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Cellular Control
Gene = length of DNA (sequence of nucleotide bases) that codes for polypeptides
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Examples of polypeptides = collagen,
haemoglobin, enzymes
Genetic code: sequence of nucleotide bases code for the construction of a polypeptide or protein
(protein is a large polypeptide)
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Gene unwinds and unzips as hydrogen bonds between complementary bases break
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This is catalysed by RNA
polymerase
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mRNA released and passes out of nucleus through a nuclear pore in the envelope
Translation: assembling amino acids into a polypeptide
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Ribosome – made of two subunits with a groove that the mRNA fits into
Sequence of amino acids:
o determines primary structure
o primary structure determines tertiary structure (3D shape) through hydrophilic
interactions, ionic bonds and hydrogen bonds
o if tertiary structure altered – active site changes shape so substrate cannot bind
tRNA – lengths of RNA that fold into a shape that has 3 exposed bases at one end (amino
acids binds here) and an anticodon at the other end (binds temporarily with complementary
codon)
some proteins have to be activated by cAMP by changing their 3D shape so it is a better fit
to the complementary molecules
mRNA binds to ribosome, two codons (six bases) attach to ribosome
tRNA, carrying the correct amino acid and with complementary anticodon forms hydrogen
bonds with first codon
Another tRNA, bearing a different amino acid, binds to second exposed codon with
complementary anticodon
Peptide bond forms between two amino acids
Ribosome moves along mRNA
Another tRNA brings another amino acid binds to exposed codon, peptide bond forms
between it and the dipeptide
First tRNA leaves and goes to collect another amino acid
Polypeptide chain grows until stop codon reached

Polypeptide formed:
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Enzymes catalyse reactions
Hormones

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Receptor proteins e
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cAMP
Homeobox genes
apoptosis

Mutations: cause changes in the nucleotide sequence
Two types of DNA mutations:
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Insertion/deletion mutations – one or more nucleotide pairs are inserted or deleted – causes
frameshift so changes a number of amino acids
 if a gene is altered by a change to its base sequence, it becomes an allele of the gene
(another version of the same gene)
 Could have a neutral effect if:
o the mutation is in a non-coding part of the DNA
o it is a silent mutation – codes for the same amino acid
o changed characteristic gives no advantage or disadvantage
 Negative effect:
o Mutation to gene determining skin colour – paler skin = burn + skin cancer
 Positive effect:
o Mutation to gene determining skin colour – paler skin = produce more vitamin D
(lack of vitamin D leads to rickets)
Lac Operon:
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Bacteria adapt to their environment by producing enzymes to metabolise certain nutrients
only when those nutrients are present
E
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coli grown in a culture medium with no lactose is put in a medium with lactose and they
increase rate of synthesis of Beta-galactosidase (catalyses hydrolysis of lactose to glucose)
and lactose permease (transports lactose into the cell)
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Regulator gene is expressed (transcribed and translated) so the repressor protein is made
(has two binding sites – one where lactose binds and one to bind to the operator region)
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RNA polymerase cannot bind to promoter region so structural genes aren’t transcribed into
mRNA
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Lactose molecule binds to other side of repressor protein changing its shape so the other
binding site cannot bind to operator region
2
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Promoter region is now unblocked so RNA polymerase binds to it and initiates transcription
of Z and Y genes to produce mRNA
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Bacteria can now take up lactose from the medium and convert it to glucose for respiration
Homeobox genes: in the homeotic gene
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Homeotic gene contains homebox sequence that codes for homeodomain
This binds to DNA
This initiates transcription/switches genes on or off
This controls the body plan
work in similar ways in most organisms
very little change by mutation because:
o These genes are extremely mportant
o A mutation would alter the body plan
o Many other genes would be affected
o Mutation selected against

Thalidomide:
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Homeobox genes HoxA11 and HoxD11 switch on genes that cause forelimb development
Thalidomide affected behaviour of these genes in embryonic development

Apoptosis: Programmed cell death

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Organelles become tightly packed (dense cytoplasm)
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Chromatin condenses – nuclear envelope breaks
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Cell breaks into vesicles – phagocytosis
Controlled by cell signalling
Rate of cells dying = rate of cells produced in mitosis
Not enough apoptosis = tumours
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g
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g
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Negative phototaxis = away from light
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Negative chemotaxis = away from chemical

Learned behaviour: shows adaptation in response to experience
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Determined by genetics and environmental influence
Not passed on to offspring
Altered by experience

Types:
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Habituation - animals ignoring stimuli because repeated exposure to stimuli results in
neither a reward or punishment e
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birds ignore scarecrow
Imprinting - young animals becoming associated with another organism - only occurs in a
sensitive/receptive period e
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goslings follow first thing they see
Classical conditioning - animals learn to relate a pair of events and respond to the first in
anticipation of the second e
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salivating when hearing a bell ring
Operant conditioning - trial and error learning - animals learn to associate an action with a
reward or punishment e
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dog begs for treat, rewarded with a treat so begs more often
Latent learning - animals explore new surrounding and retain information that is not of
immediate use but may be essential to staying alive at some future time
Insight learning - thinking and reasoning in order to solve a problem - solution to the
problem is remembered

Social behaviour: organisms living in groups with roles for each member
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Mountain gorillas - live in a troop of around 10 individuals, consists of one mature dominant
male, females and offspring
Dominant male protects members – enhances survival of young
Groom each other
Mother cares for offspring – enhances survival rate
Calls, displays and grunts used to signal danger – work together to deter predators
Learned behaviour is vital to survive

Dopamine receptor DRD4:
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Dopamine is a neurotransmitter and a hormone
Low levels = Parkinson’s disease
High levels = schizophrenia

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Increases general arousal and decreases inhibition – increase in creativity
Five dopamine receptors
50 variants of DRD4 gene
Inheritance of particular variants of DRD4 gene affects level and actions of dopamine
ADHD – drugs to treat ADHD affect dopamine levels
Particular variants of the DRD4 gene increase likelihood of addictive behaviour e
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smoking,
gambling
Animal Responses

Structure of the brain:
Cerebrum (largest part of the human brain) is divided into two hemispheres
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Outermost layer is folded and consists of the cerebral cortex
Cerebral cortex is in control of higher brain functions like o Conscious thought and emotional responses
o Ability to override reflexes
o Reasoning and judgement
Cerebral cortex is subdivided into areas o Sensory areas - receiver impulses indirectly from the receptors
o Association areas - compare input with previous experiences to interpret the input
and judge appropriate respon se
o Motor areas - sends impulses to the effectors

Cerebellum: Neurones from cerebellum carry impulses to the motor areas - so motor output can be
adjusted appropriately in relation to the requirements
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responding to changes in body position to remain balanced and upright
judging position of objects/limbs
tensioning of muscles to manipulate tools effectively
processes info from the retina, balance organs in the ear and joints

Medulla oblongata - controls non-skeletal muscles e
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Cardiac centre and respiratory centre found
here
Hypothalamus - controls body's homeostatic mechanisms - leads to the initiation of autonomic
responses to regulate body temperature and blood water potential
Why do we need to respond?
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Run away from predator
Control balance
Temperature regulation

Organisation of the nervous system:
Central nervous system: brain and spinal cord
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Mostly non-myelinated, two neurones connect at a
ganglion
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Impulse arrives at the neuromuscular junction causing vesicles to fuse with the presynaptic membrane and release acetylcholine into the gap
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Depolarisation wave travels down tubules (T system)
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Calcium ions bind to proteins in muscle - contraction
Strength of contraction - many motor neurones stimulate one muscle, each branches to a
neuromuscular junction so a cluster of muscle cells contract - motor unit
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Depolarisation of the post synaptic membrane
may be stimulatory or inhibitory

Post synaptic membrane is the sarcolemma
Neurotransmitter is ACh
Depolarisation of post synaptic membrane is
stimulatory

Differences between voluntary, involuntary and cardiac muscle:
Voluntary (skeletal)
Striated
Many nuclei
Attached to the bone

Controlled by somatic NS
Contracts quickly, tires easily

Involuntary (smooth)
Unstriated
Single nucleus
In the walls of the gut, blood
vessels and in the iris of the
eye
Controlled by the autonomic
NS
Contracts slowly, fatigues
slowly

Cardiac
Striated
Single nucleus
In the heart

Controlled by the autonomic
NS
Contracts continuously and
powerfully, without fatigue

Sliding filament model:
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Z-lines closer together during contraction as I-band and H-zone reduce in length (A-band
doesn't change length)

Protein filaments 

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Thin filaments - 2 strands made of protein actin (F actin, globular protein) coiled around
each other
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A troponin
complex is attached to each tropomyosin molecule
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Muscle contraction:
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Heads bend causing thin filament to be pulled and overlap with thick filament – power
stroke
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Head forms another cross-bridge with thin filament further along
Initiation of muscle contraction:
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Binding site on myosin head is covered with tropomyosin
When action potential arrives, calcium ions are released and bind to the troponin molecules
changing their shape and moving tropomyosin away from the myosin head binding site on
the actin filament
Actin-myosin binding site is now uncovered so cross-bridges can form

Supply of ATP:

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Aerobic respiration in mitochondria
Anaerobic respiration in the muscle cell sarcoplasm
Transfer from creatine phosphate in the sarcoplasm – transfers phosphate group to make
ATP from ADP+Pi

Fight or flight:
Physiological changes –
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Pupils dilate – iris radial muscle contracts
Heart rate increases
Arterioles to digestive system and skin constrict – smooth muscle relaxes
Arterioles to muscles dilate
Smooth muscle in airway relaxes
Hairs stand up
Ventilation rate increases contraction of intercostal muscles

A threat activates the hypothalamus – increases sympathetic nervous system stimulation and
triggers release of adrenaline from the adrenal glands in the medulla (nervous and endocrine
systems)
Adrenaline:
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Binds to complementary receptor
Activates G protein
Adenyl cyclase activated
ATP converted to cAMP
cAMP activates enzymes by changing their 3D structure
Biotechnology

Biotechnology: the industrial use of living organisms to produce food e
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mycoprotein from the
fungus fusarium, drugs e
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penicillin from penicillium or enzymes e
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detergents
Why microorganisms are used in biotechnological processes:
 Grow rapidly
 Produce pure products
 Easy to genetically engineer
 Processes occur at low temperature and pressure – cheaper/safer
 Can grow on waste materials
 No animal welfare issues
Standard growth curve of a microorganism in a closed culture:

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Log phase:
o Population doubles with every generation
o Enough space and nutrients to reproduce
o low levels of competition
o Few limiting conditions
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Death:
o Greater number dying than being produced
o Nutrient levels low
o Increased levels of toxic waste
o Organisms die
Immobilising enzymes:
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Covalent bonding: to clay
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Membrane separation:
Why immobilised enzymes are used in large-scale production:
Advantages:
 Stays separate from product
 Recoverable (not lost)
 Less downstream processing
 Reusable/cost effective
 Protects the enzyme
 Pure product produced
Disadvantages:
 Reduce reaction rate due to reduced ability to form enzyme-substrate complexes – takes
longer so is more expensive
 Expensive equipment
 Contamination means you must destroy all enzymes
 Can lose enzymes by leakage
Batch culture vs continuous culture:
Batch
slower growth rate – nutrient level declines
with time
Less efficient – not in operation all the time
Only 1 batch is lost if contaminated
Easy to setup and maintain

Continuous
Faster growth rate – nutrients added and waste
removed continuously
More efficient – in operation all the time
Huge volumes of product is lost if contaminated
Difficult to setup and maintain

Difference between primary and secondary metabolites:
 Metabolism: total sum of all chemical reactions within an organism

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Metabolites: chemicals that are produced as a result of metabolic reaction e
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hormones,
enzymes, waste products
Primary metabolites:
o produced as part of normal growth
o essential for life
o produced in line with growth curve
o produced in a continuous culture
o highest production in log phase
o e
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insulin, amino acids, fatty acids, lipids, enzymes
secondary metabolites:
o not produced as part of the normal growth
o not essential for life
o start to be produced in the stationary phase when nutrients are in short supply and
competition is high
o produced in batch culture
o e
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penicillin

Importance of manipulation the growing conditions in a fermenter:
 temperature – too hot and enzymes denature, too cold and growth is slowed
 timing of nutrient addition
 oxygen concentration – lack of oxygen = unwanted products of anaerobic respiration
 pH – reduce activity of enzymes if not kept constant at optimum
Asepsis: absence of unwanted microorganisms
Unwanted microorganisms:
 compete with culture microorganisms for nutrients and space
 reduce yield
 cause spoilage of product – don’t want contamination
How asepsis is ensured:
 sterilising apparatus
 fume cupboard use
 keep cultures closed
 washing, disinfecting, steam cleaning the fermenter
 filters on inlet and outlet pipes
Cloning
Natural vegetative propagation:
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Elm tree – reproduces asexually following damage to the parent plant
New growth in the form of root suckers appears within 2 months of destruction of main
trunk
Suckers grow in the trunk close to the ground where least damage is likely to be
Helps the elm to spread
Disease e
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Dutch elm disease spread and branches and trunks died, tree responds by
growing suckers
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Large numbers can be produced quickly
Grafting – shoot section of woody plant joined to an already growing root and stem, graft
grows and is genetically identical to parent plant

Tissue culture:
Produce huge numbers of genetically identical plants from small amount of plant material
Cut plant into small pieces, use the meristem
Sterilise with bleach
Placed on agar containing glucose
Cells in the tissue divide but do not differentiate – form mass of undifferentiated cells
(callus)
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Treat cells with growth hormone to induce growth
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Antibiotics
Minimising movement
Keep animals warm
Feed animals high energy food

Primary succession:
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Pioneer plants like lichen colonise the rock – they can tolerate low nutrient availability
As plant die and decay more nutrients accumulate – moss grows
Moss puts down small roots to bind soil – heather grows and causes competition
Shades out the moss so it dies
Juniper grows – more soil which is more acidic, more DOM, higher biodiversity
Climate climax – oak woodland

Measuring distribution and abundance:
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Random sampling – use random number generator to work out coordinates – put quadrat
down and measure percentage cover, use key to identify species
Transects – line transect – at regular intervals make a note of which species are touching the
tape or belt transect – at regular intervals place quadrat on line and count - interrupted

Nitrogen cycle:
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Nitrogen fixation:
o Lightning combines nitrogen gas with oxygen to make nitrogen oxide which goes
into rain water
o Nitrogen fixing bacteria – e
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Rhizobium provide the plant with fixed nitrogen and
receive glucose in return
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Copies of probe added to sample of DNA
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Use restriction enzyme to cut out DNA coding for the gene you want
Used to:
o Locate a specific gene for genetic engineering
o Identify the same gene on a variety of genomes
o Identify presence or absence of an allele for a disease
Making a copy of the mRNA:
 Obtain the gene you want’s mRNA
 Use reverse transcriptase to make cDNA
Sequencing + making:
 Find the sequence of the gene (below)
 Work out the base code
 Make the DNA sequence
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To make multiple copies of the DNA:
Polymerase chain reaction: artificial DNA replication
Differences to natural DNA replication:
 Can only replicate relatively short sequences of DNA
 Needs a primer
 Cycle of heating and cooling is needed
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Heat to 95 degrees – breaks hydrogen bonds making the sample single stranded
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Reduce temperature to 55 degrees – primer binds on each end
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Primer joins at the 3’ end of the template strand so DNA polymerase attaches
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If a modified nucleotide is added the reaction stops on that strand
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The strands run through a machine and a laser reads the colour from the strand with
only a single nucleotide added to one with two, three, four etc
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Sequence of colours and bases is then displayed
Electrophoresis: separate DNA fragments
 Uses slab containing agarose covered in buffer solution
 Electrodes are attached to each end of the slab so a current passes through it

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Required gene is obtained – gene probe, mRNA or sequencing
 Same restriction enzyme must be used for the DNA and the plasmid so the sticky ends are
complementary
 Base pairing of sticky ends – annealing
 Gene put into a plasmid using DNA ligase – joins the sugar-phosphate backbone
 Recombinant DNA is formed – DNA from 2 sources
 Mix with bacteria with Ca ions and give heatshock
 Forms transformation plasmid
Extracting DNA:
 Restriction enzymes cut through DNA at specific points (restriction sites)
 The enzyme catalyses a hydrolysis reaction which breaks the sugar-phosphate backbone of
the double helix in different places – sticky end
Ligase: used when putting gene into vector
 Catalyses a condensation reaction which joins the phosphate-sugar backbone
 If two are being joined from two different sources the same restriction enzyme must be
used
 When they are joined from two different sources in this way recombinant DNA is formed
Bacterial cells taking up a plasmid:
 Improves a feature of the organism –
o Plant resistance
o Promoting muscle growth
 To synthesise useful products
o Insulin into bacteria
o Produce chemicals in milk so it can be easily collected
o Beta-carotene into rice
Producing human insulin:
 Find mRNA for insulin
 Treated with reverse transcriptase to synthesise a complementary DNA strand
 Add DNA polymerase and DNA nucleotides – copies made called cDNA
 Unpaired nucleotides are added to give complementary sticky ends to those on the plasmid
 Plasmids cut open with restriction enzyme and mixed with cDNA
 Some take up the gene
 DNA ligase seals plasmids – recombinant plasmids made
 Plasmids mixed with bacteria, some plasmids are taken up to form transformation plasmid
Identifying transformed bacteria:

Choose plasmid that is resistant to two antibiotics ampicillin and tetracycline – genetic
markers
 Plasmids cut by restriction enzymes – restriction site in middle of tetracycline resistance
gene – if insulin gene is taken up = gene for tetracycline resistance doesn’t work
 Bacteria grown on agar plate
 Some cells transferred to plate with ampicillin on – only bacteria that has taken up a plasmid
will grow
 Cells transferred to plate with tetracycline on – those that don’t grow must have the insulin
gene
 Those that grow on the ampicillin but not the tetracycline must have insulin
Golden rice:
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Reduce vitamin A deficiency in Asia
Reduce blindness

Why is it bad?
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Reduce genetic diversity in rice
One disease would kill all the rice
Spread genes to wild population
Seeds are expensive
Might not grow where it is needed
Might not have enough vitamin A in
Unknown effects

Gene therapy: used to treat genetic orders
Somatic cell gene therapy: This has to be repeated regularly as it effects somatic cells
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Killing cells – eliminating certain populations of cells
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Engineering a gene into a sperm, egg or zygote
means all the cells will contain the engineered gene when it grows into an organism
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Prophase I –
 Chromatin condenses and supercoils – shorter and thicker
 Chromosomes come together in homologous pairs to form a bivalent (one maternal
and one paternal)
 Non-sister chromatids wrap around each other and attach at chiasmata
 Swap sections of chromatids as they cross over

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Can be:
o Abiotic: non-living
o Biotic: living
Some members better adapted so out-compete other members
If the environment changes the selection pressure changes
Directional selection leads to an evolutionary change
Sub-groups because of isolating mechanisms:
o Geographic – wolves avoid human settlements
o Behavioural – difference in courtship behaviour
o Mechanical – different size animals
o Seasonal – different breeding times
o Gamete incompatibility – different number of chromosomes

Phylogenetic species:
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Closely related organisms have similar molecular structures of DNA, RNA and proteins
Scientists compare base sequences
Plant Responses

Why do plants need to respond?
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Avoid being eaten
Survive long enough to reproduce
Phototropism – growing towards light
Geotropism – growing towards the pull of gravity
Hormones coordinate responses – move by active transport, diffusion, mass flow

Tropism = directional growth towards an external stimulus
Plant growth:

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Production of cellulase increases
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