Biology Unit 5 Topic 7: Run for your life Describe the structure of a muscle fibre and fibre and explain the structurall and physiological differences between fast and slow structura twitch muscle twitch muscle fibres. ach muscle is a bundle of many muscle cells called fibres. !"eletal muscles contain many myofibrils which are made up of proteins #myofilaments$ #myofilaments$ actin #thin filaments$ and myosin #thic" filaments$. The cell surface membrane of a muscle cell is "nown as the sarcolemma. The sarcoplasmic reticulum is a specialised endoplasmic reticulum reticulum which can store and release calcium ions which are re%uired for muscle contraction. The cytoplasm inside a muscle cell is called the sarcoplasm. The specialised synapse between neurones neurones and muscle cells is called the neuromuscular &unction.
There are two types of muscle fibres ' slow twitch and fast twitch fibres. Slow twitch They(re specialised for slower, sustained contraction and contraction and can cope with long periods of exercise e.g. long) distance running *ontain many mitochondria ' mitochondria ' +T, for muscle contraction comes from aerobic respiration #electron transport chain$ They contain lots of myoglobin to store oxygen and lots of capillaries to supply oxygen. This gi-es the muscle a dark colour as colour as myoglobin is a dar" red pigment They(re fatigue resistant /ow glycogen content /ow le-els of creatine phosphate
Fast twitch They(re specialised for rapid, intense contractions in contractions in shorts bursts e.g. sprinting Few mitochondria ' mitochondria ' +T, comes from anaerobic respiration respiration ' glycolysis t contains little myoglobin and few capillaries therefore the muscle has a light colour
They fatigue quickly 0igh glycogen content 0igh le-els of creatine phosphate
Test your understanding: 1$ 2hat is a muscle fibre made up of3 4$ 2hat is the difference between two myofibrils ' actin and myosin3 $ 2hat does the sarcoplasmic reticulum store3 6$ 2hat(s the name of the synapse between neurones and muscle cells3 5$ 2hat(s the difference between s"eletal cardiac and smooth muscles3 8$ 2hy are slow twitch muscle fibres dar" in colour3 7$ 2hat are fast twitch muscle fibres specialised for3 9$ 2hich type of muscle fibre re%uires more oxygen3 xplain the contraction of s"eletal muscle in terms of the sliding filament theory including the role of actin myosin troponin tropomyosin calcium ions #*a4$ ATP and ATPase. The sliding filament theory of muscle contraction The functional unit of a muscle fibre is called the sarcomere. 2hen the muscle contracts the thin actin filaments mo-e between the thic" myosin filaments shortening the length of the sarcomere and therefore shortening the length of muscle.
1$ +cetylcholine a neurotransmitter substance is released into the synapse diffuses across and attaches to specific receptors on the sarcolemma #the outer membrane of the muscle fibre$. 4$ The muscle sarcolemma is depolarised. $ Depolarisation spreads along the fibre. 6$ This causes calcium to be released from the sarcoplasmic reticulum into the sarcoplasm. 5$ *alcium attaches to troponin which mo-es tropomyosin thus unco-ering the myosin binding sites on the actin filaments. 8$ +T, attached to the myosin heads cause them to flex and attach to the actin in the o-erlapping areas. 7$ +T, is hydrolysed to +D, , using +T,ase. The energy released causes the heads to alter their angle to their tails. This pulls the actin filament past the myosin filament.
9$ The cross)bridges detach and reattach this time further along the actin filament. Test your understanding 1$ 4$ $ 6$
2hat is the role of calcium ions in muscle contraction3 2hat is acetylcholine and what is its role in muscle contraction3 2hat is the name of the en;yme in-ol-ed in hydrolysis of +T,3 2hat
Recall the way in which muscles tendons the s"eleton and ligaments interact to enable mo-ement including antagonistic muscle pairs extensors and flexors. Bones can only mo-e in relation to one another at joints. There are many different types of &oints which allow different degrees of mo-ement. The &oints mo-e due to the force of muscles acting on them. Ligaments are made of elastic connecti-e tissue and they hold bones together to restrict the amount of mo-ement possible at a &oint thus pre-enting dislocation. =uscles are attached to bones by tendons which are made of collagen fibres ' non elastic fibrous tissue which anchors muscles to bones. 2hen a muscle contracts the tendon and its attached bone are pulled towards the contracting muscle. !"eletal muscles are those attached to bones and they are arranged in antagonistic pairs. This means that there are pairs of muscles which pull in opposite directions as one set causes the &oint to mo-e one way the other set causes it to return. +n example is the elbow &oint which is controlled by the biceps and the triceps muscle. The biceps is a flexor which contracts to flex or bend a &oint whereas triceps in the arm is an extensor which contracts to extend or straighten a &oint.
Test your understanding: 1$ 2hat are &oints3 4$ 2hat are ligaments what are they made of and what is their function3 $ 2hat are tendons what are they made of and what is their function3 6$ 2hat are s"eletal muscles3 5$ 2hat is meant by the term antagonistic muscle pairs3 8$ 2hat(s the difference between flex)ors and extensors3
Describe the o-erall 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.
Describe how to in-estigate rate of respiration practically.
Rate of aerobic respiration can be determined using a respirometer by measuring the rate of oxygen absorbed by small organisms. +ny carbon dioxide produced is absorbed by potassium hydroxide solution so that any oxygen absorbed by the organisms results in the fluid in the manometer tube mo-ing towards the organisms. The tube on the right hand side compensates for any changes in pressure or temperature within the apparatus. Test your understanding 1$
2hat
4$ by3
2hy does carbon dioxide ha-e to be absorbed and what can in be absorbed
Recall how phosphorylation of +D, re%uires energy and how hydrolysis of +T, pro-ides an accessible supply of energy for biological processes.
nergy is re%uired to add a third phosphate bond to +D, to create +T,. 2hen this bond is bro"en by hydrolysis the energy released can be used in energy re%uiring processes ta"ing place within the cell such as acti-e transport. Test your understanding 1$
2hat does +T, consist of3
4$ 2hat process can be used to brea" down +T, to produce +D, and inorganic phosphate3 $
2hat is +T, used for3
Describe the roles of glycolysis in aerobic and anaerobic respiration including the phosphorylation of hexoses the production of +T, reduced co-enyme and pyru!ate acid #details of intermediate stages and compounds are not re%uired$. xplain the fate of lactate after a period of anaerobic respiration in animals. >lycolysis produces two molecules of pyru-ate two molecules of reduced ?+D and a net gain of two molecules of +T, from one molecule of glucose. t ta"es place within the cytoplasm of cells.
+naerobic respiration
>lycolysis does not re%uire oxygen. 0owe-er for glycolysis to continue a constant supply of ?+D is re%uired. n aerobic respiration the ?+D is produced by the electron transport chain. The reduced ?+D must be oxidised to ?+D. During anaerobic respiration ?+D must come from elsewhere. n animals pyru-ate from glycolysis is reduced to gi-e lactate ?+D is formed and can "eep glycolysis going.
+naerobic respiration allows animals to ma"e a small amount of +T, it is an inefficient process but it is rapid and can supply muscles with +T, when oxygen is not being deli-ered %uic"ly enough to cells. The product of anaerobic respiration lactate forms lactic acid in solution which lowers the p0. This can inhibit en;ymes and if allowed to build up it can cause muscle cramp. @nce aerobic respiration resumes most lactate is con-erted bac" to pyru-ate. t is oxidised -ia the Arebs cycle into carbon dioxide and water. The extra oxygen re%uired for this process is called the oxygen debt. Test your understanding 1$ 2hat is glycolysis3 2hat are the products of glycolysis and where does it occur3 4$ 2here does ?+D come from in anaerobic respiration3 $
2hat happens to pyru-ate in anaerobic respiration3
6$
2hat is the oxygen debt3
Describe the role of the Arebs cycle in the complete oxidation of glucose and formation of carbon dioxide #*@4$ +T, reduced "A# and reduced FA# #names of other compounds are not re%uired$ and that respiration is a many) stepped process with each step controlled and catalysed by a specific intracellular en;yme.
n the first stage of aerobic respiration pyru-ate is oxidised into carbon dioxide and hydrogen #accepted by coen;ymes ?+D and +D$. This ta"es place in the matrix of the mitochondria and in-ol-es the Arebs *ycle. The lin" reaction
ach pyru-ate molecule coming from glycolusis in the cell
Test your understanding 1$
2hat is produced in the lin" reaction3 2here does it ta"e place3
4$
2hat
$
2here does the Arebs cycle ta"e place3
Describe the synthesis of +T, by oxidati!e phosphorylation associated with the electron transport chain in mitochondria including the role of chemiosmosis and ATPase.
+T, is synthesised in aerobic respiration by electron transport chain in the inner membrane of the mitochondria #cristae$. 1$ Reduced co)en;yme carries 0 and electrons to electron transport chain on inner mitochondrial membrane. 4$ lectrons pass from one electron carrier to the next in a series of redox reactions the carrier is reduced when it recei-es the electrons and oxidised when it passes them on. $ ,rotons mo-e across the mitochondrial membrane creating high 0 concentrations in the intermembrane space. 6$ 0 diffuse bac" into the mitochondrial matrix down the electrochemical gradient 5$
0 diffusion allows +T,ase to catalyse +T, synthesised
8$ lectrons and 0 ions recombine to form hydrogen atoms which then combine with oxygen to create water. f the supply of oxygen stops the electron transport chain and +T, synthesis also stop. The o-erall reaction of aerobic respiration can be summarised as the splitting and oxidation of a respiratory substrate e.g. glucose to release carbon dioxide as a waste
product followed by the reuniting of hydrogen with oxygen to release a large amount of energy in the form of +T,. Test your understanding 1$ 2hats$ can aid the diagnosis of cardio-ascular disease #*CD$ and other heart conditions. xplain how -ariations in -entilation and cardiac output enable rapid deli-ery of oxygen to tissues and the remo-al of carbon dioxide from them including how the heart rate and -entilation rate are controlled and the roles of the cardio-ascular control centre and the -entilation centre. Describe how to in-estigate the effects of exercise on tidal -olume and breathing rate using data from spirometer traces. xplain the principle of negati!e feedback in maintaining systems within narrow limits. ?egati-e feedbac" is a process which helps to "eep the internal en-ironment constant. + change in the internal en-ironment will trigger a response that counteracts the change for example a rise in temperature causes a response that will lower body temperature. n order for negati-e feedbac" to occur there must be a norm -alue or set point such as 7.5 for core body temperature.
Discuss the concept of homeostasis and its importance in maintaining the body in a state of dynamic e%uilibrium during exercise including the role of the hypothalamus and the mechanisms of thermoregulation. 0omeostasis is the maintenance of a stable internal en-ironment within a narrow limit of the optimum conditions needed by cells so they can function properly. + homeostatic system therefore re%uires: 1$ Receptors to detect change away from the norm -alue #stimulus$
4$ + control mechanism that can respond to the information. The control mechanism uses the ner-ous system or hormones to switch effectors on and off $ ffectors to bring about the response usually to counteract the effect or initial change$. =uscles and glands are effectors. There are se-eral things that need to be regulated: The body
+bo-e or below certain temperatures homeostasis fails e.g. because the hypothalamus may be damaged. nstead positi-e feedbac" may occur resulting in a high temperature continuing to rise or a low temperature falling still further. This can result in hypothermia or hyperthermia and may lead to death. xplain how medical technology including the use of keyhole surgery and prostheses is enabling those with in&uries and disabilities to participate in sports eg cruciate ligaments repair using "eyhole surgery and "nee &oint replacement using prosthetics. The de-elopment of "eyhole surgery using fibre optics has made it possible for surgeons to repair damaged &oints such as torn cruciate ligaments in the "nee with precision and minimal damage. This is because only a small incision is needed so there is less bleeding and damage to the &oin and reco-ery is much %uic"er. + prosthesis is an artificial body part designed to regain some degree of normal function or appearance. The design of prostheses has impro-ed significantly and many disabled athletes are now able to compete at a -ery high le-el e.g. with dynamic response feet that can literally pro-ide them with a spring in the step. Damaged &oins such as "nee &oints can now be repaired with small prosthetic implants to replace the damaged ends of bones freeing the patient from a life of pain and restoring full mobility. +nalyse and interpret data on possible disad-antages of exercising too much #wear and tear on &oints suppression of the immune system$ and exercising too little #increased ris" of obesity coronary heart disease #*0D$ and diabetes$ recognising correlation and causal relationships.
There are many benefits to regular moderate exercise. The effects of a lac" of exercise o-er a prolonged period of time include: •
reduced physical endurance lung capacity stro"e -olume and maximum
heart rate •
increased resting heart rate blood pressure and storage of fat in the body
•
increased ris" of coronary heart disease type diabetes some cancers
weight gain and obesity •
impaired immune response due to lac" of natural "iller cells
•
increased le-els of /D/ and reduced le-els of 0D/
•
reduced bone density therefore increased ris" of osteoporosis
@-ertraining can lead to immune suppression and increased wear and tear on &oints. or instance damage to cartilage in syno-ial &oins can lead to inflammation and form arithritis. /igaments can also be damaged. Bursae #fluid filled sac$ that cushion parts of the &oin can become inflamed and tender. t can also result in chronic fatigue and poor athetic performance. =oreo-er there is also some e-idence of correlation between intense exercise and the ris" of infections such as colds and sore throats. This could be caused by an increased exposure to pathogens or a suppression. or example fre%uent release of hormones such as adrenaline may cause an inflammatory response which could suppress the immune system. @utline two ethical positions relating to whether the use of performance)enhancing substances by athletes is acceptable. thical framewor"s include: rights and duties maximising the amount of good in the world ma"ing decisions for yourself leading a -irtuous life. or example doping in sport could be considered not acceptable because athletes ha-e a right to fair competition but could e%ually be considered acceptable because athletes ha-e the right to exercise autonomy for example choose to achie-e their best performance and also ha-e a duty to any sponsor they may ha-e. thical absolutists see things -ery clear cut they would ta"e one of two positions e.g. it is ne-er acceptable for athletes to use performance enhancing substances or it is always acceptable for athletes to use any substance a-ailable to them to compete more effecti-ely e-en if there are associated ris"s to their health. thical relati-ists would realise that people and circumstances may be different e.g. it is wrong for athletes to use performance enhancing substance but there may be some cases and circumstances where it is acceptable.
xplain how genes can be switched on and off by D?+ transcription factors including hormones. !ome drugs such as anabolic steroids are closely related to natural steroid hormones. They can pass directly through cell membranes and be carried into the nucleus bound to a receptor molecule. These hormoneEreceptor complexes act as transcription factors they bind to the promoter region of a gene allowing R?+ polymerase to start transcription. +s a result more protein synthesis ta"es place in the cells. or example testosterone increases protein synthesis in muscle cells increasing the si;e and strength of muscle tissue. >enes are switched on by successful formation and attachment of the transcription initiation complex to the promoter region allowing R?+ polymerase to start transcription. >enes remain switched off by failure of the transcription initiation complex to form and attach to the promoter region. This is due to the absence of protein transcription factors or the action of repressor molecules.
