Download Topic 7 Checkpoint Answers File

Checkpoint answers for topic 7
Q7.1 Produce a flowchart of the steps that must occur to bring about contraction of a
sarcomere.
Nerve impulse arrives at a neuromuscular junction.
Calcium ions (Ca2+) are released from the sarcoplasmic reticulum into the sarcoplasm.
Ca2+ attach to troponin molecules.
Troponin molecules and the attached tropomyosin shift their position, exposing myosin binding sites on
the actin filaments.
Myosin heads bind with myosin binding sites on the actin filament, forming cross-bridges.
When the myosin head binds to the actin, ADP and Pi on the myosin head are released.
The myosin changes shape.
The myosin head nods forward.
The actin moves over the myosin.
An ATP molecule binds to the myosin head.
The myosin head detaches.
An ATPase on the myosin head hydrolyses the ATP, forming ADP and Pi.
The myosin head changes shape.
The myosin head returns to its upright resting position.
The cycle starts again.
When a muscle relaxes it is no longer being stimulated by nerve impulses. Calcium ions are actively
pumped out of the muscle sarcoplasm, using ATP. The troponin and tropomyosin move back, once
again blocking the myosin binding site on the actin.
Q7.2 Draw up a table of comparisons between aerobic and anaerobic respiration.
Aerobic respiration
Anaerobic respiration
Requires oxygen; occurs when sufficient oxygen
supply to cells.
Does not require oxygen; occurs when oxygen
demands in the cells exceed supply.
Reactions occur in the cytoplasm and mitochondria.
Reactions occur in the cytoplasm.
Complete oxidation of glucose to carbon dioxide and
water.
Incomplete oxidation of glucose.
C6H12O6 6O2 → 6CO2 6H2O energy released
C6H12O6 → 2pyruvate energy released
Glycolysis in cytoplasm; Krebs cycle and electron
transport chain in mitochondria.
Only glycolysis occurs.
Initial step of glycolysis involves phosphorylation of
glucose to increase the reactivity of the glucose.
Initial step of glycolysis involves phosphorylation of
glucose to increase the reactivity of the glucose.
Glucose split into two molecules of 3-carbon
compounds that are oxidised to form 3-carbon
pyruvate.
Glucose split into two molecules of 3-carbon
compounds that are oxidised to form 3-carbon
pyruvate.
Substrate-level phosphorylation produces ATP.
Reduced NAD produced.
Substrate-level phosphorylation produces ATP.
Reduced NAD produced.
Pyruvate is decarboxylated and dehydrogenated to
form a 2-carbon molecule that combines with
coenzyme A to form acetyl CoA in the link reaction.
CO2 and reduced NAD produced.
Pyruvate produced at the end of glycolysis is reduced
to lactate and the oxidised form of NAD is
regenerated.
A 2-carbon compound from each acetyl CoA enters the
Krebs cycle. Reactions involved include
decarboxylation, dehydrogenation and substrate-level
phosphorylation.
Two carbon dioxide molecules, one molecule of ATP
by substrate-level phosphorylation and reduced NAD
and reduced FAD are produced.
The reduced coenzymes ‘shuttle’ the hydrogen atoms
to the electron transport chain on the mitochondrial
inner membrane and the oxidised coenzyme is
recreated.
Using energy released as electrons pass along the
electron transport chain, ATP molecules are generated
by chemiosmosis. This method of synthesising ATP is
known as oxidative phosphorylation.
The net yield is 38 ATP molecules per glucose
molecule.
The net yield is just 2 ATP molecules per glucose
molecule.
Aerobic respiration will continue as long as oxygen is
available to act as the final carrier in the electron
transport chain, allowing the regeneration of the NAD
and FAD.
As lactate accumulates, the pH of the cell falls,
inhibiting the enzymes which catalyse the glycolysis
reactions. The glycolysis reactions and the physical
activity that depends on them cannot continue.
Q7.3 Draw a flowchart to summarise the information that you have just read about the
electrical activity of the heart.
Q7.4 Summarise the key changes that occur to ventilation and cardiac output during
exercise and describe the sequence of events that change the rate of breathing if a decline
in carbon dioxide occurs in the blood.
During exercise, cardiac output, i.e. the volume of blood pumped by the heart per minute,
increases. This occurs because both stroke volume and heart rate increase. During
exercise the heart is filling with more blood during diastole as more blood is forced back to
the heart by the action of muscles around the body, and stronger contractions occur
expelling more blood from the heart.
With exercise there are increases in breathing rate, depth of breathing and minute
ventilation (the tidal volume (average volume of one breath, in dm 3) multiplied by the
breathing rate (number of breaths per minute)).
The sequence of events that change the rate of breathing if a decline in carbon dioxide
occurs in the blood is as follows:
There is less carbon dioxide dissolved in the blood plasma so less carbonic acid forms and
dissociates.
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The pH of the blood rises.
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Chemoreceptors sensitive to hydrogen ions located in the ventilation centre of
the medulla oblongata detect the fall in hydrogen ion concentration.
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Impulses are sent to other parts of the ventilation centre.
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Fewer impulses are sent from the ventilation centre to stimulate the muscles
involved in breathing.
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Fewer and weaker contractions of the external intercostal muscles and
diaphragm muscles decrease the rate and depth of breathing.
Q7.5 Produce an annotated list of the disadvantages of exercising a too much and b too
little.
Disadvantages of exercising too much
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Poor athletic performance.
Chronic fatigue.
Sore throats and flu-like symptoms (upper respiratory tract infections) due to a
suppressed immune system with a decrease in the number and activity of cells
in the immune system. An inflammatory response in muscles due to damage to
muscle fibres and the release of hormones with exercise may contribute to the
suppression of the immune system.
Increased wear and tear on joints, which may require surgical repair. Damage to
articular cartilage can lead to inflammation and a form of arthritis. The bursae
(fluid sacs) which cushion the points of contact between bones, tendons and
ligaments can swell up with extra fluid. As a result, they may push against other
tissues in the joint, causing inflammation and tenderness.
Disadvantages of exercising too little
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Increased risk of weight gain if energy input is high, leading to obesity.
Increased risk of high blood pressure, coronary heart disease and stroke.
There will be no increase in the level of blood HDLs nor reduction in LDLs
associated with exercise, which protect against coronary heart disease and
stroke.
Loss of sensitivity of cells to insulin which increases the likelihood of developing
type II diabetes.
No protection against loss of bone density and the development of osteoporosis.
Greater risk of some cancers.
No increase in natural killer cells.
Q7.6 Write a short paragraph which summarises how transcription factors: a switch on and
b switch off the transcription of a gene.
a Protein transcription factors and an enzyme called RNA polymerase bind to a section of
the DNA adjacent to the gene to be transcribed. This section is known as the promoter
region. Once all the transcription factors and RNA polymerase have successfully bound to
the promoter region, the transcription initiation complex has formed and transcription will
proceed. The transcription factors may be present all the time in the cell. However, some
transcription factors are only synthesised when needed. They may be present in an
inactive form and will only bind when activated by signal proteins.
b Genes are switched off (not able to be transcribed) by the cell by preventing the binding
of the transcription initiation complex to the section of the DNA adjacent to the gene.
Protein repressor molecules may attach to the DNA of the promoter region blocking the
attachment sites for transcription factors. Alternatively, protein repressor molecules can
attach to the transcription factors preventing them forming the transcription initiation
complex. In some cases signal proteins acting as transcription factors may simply not be
present.
Q7.7 Outline the uses and misuses of the drugs creatine, testosterone and erythropoietin.
Suggest ethical arguments for and against the use of drugs to improve sporting
performance.
Creatine
Uses: acts as a phosphate store in cells for rapid recreation of ATP from ADP.
Misuses: creatine is not a banned substance. It is taken as a dietary supplement by
athletes to increase the amount of creatine phosphate in muscle cells. This has been
shown to improve performance in high-intensity activity. The use of creatine supplements
combined with heavy weight training has been associated with increases in muscle mass
and maximal strength, and a decrease in recovery time. Some adverse effects of taking
creatine supplements have been reported. These include diarrhoea, nausea, vomiting,
high blood pressure, kidney damage and muscle cramps.
Testosterone
Uses: binds to receptors on target cells and modifies gene expression to alter the
development of the cell; causes the development of the male sexual organs. During
adolescence it is responsible for development of the male secondary sexual
characteristics, for example the deepening of the voice, growth of facial and body hair, and
skeletal and muscular changes. Personality changes such as increased aggressiveness
have been attributed to testosterone. Synthetic anabolic steroids such as nandrolone have
been manufactured by chemical modification of testosterone. Originally developed for the
treatment of muscle-wasting diseases, anabolic steroids are also used in the treatment of
osteoporosis. In the UK they are prescription-only drugs. They are classified as Class C
drugs under the Misuse of Drugs Act and banned by the International Olympic Committee.
Misuses: some athletes and bodybuilders inject synthetic anabolic steroids to increase
muscle development. Anabolic steroids can cause high blood pressure, liver damage,
changes in the menstrual cycle in women, decreased sperm production and impotence in
men, kidney failure and heart disease. They can increase aggression in both men and
women. The illegal use of steroids occurs not only in human sport but also in animal sports
such as horse racing and dog racing.
Erythropoietin (EPO)
Uses: stimulates the formation of new red blood cells in bone marrow. EPO is used to treat
anaemia.
Misuses: endurance athletes take EPO to increase their number of red blood cells and
hence the oxygen-carrying capacity of their blood. There are health risks associated with
high levels of red blood cells; there is an increased risk of thrombosis, which can lead to
heart attack and stroke.