F215 notes

Immobilising enzymes


  • Enzyme molecules mixed with carrier e.g. clay, activated glass minerals or gold - binds to carrier by hydrophobic interactions and ionic links 
  • Weak bonding forces - detachment (leakage
  • Active site isnt altered and easily accessible - fast reaction rate 


  • Enzymes covalently bind to a support - cellulose or collagen 
  • Enzymes covalently linked to insoluble material using cross linking agent 
  • Doesnt immobilise large amount of enzyme 
  • Strong covalents bond - little leakage 


  • Trapped in gel bead/network of cellulose fibres in natural state (inclusion)
  • Or physically separated from mixture by semi-permeable membrane - substrate molecules pass through (microcapsule)
  • Reaction rates reduced - harder to access active site 
  • Found in glucose test strps 
  • Active site may be orientated away from substrate 
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Cloning in animals


  • Donor cells - differentiated somatic cells e.g. taken from udder 
  • Cultured on low nutrient medium = stop dividing, dormant - undifferentiate 
  • Ovum taken from another animal - nucleus removed = enucleate ovum 
  • Donor cell + enucleate ovum placed next to each other - electric pulse causes them to fuse 
  • 2nd electric pulse = cell divsion 
  • Placed in tied oviduct in sheep - develop as embryo and then be removed 
  • Embryo placed in surrogate mother's uterus 


  • Ovum's collected from high value female e.g. high milk yield 
  • Sperm cells taken from high value male - test progeny
  • IVF occurs using collected egg and sperm - cell is grown in vitro until a 16 cell embryo 
  • Embryo is split into several separate segments - implanted into surrogates 
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Codominance and autosomal linkage


  • 2 alleles of the same gene
  • Both are expressed in the phenotype of a heterozygote
  • Examples are human blood groups and roan cattle 


  • Genes for different characteristics 
  • Present at different loci but on the same chromosome 
  • Linked - often inherited together as dont segregate independently in meiosis
  • Reduces number of phenotypes from a cross 
  • Example is red eyed and brown coated
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Types of variation


  • Qualitative differences between phenotypes
  • Fall into clear categories 
  • Gender, blood type
  • Different alleles at single gene locus = large effect on phenotype 
  • Co-dominance, dominance and recessive 


  • Quantitative differences between phenotypes 
  • No distinct categories - wide range of variation 
  • Height, weight, yield
  • Traits controlled by 2 or more genes - different alleles at each gene locus = small effect on phenotype 
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Genetic drift

  • Random fluctuations in the number of different alleles in a population 
  • There is changes in allele frequency 
  • Occurs in small populations 
  • Variants of alleles can disappear completely and reduce the genetic variation of the population 
  • Reduced gene pool
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The Sanger Method - Sequencing a genome

  • Genome is mapped 
  • Mechanically cut into smaller sections of around 100,000 base pairs 
  • Restriction enzymes are used to cut the DNA into smaller fragments 
  • Different restriction enzymes are used to different fragment types 
  • Fragments are separated in terms of size using gel electrophoresis 
  • PCR is used to make many copies 
  • Involves addition of free nucleotides - double oxidised and labelled with fluorescent marker 
  • Each base has a different colour
  • If modified nucleotide is added to the DNA DNA polymerase stops 
  • Means all fragments end on a labelled marker 
  • Electrophoresis is used 
  • Strands are run through a machine - laser reads the colour sequence 
  • Sequence of colours = sequence of bases 
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Polymerase chain reaction

  • Double stranded DNA sample mixed with supply of free nucleotides and DNA polymerase 
  • Heated to 95 = breaks hydrogen bonds to give single stranded DNA 
  • Primers added - short lengths of single stranded DNA (10-20 bases long)
  • Temperature reduced to 55 - primers anneal and form small sections of double stranded DNA at either end of sample 
  • DNA polymerase binds to double stranded sections 
  • Temperature increased to 72 degrees (optimum for Taq) - extends primers by adding free nucleotides to the unwound DNA
  • Repeated many times - amount of DNA increases exponentially  
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Gene therapy

  • Any therapeutic technique where functioning allele of particular gene is placed in cells of individual lacking the functioning allele for that particular gene
  • Treats some recessive conditions but not dominant conditions 


  • Functioning allele introduced into target somatic cells - removed, treated and replaced
  • Short lived as somatic cells - repeated reguarly 
  • Specialised cells wont divide to pass on allele 
  • Hard to get allele into genome in functioning state
  • Hosts become immune to viruses and liposomes inefficient 
  • Restricted to patient - not passed onto offspring 


  • Functioning allele introduced into germline cells - delivery more straightforward 
  • All cells derived from germline cells have a copy 
  • Unethical as it affects offspring - genetically engineering embryo, unsure of damage 
  • Passed onto children 
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Ethical issues of genetic manipulation

  • Religous objections 
  • Fears of unforeseen effects of gene 
  • Fears of consequence of escaping into wild 
  • Growing GM plants may damage the environment 
  • Eating GM plants may be bad for health 
  • Microorganisms may transfer gene to another microorganism 
  • Animal welfare 
  • Organs for xenotransplantation 
  • Plant resistance passed on - affect food chains 
  • Germline cell patients dont get opinion as not born 
  • Unpredictable effects of gene therapy 
  • Germline gene therapy enhances desirable characteristics - lead to designer babies 
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Role of hormones in leaf loss

  • Young leaves produce auxin - inhibits leaf loss
  • As leaf gets older less auxin is produced
  • Ethene is produced in older leaves - stimulates leaf loss
  • Abscission layer of cells develops where leaf joins the stem - separates the leaf from the rest of the plant 
  • Ethene stimulates cells in abscission layer to expand - breaks cell walls, leaf falls off
  • Before leaf falls off - grows layer of protective tissue where leaf will break off - scar prevents entry of pathogens 
  • Cells in the layer have suberin in cell walls 
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Arrival of an action potential at a neuromuscular

  • Impulse arrives - causes vesicles to fuse with the pre-synaptic membrane and release acetylcholine into the synaptic cleft 
  • Acetylcholine diffuses across synpatic cleft and binds to receptors on sarcolemma of muscle cell causing depolarisation 
  • Depolarisation travels down T tubules 
  • Calcium ions are released from stores in sarcoplasmic reticulim 
  • Bind to troponin in the muscle, leading to contraction 
  • Acetylcholine esterase breaks down acetylcholine so contraction only occurs when impulses arrive 
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Different types of muscle

  • Voluntary = long multinucleate fibres
  • Involuntary = short spindle shaped cells, single nucleate
  • Cardiac = branched fibres, intercalated discs join cells at their ends 
  • Voluntary and cardiac are striated, involuntary is unstriated 
  • Voluntary = contracts and fatigues quickly 
  • Involuntary = contracts and fatigues slowly 
  • Cardiac = contracts quickly and doesnt fatigue 
  • Voluntary = voluntary nervous system control 
  • Involuntary = autonomic nervous system control 
  • Cardiac = myogenic, autonomic control 
  • Voluntary = voluntary movements of bones of the skeleton about joints 
  • Involuntary = movement of materials along internal tubes and autonomic reflexes
  • Cardiac = pumps blood around the body 
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Coordination of fight or flight response in mammal

  • Threat occurs - usually visual or auditory stimuli 
  • Hypothalamus activated - stimulates activity in sympathetic nervous system 
  • Causes release of adrenaline from adrenal medulla into blood 
  • Hypothalamus releases corticotrophin releasing factor (CRF) into pituarity, causing the anterior pituarity gland to release ACTH 
  • Stimulates release of corticosteroid hormones from adrenal cortex - help body to resist stressors 

Causes physiological changes:

  • Increases blood pressure - less blood flows to gut and skin 
  • Causes skin to turn pale 
  • Smooth muscle in the gut and airways relaxes 
  • Pupils dilate 
  • Diaphragm and breathing rate increases 
  • More blood flows to the skeletal muscles 
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