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What is aerobic respiration?
Process of breaking down a respiratory substrate in order to produce ATP using oxygen
What is the word equation for aerobic respiration?
Glucose + Oxygen → Carbon Dioxide + Water (+ energy)
What are the 4 stages of aerobic respiration?
Glycolysis, Link Reaction, Krebs Cycle and Oxidative Phosphorylation
What is aerobic respiration controlled by?
Intracellular enzymes that catalyse reactions within the cell (determines respiration rate)
Why are intracellular enzymes involved in aerobic respiration?
Ensures gradual energy release so enzymes do not denature from sudden increase in body temp
What are the 3 coenzymes in aerobic respiration?
NAD + FAD → transfers hydrogen between molecules
Coenzyme A → transfers acetate between molecules
What are the 4 structures of the mitochondria?
Outer Membrane, Inner Membrane, Intermembrane Space and Matrix
What does the outer membrane of the mitochondria do?
Smooth, permeable to several small molecules
What does the inner membrane of the mitochondria do?
Folded (cristae), less permeable, site of ETC + ATP synthase
What does the intermembrane space of the mitochondria do?
Low pH due to high proton conc., conc. gradient formed during oxidative phosphorylation + essential for ATP synthesis
What does the matrix of the mitochondria do?
Aqueous solution in inner membranes, contains ribosomes + enzymes + mtDNA
What is glycolysis?
First stage of cellular respiration + occurs in cytoplasm, common to both aerobic + anaerobic respiration
What does glycolysis result in?
2 pyruvate molecules (moves into matrix for link reaction)
2 ATP molecules
2 NADPH
What does glycolysis involve?
Trapping glucose in cell by phosphorylating molecule and oxidising triose phosphate
What are the steps of glycolysis?
Phosphorylation of glucose
2 ATP provides 2 phosphates needed
Produces 2 triose phosphates + 2 ADPs
Oxidation of triose phosphates
Triose phosphate loses H + forms 2 pyruvate molecules
H+ ions are collected by NAD to form 2 NADPH
What is pyruvate?
Contains large amounts of chemical energy therefore used in respiration to create more ATP
What is the link reaction?
Occurs in matrix + links glycolysis to Krebs cycle
What are the steps of the link reaction?
Pyruvate oxidises by enzymes to produce acetate
Pyruvate is decarboxylated in the form of CO2
NAD reduces to NADH by hydrogen to form pyruvate
Acetate combines with coenzyme A to form acetyl CoA
What does the link reaction result in?
Acetyl CoA, CO2 and NADH produced
What is the word equation for the link reaction?
Pyruvate + NAD + CoA → acetyl CoA + CO2 + NADH
What is the Krebs cycle?
Consists of multiple enzyme-controlled reactions
What are the steps of the Krebs cycle?
2C acetyl CoA enters circular pathway from link reaction in glucose metabolism
4C oxaloacetate accepts 2C acetyl fragment from acetyl CoA to form 6C citrate.
Citrate converts back to oxaloacetate via redox reactions.
How does acetyl CoA and amino acids enter the Krebs cycle?
Acetyl CoA → formed from fatty acids after lipid breakdown
Amino acids → from other metabolic pathways
What are the steps of the regeneration of the regeneration of oxaloacetate?
Decarboxylation of citrate → releases 2CO2 as waste gas.
Dehydrogenation of citrate → releases H atoms to reduce NAD + FAD.
Substrate linked phosphorylation → phosphate transfers from intermediate to ADP so ATP is produced.
What is the chemical equation of the regeneration of oxaloacetate?
3NAD + FAD → 3NADH + H+ + FADH2
What are the products after 2 Krebs cycles?
2 ATP, 6 NADH, 2 FADH2, 4CO2
What is oxidative phosphorylation?
Last stage of aerobic respiration; takes place in inner mitochondrial membrane, produces ATP and H2O
What are the steps of the chemiosmotic theory?
Energy from electrons is passed through chain of proteins in membrane (ETC)
Energy is used to pump H+ ions against conc. gradient into intermembrane space
H+ ions flow by faciliated diffusion through ATP synthase (channel enzyme) into matrix
Energy of H+ ions results in phosphorylation of ADP into ATP
What is the process of oxidative phosphorylation?
H atoms split into H+ ions and electrons
Electrons enter ETC + release energy as they move through
Energy released transports H+ ions across inner mitochondrial membrane from matrix to intermembrane space
Concentration gradient of H+ ions established between intermembrane space + matrix
Protons return to matrix via facilitated diffusion through ATP synthase
Movement of H+ ions down conc. gradient provides energy for ATP synthesis
O2 acts as final oxygen acceptor + combines with H+ ions and electrons at the end of ETC to form H2O
What is the electron transport chain?
Made of multiple membrane proteins/electron carriers
What are the 2 features of the ETC?
Membrane proteins are positioned closer together so electrons pass between carriers
Inner mitochondrial membrane is impermeable to H+ ions so carriers pump H+ ions to create conc. gradient
What are the consequences of low oxygen availability?
No final acceptor of electrons to form ETC
ETC stops functioning
No ATP produced via oxidative phosphorylation
NADH + FADH2 not oxidised by electron carrier
No NAD + FAD available for drhydrogenation
Krebs cycle stops
Link reaction stops
What is the anaerobic pathway for yeast and microorganisms?
Ethanol fermentation
What is the anaerobic pathway for mammalian cells and other microorganisms?
Lactate fermentation
What are the steps of lactate fermentation?
NADH transfers H to pyruvate to form lactate (NAD reused in glycolysis)
Pyruvate reduces to lactate by lactate dehydrogenase (pyruvate is the hydrogen acceptor)
Final lactate can be further metabolised + some ATP produced
What are the 2 ways to process lactate?
Oxidises back to pyruvate then used in Krebs cycle for ATP production
Converts into glucose by liver cells for respiration/storage
What are the steps of ethanol fermentation?
Pyruvate decarboxylates to ethanal (produces CO2)
Ethanal reduces to ethanol by alcohol dehydrogenase (ethanal is hydrogen acceptor)
What is the respiratory quotient?
Ratio of CO2 produced to O2 taken in during respiration
Why do different respiratory substrates have different RQ values?
More C-H bonds = more H atoms to create proton gradient
More H = more ATP molecules can be produced
More oxygen needed to break down the molecule
How can RQ values tell us about respiration?
Aerobic respiration = RQ < 1 (oxygen used to break down substrate)
Anaerobic respiration = RQ > 1 (very little oxygen used)
What is a muscle?
Effectors stimulated by nerve impulses from motor neurones
What are tendons?
Lengths of strong connective tissue that connect muscles to bones
What are ligaments?
Lengths of strong connective tissue that connect bones to bones
What is antagonistic muscle action?
A muscle pulls in one direction at a joint + other muscle pulls in opposite direction
What are flexors?
Muscles that flex a joint
What are extensors?
Muscles that extend a joint
What makes a muscle fibre a highly specialised, cell-like unit?
Contains organized arrangement of contractile proteins in cytoplasm, surrounded by cell surface membrane, contains many nuclei
Why are muscle fibres not considered cells?
Contains many nuclei so it is not a cell
What is the muscle fibre equivalent of cell surface membrane?
Sarcolemma
What is the muscle fibre equivalent of cytoplasm?
Sarcoplasm
What is the muscle fibre equivalent of endoplasmic reticulum?
Sarcoplasmic reticulum
What is the sarcolemma?
Have many tube-like projections that fold in from outer surface (transverse system tubules)
Run close to SR + help spread electrical impulses
What is the sarcoplasm?
Contains mitochondria (for aerobic respiration to generate ATP) + myofibrils (bundles of actin/myosin filaments that slide past each other during contraction)
What is the sarcoplasmic reticulum?
Contain protein pumps in membranes to transport Ca+ ions (needed for contraction) into lumen of SR
What are myofibrils made of?
2 protein filaments: thick myosin + thin actin
What is H band?
Only myosin
What is I band?
Only actin
What is A band?
Areas of only myosin + areas of both overlapping
What is M line?
Attachment for myosin
What is Z line?
Attachment for actin
What is a sarcomere?
Section of myofibril between 2 Z lines
What is a fast twitch muscle fibre?
Contract rapidly - myosin heads bind + unbind from actin-binding sites 5x faster than slow twitch
Why do fast-twitch muscle fibres need large amounts of Ca+ ions?
For rapid contraction-relaxation cycles
Why do fast-twitch muscle fibres rely on anaerobic respiration for ATP?
Suited for short bursts of high-intensity activity + fatigue quickly due to lactate produced
Where is fast-twitch muscle fibres found in high proportions?
Muscles needed to flee/hunt at high speeds
Human eyelids because they contract in short bursts
Why do fast-twitch muscle fibres have fewer capillaries?
Slow supply of oxygen + glucose for aerobic respiration
How much myoglobin do fast-twitch muscle fibres have?
Low amounts; myoglobin store oxygen in muscles + increases rate of oxygen absorption from capillaries
Why do fast-twitch muscle fibres appear pale?
Low amounts of myoglobin (red pigment)
What is a slow-twitch muscle fibre?
Contract slowly: better suited for sustained activities e.g., walking
Why do slow-twitch muscle fibres rely on aerobic respiration for ATP?
Fatigue less quickly due to less lactate production so ideal for endurance
Where are slow-twitch muscle fibres found in high proportions?
Muscles needed to migrate/stalk over long distance
Human back muscles to keep skeleton next
Why do slow-twitch muscle fibres have a dense network of capillaries?
Short diffusion distance + good supply of oxygen and glucose
How much myoglobin, haemoglobin and mitochondria do slow-twitch muscle fibres?
High amounts; increases rate of oxygen supply/absorption + respiration
What are thick filaments made of?
Myosin molecules
What is myosin?
Fibrous protein molecules with a globular head
What does the fibrous part of myosin do?
Anchors molecule into thick filament
How do myosin molecules lie?
Next to each other with globular heads pointing away from M line
What are thin filaments made of?
Actin molecules
What is actin?
Globular protein molecules that link together to form a chain
What is 1 thin filament made of?
2 actin molecules
What is tropomyosin?
Fibrous protein that twists around 2 actin chains
What is troponin?
Protein that attaches to actin chains at regular intervals
What is sliding filament theory?
Sarcomeres shorten as Z discs are pulled closer together
What is the process of the sliding filament theory?
Action potential arrives at neuromuscular junction
Ca+ ions release from SR + bind to troponin - stimulates to change shape
Troponin + tropomyosin change position on actin filaments
Myosin binding sites are exposed on actin molecules
Myosin globular heads bind to sites + form cross-bridges between thick and thin filaments
Myosin heads bend so pull actin filaments to centre of sarcomere - muscle contracts a small distance (power stroke)
ATP binds to myosin heads - change shape + detach from actin filaments
ATPase hydrolyses ATP into ADP + Pi - myosin heads move back to original position (recovery stroke)
Myosin heads bind to sites closer to Z disc - releases ADP + Pi and new power stroke
Myosin heads pull actin filaments closer to sarcomere centre - pull Z discs closer
ATP binds again so myosin heads detach
What are the conditions for the sliding filament theory to repeat?
If troponin + tropomyosin do not block binding sites
Muscle has ATP supply
What happens when muscle contraction stops?
Ca+ ions leave binding sites on troponin
Ca+ ions are actively transported back to SR
Troponin returns to original shape - tropomyosin blocks binding sites
Sarcomere lengthens as actin filaments slide back
What is a sinoatrial node?
Group of cells in right atrium, generates regular electrical signal + acts as natural pacemaker
What is an atrioventricular node?
Group of cells stimulated by SAN, imposes delay before transmitting impulse
What is the Bundle of His?
Group of conducting fibres in the septum of the heart
What are Purkyne fibres?
Conducting fibres that penetrate through septum of heart, spreads around ventricles
What is the process of one heartbeat?
SAN establishes wave of depolarisation - atria contracts
Depolarisation spreads to atrioventricular node - produces slight delay then wave passes through Bundle of His
Bundle of His splits into 2 branches + carries wave onto Purkyne tissue
Purkyne tissue spreads around ventricles - ventricles contract bottom upwards + blood is pumped out
What are the components shown on an ECG?
P wave, QRS complex, T wave, U wave
What is the cause of the P wave?
Depolarisation of atria, causing atrial systole
What is the cause of the QRS complex?
Depolarisation of ventricles, causing ventricular systole (largest wave due to largest muscle mass)
What is the cause of the T wave?
Repolarisation of ventricles, causing ventricular diastole
What is the cause of the U wave?
Unknown, may be due to repolarisation of Purkyne fibres
What is tachycardia?
>100 bpm, heart is beating too fast, peaks are too close together
What is bradycardia?
<60 bpm, heart is beating too slowly, peaks are too far apart
What is an ectopic heart beat?
Heart beat comes too early + is followed by a pause
What is fibrillation?
Heartbeat is irregular so rhythm is lost
