Some of harder concepts in F214

This isnt the full course - just some of the harder parts that I struggle with

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Compare sensory and motor neurones

SENSORY NEURONES:

Cell body isnt in the CNS - its in the PNS, also in middle of neurone not at the end 

Dendrites are at the end of the dendron/axon 

Shorter axon 

Dendron is present 

Starts at and connects to sensory receptor 

FUNCTION = Carry action potential from sensory receptor to CNS 

MOTOR NEURONES:

Cell body is in the CNS and at the end of the neurone 

Dendrites connect directly to cell body 

Longer axon 

No dendron 

Neurone ends at motor end plate

FUNCTION = Carry action potential from CNS to an effector e.g. muscle or gland

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Generation of an action potential

  • Membrane starts in resting state - polarised at -60mV 
  • Stimulus excites neurone cell membrane - causes sodium ion channels to open 
  • Increased permeability to sodium - ions diffuse in
  • Causes inside to become more positive - membrane depolarises
  • Reaches threshold potential of -50mV - voltage gated sodium ion channels open 
  • Depolarises fruther - +40mV
  • Action potential has been generated - voltage gated sodium channels close and potassium open 
  • Potassium ions diffuse out of cell - membrane repolarises 
  • Overshoots slightly - hyperpolarisation, neurone is in refractory period so cannot generate another action potential 
  • SOPI pumps restore the cell to resting potential 
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Transmission of an action potential in a myelinate

  • Myelinated neurone - ionic movements can only occur at gaps in myelin sheath called nodes of Ranvier 
  • Action potential is generated - sodium ions have moved into cell by diffusion (higher concentration outside of cell) 
  • This upsets balance created by SOPI pumps 
  • Increased sodium ion concentration at point where sodium ion channels are open 
  • Sodium ions diffuse sideways from region of high concentration to region of lower concentration 
  • This is a local current 
  • Alters potential difference across membrane at different point - voltage gated sodium ion channel open 
  • Sodium ions enter neurone at node of Ranvier further along membrane - action potential occurs 
  • Saltatory conduction - impulse effectively jumps from one node of Ranvier to another 
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Control of insulin secretion

  • High blood glucose - more glucose enters beta cells by facilitated diffusion 
  • Rate of respiration in beta cell increases - more ATP is produced 
  • Causes potassium ion channels to close - build up inside cell 
  • Inside becomes less negatively charged - membrane is depolarised 
  • Triggers calcium ion channels to open 
  • Calcium ions diffuse into beta cell 
  • Vesicles of insulin move and fuse with cell membrane - insulin released by exocytosis 
  • Lowers blood glucose concentration to normal levels 
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Ultrafiltration

  • Takes place in glomerulus of nephron 
  • Blood flows into glomerulus from afferent arteriole - wider than efferent 
  • Therefore blood in capillaries in glomerulus is under higher pressure than the Bowmans capsule 
  • Pressure difference pushes fluid from blood into Bowmans capsule
  • Has to pass through 3 layers:
  • CAPILLARY ENDOTHELIUM - narrow gaps between cells, blood plasma and substances dissolved in it can pass through
  • MEMBRANE - basement membrane made of fine mesh of collagen and glycoproteins, filter for large molecules e.g. proteins and RBC's 
  • BOWMANS CAPSULE EPITHELIUM - contains podocytes, major processes ensure gaps between cells. Fluid from glomerulus passes between these cells into lumen of Bowmans capsule
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Selective reabsorption

  • Occurs in the PCT
  • SOPI pumps - remove sodium ions from cells lining PCT, reduced concentration 
  • Sodium ions transported into cell with glucose/amino acid by facilitated diffusion 
  • Increased glucose and amino acid concentration - diffuse out into tissue fluid 
  • Can be enhanced by active transport of glucose and amino acids 
  • Diffuse from tissue fluid to blood 
  • The reabsorption of sodium, glucose and amino acids - reduces water potential in cells, increases water potential in tubule fluid 
  • Water enters cells and be absorbed into blood by osmosis 
  • Larger molecules are reabsorbed by endocytosis 
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Water regulation - Loop of Henle

  • Top of ascending limb - Sodium and chloride ions actively transported into medulla, water remains in nephron as impermeable to water 
  • Medulla = high ion concentration so low water potential 
  • Water moves out of descending limb into medulla by osmosis - filtrate more concentrated, impermeable to ions 
  • Water reabsorbed into blood by capillary network 
  • Bottom of ascending limb - Sodium and chloride ions diffuse out into medulla, lower water potential more 
  • Water moves out of collecting duct by osmosis, absorbed back into blood 
  • Amount of water reabsorbed depends on needs of the body
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Water regulation - the brain

  • Osmoreceptors in hypothalamus monitor water potential of blood 
  • Low water potential = osmoreceptors lose water, shrink and stimulate neurosecretory cells 
  • Release ADH - travels to pituarity gland where it is stored 
  • Stimulation of neurosecretory cells - action potentials to pituarity gland, release of ADH 
  • ADH - acts on collecting duct walls - have membrane bound receptors 
  • ADH binds to receptors, causes chain of enzyme controlled reactions inside cell 
  • Aquaporins inserted into cell membrane of collecting duct (water permeable channels) 
  • Increased permeability to water 
  • More water diffuses into medulla, absorbed by blood - less urine of lower water potential 
  • Less ADH secreted = cell membrane folds inwards, creates new vesicles that remove aquaporins from membrane 
  • Walls less permeable - less water reabsorbed, more dilute urine 
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Pregnancy testing

  • Embryo implanted in uterus lining - secretes pregnancy hormone called human chorionic gonadotrophin (hCG)
  • Pregnancy stick - application area has antibodies for hCG bound to coloured bead 
  • Urine applied, any hCG binds to antibody/bead 
  • Urine/beads move up strip 
  • Reaches test strip - has immobilised antibodies for hCG - hCG binds to them concentrating coloured beads in that area 
  • One control line 
  • 2 lines = positive result, pregnancy 
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Structure/function of a chloroplast

  • Many grana = large surface area for light dependent reaction (photosynthetic pigments, electron carriers, ATPase enzymes)
  • Arrangement of pigments in photosystems - maximum absorption of light energy 
  • Proteins embedded in grana - hold photosystems in place 
  • Stroma = contains all enzymes needed to catalyse light independent stage e.g. rubisco 
  • Grana surrounded by stroma = products of light dependent reaction easily pass into stroma and take part in light independent reaction 
  • Can make their own proteins = genetic instructions in chloroplast DNA, ribosomes assemble proteins e.g. rubisco 
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Light dependent reaction - non cyclic photophospho

NON-CYCLIC PHOTOPHOSPHORYLATION

  • Photosystem 1 - chlorophyll b, 700nm light and photosystem 2 - chlorophyll a, 680nm light 
  • Light hits PS 2 - excites two electrons, leave PRC 
  • Electrons pass along chain of electron carriers - energy used to synthesise ATP
  • Light hits PS1 - excites two electrons - join NADP 
  • Water is photolysed at PS1 - protons and electrons 
  • Electrons replace those lost at PS1, protons take part in chemiosmosis to make ATP, then join NADP - NADP is reduced 
  • Electrons from PS 2 replace those lost at PS1 
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Light dependent reaction - non cyclic photophospho

NON-CYCLIC PHOTOPHOSPHORYLATION

  • Photosystem 1 - chlorophyll b, 700nm light and photosystem 2 - chlorophyll a, 680nm light 
  • Light hits PS 2 - excites two electrons, leave PRC 
  • Electrons pass along chain of electron carriers - energy used to synthesise ATP
  • Light hits PS1 - excites two electrons - join NADP 
  • Water is photolysed at PS1 - protons and electrons 
  • Electrons replace those lost at PS1, protons take part in chemiosmosis to make ATP, then join NADP - NADP is reduced 
  • Electrons from PS 2 replace those lost at PS1 
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Structure/function of a mitochondria

  • Matrix - enzymes needed to catalyse link reaction and Krebs cycle and molecules of NAD and coenzyme A
  • Matrix - has oxaloacetate that accepts acetate in Krebs cycle 
  • Can make own proteins e.g. enzymes - mitochondrial DNA and ribosomes to code for and assemble proteins 
  • Outer membrane - protein channels/carriers allow passage of pyruvate into matrix 
  • Inner membrane - has electron carriers and ATPsynthase enzymes for oxidative phosphorylation and chemiosmosis
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Krebs cycle

1. Coenzyme A offloads acetate - acetate combines with oxaloacetate (4C) to form citrate (6C) 

2. Citrate is decarboxylated and dehydrogenated - 5C compound. NAD accepts hydrogen atoms - NADH and CO2 produced 

3. 5C compound decarboxylated and dehydrogenated - 4C compound. NADH and CO2 produced again 

4. 4C compound changed into different 4C compound - ADP phosphorylated to form ATP 

5. 4C compound dehydrogenated to another 4C compound - reduced FAD produced 

6. This 4C compound is dehydrogenated - oxaloacetate regenerated, NADH produced 

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Oxidative phosphorylation

  • Takes place in cristae
  • Cristae have electron carriers - joined to make up electron transport chain 
  • Reduced NAD from Krebs release Hydrogen atoms - split into H+ and e-
  • Electron picked up by first carrier - reduced, passes it to next carrier
  • Electron passed along chain - oxidising and reducing carriers  
  • NAD oxidised - can pick up more hydrogens in Krebs 
  • As electron moves along - releases energy used to make ATP 
  • At end of electron chain, electron combines with oxygen and hydrogen to form water
  • Oxygen is final electron acceptor in aerobic respiration 
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Chemiosmosis

  • Energy released by electrons used to pump H+ across cristae and into inter membrane space 
  • Builds up H+ gradient (pH and electrochemical gradient)
  • H+ ions diffuse down gradient through protein channel 
  • Membrane impermeable to ions apart from protein channels 
  • Channel proteins act as ATPase's - energy from active transport released and used to make ATP from ADP and Pi
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