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    • Thread Starter

    OK, I thought, now I've spent all day learning bits of biology, I'd type them out here from memory. This'll help me learn them, and I'm happy to help others if they're confused too... PM me if you've got any specific requests, and if they're on my syllabus I'll try to put them in.
    I'm doing a random board (SNAB) so I'm sorry if it doesn't all correspond to various syllabuses

    Muscle contraction
    Sarcomere = a section of a muscle cell, membrane bound by the sarcoplasmic reticulum. Made up of actin (thin) and myosin (thick) filaments.
    When a nerve impulse arrives at the sarcoplasmic reticulum Ca2+ ions are released into the sarcoplasm.
    They bind to troponin which is attatched to tropomyosin.
    This changes the shape of the troponin, allowing it to move tropomyosin out of the way of the myosin binding sites.
    Myosin heads can then bind to the actin.
    On binding, ADP+Pi are released from the myosin heads.
    Myosin heads move, 'pulling' the actin fillament towards the centre of the sarcomere.
    ATP binds to the myosin head, causing it to detatch and return to its upright position.
    This repeats until the actin filament is fully pulled to the middle of the sarcomere - this is contraction.
    ATP is needed to allow myosin heads to release (this is why you get rigor mortis, as there isn't any ATP left to detatch the myosin and allow the muscles to relax).

    Respiration - glycolysis
    Glucose is phosphorylated using Pi from ATP.
    2 molecules of ATP are used up for every one glucose.
    Then the molecule splits, forming 2 molecules of pyruvate (3 carbons).
    The Pi is returned to 2 ADP, forming 2ATP, and 2 more ATP are also formed.
    H+ ions are released which reduce NAD, producing 2NADH2

    Respiration - link reaction
    The 2 molecules of pyruvate split into 2 molecules of acetyl (2 carbon) and 2CO2
    H+ is released, allowing 2 molecules of NAD to be reduced to 2NADH2
    Acetyl binds with Coenzme A producing 2 acetyl CoA

    Respiration - the Krebs cycle
    A 4 carbon molecule binds with the acetyl (CoA is released and returns to the link reaction), forming a 6 carbon molecule.
    This is then broken down to the 4 carbon molecule again.
    For every molecule of acetyl
    H+ ions are released and reduce 3NAD and 1FAD.
    2 C atoms are released and react with O2 to form 2CO2
    1 ATP is formed from ADP + Pi (so 2 from each glucose)

    Respiration - the electron transport chain
    All the NADH2 and FADH2 arrives at the electron transport chain.
    They release their H atoms which split into H+ and e-
    The electrons enter the electron transport chain and pass down a series of carrier molecules.
    At every carrier molecule, energy is released and pulls one H+ ions through to the intermembrane space.
    This creates a high concentration of H+ in the intermembrane space and so electrical and chemical gradients.
    This then passes back through into the mitochondrial matrix via a stalked protein molecule in the membrane.
    Their movement through the protein changes the shape of ATPase, allowing it to accept ADP + Pi which are then changed to ATP.
    In the mitochondrial matrix, the H+ ions and electrons bond with O2 to form water.
    For every glucose molecule, 34 ATP are produced in the electron transport chain.
    The entire process of respiration produces 38 ATP

    Transmission of impulses along neurons
    At rest, a cell has a resting potential difference (p.d.) across the cell membrane of about -70mV.
    An Na+/K+ ion pump constantly pumps Na+ ions out of the cell and K+ ions in.
    If a sufficient stimulus arrives at the neuron, Na+ ions channels open and Na+ moves into the cell, down a concentration gradient.
    This triggers a positive feedback - more Na+ channels open allowing more ions to flood in.
    This depolarises the membrane (an action potential).
    At 40mV both Na+ and K+ ion channels shut, causing a plateau.
    Then K+ ions channels open and K+ moves out of the cell down an electrical gradient, repolarising the membrane.
    Too many K+ ions leave the cell due to the high concentration of Na+ ions, and the p.d. falls below -70mV, preventing the neuron from being immediately restimulated.
    The distribution of ions levels out due to the ion pump and a resting potential is restored.
    This is one action potential in one section of the membrane.
    This then acts as a stimulus for the next section of membrane, causing the whole process to be repeated there.
    The action potential will pass along the neuron, a wave of depolarisation or nerve impulse.
    If the neuron is myelinated the action potentials will not be able to form where the myelin is present (as it insulates the neuron).
    Instead, it will 'jump' between the Nodes of Ranvier, speeding up conduction.

    Transmission of impulses at synapses
    An impulse will arrive in the presynaptic membrane, depolarising it.
    This causes Ca2+ ions to move into the synaptic button.
    The Ca2+ ions cause vesicles containing neurontransmitters (e.g. acetyl choline, ACh) to fuse with the membrane.
    The neurotransmitters are released into and diffuse across the synaptic cleft, bonding with specific receptors on the post synaptic membrane.
    This changes the shape of Na+ ion channels, allowing Na+ ions to flood into the postsynaptic neuron.
    This is an action potential.
    The neurotransmitter also binds to specific receptors in the presynaptic membrane, causing vesicles containing the enzyme which breaks down the neurotransmitter (e.g. acetyl cholinesterase) to fuse with the presynaptic membrane.
    The neurotransmitter is released into the synaptic cleft and breaks down the neurotransmitter preventing prolonged stimulation.
    The products of the breakdown are then absorbed into the presynaptic neuron and resynthesised using ATP from the mitochondria.

    Temporal and spatial summation
    Temporal summation is where several little impulses in one pre-synaptic neurone cause an impulse in the post synaptic neurone.
    Spatial summation is where several pre-synaptic neurones converge on one post-synapitc neurone and several impulses from several different neurones stimulate an impulse in the post synaptic neurone.
    Think spatial = space, many impulses from different points in space, i.e. different neurones.
    Temporal = time, many different impulses over a short space of time (nothing to do with lots of neurones).

    Rod cells in the eye
    Light falls on the rhodopsin in the rod cells. (rhodopsin = opsin + retinal).
    The light causes retinal to change shape (position of molecules in space actually change, not the chemical structure, but i think you only need to know that if you're doing chemistry) from a cis to a trans isomer.
    The retinal can no longer form bonds with opsin so the rhodopsin 'splits' (bleaching).
    This causes Na+ channels to close which hyperpolarises the membrane creating a generator potential (note this is a different way round - in most other receptors Na+ channels open to cause a GP).
    If the stimulus is great enough (all or nothing law) then it stops vesicles fusing with the pre-synaptic membrane.
    The vesicles contain an inhibiting neurotransmitter which prevent an action potential being created across the bipolar cell membrane.
    When the neurotransmitter is not released, an action potential is created in the bipolar cells (-> ganglion cells which make up the optic nerve).
    Be aware that this is the wrong way round compare to a normal neuron - the neurotransmitter is inhibitory.

    Phew. Well I'm exhausted now. Hope that helps some people at least
    skevvybritt x

    wow, terrific notes...i was learning the same things today so this was a gd recap
    • Thread Starter

    (Original post by the_wizzz)
    wow, terrific notes...i was learning the same things today so this was a gd recap
    Thank you!
    Did it all look OK to you then? I was hoping I'd got it straight in my head but it was from memory so I wasn't 100% sure (left my notes in the car so I can't check it :rolleyes: )

    i can't fault anything though you go into more detail than my board requires

    thumbs up for temporal + spatial summation, couldnt find that information anywhere
    • Thread Starter

    (Original post by the_wizzz)
    i can't fault anything though you go into more detail than my board requires
    Yay! I made sense...
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