Unit 5 - Respiration, Internal Environment, Coordination and Gene Technology

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?

1. Phosphorylation of glucose

   2 ATP provides 2 phosphates needed

   Produces 2 triose phosphates + 2 ADPs

2. 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?

1. Pyruvate oxidises by enzymes to produce acetate

2. Pyruvate is decarboxylated in the form of CO₂

3. NAD reduces to NADH by hydrogen to form pyruvate

4. 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?

1. 2C acetyl CoA enters circular pathway from link reaction in glucose metabolism

2. 4C oxaloacetate accepts 2C acetyl fragment from acetyl CoA to form 6C citrate.

3. 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?

1. Decarboxylation of citrate → releases 2CO₂ as waste gas.

2. Dehydrogenation of citrate → releases H atoms to reduce NAD + FAD.

3. 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?

1. Energy from electrons is passed through chain of proteins in membrane (ETC)

2. Energy is used to pump H⁺ ions against conc. gradient into intermembrane space

3. H⁺ ions flow by faciliated diffusion through ATP synthase (channel enzyme) into matrix

4. Energy of H⁺ ions results in phosphorylation of ADP into ATP

What is the process of oxidative phosphorylation?

1. H atoms split into H⁺ ions and electrons

2. Electrons enter ETC + release energy as they move through

3. Energy released transports H⁺ ions across inner mitochondrial membrane from matrix to intermembrane space

4. Concentration gradient of H⁺ ions established between intermembrane space + matrix

5. Protons return to matrix via facilitated diffusion through ATP synthase

6. Movement of H⁺ ions down conc. gradient provides energy for ATP synthesis

7. 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?

1. NADH transfers H to pyruvate to form lactate (NAD reused in glycolysis)

2. Pyruvate reduces to lactate by lactate dehydrogenase (pyruvate is the hydrogen acceptor)

3. Final lactate can be further metabolised + some ATP produced

What are the 2 ways to process lactate?

1. Oxidises back to pyruvate then used in Krebs cycle for ATP production

2. Converts into glucose by liver cells for respiration/storage

What are the steps of ethanol fermentation?

1. Pyruvate decarboxylates to ethanal (produces CO₂)

2. 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?

1. Action potential arrives at neuromuscular junction

2. Ca⁺ ions release from SR + bind to troponin - stimulates to change shape

3. Troponin + tropomyosin change position on actin filaments

4. Myosin binding sites are exposed on actin molecules

5. Myosin globular heads bind to sites + form cross-bridges between thick and thin filaments

6. Myosin heads bend so pull actin filaments to centre of sarcomere - muscle contracts a small distance (power stroke)

7. ATP binds to myosin heads - change shape + detach from actin filaments

8. ATPase hydrolyses ATP into ADP + Pi - myosin heads move back to original position (recovery stroke)

9. Myosin heads bind to sites closer to Z disc - releases ADP + Pi and new power stroke

10. Myosin heads pull actin filaments closer to sarcomere centre - pull Z discs closer

11. 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?

1. SAN establishes wave of depolarisation - atria contracts

2. Depolarisation spreads to atrioventricular node - produces slight delay then wave passes through Bundle of His

3. Bundle of His splits into 2 branches + carries wave onto Purkyne tissue

4. 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