TKOKI1993 Unit 5 Biology Notes Topic 7: Run for Your Life 2. Describe the structure of a muscle fibre and explain the structural and physiological differences between fast and slow twitch muscle fibres. Muscle is made up of myofibrils lying parallel to each other. Each myofibril is made up of sarcomeres. Actin and myosin are proteins that make up a large part of the sarcomeres. The cytoplasm of myofibrils is called the sarcoplasm. There are a lot of mitochondria to provide energy. The sarcoplasmic reticulum is a network of membranes that stores and releases calcium ions. Properties of slow twitch muscle fibres Have steady action over a long period of time Contract slowly and stay in tetanus long Used to maintain body posture Rely on glucose for fuel Known as oxidative/red muscle due to rich blood supply and high levels of myoglobin Rich blood supply, a lot of mitochondria and plenty of myoglobin means they can continue their activity without the need to respire anaerobically Properties of fast twitch muscle fibres Contract rapidly so suited for rapid bursts of activity Functions anaerobically so pale in colour; lack of blood supply. This is why it is known as white muscle fibre Relatively few blood vessels and low levels of myoglobin Fatigues quickly Small number of mitochondria Rich glycogen stores High levels of creatine phosphate. Also known as phosphocreatine 3. Explain the contraction of skeletal muscle in terms of the sliding filament theory, including the role of actin, myosin, troponin, tropomyosin, calcium ions, ATP and ATPase Sliding filament theory – Theory developed by Hugh Huxley and Jean Hanson in the 1950s to explain the patterns seen when muscle contracts Actin – One of the contractile proteins that make up the structure of the muscle cells. It is made up of two chains of actin monomers joined together like beads on a necklace. Actin’s shape produces myosin binding sites where myosin’s globular heads can fit. Myosin – Contractile protein that interacts with actin to bring about the contraction of a muscle. It is made up of two long polypeptide chains twisted together, each ending in a large globular head which has ADP and inorganic phosphate molecules bound to it. The head can act as an ATPase enzyme Troponin – A protein associated with tropomyosin in the muscle structure. It is attached regularly along the chain of tropomyosin. It has 3 sub units, one binds to actin, one binds tropomyosin and the final one binds calcium ions. Tropomyosin – Long chain protein which wraps around actin chains in the structure of a muscle and, in a relaxed muscle, it covers up the myosin binding sites on actin filaments. Calcium ions – Released from the sarcoplasmic reticulum as a result of a stimulus. Ca 2+ binds to troponin molecules causing it to change shape. It is also required in the activation of ATPase in the myosin globular head.
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TKOKI1993
Unit 5 Biology Notes
Topic 7: Run for Your Life 2. Describe the structure of a muscle fibre and explain the structural and physiological differences between fast and slow twitch muscle fibres. Muscle is made up of myofibrils lying parallel to each other. Each myofibril is made up of sarcomeres. Actin and myosin are proteins that make up a large part of the sarcomeres. The cytoplasm of myofibrils is called the sarcoplasm. There are a lot of mitochondria to provide energy. The sarcoplasmic reticulum is a network of membranes that stores and releases calcium ions. Properties of slow twitch muscle fibres
Have steady action over a long period of time
Contract slowly and stay in tetanus long
Used to maintain body posture
Rely on glucose for fuel
Known as oxidative/red muscle due to rich blood supply and high levels of myoglobin
Rich blood supply, a lot of mitochondria and plenty of myoglobin means they can continue their activity without the need to respire anaerobically
Properties of fast twitch muscle fibres
Contract rapidly so suited for rapid bursts of activity
Functions anaerobically so pale in colour; lack of blood supply. This is why it is known as white muscle fibre
Relatively few blood vessels and low levels of myoglobin
Fatigues quickly
Small number of mitochondria
Rich glycogen stores
High levels of creatine phosphate. Also known as phosphocreatine
3. Explain the contraction of skeletal muscle in terms of the sliding filament theory, including the role of actin, myosin, troponin, tropomyosin, calcium ions, ATP and ATPase Sliding filament theory – Theory developed by Hugh Huxley and Jean Hanson in the 1950s to explain the patterns seen when muscle contracts Actin – One of the contractile proteins that make up the structure of the muscle cells. It is made up of two chains of actin monomers joined together like beads on a necklace. Actin’s shape produces myosin binding sites where myosin’s globular heads can fit. Myosin – Contractile protein that interacts with actin to bring about the contraction of a muscle. It is made up of two long polypeptide chains twisted together, each ending in a large globular head which has ADP and inorganic phosphate molecules bound to it. The head can act as an ATPase enzyme Troponin – A protein associated with tropomyosin in the muscle structure. It is attached regularly along the chain of tropomyosin. It has 3 sub units, one binds to actin, one binds tropomyosin and the final one binds calcium ions. Tropomyosin – Long chain protein which wraps around actin chains in the structure of a muscle and, in a relaxed muscle, it covers up the myosin binding sites on actin filaments. Calcium ions – Released from the sarcoplasmic reticulum as a result of a stimulus. Ca2+ binds to troponin molecules causing it to change shape. It is also required in the activation of ATPase in the myosin globular head.
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The Process
Calcium ions bind to troponin, changing their shape. Troponin molecules pull on the tropomyosin molecules they are attached to, moving tropomyosin away from the myosin binding site, exposing them, ready for action
Myosin’s globular head bind to actin forming an actomysosin bridge
ADP and an inorganic phosphate group are released from the myosin head. Myosin changes shape – the head bends forward moving the actin along the myosin filament, shortening the sarcomere.
Free ATP binds to myosin’s head causing myosin to change shape again. This breaks the actomysosin bridge. ATPase is activated in the myosin head; this requires calcium ions as well. ATP is hydrolysed to provide energy to return the myosin head to its original position.
Calcium ions remain in the sarcoplasm and the cycle is repeated if there is continuous stimulation. If not, ATP is used to pump calcium ions back into the sarcoplasmic reticulum. Troponin and tropomyosin return to their original positions.
4. Recall the way in which muscles, tendons, the skeleton and ligaments interact to enable movement, including antagonistic muscle pairs, extensors and flexors. Muscle - Largely made up of protein. They can shorten to do work Tendons – Made up of white fibrous tissue and has bundles of collagen fibres. The tissue is strong but relatively inelastic. It attaches muscle to bone Skeleton – It is made up of bone. It is strong and hard. Made up of bone cells embedded in a matrix of collagen and calcium salts. It is strong under compression but not dense. This is to reduce the weight moved about Ligament – Holds bones together in the correct alignment. Elastic to allow the bones of the joint to move Cartilage – Hard, flexible and elastic. Made up of cells called chondrocytes in a matrix of collagen. It is a good shock absorber. There are two types of cartilage; hyaline is found at the ends of bones. White fibrous cartilage has densely packed collage in the matric and has great tensile strength but it however less flexible. Muscles work in antagonistic pairs. This means that when one muscle contracts, the other relaxes. 5. Describe the overall reaction of aerobic respiration as splitting of the respiratory substrate (eg glucose) to release carbon dioxide as a waste product and reuniting of hydrogen with atmospheric oxygen with the release of a large amount of energy. C6H12O6 + 6O2 → 6CO2 +6H2O + ATP Glucose + oxygen → carbon dioxide + water + energy 6. Describe how to investigate rate of respiration practically.
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Rate of respiration can be determined by measuring the uptake of oxygen or output of carbon dioxide by organisms
A basic respirometer has a sealed chamber containing living organisms such as mice or germinating seeds
The volume of carbon dioxide given off is equivalent to the volume of oxygen taken in. Therefore a chemical such as potassium hydroxide is used absorb carbon dioxide produced during respiration
The loss of carbon dioxide is measured by observing the moment of fluid in a capillary tube. The amount of oxygen used is calculated from this.
The effect on the rate of respiration can be measured by recording changes in oxygen uptake in different conditions.
7. Recall how phosphorylation of ADP requires energy and how hydrolysis of ATP provides an accessible supply of energy for biological processes. 8 Describe the roles of glycolysis in aerobic and anaerobic respiration, including the phosphorylation of hexoses, the production of ATP, reduced coenzyme and pyruvate acid (details of intermediate stages and compounds are not required).
Occurs in the cytoplasm
4ATPs & 2NADHs are made, 2 ATPs are used.
ATP is sued to phosphorylate glucose to a 6 carbon sugar with a phosphate group.
The phosphorylated sugar splits into two molecules of GALP
GALP is converted to pyruvate.
2 hydrogens from GALP are taken up by NAD to form reduced NAD.
Reduced NAD goes into the electron transport system and provides energy to phosphorylate ADP to ATP
In the presence of oxygen, pyruvate goes into the Krebs cycle via the link reaction. In anaerobic conditions, pyruvate is converted to lactic acid
9 Describe the role of the Krebs cycle in the complete oxidation of glucose and formation of carbon dioxide (CO2), ATP, reduced NAD and reduced FAD (names of other compounds are not required) and that respiration is a many-stepped process with each step controlled and catalysed by a specific intracellular enzyme.
Pyruvate splits into a 2C molecule and CO2
2C molecule attaches to coenzyme A to form acetyl coenzyme A
NAD accepts hydrogen from pyruvate to form reduced NAD
Acetyl coenzyme A combines with a 4C compound to for 6C citric acid.
Citric acid is broken down in a series of reactions to form the original 4C compound
2 molecules of CO2 are liberated
For each pyruvate, 2 molecules of reduced NAD, 1 reduced FAD, 2 CO2 and 1 ATP are made 10 Describe the synthesis of ATP by oxidative phosphorylation associated with the electron transport chain in mitochondria, including the role of chemiosmosis and ATPase. Electron Transport Chain
Occurs in the cristae of mitochondria
Electrons are passed down energy levels releasing energy to power the phosphorylation of ADP
Oxygen is the terminal acceptor, forming H2O
Without oxygen, the electron transport chain cannot occur as all the electron acceptors are saturated with electrons
It is called oxidative phosphorylation as it is a process dependent on oxygen to phosphorylate ADP
Chemiosmosis
NADH and FADH2 contain stored chemical energy
Energy is used to pump H+ ions into the mitochondrial membrane, against a concentration gradient
The inner membrane is impermeable to protons creating a concentration, electrochemical and pH gradient
H+ leaves the envelope through ATPase proteins. The energy generated is used to phosphorylate ATP
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11 Explain the fate of lactate after a period of anaerobic respiration in animals.
Oxidative phosphorylation stops as oxygen is not available to accept electrons; electron carriers are saturated meaning NAD and FAD cannot be regenerated
Krebs cycle stops as coenzyme A is not regenerated and pyruvate builds up in cell
Cells convert pyruvate to lactic acid which generates less ATP than in aerobic conditions
When oxygen is available, lactic acid is converted back to pyruvate in the liver using oxygen. This is known as repaying the oxygen debt. It is important that this happens as lactic acid is poisonous.
12 Understand that cardiac muscle is myogenic and describe the normal electrical activity of the heart, including the roles of the sinoatrial node (SAN), the atrioventricular node (AVN) and the bundle of His, and how the use of electrocardiograms (ECGs) can aid the diagnosis of cardiovascular disease (CVD) and other heart conditions. Myogenic – The heart is said to be myogenic as it beats without external stimulation from the central nervous system. It sets up its own wave of depolarisation Sequence of heart beat – The sinoatrial node initiates the depolarisation. The depolarisation passes through the wall of the atria causing an atrial systole. The depolarisation passes to the atrioventricular node. It is held here as the right and left atria are emptying blood into the ventricles. The impulse is then taken to the bundle of His, bundle of his carries the excitation from the AVN to the Purkyne tissue. The ventricles contract from the apex up. This is known as ventricular systole. The atrioventricular valves close to prevent the backflow of blood to the atria. The semilunar valves are forced open by the build-up of pressure. Blood is then forced into the arteries. Change of pressure during diastole closes the semilunar valves. Normal electrical activity of the heart
The peak at p represents an atrial systole. A wave of depolarisation has been sent from the SAN causing the atria to contract. The time between P and the QRS complex is known as the PR interval. During this time, the impulse is at the atrioventricular node. This delay allows for atria to completely empty blood into the ventricles The electrical impulse travels from the bundle of his to the Purkyne tissue. The Purkyne tissue passes the impulse to ventricles, and the ventricles contract base up. This is known as the ventricular systole. The QRS complex represents the ventricular systole. The T wave represents the rapid repolarisation of the Purkyne tissue in the ventricles. This is also known as diastole. How ECGs can aid the diagnosis of CVDs and other heart conditions An ECG is used to investigate the rhythms of the heart by producing a record of the electrical activity of the heart. The depolarisation in the heart causes tiny little electrical changes on the surface of the skin. Electrodes attached to the skin measure these changes. Usually, when an ECG is taken, the patient is lying down. However, some heart conditions are only shown when the patient is exercising. Therefore, during a stress test, the patient is exercising.
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Arrhythmias are when the heart has different rhythms to what is expected. Atrial fibrillation is when the atria are contracting too fast and ineffectively; blood is not pumped under a high enough pressure. Tachycardia is when the heart beats too quickly. 13 Explain how variations in ventilation and cardiac output enable rapid delivery of oxygen to tissues and the removal of carbon dioxide from them, including how the heart rate and ventilation rate are controlled and the roles of the cardiovascular control centre and the ventilation centre. During exercise, extra oxygen is needed in rapidly respiring tissue. Also CO2 and lactate need to be removed quickly. In order to cope with this, the hear uses negative feedback systems. To increase the amount of oxygen, the heart increases the number of beats per minute and the volume of blood pumped per heartbeat. These are known as heart rate and cardiac volume respectively. The combination of these gives the cardiac output During exercise, blood is redirected from other parts of the body to the areas of the body where it is needed. Tidal Volume – The volume of air that enters and leaves the lings at each natural resting breath Ventilation Rate – Tidal volume X frequency of inspiration – It is a measure of the volume of air breathed in per minute. How the heart rate is controlled Nervous control of the heart
The cardiovascular centre in the medulla controls the heart rate.
Chemical and stretch receptors in the lining of blood vessels and chambers of the heart send impulses to the
cardiovascular centre
Nervous control of the heart is autonomic and is divided into the sympathetic and parasympathetic nervous
systems. Sympathetic is excitatory and parasympathetic is inhibitory.
Impulses travelling down the sympathetic nerve increase the frequency of impulses from the SAN. The
parasympathetic does the opposite.
Hormonal control
The heart rate increases when you are nervous. The hormone adrenaline is produced. This speeds up the
frequency of impulses from the SAN, thereby increasing the heart rate.
How is the ventilation rate controlled?
The ventilation centre in the medulla provides the basic stimulus to inhale and exhale. It involves a feedback
system based on the stretching of the bronchi during exercise.
We inhale as a result of impulses travelling along the sympathetic nerves. This causes the intercostal muscles
and the diaphragm to contract
As the lungs get larger, stretch receptors in the walls of the bronchi send impulses to the respiratory centre.
The impulses from the stretch receptors inhibit impulses from the respiratory centre thereby stopping the
muscles from being stimulated
Conscious areas of the brain can override the respiration centre. This is why we can hold our breath
The level of carbon dioxide is the main stimulus that affects breathing rate.
An increase in CO2 levels leads to a fall in pH which then leads to an increase in the rate and depth of
breathing. This is because the diaphragm and intercostal muscles are contracting harder and more frequently
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14 Describe how to investigate the effects of exercise on tidal volume and breathing rate using data from
spirometer traces.
A Spirometer trace
15 Explain the principle of negative feedback in maintaining systems within narrow limits.
A negative feedback system is a system enabling the body to maintain a condition within a narrow range. For
example if one factor goes up, system instigates change to bring it back down again.
Change in normal level of a factor
Receptor detects change
Receptor sends a communication hormonally or via the nervous syste,
The effector carries out a response to bring about corrective change
Return to normal level of factor
Negative Feedback system in the heart -1
Baroreceptors are sensitive to pressure. They detect changes in pressure in the carotid arteries.
An increase in blood pressure in the arteries stretches the baroreceptors
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Baroreceptors send impulse to the cardiovascular centre
Cardiovascular centre sends impulses through the parasympathetic nerves to slow down the heart rate and
widens the blood vessels, thereby lowering the blood pressure
Negative feedback system in the heart -2
During exercise, adrenaline dilates the blood vessels causing the blood pressure to fall
The baroreceptors stop sending impulses
The cardiovascular centre detects this and sends impulses down the sympathetic nerve to stimulate the heart
and increase blood pressure.
Negative feedback system in the lungs
Chemoreceptors detect fall in pH of the blood
Impulse sent to respiratory centre
Respiratory centre sends impulse sent to diaphragm and intercostal muscles to contract harder and more
rapidly to increase breathing rate
16 Discuss the concept of homeostasis and its importance in maintaining the body in a state of dynamic
equilibrium during exercise, including the role of the hypothalamus and the mechanisms of thermoregulation.
Homeostasis is controlling the internal conditions within very narrow limits. Thanks to many feedback systems,
we are able to maintain a fairly constant internal temperature even if there are fluctuations in the external
conditions. The low critical temperature is the temperature at which the normal thermoregulatory measures to
conserve heat and the metabolic rate increases to produce extra heat. The low lethal temperature is the
temperature below which chemical reactions of the body can no longer take place at a quick enough rate to meet
the demand. If the temperature gets too high, enzymes are denatured. This means that biological reactions can
no longer take place.
The Role of the hypothalamus
Receptors in the brain detect changes in blood temperature. Receptors in skin detect changes in external
temperature. The temperature receptors are found in the hypothalamus.
Increase in blood temperature
Heat loss centre activated
Impulse sent to effectors to increase blood flow close to skin and increase sweating
Erector pilli muscles are relaxed so hairs lie flat
Any shivering stops
Decrease in blood temperature
Heat gain centre activated
Impulse sent to effectors to decrease blood flow close to skin and decrease sweating
Erector pilli muscles contract so hairs stand trapping an insulating layer of air