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240 Cards in this Set
- Front
- Back
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Stimulus |
Detectable change in the internal or external environment that produces a response in an organism |
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What is the advantage of being able to respond to stimuli? |
Move away from threats, increasing the chance of survival. Those will therefore have a greater chance of raising offspring and passing on their beneficial alleles to the next generation (acting as a selection pressure) |
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Taxis |
Directional response to a directional stimulus |
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Kinesis |
Random response to a changing stimulus by changing the amount of activity |
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What is the aim of kinesis? |
Keep the organism in a favourable environment |
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Tropism |
Growth movement of a part of a plant in response to a directional stimulus |
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Tropsim present in plant shoots? |
Positive phototropism |
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Tropism present in plant roots? |
Positive geotropism Negative phototropism Positive hydrotropism |
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What are kinesis and taxis both examples of? |
Behavioural mechanisms aimed to maintain homeostasis |
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State sequence of events from stimulus to response |
Stimulus Receptor Sensory neurone Interneurone Motor neurone Effector Response |
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Two major divisions of the nervous system |
Central nervous system Peripheral nervous system |
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Two divisions of the central nervous system |
Motor neurones Sensory neurones |
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Two divisions of motor neurones |
Autonomic nervous system Voluntary nervous sytem |
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Description and importance of reflex arcs |
Controlled by the autonomic nervous system producing an involuntary response protecting the body from harmful stimuli. Quick because does not require decision-making powers of the brain and is monosynaptic meaning that the neurone pathway is short |
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Two divisions of the autonomic nervous system |
Parasympathetic - rest or digest Sympathetic - fight or flight |
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Difference between conditioned/unconditioned reflexes |
Unconditioned reflexes are not learned |
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Neurotransmitter of parasympathetic nervous system |
acetylcholine |
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Neurotransmitter of sympathetic nervous system |
noradrenaline |
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Coordinator for controlling heartbeat |
Medulla oblongata |
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Process for decreasing heartbeat |
Parasympathetic Impulse sent via neurones from medulla oblongata's cardioinhibitory centre to the heart releasing neurotransmitter acetylcholine into the sinoatrial node inhibiting the production of impulses at SAN meaning that rate of heartbeat and strength of each contraction decreases |
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Process for increasing heartbeat |
Sympathetic Impulse sent via neurones from medulla oblongata's cardioaceletatory centre to the heart releasing noradrenaline into the sinoatrial node stimulating the production of impulses at SAN meaning that rate of heartbeat and strength of each contraction increases |
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Where are chemoreceptors/baroreceptors located? |
Carotid arteries Walls of aorta |
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Effect of exercise on cardiac output |
Chemoreceptors found in carotid arteries/walls of aorta detect the decrease in pH of the blood as a result of the increased production of CO2 from respiration. Chemoreceptors send a higher frequency of impulses via neurones to the medulla oblongata's cardioacceletory centre which increases the frequency of impulses sent via sympathetic nervous system to the heart's sinoatrial node which in turn increases the heart rate. This increases blood flow and so carbon dioxide is removed by the lungs more quickly so that the blood's pH reverts to normal. |
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Which system is stimulated when blood pressure is higher than normal? |
Cardioinhibitory centre of medulla oblongata Nerve impulse along vagus nerve Parasympathetic nervous system |
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Which system is stimulated when blood pressure is lower than normal? |
Cardioacceletory centre of medulla oblongata Sympathetic nervous system |
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Describe structure and function of Pacinian corpuscle |
Sensory mechanoreceptor found in the skin which detects pressure acting as a transducer to produce an generator potential Senesory neurone ending surrounded by a capsule - layers of lamella - which are fluid filled |
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What happens when pressure is applied to the Pacinian corpuscle? |
Capsule is deformed and so increases permeability of the stretch mediated sodium channels meaning that sodium ions diffuse towards the sensory neurone ending producing a generator potential which in turn creates an action potential (if the generator potential exceeds the threshold) |
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What is retinal convergence and which type of photoreceptors have it? |
Number of different rod cells connected to the same bipolar cell |
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Describe sequence of events of eye enabling us to see |
Light enters pupil of eye, hitting photoreceptors and is absorbed by light-sensitive pigments Light bleaches the pigments, causing a chemical change and altering the membrane permeability to sodium creating a generator potential. Nerve impulse is sent along a bipolar neurone to the optic nerve (brain) |
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Rods: distribution,visual acuity, sensitivity |
high in peripheral, low in fovea low visual acuity very sensitive, works at low light intensities |
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Cones: distribution, visual acuity, sensitivity |
high in fovea, low in peripheral high visual acuity only works at high light intensities |
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Why do cones have high visual acuity? |
Cones lack retinal convergence and so if two adjacent cone cells are stimulated then two separate impulses are received meaning that two dots appear as two dots |
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Why do cone cells have low light intensity |
Cones lack retinal convergence and so in order for a generator potential to exceed the threshold to produce an action potential they cannot rely on summation. |
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Pigment in rods |
Rhodopsin -> retinal and opsin |
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Pigment in cones |
Iodopsin (three types which correlate to the trichromatic theory) |
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Pathway of sensory neurones |
Receptors to CNS |
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Pathway of motor neurones |
CNS to effector |
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Pathway of interneurone |
Sensory neurone to motor neurone |
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Two forms of coordination and their differences |
Hormonal - long lasting, widespread, blood stream Nervous system - short lasting, localised, neurones |
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IAA |
Auxin which stimulates shoot growth and inhibits root growth Controls apical dominance Made in the shoot apex, transported cell to cell via diffusion or via phloem |
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Effect of unilateral light on plant shoot |
Light induced destruction of auxin causes increased concentration of auxin to accumulate on darkened side causing shoot cells to elongate and thus bend towards the light |
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Effect of unilateral light on plant root |
Auxin accumulates on darkened side but decreases root growth meaning that root cells elongate and thus bend away from the light |
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What is apical dominance? |
Main stem grows faster than lateral shoots |
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Effects of these different plant growth factors: Ethene Gibberellins Cytokinins Abscisic acid |
Ethene - Seed dormancy, fruit ripening and leaf absicion (falling leaves in autumn) Gibberellins - Promotes stem elongation Cytokinins - promotes growth Absicisic acid - inhibits growth |
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Function of cell body in neurones |
Contains nucleus and rough endoplasmic reticulum in order to synthesise neurotransmitters |
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Function of Schwann cells in neurones |
Provide electrical insulation and protect axon Phagocytosis of damaged neurone cell debris |
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Structure, function and importance of myelin sheath |
Lipid layer wraps around axon providing electrical insulation and so results in faster transmission of electrical impulse |
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In which direction does a nerve impulse travel along an axon? |
Away from cell body |
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In myelinated neurones where does depolarisation occur? |
Nodes of Ranvier where sodium ion channels are concentrated |
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Name of process of transmission of nerve impulse in myelinated neurone |
Saltatory conduction |
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Name of process of transmission of nerve impulse in unmyelinated neurone |
Propagation |
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Is it an advantage for an axon to have a big/small diameter? Why? |
Big - results in quicker conduction Less resistance to flow of ions so depolarisation reaches parts of neurone cell quicker |
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How is speed of conduction affected by temperature? |
Higher temperature results in faster conduction because ions will therefore diffuse faster (up until point of denaturing) |
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What is the voltage across a membrane at its resting potential? |
-65mV |
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Compare relative charges either side of membrane at resting potential? Why is this so? |
Inside of axon is more negative than the outside. More positively charged ions (Na+) actively transported out of axon than positively charged ions (K+) being transported into the axon. This creates a chemical gradient. |
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What does the sodium-potassium pump do? What is the sodium-potassium pump? |
Actively transports three sodium ions out of the axon and two potassium ions into the axon. Intrinsic ion channel found within phospholipid bilayer |
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Which ion channels are open/closed at resting potential? What is the result of this? |
Sodium ion channels closed so they cannot diffuse back into axon. Potassium ion channels open meaning that they can diffuse out of axon. Causes greater potential difference as more positively charged ions move/held outside of axon. |
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Why is further outward movement of potassium ions difficult at resting potential? |
Repulsion occurs from positive surrounding tissue fluid Attraction occurs between high relatively positive outside of axon and negative inside of axon. |
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What does equilibrium mean in regards to resting potential? |
Electrical and chemical gradients balanced No net movement of ions |
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State sequence of events of action potential |
Stimulus Depolarisation Repolarisation Hyperpolarisation Resting Potential |
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What happens when the axon is stimulated? |
Voltage-gated sodium channels open causing influx of sodium ions into the axon down electrochemical gradient making the inside of the axon less negative....Depolarisation |
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What occurs during depolarisation of axon? What voltage is it? |
Influx of sodium ions into neurone by diffusion causes inside of neurone to be more positive than outside. +40mV |
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What occurs during repolarisation of axon? What voltage is it? |
Voltage gated sodium ion channels close so that sodium ions can no longer move into inside of axon. Potassium ion channels open meaning that potassium ions move out of axon via facilitated diffusion down electrochemical gradient. -65mV |
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What occurs during hyperpolarisation of axon? What voltage is it? |
Potassium ion channels slow to close and so too many potassium ions diffuse out of neurone meaning that inside of axon becomes too negative. More negative than -65mV |
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What is the refractory period and what is the importance of it? |
Time delay after an action potential whereby ion channels are unable to open meaning that action potentials are discrete, don't overlap and are unidirectional. |
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What does a bigger stimulus mean in regards to an action potential? |
More nerve impulses fired, more frequently Action potential is THE SAME SIZE |
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What is the purpose of large negative proteins in the axoplasm? |
Adhere to positive K+ ions in axoplasm (inside of neurone) buffering potential difference at -65mV |
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Nerve impulse |
Self propagating wave of electrical disturbance that travels along the surface of the axon membrane |
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State all-or-nothing principle |
If a stimulus does not exceed the threshold value then an action potential will not be triggered = nothing If a stimulus does exceed the threshold value then an action potential will be triggered = all |
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State process of propagation in unmyelinated axon |
Stimulus triggers voltage gated channel proteins to open causing depolarisation. Localised electrical circuits cause the opening of sodium voltage gated ion channel proteins further along axon. Behind this region repolarisation occurs by the closing of sodium ion channels/opening of potassium ion channels Impulse is continuously conducted along axon |
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State the process of saltatory conduction in myelinated axon |
Action potentials arise at adjacent nodes of Ranvier where voltage gated sodium ion channels are located, and so this allows nerve impulse to bypass the insulating lipid-rich myelin sheath. Localised circuits jump from node to node causing faster conductance of nerve impulse. |
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Synapse |
Point where axon of one neurone meets effector/ dendrite of another neurone |
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Function of synapse |
Transmit impulses from one neurone to the next neurone |
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How can we identify the presynaptic neurone? What does this ensure? |
Contains synaptic vesicles containing neurotransmitters Unidirectionality |
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What is the small gap between neurones called? |
Synaptic cleft |
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When and how is the neurotransmitter transmitted across a synapse? |
Action potential reaches presynaptic neurone (knob) causing synaptic vesicle to fuse with presynaptic knob's membrane and be diffused across the synaptic cleft. Neurotransmitter reaches receptor molecules on postsynaptic neurone |
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Name and explain the 2 types of summation? What is the point? |
Allows small stimuli which generate insufficient amounts of neurotransmitter to exceed threshold value required to generate action potential - effect of stimulus is amplififed Temporal - single presynaptic neurone releases neurotransmitter in quick succession over short period of time. Spatial - number of different presynaptic neurones release enough neurotransmitter. |
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Why are synapses slower in transmitter nerve impulses? |
Rate of diffusion slower than propagation |
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Describe inhibition of nerve impulses |
Neurotransmitter prevents action potential being generated in postsynaptic neurone
Chloride ion channels open causing influx diffusion of negative ions causing hyperpolarisation of postsynaptic neurone so that new action potential is less likely |
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Cholinergic synapse |
Neurotransmitter is acetylcholine |
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Mechanism of transmission across cholinergic synapse |
Incoming action potential causes depolarisation in the synaptic knob. Calcium channels open and calcium ions flood into synaptic knob. Influx of calcium ions causes synaptic vesicles to fuse with presynaptic membrane, releasing neurotransmitter acetycholine across synaptic cleft via diffusion before binding to sodium ion channels on postsynaptic neurone. When the neurotransmitter binds there is a conformational change opening the sodium ion channels allowing sodium ions to influx down electrochemical gradient. Postsynaptic neurone becomes depolarised, if this exceeds the threshold value then an action potential is sent along the axon. |
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Describe the two ways in which a drug can cause effect on synapses |
1.Stimulate more neurotransmitter to be released/create more action potentials/break down enzyme that breaks down neurotransmitter 2.Inhibit release of neurotransmitter/block receptors of postsynaptic neurone/create fewer action potentials |
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Why can sodium and potassium ions only cross axon membrane through proteins? |
Phospholipid bilayer isn't lipid soluble |
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Where is skeletal muscle found? |
Attached by tendons to bones - voluntary muscle |
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Where is smooth muscle found? |
Lining of digestive system - involuntary muscle |
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What are the two types of skeletal muscle? |
Slow-twitch fibre Fast-twitch fibre |
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Properties of fast-twitch fibres |
Respires anaerobically (enzymes present) Short bursts of activity - sprinting Fast contraction speed Lactate production leads to low pH and muscle fatigue Contains lots of glycogen Uses phosphocreatine to generate ATP from ADP |
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Properties of slow-twitch fibres |
Respires aerobically Long bursts of activity - endurance Slow contraction speed Not susceptible to muscle fatigue Contains many mitochondria and myoglobin |
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Two types of protein filament in myofibrils |
Actin - thinner, two strands twisted around each other Myosin - thicker, protruding bulbous heads |
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Sarcoplasm |
Cytoplasm fused/ shared by many muscle fibres containing many nuclei, mitochondria and endoplasmic reticulum |
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Name of lighter bands of muscle? Why are they lighter? |
isotropic band I-band Actin and myosin do not overlap/ only actin present |
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Name of darker bands of muscle? Why are they darker? |
anisotropic band A-band Thicker myosin present/ overlaps with actin |
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Centre of A-band is called |
H-band |
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Centre of I-band is called |
Z-band |
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Sarcomere |
Distance between adjacent Z-lines (run parallel to one another to withstand high tension) |
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Neuromuscular junction- what is it and why are they important? |
Where motor neurone meets skeletal muscle fibre Allows rapid wave of contraction across entire muscle through simultaneous stimulation by action potentials |
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What is the purpose of acetylcholinerase |
Break down acetylcholine neurotransmitter to prevent over-stimulation of muscle |
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Structure of actin |
Helix of actin containing binding site for myosin head Protein tropomyosin wound around actin Troponin (containing calcium binding sites) bound to tropomyosin |
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Describe process of myofilament contraction |
When muscle is relaxed tropomyosin blocks myosin binding site on actin. Action potential penetrates to centre of muscle fibres via transverse tubules causing calcium ions in sarcoplasmic reticulum to diffuse out of the myofibrils and bind to the troponin causing them to change shape and move the tropomyosin out of the way, exposing the binding site for myosin. Myosin head binds to binding site on actin filament before flexing, pulling the actin filament along with it. Breakdown of ATP in myosin head (activated by calcium ions) causes myosin head to release from actin and unflex, freeing the myosin head to bind with a different actin molecule, farther up the actin filament. |
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Describe process of myofilament relaxation |
Calcium ions actively transported back into sarcoplasmic reticulum powered by hydrolysis of ATP causing tropomyosin molecules to block myosin binding sites on actin. |
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How do very active muscles rapidly generate ATP |
Phosphocreatine provides supply of inorganic phosphate which combines with ADP to form ATP |
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Describe changes to sarcomere in sliding-filament theory |
I-band narrower Sarcomere shortens H-zone narrower A-band remains same as length of myosin stays same |
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Homeostasis |
Maintaining a constant internal environment |
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Set point of blood glucose concentration |
90mg per 100cm^3 |
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Importance of homeostasis |
Prevent osmotic lysis - water potential Prevent denaturing of enzymes - temperature/pH Independence - thermoregulation |
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Ways of gaining heat |
Metabolism of food generates heat Conduction/convection/radiation from environment |
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Ways of losing heat |
Evaporation of sweat Conduction/convection/radiation from environment |
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Conduction |
Transfer of energy in solids via vibrations and kinetic energy |
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Convection |
Transfer of energy in fluids/gases |
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Radiation |
Transfer of energy from electromagnetic waves (sun) |
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Differences between ectotherms and endotherms |
Endotherms are warm blooded; ectotherms are cold blooded. Endotherms have a higher metabolic rate Endotherms are more dependent meaning that they don't rely on their environment for thermoregulation |
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Exceptions to set points |
During a fever our temperature rises in an effort to kill pathogens During hibernation metabolic rate decreases to conserve energy/food |
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Control mechanisms when body temperature rises: Stimulus-Receptor Control centre Effector Response Negative feedback |
Thermoreceptors in skin detect increase in temperature and send nerve impulses along autonomic nervous system to hypothalamus. Hypothalamus (heat loss centre) in brain sends nerve impulse to blood vessels and sweat glands. Vasodilation and increased sweating Homeostasis restored - no more stimulus |
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Control mechanisms when body temperature decreases: Stimulus-receptor Control centre Effector Response Negative feedback |
Thermoreceptors in skin detect decrease in temperature and send nerve impulses along autonomic nervous system to hypothalamus. Hypothalamus (heat gain centre) in brain sends nerve impulses to sweat glands and blood vessels. Vasoconstriction, shivering and decreased sweating Homeostasis restored - no more stimulus |
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Vasoconstriction |
Diameter of arterioles decrease reducing volume of blood reaching surface of skin (little heat radiated) through capillaries Shunt vessel dilated and so most blood passes beneath insulating layer of fat. |
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Vasodilation |
Diameter of arterioles increase, increasing volume of blood reaching surface of skin (more heat radiated) through capillaries Shunt vessel constricted and so most blood passes through capillaries instead. |
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Describe process and explain importance of hair raising |
Heat gain centre in hypothalamus sends motor neurone to neuromuscular junction for hair erector muscles in skin to contract, trapping a layer of warm air close to the skin (insulation) and reducing loss of heat to environment through radiation by reducing temperature gradient. |
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Glycogenolysis |
Stored glycogen broken down into glucose |
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Gluconeogenesis |
Conversion of non-carbohydrates such as amino acids into glucose |
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Is oestrogen lipid soluble? |
Yes |
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Is insulin lipid soluble? |
No |
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Hormones used in control of blood glucose concentration and where secreted from? |
Glucagon - secreted from alpha cells of islets of Langerhans in pancreas, used to increase blood glucose concentration Insulin - secreted from beta cells of islets of Langerhans in pancreas, used to decrease blood glucose concentration |
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State events which occur when blood glucose concentration is too high |
Insulin released from beta cells and binds to specific (glycoprotein) receptors on liver and muscle cells increasing their permeability to glucose (all glucose channels present open). Insulin activates enzymes which drive glycogenesis and increases the rate of respiration of glucose |
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State events which occur when blood glucose is too low |
Glucagon released from alpha cells and binds to specific (glycoprotein) receptors on liver cells. Glucagon activates enzymes which drive glycogenolysis and gluconeogenesis, and decreases rate of respiration of glucose |
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How and where to are hormones carried? |
Carried in blood plasma to target cells |
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What is the first messenger and what does it do? |
Hormone Activates an enzyme that acts as secondary messenger |
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What does a secondary messenger do? |
Cause a cascade of reactions to bring about the required response cAMP |
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hypoglycaemia |
low blood glucose concentration |
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hyperglycaemia |
high blood glucose concentration |
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Examples of antagonism |
Muscles Insulin/Glucagon |
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Describe second messenger model |
Primary messenger binds to receptor activating an enzyme called adenyl cyclase to convert ATP into cAMP which acts as a second messenger to activate other enzymes for glucogenesis/glycogenolysis |
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Where is adrenaline produced and how does it raise blood glucose levels? |
Adrenal glands Activates enzyme for glycogenolysis Activates enzyme for gluconeogenesis |
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Type 1 diabetes |
Beta cells of islets of Langerhans in pancreas don't produce any insulin and so after a rise in blood glucose level it remains high resulting in hyperglycaemia. Kidneys cannot absorb all this glucose so excess is excreted in urine. Regular injections of insulin given |
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Type 2 |
Beta cells of islets of Langerhans don't produce enough insulin or insulin receptors have lost their responsiveness to insulin Linked with obesity, acquired later in life Control carbohydrate intake and lose weight |
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What triggers negative feedback? |
Deviation from set point triggers corrective mechanisms until set point reached and so corrective measures turned off |
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Ideal body temperature set point |
37 degrees celsius |
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What is positive feedback? |
Corrective measures remain turned on and so a deviation from normal conditions is amplified, leading to a further deviation |
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Function of FSH |
Stimulate development of follicles |
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What does FSH stimulate? |
Oestrogen |
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Function of LH? |
Ovulation |
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What does LH stimulate? |
Progesterone from the corpus luteum |
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Function of oestrogen |
Rebuilding of uterus |
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What does oestrogen stimulate? |
LH |
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Function of Progesterone |
Maintain lining of uterus |
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What does progesterone inhibit? |
FSH |
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What two hormones are released from the pituitary gland? |
FSH and LH |
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What two hormones are released from the ovaries? |
Oestrogen and progesterone |
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What do low levels of oestrogen cause? |
Inhibition of LH and FSH |
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What does inhibition of LH by low levels of oestrogen do? |
Prevent early ovulation |
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What does inhibition of FSH by low levels of oestrogen do? |
Ensure only one follicle is developed |
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What does inhibition of FSH by progesterone do? |
Ensure only one follicle is developed and so that only one fertilised embryo develops if pregnant |
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What causes bleeding during oestrous cycle? |
Low levels of progesterone |
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How is infertility treated? |
FSH stimulates production of more eggs by promoting development of follicles |
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How do birth control tablets work? |
High levels of progesterone inhibits FSH which in turn stops eggs maturing in the ovaries |
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What occurs at point of surge of LH |
Ovulation |
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What is a corpus luteum? |
Empty follicle (after ovulation) which secretes progesterone |
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Genome |
Total amount of genetic information in a single set of chromosomes of an organism |
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Function of DNA |
Contain all information necessary for growth, development and replication of an organism in a stable state to pass onto future generations |
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Phosphodiester bond |
Bond between inorganic phosphate and ribose sugar of neighbouring nucleotides in DNA |
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Pyrimidines |
Single ring nitrogenous bases - thymine and cytosine |
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Purines |
Double ring nitrogenous bases - adenine and guanine |
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Gene |
Specific sequence of bases which code for a particular protein |
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How many hydrogen bonds between complementary base pairs adenine and thymine? |
2 |
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How many hydrogen bonds between complementary base pairs cytosine and guanine? |
3 |
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Codon |
Sequence of three nucleotides coding for one amino acid |
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Shape of DNA |
Coiled double helix |
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Shape of mRNA |
Linear, single strand |
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Shape of tRNA |
Clover shape |
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When does quantity of DNA change? |
During replication in preparation for cell division |
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Why is the quantity of RNA variable? |
Quickly degrades due to its instability |
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Why is it necessary for mRNA to be unstable? |
So that when you have an adequate supply of a particular protein you need not make any more as this would be wasteful. |
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A gene always starts with what codon? |
AUG |
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A gene always finishes with what codon? |
Stop codon |
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Features of DNA |
Read in one direction One triplet codes for one amino acid Each amino acid may be encoded by one or more different DNA triplets - degenerate Non-overlapping Universal |
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Exons |
Functional sections of DNA used for protein synthesis |
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Introns |
Non-functional sections of DNA not used in protein synthesis and so are spliced out |
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Splicing |
pre-mRNA is spliced by snRPS which form a lariat to break the covalent sugar-phosphate bonds, producing a spliceosome to excise the intron and ligate the two exons together. This creates mature mRNA which can be used for translation |
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Spliceosome |
large complex of snRNPs |
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Evolutionary advantages of introns |
Change in genotype in introns will not result in a mutation in the amino acid sequence. There will be no change in phenotype. |
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Evolutionary advantages of not having introns |
Less DNA allows faster replication meaning that organism can adapt to environment more rapidly and thus outcompete other organisms |
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Structure of tRNA |
Three organic bases = anticodon Carries amino acid |
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Transcription |
DNA helicase breaks the hydrogen bonds separating the two strands and thus exposing the nucleotide bases in the region of the gene to be copied. RNA polymerase joins free complementary nucleotides from within the nucleus to those on template strand. DNA strands rejoin behind this process limiting the number of base pairs exposed at one time. Transcription finishes once the stop codon is reached. mRNA strand is now formed and passes out the nuclear pore and goes to the ribosome for protein synthesis. |
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Translation |
Starting codon on mRNA attaches to ribosome and tRNA molecules with complementary anticodons to the mRNA's codons carry a specific amino acid into position so that peptide bonds can form to create a polypeptide chain |
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What is a substitution gene mutation, what are the three kinds and what are their effects? |
Replacing one nucleotide with another 1.Nonsense- forms a stop codon causing production of polypeptide to stop prematurely 2.Mis-sense - forms a different amino acid which may result in a non-functional protein 3. Silent - formation of same amino acid despite having a different nucleotide as a result of the degeneracy of the code |
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What is a deletion gene mutation and what is its effect? |
Losing a nucleotide from the DNA sequence resulting in a frame shift meaning that the triplets read code for complemetely different amino acids which may lead to the formation of a non-functional protein. |
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List three mutagens |
Random, spontaneous during DNA replication High energy radiation Chemicals i.e tar in cigarette smoke |
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Will a deleted base at the beginning or end of a sequence have a greater impact? |
Beginning - all triplets downstream are affected |
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Benefits of random mutations |
Produce the genetic diversity necessary for natural selection and speciation |
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Cons of random mutations |
May result in an organism being less well suited to its environment and so will be out-competed by other organisms. |
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What is the difference between mutations in body cells and mutations in gametes? |
Mutations in body cells are not inheritable whereas mutations in gametes can be passed on to the next generation |
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Function of proto-oncogenes |
Stimulate cell division |
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Function of tumour suppressor genes |
Slow cell division (by producing proteins that stop cells dividing or cause them to self destruct-apoptosis) |
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Why do most cells divide at a fairly constant rate? |
Replace won out/dead cells |
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Control of cell division in a normal cell and how a mutated proto-oncogene (oncogene) can affect this. |
Growth hormone binds to complementary receptor protein on cell surface membrane which send relay proteins through the cytoplasm to activate the genes necessary for DNA replication. A mutated proto-oncogene (oncogene) may cause the receptor protein to continuously be activated even in the absence of growth factors. An oncogene may produce excessive amounts of the growth hormone. |
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Which cells are most prone to the effects of mutations? |
Those most rapidly dividing |
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Benign cancer |
Doesn't spread to other parts of the body |
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Malignant cancer |
Does spread to other parts of the body and affect the functioning of the cells around it. |
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Features of stem cells |
Unspecialised Embyonic - pluripotent Proliferate (divide) infinitely |
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Why do differentiated cells differ from each other? |
Each have different genes which are/aren't expressed and so they each produce the different proteins required for their specific function as stimulated by their microenvitronment |
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Two types of human stem cells |
Embryonic Somatic |
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Where are adult (somatic) stem cells found? |
Lining of small intestine Bone marow Dental pulp of wisdom teeth |
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Hayflick limit |
Number of times a cell can divide via mitosis beofe it stops dividing (senescence) and dies (apoptosis) |
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Which type of cells have no Hayflick limit? |
Embryonic stem cells |
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Arguments for embryo cell research |
Pluripotency opens the possibilities of using them to treat life-threatening diseases Makes use of spare embryos such as those following abortion The blastocyst used is not in fact a human, it is merely a group of 3-5 day old unspecialised cells which have no feelings. |
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Arguments against embryo cell research |
Un-ethical to kill what could eventually become a human May devalue life Could lead to dehumanising creation of clones |
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Arguments for adult stem cell research |
Found in more parts of the body than thought and found to be more potent than originally thought Could be taken from the patient themselves, reducing the risk of rejection by the patient's immune system |
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Arguments against stem cell research |
Lower potency than embryonic stem cells Obtaining adult stem cells requires invasive surgery - high chance of infection More time consuming and less cost effective |
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Differentiation |
Process of becoming specialised |
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Totipotent |
A cell that has the potential to divide and form any other specialised cell type, including undifferentiated stem cells |
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Pluripotent |
A cell that can divide to form a wide range but not all other specialised cell types |
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Multipotent |
A cell that can divide to form a limited number of other specialised cell types |
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Explant |
Sectioned piece of plant with desirable characteristics containing undifferentiated totipotent cells |
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How can totipotent cells be maintained in an undifferentiated state? |
Regularly transferred to a fresh nutrient medium |
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Why must the nutrient medium be sterile for micropropagation? |
Microorganisms can't grow and compete with the plant cells |
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Advantages of micro-propagation |
Produces genetically identical clones with the same desirable characteristics Rapid way of selective breeding High success rate Important for conservation as could be used to clone endangered plants |
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Disadvantages of micro-propagation |
Growth hormones can be costly Bacteria can ruin large numbers of plants All genetic flaws passed on to next generation Lower genetic variation means more prone to devastation when exposed to disease/predators |
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What must occur for transcription to occur? |
Transcription factor must bind to target promotor section of DNA |
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Describe position of transcription factor when a gene is not being expressed |
Unable to bind to target promotor section of DNA because inhibitor molecule is in the way |
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Effect of oestrogen on gene transcription |
Pre transcription: Oestrogen passes through plasma membrane into cytoplasm before binding to receptor molecule of transcription factor, which changes the shape of the receptor, causing the inhibitor to be released. Transcriptional factor can now pass through the nuclear pore and bind to target section of DNA to stimulate transcription |
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Effect of siRNA on gene expression |
After transcription: RNA molecules base pair with themselves to form a hairpin loop and are then placed in a lipid solution. Enzyme Dicer cuts the RNA to form siRNA. One of the two siRNA molecules binds to enzyme RISC causing that siRNA to bind to complementary base pairs on mRNA. Induced cleavage of mRNA causes it to be cut into non-translatable sections - gene will not be expressed |
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What is siRNA? |
Small double stranded sections of RNA
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Why is dsRNA placed in a liposome for in vitro post-transcriptional gene regulation? |
Allows liposome to fuse with cell membrane and thus deliver the dsRNA via endocytosis |
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Why is inserting siRNA less effective than dsRNA for post-transcriptional |
One dsRNA can be broken down by Dicer into lots of different types of siRNA to target the gene(s) for down-regulation more heavily |
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Pre-transcriptional gene regualtion |
Oestrogen |
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Post-transcriptional gene regulation |
siRNA |
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Post-transcriptional modification |
Splicing |
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What form is the genetic information in retroviruses? |
RNA |
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Function of reverse transcriptase |
Synthesise DNA from RNA (sourced from retroviruses) |
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Details of how reverse transcriptase works |
mRNA coding for gene of interest is extracted. Reverse transcriptase produces cDNA from this mRNA template strand. cDNA is then used as a template strand for DNA polymerase in order to form double-stranded DNA |
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What is cDNA? |
Complementary DNA Formed by reverse transcriptase Complementary sequence of nucleotides to the mRNA strand |
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Why does isolation of mRNA require cooling down whereas extracting DNA doesn't? |
DNA is more stable than mRNA. Cooling reduces RNAase enzyme activity. |
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How do we isolate DNA/mRNA? |
Homogenise and then undergo differential ultracentrifugation |
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How do we isolate the gene of interest in DNA technology? |
Restriction endonucleases |
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How do restriction endonucleases work? |
Cuts through phosphodiester and hydrogen bonds at recognition sites. Cutting palindromic bases leaves overhanging bases called sticky ends Can cut at two opposite base pairs leaving a blunt end |
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Why must we use the same restriction endonuclease for the DNA and plasmid? |
Produce complementary sticky ends which are able to ligate together (using enzyme DNA ligase) to form recombinant DNA |
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Function of a vector |
Transport DNA into a host cell (commonly a bacterium's plasmid) |
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Transformation |
The process in which plasmids that have DNA incorporated into them are reintroduced into bacterial cells. |
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What do calcium ions do to bacterium's cell membrane? |
Make the bacteria permeable to allow the plasmid to be incorporated. |
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Difficulties of transformation |
Not all bacteria will take up the plasmid Not all plasmids will have taken up the DNA fragment of interest. |
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Polylinker |
Region containing a selection of restriction enzyme sites that only appear once in the whole vector/plasmid |
