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