Topic 7: Run for your life

Question 1

Tendon

Answer 1

Non-elastic tissue which connects muscle to bone.

Question 2

Ligaments

Answer 2

elastic tissue that joins bone together & determines the amount of movement possible at a joint.

Question 3

Joints

Answer 3

The area where two bones bone are attached for the purpose of permitting body parts to move. They’re made of fibrous connective tissues & cartilage.

Question 4

Skeletal muscles

Answer 4

Muscles attached to bones, they are arranged in antagonistic pairs.

Question 5

Antagonistic muscle pairs

Answer 5

Pairs of muscles which pull in opposite directions - as one muscle contracts (the agonist), the other relaxes (the antagonist). Extensors act to straighten the joint, while flexors act to bend the joint.
Examples:
When the triceps (the extensor) relaxes, the biceps (the flexor) contracts to lift the arm.
When the quadriceps (the extensors) relax, the hamstrings (the flexors) contract to bend the leg.

Question 6

Muscle fibre structure

Answer 6

• sarcolemma = Cell membrane
• sarcoplasm = cytoplasm
• T-tubules = Inward folds of the sarcolemma across the muscle fibre, which stick into the sarcoplasm. Help to send electrical impulses through the sarcoplasm so they reach all parts of the muscle fibre.
• Sarcoplasmic reticulum = internal membranes running through the sarcoplasm. Store & release calcium ions needed for muscle contraction.
• mitochondria = provides ATP needed for muscle contraction
• multinucleate
• contain myofibrils = long, cyndrical organelles made of proteins. Highly specialised for contracion.

Question 7

Myofibril structure

Answer 7

Contain bundles of thick and thin myofilaments, which move past each other to make muscles contract:
- Thick myosin filaments - dark bands
- Thin Actin filaments - light bands

Areas of a myofibril:
H band - area containing only thick myosin filaments
I band - Only thin actin filaments present
A band - Contains areas where only myosin filaments are present & areas where myosin & actin overlap
M line - Middle of myosin filaments
Z line - Attchments for actin filaments. Mark the ends of each sarcomere. Sarcomeres are joined lengthways at their Z-lines.
Sarcomere - The section of a myofibril between two Z-line.

Question 8

What happens to the bands when a sarcomere contracts?

Answer 8

Myosin and actin filaments slide over one another to make the sarcomere contract. As a result:
- I band gets shorter
- H zone gets shorter
- A band stays the same length
- Sarcomere gets shorter

Question 9

Muscle contraction: Sliding Filament Theory

Answer 9

1. Calcium ions released from sarcoplasmic reticulum (SR) upon nervous stimulation (arrival of an AP at neuromuscular junction). Bind to troponin molecule - changing its shape.
2. Myosin binding sites exposed, myosin head moves forward to form an actomyosin cross bridge.
3. ADP + Pi released, myosin head moves forward, pulling the actin filaments and shortening the sarcomere.
4. Free ATP binds to myosin head , myosin head changes shape and detaches from actin filament.
5. ATPase in myosin head hydrolyses ATP (to ADP+Pi), which causes myosin head to move back to its original position - recovery stroke.
6. Repeated stimulation, the presence of calcium ions and ATP causes continued contraction.
7. If stimulation is stopped, ATP released is used to actively transport Ca2+ ions back into the sarcoplasmic reticulum. Actin filaments slide back to their relaxed position, which lengthens the sarcomere.

Question 10

Fast twitch muscle fibres

Answer 10

• Short contraction-relaxation cycle.
• Fewer capillaries & low amounts of myoglobin - appear lighter
• ATP supplied mostly from anaerobic respiration
• Fewer, smaller mitochondria present
• Large store of calcium ions in the sarcoplasmic reticulum
• Large amounts of glycogen & phosphocreatine present
• Faster rate of ATP hydrolysis in myosin heads
• Fatigue rapidly due to greater lactate formation

Question 11

Slow twitch muscle fibres

Answer 11

• Long contraction-relaxation cycle
• Denser network of capillaries, high amounts of myoglobin and haemoglobin - appear dark red
• ATP supplied mostly from aerobic respiration
• Many large mitochondria present
• Small store of calcium ions in the sarcoplasmic reticulum
• Small amounts of glycogen present
• Slower rate of hydrolysis in myosin heads
• fatigues more slowly due to reduced lactate formation

Question 12

Summaries the stages of aerobic respiration

Answer 12

1. Glycolysis - phosphorylation & splitting of glucose - occurs in cytoplasm.
2. Link reaction - Decarboxylation & dehydrogenation of pyruvate - occurs in matrix of mitochondria.
3. Krebs cycle - cyclical pathway with enzyme controlled reaction - occurs in matrix of mitochondria.
4. Oxidative phosphorylation - production of ATP through oxidation of hydrogen atoms - occurs in innermembrane of mitochondria.

Question 13

Glycolysis

Answer 13

1. Phosphorylation of glucose
   - Requires 2 ATP molecules to provide phosphates and produces 2ADPs and 2 triose phosphates.
2. Oxidation of triose phosphate
   After triose phosphate loses hydrogen, it forms two molecules of pyruvate.
   The hydrogen ions are collected by NAD which forms two reduced NAD.
   Triose phosphates are dephosphorylated
   4ATPs are produced but 2 were used in phosphorylation of glucose meaning there is a net gain of 2ATP molecules.

Question 14

Aerobic respiration

Answer 14

Aerobic respiration is the splitting of a respiratory substrate, including glucose, reuniting hydrogen with atmospheric oxygen to release a large amount of energy and carbon dioxide as a waste product. It is a multi-step process, with each step controlled and catalysed by a specific intracellular enzyme. It yiels ATP, which is used a source of energy for metabolic reaction.

Question 15

Link reaction

Answer 15

1) Pyruvate (3C) is decarboxylated (one carbon atom is removed in the form of CO2)
2) Pyruvate is oxidised/dehydrogenated, changing into acetate (2C). NAD collects the hydrogen atom from pyruvate becoming reduced NAD.
3. Acetate combines with coenzyme A (CoA) to form acetyl conenzyme A (acetyl CoA).

Occurs 2x for every glucose molecule.

Question 16

Krebs Cycle

Answer 16

In the mitochndrial matrix:

1. Acetyl CoA (2C) enters the krebs cycle and acetyl is accepted by the four carbon compound oxaloacetate (4C) to form citrate (6C). CoA is released and reused in the link reaction
2. 6C citrate is converted to a 5C molecule
   - Decarboxylation of citrate releases CO2 as a waste.
   - Oxidation (dehydrogenation) of citrate, releases a H atom that reduces NAD.
3. 5C molecule converts back to oxaloacetate (4C)
   decarboxylation & dehydrogenation occur sagain, producing 1reducedFAD and 2reducedNAD.
   Substrate-linked phosphorylation occurs when a phosphate is transferred from an intermediate compound to ADP, forming 1ATP to supply energy.

Total products:
1xCoA
Oxaloacetate
2xCO2
1xATP
3xreducedNAD
1xreducedFAD

Question 17

What is substrate level phosphorylation

Answer 17

Substrate level phosphorylation is when ATP is produced due to a phosphate group from an intermediate compound being directly transferred/added to ADP.
(when a phosphate group is directly transfered from one molecule to another).

Question 18

Oxidative phosphorylation

Answer 18

The process in which ATP is synthesised via chemiosmosis in the electron transport chain.

1. Reduced coenzymes carry hydrogen ions and electrons to the electron transport chain, which occurs on the inner mitochondrial membrane.
2. Hydrogen atoms are split into protons & electrons: H > H+ + e-
3. Electrons are carried from one electron carrier to another is a series of redox reactions (the electron carrier which passes the electron on is oxidised, whereas the electron carrier which receives it is reduced).
4. protons are actively transported across the membrane into the intermembrane space - using the energy released for the redox reactions. As a result, the concentration of protons in the intermembrane space is high.
5. The protons return to the matrix via facilitated diffusion through the channel enzyme ATPsynthase.
6. The movement of protons down their electrochemical gradient provides energy for ATP synthesis, which occurs on stalked particles using ATP synthase.
7. oxygen acts as the ‘final electron acceptor’ and combines with protons and electrons at the end of the ETC to form water.

Question 19

Work out how many molecules of ATP can be made from one glucose molecule during aerobic respiration

Answer 19

• 3ATP are made from each reduced NAD
• 2ATP are made from each reduced FAD

Glycolysis = 2ATP
Glycolysis = 2reducedNAD = (2x3) = 6ATP
Link Reaction (x2) = 2reducedNAD = (2x3) = 6ATP
Krebs cycle (x2) = 2ATP
Krebs cycle (x2) = 6reducedNAD = (6x3) = 18ATP
Krebs Cycle (x2) = 2reducedFAD = (2x2) = 4ATP

Total ATP = 38

Question 20

Describe the effect of metabolic poisons such as carbon monoxide on anearobic respiration

Answer 20

Some metabolic poisons target electron carriers in oxidative phosphorylation, preventing them from passing on electrons down the electron tansport chain. This stops chemiosmosis. There’s no energy released to phosphorylate ADP/produce ATP, consequently ATP synthesis in the cell is hugely reduced.
Reduced NAD and FAD are no longer oxidised, so NAD and FAD aren’t regenerated for the krebs cycle, causing the kreb cycle to also stop.

Question 21

Why do the link reaction and the kreb cycle occur in the mitochondria when glycolysis occurs in the cytoplasm?

Answer 21

The matrix contains all the enzymes necessary (I.e coenzyme A) for the biochemical reactions involved in the link reaction and kreb cycle.

Question 22

Core practical 16: Investigate the rate of respiration
1) Describe how a respirometer works
2) What is the control for this practical?
3) How do you find the volume of oxygen consumed using a respirometer?
4) How can the volume of carbon dioxide produced be found?
5) How is the rate of respiration calculated using data from the respirometer?
6) State the hazard andsafety precaution involved in the practical

Answer 22

1) It is a chamber/test tube connected to a capillary tube with a drop of dye. As the organism in the chamber respires and uses oxygen, the pressure decreases and the liquid moves in the capillary.
2) Replace the organism with an inert object of the same mass.
3) Place a fixed mass of soda lime in the respirometer with the organism. Measure the distance moved by the dye, and use the formula: volume = distance X πr^2 (area of respiratory tube)
4) Perform two set-ups, one with soda lime (A), and one without (B). Find the volume of gas used in a given time. Volume of carbon dioxide: Volume of A - Volume of B
5) Rate = Volume of oxygen used / mass of organism / time
6) The soda lime is corrosive. Wear eye protection and handle with gloves.