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Summary Biology Topic 7 A-level notes
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- PEARSON (PEARSON)
Notes on all of topic 7 for Biology Edexcel A level paper 2 on 17/06/22. Written as bullet points and covers the whole topic.
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Topic 7 notesJoints:
In a synovial joint, the bones that move are separated by a cavity filled with synovial fluid, which
enables them to move freely
Bones are held in position by ligaments to control and restrict the amount of movement in the joint
Tendons join muscle to bones, enabling muscles to power joint movement
Tendon = muscle to bone
Ligament = bone to bone, strong and flexible
Synovial membrane – secretes synovial fluid
Synovial fluid – acts as a lubricant
Cartilage – absorbs synovial fluid, acts as a shock absorber
Pads of cartilage – additional protection
Fibrous capsule – encloses joints
Muscle:
Muscle - made up of muscle fibres
Muscle fibre – single muscle cell surrounded by cell surface membrane
Myofibril – numerous inside a muscle fibre
Sarcomere – a repeated unit that makes up a myofibril, made up of actin (thin filament) and myosin
(thick filament)
Sliding filament theory:
Actin molecules are associated with protein molecules troponin and tropomyosin
When nerve impulses arrive at a neuromuscular junction, calcium ions are released from the
sarcoplasmic reticulum
Calcium ions diffuse through the sarcoplasm to initiate the movement of the protein filaments:
Calcium ion attaches to the troponin molecule, causing it to move
Tropomyosin on actin filament shifts its position, exposing myosin-binding sites on the actin filaments
Myosin heads bind with myosin-binding sites on the actin filament, forming cross-bridges
When myosin heads bind to actin, ADP and Pi on myosin heads are released
Myosin changes shape, causing head to nod forward, the movement results in the relative movement
of the filaments, attached actin moves over the myosin
An ATP molecule binds to the myosin head, this causes the myosin head to detach from the actin
An ATPase on myosin head hydrolyses ATP to form ADP and Pi
This hydrolysis causes a change in shape of the myosin head, so it returns to its upright position,
enables cycle to start again
Collective bending of many myosin heads combines to move actin filament relative to the myosin
filament = muscle contraction
Carbohydrate oxidation:
Glucose oxidised to release energy
Input energy needed to break bonds in glucose and water is not as large as energy release when
bonds in carbon dioxide and water are formed, so there’s an overall release of energy
Glucose and oxygen aren’t directly brought together, this would release large amount of energy
which would be damaging to the cell
Glucose is split in a series of small reactions controlled by a specific intracellular enzyme
Glycolysis:
, Stores of glycogen from muscle or liver cells must be converted to glucose (main respiratory
substance)
Glucose is stable and unreactive, so an input of energy from ATP is needed to start the process
2 phosphate groups are added to glucose from 2 ATP to increases reactivity of glucose – energy
released from reaction
Energy can be used in regeneration of ATP, this is substrate level phosphorylation as energy comes
from substrates
This is now split into 2 x phosphorylated 3C compound, each oxidised to pyruvate
2 hydrogens removed here are taken up by coenzyme NAD producing a reduced coenzyme
Link reaction:
Pyruvate is decarboxylated - carbon dioxide released as a waste product
Pyruvate is dehydrogenated – 2 hydrogens removed and taken up by coenzyme NAD
Results in a 2C compound which combines with coenzyme A = acetyl CoA
CoA carries the 2C acetyl group into Krebs cycle
Krebs cycle:
Each 2C acetyl CoA combines with a 4C to create a 6C compound
6C undergoes decarboxylation and dehydrogenation = CO2 and 2H, hydrogen combines with NAD to
reduced it
5C compound then undergoes carboxylation = CO2, substrate level phosphorylation = ATP,
dehydrogenation = 6H to reduce 2NAD and an FAD
Overall products of Krebs = 2CO2, ATP, 3NADH, FADH
Electron transport chain:
Reduced coenzymes shuttle hydrogen atoms to the electron transport chain on the mitochondrial
inner membrane
Each hydrogen’s electron and proton separate, electron passes along a chain of electron carriers
Energy released as electrons pass down the chain
Energy used to move hydrogen ions from the matrix across the inner mitochondrial membrane into
the intermembrane space = steep electrochemical gradient across inner membrane
There’s a large difference in concentration of hydrogen ions across membrane and a large electrical
difference so the intermembrane space is more positive than matrix
Hydrogen ions diffuse down this electrochemical gradient through hollow protein channels situated in
ATP synthase (stalked particle) embedded and protruding from the inner mitochondrial membrane
As H ions pass through channel, ATP synthesis is catalysed by ATP synthase as H ions have causes a
conformational change in enzyme’s active site, enabling ADP and Pi to bind to the site
Within the matrix, hydrogen ions and electron recombine to form hydrogen atoms, these combine
with oxygen to form water molecules
Oxygen is the final electron acceptor
This method of ATP synthesis is oxidative phosphorylation
Amount of ATP produced depends on efficiency, and some hydrogen ions are used to exchange ADP
and ATP across membrane which used up hydrogen ions, so less hydrogen ions available for
generation of ATP
Rate of respiration:
Rate of aerobic respiration can be determined by measuring uptake of oxygen using a respirometer
As respiration is a series of enzyme catalysed reactions, its rate will be affected by concentration of
enzyme and substrate, by temperature and pH
Concentration of ATP in a cell will also control rate
ATP inhibits the enzyme in the first step of glycolysis
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