Q

Describe the two types of gene therapy

A

Somatic: involves altering alleles in body cells that suffer from the disorder.

Germ line: altering the alleles in the sex cells. All offspring produced will be affected.

37
Q

Where can sequenced genes and genomes be used

A
  • studying genotype-phenotype relationships
  • epidemiological studies: heath and disease
  • to help understand evolutionary relationships
38
Q

Describe the chain termination method

A
  1. The following mixture is added to 4 tubes:
    - single stranded DNA template
    - DNA primer
    - DNA polymerase- Free nucleotides
    - Fluorescently labelled modified nucleotide
  2. Tube undergoes PCR
  3. Once the modified nucleotide is added to the sequence, the PCR stops
  4. Each tube goes through electrophoresis and is visualised under UV light
  5. Read it from bottom to top because the smallest nucleotide will be at the bottom of the gel.
39
Q

What is high throughput sequences and give and example of it.

A

Techniques that sequence a lot faster than the chain termination method are called high throughput sequencing methods. An example is pyrosequencing

Pyrosequencing:
- DNA is cut into fragments and split into single strands
- each fragment is attached to a small bead
- PCR amplifies the DNA
- electrophoresis occurs and computers analyse it.
- can sequence 400 million bases in 10 hours

40
Q

Describe some ways that plants naturally produce clones of themselves

A

Vegetative propagation: a way for plants to clone themselves without using reproductive tissue.
- rhizomes: have nodes from which shoots and roots grow.
- stolons: new shoots and roots grow from the nodes or from the end of the stolen.
- suckers: shoots that grow from sucker buds
- tubers: eyes that form on underground vegetation which are able to sprout to form a new plant.
- bulbs: underground food stores used by some plants they can develop into new plants.

41
Q

How do you produce a clone from cuttings

A

Use rooting powder, a nutrient mix of plant hormones.

42
Q

How do you produce a plant clone using tissue culture

A

Take meristem tissue, sterilise, place in growth medium and grow to plant in soil.

43
Q

Describe the process of artificial embryo twinning.

A
  1. Egg cell extracted from female
  2. Fertilised egg allowed to divide at least once to form an embryo
  3. Individual cells from the embryo are separated and are allowed to grow in separate Petri dishes
  4. New embryos are implanted into more females, they’re all clones
44
Q

Describe the process o somatic cell nuclear transfer

A
  1. Somatic cell taken, nucleus is removed.
  2. Immature egg cell from a female and nucleus is removed.
  3. Nucleus of somatic cell inserted into empty egg .
  4. Fuses together via electrofusion
  5. Embryo forms and is planted into a surrogate mother.
45
Q

Compare batch and continuous fermentation

A

Batch:
- microorganisms grown in continuous batches
- one after another

Continuous:
- microorganisms are continuously grown without stopping.
- nutrients and waste products are continuously being added and removed

46
Q

Describe the standard growth curve

A

Used for closed culture or batch fermentation
1. Lag phase: reproduction rate is low because the organisms are still adjusting
2. Exponential phase: population size increases fast because conditions are most favourable.
3. Stationary phase: death rate is equal to birth rate because waste builds up
4. Decline phase: more deaths than reproduction because there’s toxic waste and not enough food

47
Q

Give 4 ways in which enzymes can be immobilised

A

Encapsulation in alginate beads
Trapped in silica gel matrix
Covalently bonded
Membrane separation

48
Q

Describe where immobilised enzymes are being used in industry

A
  • convert lactose to glucose and galactose: hydrolysis reaction
  • production of semi-synthetic penicillin: effective on penicillin resistant organisms
  • conversion of dextrins to glucose: glucosmylase breaks down starch to dextrins then to glucose which is a sweetener
  • conversion of glucose to fructose: isomerise converts glucose to fructose which is much sweeter than glucose
  • production of pure L amino acids: amino acids have two isomers of which only the L form is used by the body. Aminoacylase separates the L and D isomers.
49
Q

What is the equation to calculate net productivity?

A

Net productivity = gross productivity - respiratory loss

50
Q

State the nitrogen cycle stages

A
  1. Nitrogen fixation
  2. Ammonification
  3. Nitrification
  4. Denitrification
51
Q

Describe nitrogen fixation

A
  • when bacteria like rhizobium and azotobacter turn nitrogen gas to ammonia which can be used by plants
  • rhizobium are found in root nodulesof leguminous plants
  • bacteria form a mutualistic relationship with the plant: in return for carbohydrates, the plant is supplied with nitrogen compounds
  • azotobacter is present in the soil and they don’t form mutualistic relationships.
52
Q

Describe ammonification

A

Nitrogen compounds from dead organisms are turned into ammonia by decomposes, eventually the ammonia becomes ammonium ions.
Animal waste also contains nitrogen compounds which are turned into ammonia by decomposes then eventually ammonium ions.

53
Q

Describe nitrification

A
  • ammonium ions in the soil are changed into nitrogen compounds to be used by plants.
  • nitrosomonas turns ammonium ions to nitrites
  • nitrobacteria turn nitrites into nitrates
54
Q

Describe denitrification

A
  • nitrates in the soil are converted to nitrogen gas by denitrifying bacteria
  • happens under anaerobic conditions
55
Q

WHat are the two types of succession, briefly describe them both

A

Primary succession:
- land must be newly formed
- the way that the new ecosystem changes over time.

Secondary succession:
- occurs on land that has been cleared of all plants
- the way that an old ecosystem changes over time

56
Q

Give a detailed example of how primary succession works

A
  1. Pioneer species colonise the rocks
  2. Pioneer species die and are decomposed to form a thin soil in which other species can grow
  3. Organic matter slowly builds up over time and soil volume increases., larger plants are able to movie in.
  4. Shrubs, ferns and small trees start to grow
  5. Finally, the soil is deep and rich enough in nutrients to support large trees. This becomes the dominant species as the climax community is formed
57
Q

What is the climax community for a particular climate called?

A

Climatic climax

58
Q

What is deflected succession

A

When human activities interrupt the natural flow of succession.

59
Q

Which biotic factors affect population size

A

Interspecific competition - between different species
Intraspecific competition - between same species
Predations - predator and prey populations is controlled by negative feedback.

60
Q

What is carrying capacity of an ecosystem

A

Maximum stable population size of a species that an ecosystem can support

61
Q

What is conservation, and why is conservation dynamic. How is conservation different to preservation.

A

Conservation is the protection and management of ecosystems so that natural resources in them can be used without running out. It’s dynamic because conservation methods must be adapted to constant changes of ecosystems

Preservation is the protection of ecosystems so they are kept exactly as they are.

62
Q

What methods ensure that woodlands can give wood sustainably.

A

Coppicing - felling trees at their base so shoots grow out of the stump. It will have many thin trunks.
Pollarding- essentially pruning trees so that they do not grow past a certain height.
Clearing trees in strips as they grow back faster like this
Planting only native treee species
Trees aren’t planted too close together.

63
Q

Give some strategies used to conserve fishes while fishing

A

Using fishing quotas
Increasing mesh size of nets

64
Q

What does it mean to reclaim and ecosystem

A

Restore an ecosystem that has been damaged for reuse.

Bio Ocr A A Level (6 decks)

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