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A2 Biology Revision Guide Version 6
PHOTOSYNTHESIS: SITE OF PHOTOSYNTHESIS
β Chloroplast
ADAPTATIONS OF THE LEAF β Large SA absorbs as much sunlight as possible β Thin, short diffusion distances of gases β Numerous stomata for gas exchange
STRUCTURE OF CHLOROPLAST β Double membraned β Grana are stacks made up of thylakoids β Stroma is a matrix surrounding the different organelles
SITE OF LIGHT DEPENDENT REACTION β Thylakoid membrane
LIGHT DEPENDENT REACTION PROCESS β Photolysis of water, H2O ----> 2H+ + O2 + 2e-
β Photoionization of electrons β Excited go through carriers, lose energy each time β Lost energy used to make ATP from ADP + Pi β Remaining energy used in ATP synthase to make ATP from reaction ADP + Pi ----> ATP β H+ travel through membrane into thylakoid intermembrane space by active transport using
ATP β Creates gradient, H+ then just diffuse down into ATP synthase creating a change in the
enzymeβs 3D structure (conformational change) also producing ADP + Pi ----> ATP
β H+ combines with coenzyme NADP to make NADPH β End result = ATP + NADPH
SITE OF THE CALVIN CYCLE β Stroma matrix
CALVIN CYCLE PROCESS β CO2 diffuses through stomata into stroma β CO2 reacts with ribulose bisphosphate catalysed by enzyme rubisco β This produces glycerate-3- phosphate β Glycerate-3- phosphate is reduced by NADPH using energy from ATP ----> ADP + Pi to make
triosephosphate β Triosephosphate is then converted to other organic materials i.e. glucose
FACTORS AFFECTING PHOTOSYNTHESIS β Light intensity, increases photolysis, increases uptake of CO2, increase oxygen output β Temperature, increase KE increase rate β Carbon dioxide conc. More = higher rate
MEASURING PHOTOSYNTHESIS
β Water bath used to maintain a constant temperature β Potassium hydrogen carbonate used around plant to give source of carbon dioxide β Adjustable source of light β Plant left in dark before experiment β Light source switched on to allow air spaces to fill with oxygen β Oxygen produced collects in funnel end of capillary tube β Collected in gas syringe and measured
RESPIRATION: GLYCOLYSIS
β Glucose phosphorylated β Split to triose phosphate β Oxidation of triose phosphate to pyruvate via NAD ---> NADH
ENERGY YIELDS OF GLYCOLYSIS β Net gain of 2 ATP
LINK REACTION β Pyruvate oxidised to acetate ( NAD ----> NADH) (+ carbon dioxide) β Combines with coenzyme A to produce acetyl coenzyme A
KREBS CYCLE β Acetyl coenzyme A combines with 4 carbon molecule to make 6 carbon molecule β In series of reactions involving the loss of carbon dioxide the 4 carbon molecule is produced
again β The purpose of the Krebs Cycle is to produce reduced coenzymes which can produce ATP in
the electron transport chain β Energy yields = 1 ATP β Waste products = 3 carbon dioxide molecules
ELECTRON TRANSPORT CHAIN β FADH ---> FAD + e- & NADH ----> NAD + e-
β Hydrogen ions are actively transported into intermembrane space using ATP β Creates and maintains gradient, hydrogen ions diffuse down into ATP synthase creating
conformational change in enzyme producing ADP + Pi ---> ATP β Oxygen acts as terminal receptor with H+ to produce water β The electrons produced travel through carriers losing energy each time producing ATP β They then provide the energy needed by ATP synthase to make ADP + Pi ---> ATP β End products = Carbon dioxide, water and ATP
RESPIRATION OF LIPIDS β Lipids to hydrolysed β Glycerol then phosphorylated to triose phosphate and can enter glycolysis β Lipids release X2 the energy of carbohydrates
RESPIRATION OF PROTEIN β Hydrolysed to amino acids β Deamination β Enter respiration at different points depending on carbon length
ANAEROBIC RESPIRATION β In plants = pyruvate + NADH ---> ethanol + carbon dioxide + NAD β In animals = pyruvate + NADH ----. Lactate + NAD β Energy yields lower because only go through glycolysis as no oxygen to be the terminal
receptor
ENERGY AND ECOSYSTEMS PRODUCERS
β Are autotrophic β Create energy from sunlight
CONSUMERS β Consume organisms for energy β Primary = Eat producers β Secondary = Eat primary consumers β Tertiary = Eat secondary consumers β Secondary + Tertiary = predators
SAPROBIONTS β Decomposers β Breakdown complex organisms
FOOD CHAIN β Line of succession of food consumption
FOOD WEBS β A more complex representation of a food chain
BIOMASS β Total mass of living organisms in a specific place at a specific time β Dry mass measures organic material and is more reliable as water content varies in living
organisms but have to kill organism How to Produce Dry Mass
β Weigh samples at intervals during drying β Weigh to constant mass
MEASURING BIOMASS β Bomb calorimetry β Burning heats water measure temp change β Sub into equation q= mcΞt
ENERGY TRANSFER AND PRODUCTIVITY HOW PLANTS LOSE ENERGY
β 90% of sunlight reflected back into space β Not all wavelengths are used in photosynthesis β Not all parts of plant contain chloroplast
EQUATION β NPP = GPP - R
HOW CONSUMERS LOSE ENERGY
β Not all consumed β Not all digested β Feaces
EQUATION β N = I - (F+R)
PERCENTAGE EFFICIENCY: β (Energy after transfer / Energy before transfer) x 100
NUTRIENT CYCLES NITROGEN CYCLE Nitrogen Fixation:
β Nitrogen converted to nitrogen containing compounds β Can be done by lightening or by free living or mutualistic bacteria
Nitrification: β Nitrifying bacteria aerobically respire β Creates nitrates by reaction NH3 ----> NO2- ----> NO3-
OR Denitrification:
β No oxygen in the soil β So is water logged β Bacteria anaerobically respire β Nitrates to atmospheric nitrogen
Nitrate ions are then absorbed by plants and eaten by consumers, dead/feces Ammonification:
β Saprobionts convert nitrogen containing compounds to ammonia PHOSPHORUS CYCLE
β Weathering of rocks β Phosphate ions absorbed by plants β Animals eat plants β Animals/ plants die β Saprobionts break down into phosphate ions β Either go back into soil or taken into streams to turn back into rocks
ROLE OF MYCORRHIZAE IN NUTRIENT CYCLES β Fungi acts as extension of root so makes larger SA for minerals β Also acts as sponge holding onto water making plants more drought resistant
USE OF NATURAL AND ARTIFICIAL FERTILISERS NEED FOR FERTILISERS
β Help increase yields for crops by giving plants necessary nutrients β Increase energy efficiency for trophic levels
NATURAL AND ARTIFICIAL FERTILISERS β Natural = dead and decaying remains of plants or feces β Artificial = Mined from rocks, NPK
ENVIRONMENTAL ISSUES CONCERNING USE OF NITROGEN CONTAINING FERTILISERS EFFECTS OF NITROGEN CONTAINING FERTILISERS
β Extra growth leads to bigger leaves = more photosynthesis β Reduced species diversity β Leaching and eutrophication
LEACHING β Nutrients removed from soil β Can leach into watercourses cause health problems
EUTROPHICATION β Leaching β Lakes have naturally low nitrate concs. β So when theyβre in excess causes algae bloom β Blocks the sun from reaching plants underneath, canβt photosynthesise β Plants die β Saprobionts break them down aerobically β Less oxygen in lake β Fish die β Saprobionts break them down aerobically leading to very little oxygen left in lake β Anaerobic bacteriaβs population rise β Leading to the lake becoming putrid due to the anaerobic waste products
SURVIVAL AND RESPONSE STIMULUS AND RESPONSE
β Stimulus β Receptor β Coordinator β Effector β Response
TAXES β Direction of movement is determined by stimulus
KINESES β Rate and speed of movement is determined by stimulus
TROPISMS β Plant growth in response to a directional stimulus
PLANT GROWTH FACTORS PHOTOTROPISM IAA
β Cells in shoot tip produce IAA β IAA initially evenly distributed throughout all regions as plant grows β Light causes IAA to move to shady side β Build up of IAA on shady side causes it to bend towards the light
GRAVITROPISM IAA β Cells in roots produce IAA β Gravity influences this by moving IAA from upper side to lower side β Greater conc. On lower side β IAA inhibits elongation of root cells β Causing the lower side to grow slower than the upper side β Causes root to bend towards gravity
ROLE OF IAA IN ELONGATION β Transport of IAA is unidirectional β Response is only to young cells as old cells are rigid and cannot elongate β Elongates by having hydrogen ions being actively transported into spaces in the cell wall
causing to be more stretchy
A REFLEX ARC A REFLEX ARC
β Stimulus β Receptor β Sensory neuron β Coordinator (intermediate neuron) β Motor neuron β Effector β Response
A SIMPLE REFLEX ARC β Have fewer steps
IMPORTANCE OF REFLEX ARCS β Survival mechanism β Involuntary β Fast β Protect against damage to body tissue β Help escape from predators
RECEPTORS FEATURES OF SENSORY RECEPTION AS DEMONSTRATED BY THE PACINIAN CORPUSCLE
β Is specific to a single type of stimulus β Produces a generator potential by acting as a transducer
STRUCTURE AND FUNCTION OF A PACINIAN CORPUSCLE β Respond to pressure β At resting potential stretch-mediated sodium ion channels are too narrow for sodium ions to
pass along β When pressure is applied stretch-mediated channels become deformed β They widen allowing sodium ions to pass through and into the neuron β Itβs then depolarised and a generator potential happens β Then the action potential happens β Greater pressure more channels open more sodium ions diffuse through
ROD CELLS β Black and white β More numerous β Many rod cells are connected to a single sensory neuron so they have to summate to create a
generator potential β This means low visual acuity β Pigment = rhodopsin
CONE CELLS β Colour β Less numerous β One cone cell per sensory neuron β So high visual acuity β Pigment = iodopsin
CONTROL OF HEART RATE
SYMPATHETIC
β Stimulates β Speeds up
PARASYMPATHETIC β Inhibits effectors β Slows down
CONTROL OF HEART RATE β SAN sends out electrical signal to both atria causing them to contract β Atrioventricular septum, a non-conductive tissue stops it spreading to the ventricles β Electrical signal moves to AVN β Electrical signal moves down the purkinje fibres in the bundle of His β Electrical signal goes to base of ventricles and they both contract
CONTROL BY CHEMORECEPTORS β When blood has high conc. Of carbon dioxide blood pH is lowered β Chemoreceptors in carotid arteries and aorta detect this and increase impulses to the medulla
oblongata β Sympathetically the medulla sends signals to the SAN leading to faster heart rate β This causes greater blood flow meaning greater removal of carbon dioxide in the blood β Blood pH is normal, medulla oblongata reduces signals to SAN
CONTROL BY PRESSURE RECEPTORS β When higher than normal pressure receptors send signals to the medulla oblongata β Parasympathetically the SAN receives sends signals so decrease in heart rate β Lower blood pressure = opposite
NERVOUS COORDINATION AND MUSCLES DIFFERENCES BETWEEN THE NERVOUS AND HORMONAL SYSTEM
β Nervous system = slow and reversible β Hormonal system = fast and irreversible β Nervous System = localised β Hormonal system = widespread β Nervous system= Short lived β Hormonal system = Long lasting
STRUCTURE OF A NEURON β Cell body = Contains all the organelles β Dendrones / dendrites = Carry impulse to cell body β Axon = Carry nerve impulses away from cell body β Schwann Cells = Protection, insulation, phagocytosis
β Myelin sheath = Covers the schwann cells β Node of Ranvier = Parts between schwann cells which have no myelin sheath
NEURON CLASSIFICATION β Sensory neurons = Transmit nerve impulses from receptor to intermediate β Motor neurons = Transmits from relay or intermediate to effector β Intermediate / relay neurons = Transmits impulses between neurons
THE NERVE IMPULSE RESTING POTENTIAL
β Inside of axon is negatively charged relative to the outside making it polarised β Resting potential = -75mV
Maintained By: β Actively transporting sodium ions out of the axon β Actively transporting potassium ion into the axon β For every 3 sodium ions that move out 2 potassium ions move in β This is because membrane more permeable to potassium ions and less permeable to sodium
ions
ACTION POTENTIAL β Stimulus β Stimulus energy causes sodium gates to open and potassium gates to close β Sodium ions diffuse into axon causing more gates to open causing more sodium ions to
diffuse in β Once action potential of +40mV is established sodium gates close and potassium ones open β Potassium ions diffuse out of axon
HYPERPOLARIZATION
β Temporarily the potential difference is too negative (-90mV)
REPOLARISATION β Potassium sodium pump starts again and actively transports out sodium ions until the axon is
repolarised Note:
β For whatever reason the sodium ion channels are always open the neurons remain depolarised and no action potentials are generated leading to death
PASSAGE OF AN ACTION POTENTIAL UNMYELINATED NEURON
β Axon is polarised β Action potential β Axon depolarised β Localised electron currents cause the opening of sodium ion channels next it β Behind the localised current potassium starts leaving the axon, ensuring the current is
propagated in one direction across the axon β Behind the action potential the axon has repolarized β So is slower as cannot do saltatory conduction and the depolarisation is over the area of the
entire membrane
MYELINATED NEURON β Localised circuits occur at the nodes of ranvier β Jump from node to node, saltatory conduction so therefore faster
SPEED OF THE NERVE IMPULSE FACTORS AFFECTING NERVE IMPULSE
β Myelin sheath β Diameter of axon β Temperature
ALL OR NOTHING PRINCIPLE β If the stimulus doesnβt exceed the threshold value no action potential can be generated
THE REFRACTORY PERIOD β Sodium voltage, gated channels are closed so impossible for action potential to generated β Ensures action potentials are only propagated in one direction β Ensures the production of discrete impulses β Limits the number of action potentials
STRUCTURE AND FUNCTION OF SYNAPSE STRUCTURE OF A SYNAPSE
FEATURES OF SYNAPSE β Unidirectionality
Summation β Spatial Summation: Number of presynaptic neurons release neurotransmitter to exceed
threshold value β Temporal Summation: One presynaptic neuron releases neurotransmitter over s period of
time to exceed threshold value
INHIBITION β Presynaptic neuron releases neurotransmitter which binds to chlorine channels β Chlorine channels open β Cl- moves into post synaptic neuron by facilitated diffusion β At the same time K+ channels are open and K+ is diffusing out of postsynaptic neuron β Hyperpolarization, harder to create action potential
,
FUNCTIONS OF A SYNAPSE β Allows to only propagate in one direction because neurotransmitter in only produced in
presynaptic neuron
TRANSMISSION ACROSS THE SYNAPSE EFFECTS OF DRUGS ON SYNAPSE
β Drugs like Prozac:Produce more action potentials in the postsynaptic neuron β Drugs like Valium:Inhibits by binding Cl- channels so decreases the amount of action
potentials propagated
TRANSMISSION β Action potential causes Ca2+ channels to open β Vesicles that contain acetylcholine bind to presynaptic membrane β Acetylcholine diffuses across the cleft β Binds to Na+ channels on postsynaptic membrane β Influx of Na+ causes an action potential β Enzyme acetylcholinesterase breaks down neurotransmitter into acetate and choline β Diffuses back across cleft β Reformed by ATP produced by mitochondria in presynaptic neuron
STRUCTURE OF THE SKELETAL MUSCLE STRUCTURE
MICROSCOPIC STRUCTURE
β Actin - Thinner β Myosin - Thicker β I Band - Lighter because actin and myosin donβt overlap β A Band - Darker because actin and myosin do overlap β Z Line - Defines the limit of the sacrometer β M Line - The middle of the sarcomere
TYPES OF MUSCLE FIBRE Slow Twitch:
β Less powerful contraction β Aerobic, so numerous mitochondria and so many capillaries for good blood supply β Made for endurance
Fast Twitch:
β Powerful contraction β Thicker and more numerous myosin filaments β High conc. of glycogen β High conc. of enzymes involved in anaerobic respiration β Store of phosphocreatine, which can regenerate ADP β ATP in anaerobic conditions
COMPARISON OF THE NEUROMUSCULAR JUNCTION AND A SYNAPSE Neuromuscular Junction:
β Only excitatory β Only links to muscles β Only motor neurons involved β End of the neural pathway
Cholinergic Synapse:
β Maybe excitatory or inhibitory β Links to neurons or to effector organs β Motor, sensory and intermediate neurons may be involved β New action potential produced at postsynaptic neuron
CONTRACTION OF THE SKELETAL MUSCLE EVIDENCE FOR THE SLIDING FILAMENT MECHANISM
β I band becomes narrower β Z-lines move closer together β H-zones becomes narrower β A-band stays the same width
MUSCLE CONTRACTION β Action potential travels down the t-tubules β T-tubules are in contact which the sarcoplasmic reticulum which has calcium ion channels β Action potential opens these channels, Ca2+ diffuses into muscle cytoplasm down conc.
gradient β Ca2+ has receptors which bind to tropomyosin β Ca2+ moves the tropomyosin blocking the actin binding sites β Myosin binds to the binding sites forming a cross bridge β An ADP molecule is released once the myosin heads change their angle β ATP attaches to myosin head making it become detached β Ca2+ activates ATPase which hydrolyses ATP β ADP β Myosin heads then return to their original position
MUSCLE RELAXATION β Reabsorption of Ca2+ ions allows tropomyosin to block the binding sites again β Myosin heads are now unable to bind
HOMEOSTASIS WHAT IS HOMEOSTASIS
β The maintenance of an internal environment within the restricted limits of an organism
CONTROL MECHANISMS β Optimum point β Receptor β Coordinator β Effector β Feedback mechanism
COORDINATION OF CONTROL MECHANISMS Positive Feedback
β Deviation from the optimum causes a greater deviation from the optimum
Negative Feedback β Deviation from the optimum causes that deviation to be reversed
THERMOREGULATION IN ENDO AND ECTOTHERMS Endotherms
β Gain heat from metabolic activity β Ones that live in cold climates have a small surface area to volume ratio β Vasoconstriction: Diameter of arterioles near surface of skin become smaller so less heat
loss to environment Ectotherms
β Gain heat from the environment β Bask in the sun or seek shade
HORMONES AND THE REGULATION OF BLOOD GLUCOSE CONCENTRATION HORMONES AND THEIR MODE OF ACTION
β Produced in glands, excreted into the blood β Carried in blood plasma, acts on target cells β They have complementary shape to the specific hormone β Effective in small concs. have widespread effects
SECOND MESSENGER MODEL β Adrenaline binds to transmembrane receptor on hepatocyte CSM β Binding causes conformational shape in the 3D structure of the protein β Activates enzyme adenyl cyclase causes conversion of ATP β cAMP β cAMP = Secondary messenger activates enzyme kinase β Converts glycogen to glucose
THE ROLE OF THE PANCREAS IN REGULATING BLOOD GLUCOSE Has the islet of Langerhans
β Alpha cells - Produce glucagon β Beta cells - Produce insulin
THE ROLE OF THE LIVER IN REGULATING BLOOD SUGAR β Glycogenesis - Glucose β Glycogen β Glycogenolysis - Glycogen β Glucose β Gluconeogenesis - Production of glucose from non-carb sources
INSULIN AND THE BETA CELLS β When glucose concentration in the blood is too high β Insulin binds to glycoprotein receptors β Change in 3D structure of glucose transport channel protein allows more glucose into cells by
facilitated diffusion
β An increase in insulin causes an increase in vesicles with the channels in them. β So more of these vesicles bind to cells β Glycogenesis
GLUCAGON AND THE ALPHA CELLS β Glucagon attaches to specific protein receptors on liver CSM β Glycogenolysis β Gluconeogenesis
ROLE OF ADRENALINE β Attaches to specific proteins receptors on CSM of target cells β Glycogenolysis
DIABETES AND ITS CONTROL TYPES OF SUGAR DIABETES Type 1
β Canβt produce insulin Type 2
β Cells lose their responsiveness to insulin CONTROL OF DIABETES Type 1
β Injections of insulin Type 2
β Diet control
CONTROL OF BLOOD WATER POTENTIAL - STRUCTURE OF THE NEPHRON STRUCTURE OF THE MAMMALIAN KIDNEY
β Fibrous capsule - Outer membrane which protects the kidneys β Cortex - Lighter region made up of the Bowmanβs capsule and blood vessels β Medulla - Darker, made up of collecting ducts and loop of Henle β Renal pelvis - Funnel-shaped cavity that collects urine into the ureter β Ureter - Tube which carries urine into the bladder β Renal artery - Supplies kidney with blood via the aorta β Renal vein - Returns blood to the heart via the vena cava
STRUCTURE OF THE NEPHRON β Bowmanβs Capsule - Closed end at start of nephron, inner layer made of podocytes β Proximal convoluted tubule - A series of loops surrounded by blood capillaries β Loop of Henle - Extends from medulla to cortex surrounded by blood capillaries β Distal convoluted tubule - Same as PCT except surrounded by fewer capillaries β Collecting Duct - Where the contents of the DCT other nephrons empty into β Afferent arteriole - Bigger diameter, comes from the renal side and into the glomeruli
β Efferent arteriole - Smaller diameter, carries blood away from renal capsule β Glomerulus - Knot of capillaries, where ultrafiltration happens β Blood capillaries - Concentrated network of capillaries that merge together to form the
Bowmanβs capsule
ROLE OF THE NEPHRON IN OSMOREGULATION FILTRATE DEFINITION / EXPLANATION
β The product left over when water, glucose and inorganic ions are reabsorbed β Water lowers the concentration of filtrate
FORMATION OF GLOMERULAR FILTRATE BY ULTRAFILTRATION
β Blood enters through renal artery β Branches frequently to increase SA β Each arteriole enters the Bowmanβs capsule β This is called the afferent arteriole and merges to from the glomerulus and then merges to
form the efferent arteriole β The difference in pressure and diameter between the arterioles causes a build of hydrostatic
pressure within the glomerulus forcing water out, glucose and ions out β This forms glomerular filtrate β Blood and proteins are too big to leave the glomerulus
REABSORPTION OF WATER AND GLUCOSE BY THE PCT β 85 % of filtrate is reabsorbed β Na+ is actively transported out of PCT β Na+ diffuses down conc. Gradient of PCT lumen and by carrier proteins doing co-transport by
facilitated diffusion β The co-transported molecules then diffuse back into blood
Adaptations: β Microvilli for large SA β Lots of mitochondria for ATP for active transport
MAINTENANCE OF A GRADIENT OF SODIUM IONS BY THE LOOP OF HENLE Descending Limb
β Narrow, thin walls permeable to water Ascending Limb
β Wider, thicker walls impermeable to water Process
β Na+ actively transported out of ascending using ATP β Creates low WP, high ion conc., in the region of the medulla between the two limbs β Water doesnβt osmosis because thick walls β Descending has permeable walls so passes out of filtrate by osmosis into interstitial space
and enters blood capillaries
β Filtrate loses water creating lower WP at tip of ascending β Na+ is actively pumped out at base of ascending β Filtrate gets higher WP β In interstitial space between ascending and collecting duct thereβs a WP gradient, with the
lowest being in the surrounding capillaries β Water moves by osmosis out of collecting duct into blood β Countercurrent multiplier always ensures thereβs a WP gradient
THE DCT β Have high amounts of mitochondria in walls so can produce ATP to reabsorb material from
filtrate
COUNTERCURRENT MULTIPLIER β Fluid from collecting duct with low WP meets interstitial fluid with even lower WP β This means the maintenance of a conc. gradient for the entire length of the collecting duct
THE ROLE OF HORMONES ON OSMOREGULATION REGULATION OF THE WATER POTENTIAL OF THE BLOOD
β Osmoreceptors in the hypothalamus detect a the fall in the WP β Thought that when WP is low in blood osmoreceptors shrink β Causes hypothalamus to release ADH β ADH passes to posterior pituitary gland and secretes into the capillaries β ADH goes to the kidney β ADH binds to collecting duct CSM activates phosphorylase β Phosphorylase causes vesicles which contain aquaporins to bind to CSM β More then moves by osmosis back into blood β As blood WP increases less signals are sent by the hypothalamus so a decrease in ADH
INHERITED CHANGE GENOTYPE
β Genetic makeup of organism β All the alleles of an organism
PHENOTYPE β Observable characteristics of an organism β Result of the interaction between a genotype and the environment
GENE β Sequence of DNA which codes for a polypeptide
LOCUS β The position of a gene on the DNA molecule
ALLELE β Different form of a gene
DOMINANT β An allele which is always expressed in the phenotype
RECESSIVE β An allele which is only expressed in the phenotype if itβs homologous
HOMOZEYGOUS β Alleles of a gene are the same
HETROZEYGOUS β Alleles of a gene are different
MONOHYBRID INHERITANCE DEFINITION
β Breeding of alleles of one gene
TABLE
RATIOS
β The simplest proportion of expression of two different classes β Always divide by the smallest value
WHY OBSERVED RATIOS ARE DIFFERENT THAN EXPECTED β Fertilisation is random β Sample is too small β Natural selection advantage / disadvantage
DIHYBRID INHERITANCE DEFINITION
β The breeding of alleles of two genes
NOTATION β Example: Seed shape; Round = dominant Wrinkled = Recessive Seed Colour: Yellow=
Dominant Green= Recessive β So notation: R = Round, r = Wrinkled G = Yellow g = Green
TABLE
THE THEORETICAL RATIO
β 9:3:3:1, statistical test can compare results against this
CODOMINANCE AND MULTIPLE ALLELES CODOMIANCE
β Equally dominant alleles which are both expressed in the phenotype
NOTATION β Xy Where X = Gene and Y = Alleles
TABLE
MULTIPLE ALLELES
β Where a gene has multiple variations
EXAMPLE Blood Groups
β IA = Production of antigen A β IB = Production of antigen B β IO = Recessive only expressed if homozygous
SEX-LINKAGE DEFINITION
β X chromosome is longer than Y, so therefore the Y chromosome doesnβt have the equivalent homologous portion.
β If the X chromosome has a recessive allele on the equivalent homologous portion which is missing on the Y then recessive traits can be expressed in the phenotype
HEMOPHILIA β Recessive traits which cause the DNA of clotting factor to be altered so blood no longer clots
PEDIGREE CHARTS β If parents donβt have disease but kids do then itβs recessive β If itβs only in males then itβs sex linked
AUTOSOMAL LINKAGE DEFINITION
β Genes which are on the same chromosome
ASSUMPTIONS β No crossing over β No independent segregation β Less genetic diversity
EPISTASIS DEFINITION
β When one gene effects or masks the expression of another
CHI-SQUARED NULL HYPOTHESIS
β Assumption that there will be no statistical significance between different sets of results
CRITERIA β Sample size must be large β Must fall into discrete categories
CLASSES β Catagories
DEGREES OF FREEDOM β Number of classes - 1
ACCEPTING OR REJECTING NULL HYPOTHESIS β If above critical value accept null hypothesis as difference not significant and due to chance β If at or below critical value reject null hypothesis as difference significant and not due to
chance
POPULATION GENETICS GENE POOL
β All the alleles of all genes of all individuals at a particular time
ALLELIC FREQUENCY β The number of times an allele occurs within a gene pool
HARDY - WEINBERG PRINCIPLE WHAT IT MEASURES
β Allelic frequencies of dominant and recessive alleles
ASSUMPTIONS β No mutations β No immigration/ migration β No selection β Large population
β Random mating
EQUATIONS β q + p = 1 β q2 + 2pq + p2 = 1
CALCULATIONS β q2 = 1/fraction in population β q = square root of that β 1 - q = p β Sub into q2 + 2pq + p2 = 1
VARIATION IN PHENOTYPE VARIATION DUE TO GENETIC FACTORS All members in a population have the same genes but differences arise
β Mutations β Meiosis β Random fertilisation of gametes
VARIATION DUE TO ENVIRONMENTAL FACTORS β Environment can influence how genes are expressed β Genes have set limits but the environment sets where organism lies within these limits β All variation of genes are on a continuum (bell curve) and the environment dictates where
they land on that
NATURAL SELECTION PROCESS OF EVOLUTION
β Mutation in population β Mutation either selected for or against due to environmental pressures β If selected for then they are able to survive and reproduce and pass on their advantageous
alleles β Then theyβre able to survive and reproduce and on their advantageous alleles β The cycle continues
ROLE OF OVERPRODUCTION OF OFFSPRING IN NATURAL SELECTION
β Overproduction helps to overcome high death rate from predation and competition for food
ROLE OF VARIATION IN NATURAL SELECTION β Variation in offspring helps species to adapt to changing conditions β Larger populations = more genetic diversity β Variation provides opportunities for speciation
EFFECTS OF DIFFERENT FORMS OF SELECTION ON EVOLUTION STABILIZING SELECTION
β Preserves average phenotype, eliminates extremes
DIRECTIONAL SELECTION β Moves towards either extremes, average phenotype eliminated
DISRUPTIVE SELECTION β Selects both extreme phenotypes
ISOLATION AND SPECIATION
SPECIATION β Evolution of a new species from an existing one β Species are individuals with a common ancestry β Individuals in the same species can reproduce together to produce fertile offspring
ALLOPATRIC β Species become geographically separated β So canβt breed β Each environment has different selection pressures β Leading them to evolve until they become different species and canβt produce fertile offspring
SYMPATRIC β Speciation which happens in the same area β Can happen due to different selection pressures and young being brought up different areas
and only breeding with the young in that same area
POPULATIONS IN ECOSYSTEMS ECOSYSTEMS
β The community of different organisms and the abiotic factors within it
POPULATIONS β Group of individuals from a single species
COMMUNITY β All the populations of different species living and interacting in a particular place at a particular
time
HABITAT β A place where an organism lives
NICHE β How an organism fits into an environment and its purpose in that environment
ABIOTIC FACTORS Non-living factors
β Temperature β Light β pH β Water and humidity
COMPETITION INTRASPECIFIC
β In the same species
INTERSPECIFIC β Within different species
INVESTIGATING POPULATIONS QUADRATS
β Random coordinate generator β Placed not thrown β All organisms that are being measured are counted β Find area of quadrat β Find area of tested area β Area of field / Area of transect x counted organisms = Amount of organisms overall
TRANSECTS β Systematic β Allows to measure variation across the transect
MARK-RELEASE-RECAPTURE Sampling Techniques
β Draw grid over map of area β Use random coordinate generator
Equation β Total in 1st sample * total in 2nd sample / no. of marked recaptured
Assumptions β No immigration / migration β Marking method doesnβt kill or make more vulnerable to predators β No death in population β Mark isnβt rubbed off
SUCCESSION STAGES OF SUCCESSION
β Natural disaster
β Colonization of environment by pioneer species (e,g, fungi) β Pioneer species weather rocks to produce sand and soil β Then then die to produce nutrients for that soil β This allows for plants to grow in the nutrient dense soil β New species colonise and eat these plants β Plants die creating second layer to soil β More plants grow changing the environment so itβs less hostile so other organisms can live
there β Climax community, equilibrium
SECONDARY SUCCESSION β Happens after climax community established but a natural disaster happens again β Happens more rapidly
FEATURES OF A CLIMAX COMMUNITY β Stable community over a long time period β Abiotic factors are constant β Populations stable
GENE MUTATIONS SUBSTITUTIONS
β Change the structure the 3D structure of a protein by either causing the production a stop codon, making a codon for a completely different AA
DELETION/ ADDITION/ DUPLICATION β Change the structure the 3D structure of a protein by causing a frameshift causing a different
codon to be made
INVERSION
β Change the structure the 3D structure of a protein by section of DNA becoming detached and rejoining at the same place but at a different angle
TRANSLOCATION β Change the structure the 3D structure of a protein by section of DNA becoming deatched and
rejoining at a different place
CAUSES OF MUTATIONS
β Carcinogens β Ionising radiation
STEM CELLS AND TOTIPOTENCY CELL DIFFERENTIATION AND SPECIALISATION
β Every cell is capable of making every cell in the body because all cells have all genes
β However only certain genes are expressed in specialised, differentiated cells β Some genes are permanently switched on important chemicals
TOTIPOTENCY β Can become any cell in the body because all cells have all genes
STEM CELLS β Undifferentiated dividing cells which are in adult tissues
SOURCES OF STEM CELLS β Embryo β Umbilical cord β Placenta β Adult stem cells
TYPES OF STEM CELLS β Totipotent - Capable of being any cell because all cells contain all genes β Pluripotent - Capable of being almost any cell β Multipotent - Can differentiate into most type of cells β Unipotent - Can only differentiate into one type of cell
INDUCED PLURIPOTENT CELLS β Pluripotent cell made from a unipotent one β Capable of self renewal though β Could have infinite supply
REGULATION OF TRANSCRIPTION AND TRANSLATION EFFECT OF OESTROGEN ON GENE TRANSCRIPTION
β Transcriptional factors signal for transcription to begin so the gene is expressed as a protein β When the gene is not being expressed the transcriptional factor is not active
Process β Oestrogen is small and non-polar so therefore is lipid soluble and can diffuse the phospholipid
bilayer β Oestrogen binds to complementary receptor on TF β Conformational shape change reveals binding site β TF enters nucleus through nuclear pore β Binds to specific base sequence which itβs complementary to β Stimulates transcription
EPIGENETIC CONTROL OF GENE EXPRESSION EPIGENETICS
β Heritable changes in gene transfer β Which happen without a change to the nucleotide base sequence in DNA
EPIGENOME β The chemical tags on the DNA histone complex determines how spaced out or condensed
the DNA histone complex is
INCREASE METHYLATION/ DECREASED ACYLATION β Addition of methyl groups/ taking away acyl groups β Make DNA histone complex more condensed so gene not transcribed and therefore not
expressed as a protein
INCREASED ACYLATION/ DECREASED METHYLATION β Make DNA histone complex more spaced out so gene is transcribed and therefore expressed
as a protein
EPIGENETIC THERAPY β Use drugs to inhibit the expression of enzymes involved in certain diseases like cystic fibrosis β Or reactivate beneficial genes which are beneficial
THE EFFECT OF RNA INTERFERENCE ON GENE EXPRESSION β Enzyme binds to siRNA β siRNA acts as guide to mRNA because itβs complementary to the mRNA β siRNA binds to mRNA and splices it so itβs unuseable in protein synthesis
GENE EXPRESSION AND CANCER TYPES OF TUMOR Malignant
β Grow rapidly β Cells become unspecialised β Can metastasize
Benign
β Grow slowly β Differentiated β Localised
CANCER AND THE GENETIC CONTROL OF CELL DIVISION β Mutation causes uncontrolled cell division
ONCOGENES β Proto-oncogenes stimulate cell division when growth factors attach to a protein receptor the
CSM β This can mutate into an oncogene which causes uncontrolled cell division because it either
produces too much growth factor or protein receptor on CSM becomes permanently activated
TUMOUR SUPPRESSOR GENES β TSGs slow down cell division and activate apoptosis β Prevent cancer
ABNORMAL METHYLATION OF TUMOUR SUPPRESSOR GENES
β Increased methylation = DNA histone complex condensed so can be transcribed and TSG isnβt expressed as a protein
β TSG silenced β So uncontrolled cell division, tumor, cancer
OESTROGEN CONCENTRATIONS AND BREAST CANCER β Womenβs menopausal breast fat tissue produces oestrogen β Oestrogen mutates proto-oncogenes into oncogenes β Cause breast cancer
GENOME PROJECTS GENOME
β A complete map of all the genetic material in an organism
DNA SEQUENCING β Whole-genome shotgun sequencing β Cut DNA into small easily sequenced bits so to assemble genome
PROTEOME β All the proteins produced by the genome
DETERMINING THE GENOME AND PROTEOME OF SIMPLER ORGANISMS
β Easy because prokaryotic DNA is circular has no introns and is not associated with histones
DETERMINING THE GENOME AND PROTEOME OF COMPLEX ORGANISMS
β Challenge to translate the knowledge of the genome into the proteome
PRODUCING DNA FRAGMENTS RECOMBINANT DNA
β When DNA from one organism is incorporated / transferred into another
REVERSE TRANSCRIPTASE β RNA β DNA β Cells are chosen which produce desired protein
β These cells contain the mRNA of that protein β Reverse transcriptase is applied makes cDNA which is complementary to the mRNA β DNA Polymerase used to make double strand
USING RESTRICTION ENDONUCLEASES β Enzyme which splices DNA β Cuts at the recognition sequence β When cut between two opposite bases produces blunt ends β When cuts staggered produces sticky ends β So cuts required DNA sequence so to isolate that specific gene
GENE MACHINE β Complementary DNA sequence determined by the mRNA sequence and itβs AAs β Desired nucleotide sequence fed into computer β Checked to see if meets international standards β Computer designs small overlapping chains which cancel each other out β Oligonucleotides are assembled by the computer
Advantages β Quicker than enzyme controlled reactions
IN VIVO CLONING RESTRICTION ENDONUCLEASES
β If cut with same RENs then will be complementary to each other β So can just join together
PREPARING DNA FRAGMENT FOR INSERTION β Prep involves extra lengths of DNA β For transcription of gene to take place then RNA polymerase must bind to promoter region of
DNA β RNA polymerase is released from the DNA at the terminator region
INSERTION OF DNA FRAGMENT INTO A VECTOR β Once DNA has been spliced and promoter and terminator regions added β DNA is added to vector β Most common = plasmid β Same RENs used to make complementary sticky ends β Add enzyme ligase to join together sticky ends
However β Human DNA from genome cannot be directly introduced to a bacterial cell because human
DNA contains introns and the bacteria cannot remove these introns
INTRODUCTION OF DNA INTO HOST CELLS β Plasmids + bacteria introduced to each other in solution ca2+ so to make bacteria more
permeable β Vectors move in cytoplasm β To test which has taken up vector grow in medium of ampicillin β Plasmid contain antibiotic resistance gene for ampicillin
β So ones that havenβt taken up plasmid will die
ANTIBIOTIC RESISTANCE MARKER GENES β Replica plating so culture which has gene doesnβt die β Grow bacteria in medium of tetracycline β Gene interrupts antibiotic resistant gene so all bacteria which have desired gene will die
FLUORESCENT MARKER β Green fluorescent protein inserted β Desired gene interrupts GFP expression so doesnβt glow β Get rid of all bacteria which glow
ENZYME MARKER β Gene for enzyme lactase inserted β Usually turns substrate blue β But desired gene interrupts lactase so substrate should remain colourless
IN VITRO POLYMERASE CHAIN REACTION POLYMERASE CHAIN REACTION Requires
β DNA fragment to be copied β DNA polymerase β Primers β Nucleotides β Thermocycler
Process β Separation of the DNA- All the components put in thermocycler, temp increased 95 degrees
causing the two strands to separate β Annealing of Primers- Mixture cooled to 55 degrees causing primers to bind to DNA at their
complementary points. Primers provide starting points for DNA polymerase β Synthesis of DNA- Temp increased to 72 degrees, optimum temp for DNA polymerase to
join up sugar phosphate backbone and join up complimentary free nucleotides
ADVANTAGES OF GENE CLONING β Rapid (PCR) β Doesnβt require living cells (PCR) β Useful when we want to introduce a gene to another organism (Plasmid) β No risk of contamination (Plasmid)
DISADVANTAGES OF GENE CLONING β Ecological damaged from GM organisms β Would money be better spent
LOCATING GENES, GENETIC SCREENING AND COUNSELLING DNA PROBES
β Short strand of DNA which label on it to make it more identifiable β DNA probe is complementary to part of DNA which weβre finding
Radioactive Probe β Isotopes of nucleotides which are identified with x-rays
Fluorescently Labelled Probes β Emits light when the DNA strand anneal
DNA HYBRIDISATION β Combing singles strands of DNA or RNA β Heat so double strands separate β The cool so they recombine
LOCATING SPECIFIC ALLELES OF GENES β Refer to genetic libraries to determine nucleotide sequence β Fragment produced is complementary to allele a marker is then attached β Personβs DNA is heated so separates β If allele is present will bind to probe
GENETIC SCREENING β Carriers have family history of disease β Counselors can talk about risk β 100s of DNA probes used
PERSONALISED MEDICINE β Treats patient based on individual genotype β Can be used to identify dosages
GENETIC COUNSELLING β Help make informed decisions about childrenβs likelihood for inheritance β Discuss emotional, psychological issues
GENETIC FINGERPRINTING GENETIC FINGERPRINTING
β Relies on everyone on having different variable number tandem repeats β People who are related to each other have similar VNTRs
GEL ELECTROPHORESIS β Separates DNA fragments according to their size β Fragments placed in gel and electric current is sent through it β Resistance of gel means bigger they are slower they move and vice versa
INTERPRETING THE RESULTS β Sent through computer to calculate length of DNA fragments from bands β Measures distance travelled during electrophoresis by known lengths of DNA β The odds are then calculated that the samples match
USES β Genetic relationships β Forensic science β Medical diagnosis β Plant and animal breeding
