AS Questions

Many options! It has a nucleus; chromosomes; linear (not ccc) DNA; membrane-bound organelles; mitochondria; endoplasmic reticulum (e.r.); 80S ribosomes (not 70S); much larger (20-100m, not about 1.0 m).

10 x 40 = 400.

Magnification is how much bigger an object appears; it does not give more detail! Resolution is the minimum distance between two objects that allows them to be separated. This relates directly to detail – higher resolution is always better! Resolution is determined by the quality of the lenses; by how close the object is to the lenses (nearer is better); and by the wavelength of the radiation used – the maximum resolution being about ½ the wavelength. Thus light microscopes are limited to about 0.2m (= 200nm) and transmission electron microscopes to < 0.1 nm, so they can resolve individual atoms! N.B. For AS there is no such thing as an electron microscope (e.m.)! There are, however, transmission e.m. and scanning e.m.!

Because the electron beam would be scattered by the molecules in air. The result of this is that living cells (which need water) can never be observed in an e.m. (of either sort!)

5. a

Because they have not been stained and so won’t show up;

Because the resolution of the light microscope used is not good enough.

6. a

Because water flows down the water potential gradient, it would otherwise enter membrane-bound organelles and cause them to swell up and burst (or shrink)

Because enzymes would be denatured at different pH values and so the activity of some organelles would be affected (though they might look the same)

Enzymes are denatured by heat, so the same point as b) above; also the process of homogenisation generates quite a lot of heat (friction) and so you want to prevent the proteins being ‘cooked’

Only whole cells and nuclei would have been removed, so all other organelles would remain. Remove the supernatant and re-centrifuge at 20,000G for 20 minutes, then remove the supernatant and re-centrifuge again at 100,000G for 60 minutes. Discard the supernatant this time, resuspend the pellet and repeat the last step (this ‘washes’ the pellet and ensures it is 99% pure!)

Chapter 1 - Cells and Cell Structure

Answers to Exam Questions [back to top]

1. a

Feature	Epithelial cell from small intestine	Prokaryotic cell
Golgi apparatus	a	r
Mitochondria	a	r
Nuclear Envelope	a	r
Plasmid	r	a
Ribosomes	a	a

i. With a transmission e.m., the resolution is about 1000 times better than that of the light microscope, due to the shorter wavelength of the electron beam. The better the resolution, the more fine detail can be observed.
ii The treatment of the cell that is necessary before it can be studied in any form of e.m. leads to the formation of many artefacts, or distortions of reality.

2. a

Nuclear pore.

Y = 80s ribosomes: synthesis of proteins: this is where mRNA is translated into protein

Z = Golgi apparatus: proteins are modified after synthesis (often by adding carbohydrate groups). Proteins are also surrounded with membrane, prior to secretion from the cell (e.g. hormones, digestive enzymes)

Length = 20mm ÷ 30,000 = 0.67μm

Chapter 1 - Cells and Cell Structure

Answers to Assignment Questions [back to top]

RBC’s contain uniformly distributed haemoglobin. Centre of cells is paler; thus centre must be thinner.

8mm ÷ 1000 = 8.0 μm

Evaporation of water from within the cells reduces their volume; cell membrane remains the same length, so ‘wrinkles’ appear

Evaporation of water from the plasma around the cells lowers its water potential. This causes water to leave the cells by osmosis, thus causing the cells to shrink in volume and the ‘wrinkles’ to appear as above.

It contains lipid. This is dissolved by the detergent, causing the cells to burst. This is why detergents are very good disinfectants – they dissolve bacterial cell membranes and disable those viruses that rely on a lipid coat to penetrate the host cell

5. a

[left] ‘dog’s bone’
[right] ‘oval’
[horizontal] ‘ring doughnut’

In this scanning e.m. electron micrograph (book is wrong!) the cells are all at different angles and so all have different shapes.

Great resolution and the obviously false colours.?

Conclusion	Evidence
The plasma membrane allows water molecules to pass through it	The RBC’s in a smear that is left to dry slowly appear smaller and crinkled around the edges
Many of the molecules in the cytoplasm are of the same type	The RBC’s in the picture are a uniform dark colour
RBC’s do not use oxygen and cannot respire aerobically	There are no mitochondria present
RBC’s are biconcave in shape	The appearance of the cells when seen with a scanning e.m.
RBC’s do not contain DNA, so they cannot make proteins	There is no nucleus present

Chapter 2 - Getting In and Out of Cells

In Chapter Questions [back to top]

Raw materials - oxygen; glucose; amino-acids; lipids; mineral ions; water etc.

Waste products – Carbon dioxide; urea

Membranes are made of organic molecules (proteins and phospholipids). These are made of elements with low atomic numbers and so do not absorb electrons and do not show up well in transmission e.m. photomicrographs. In addition, the membrane is fluid and so the image will only show one moment (which might not be typical).

Hydrophilic = ‘water-loving’ so found where the water is (outside)

Hydrophobic = ‘water-hating’ so found where there is no water – inside the membrane. Note that it is possible for the centre of any large molecule (e.g. protein) to be ‘dry’ even though the molecule itself is in water – just like the inside of a submarine is dry.

Cholesterol will reduce the movement of the membrane proteins which are essential for molecules to cross the membrane – particularly by active transport. Note that cholesterol is essential in our diet (we cannot make it) and that without it our membranes would not function. It is only when excess cholesterol is deposited within our blood vessels that a problem occurs.

If the concentration difference across tissue B was much greater than the concentration difference across tissue A; OR if tissue A had a higher concentration inside it; OR if the temperature of tissue B was higher, allowing the membrane to be more fluid AND, since the molecules will have more kinetic energy, they will collide more often with the membrane and so tend to cross it more readily

B is the slowest; A has a shorter distance across it (thus faster diffusion); C has a much larger surface area (microvilli), thus faster diffusion.

7. a

Lipid-soluble molecules are soluble in the hydrophobic core of the membrane and so can cross it (how they ever reached the cell membrane in the first place, given that there is a very wet solution (blood or tissue fluid) outside the cell is a moot point!)

Small molecules (mainly gases) can diffuse between the various molecules that make up the membrane.

Easy questions! Water always flows DOWN the water potential gradient, so it will flow from solution P to solution Q and from solution S (pure water) to solution R.

Chapter 2 - Getting In and Out of Cells

Answers to Exam Questions [back to top]

1 a

i. Messed up question! Pressure potential is positive, so the net water potential is: -10 +3 = -7Mpa

Water always flows down the water potential gradient, so water will flow into the cell top right (-12Mpa) from both the other cells.

ii. Pure water is 0, so any solution must have less water in it, i.e. a negative water potential.

i. Because glycerol is equally soluble in the lipid membrane and in the biological membrane

i. Because the biological membrane pumps sodium ions as part of its active transport system. It also has protein channels that allow specific ions through, which the synthetic membrane lacks

2. a

i.    level of detail visible in the mitochondria;
      level of detail visible in the nuclear envelope;
      the nuclear pores are visible
      the microvilli are clearly visible

ii. A bacterial toxin has damaged the membrane (it actually blocks the sodium pump channels), destroying the microvilli, thus reducing the surface area available for absorption and so reducing water uptake from the gut (i.e. you get the squits!)

Slow down absorption due to the reduced surface area, as described above. Glucose absorption is an active process, so the damage to the microvilli will have a profound effect; you pump water out (with sodium ions) and then allow then to re-enter ‘dragging’ glucose with them. If the reabsorption cannot take place, you both dehydrate and also lose salt, leading to an erratic heartbeat, severe cramps and death.

Chapter 2 - Getting In and Out of Cells

Answers to Assignment Questions [back to top]

A = Ultra-filtration of the blood caused by the high blood pressure in the glomerulus, in which 10% of the water and an equivalent quantity of soluble molecules with a RMM below 48,000 (haemoblobin is 44,000, hence a simple solution of haemoglobin would not be effective as blood)

B = re-absorption of 90% of the water and 100% of the glucose (by active transport) and amino-acids, means that by the time the fluid enters the Loop of Henlé it contains few organic molecules of use to the body.

2. a

The only process that could ensure that all the glucose is re-absorbed, is active uptake

Microvilli give a large surface area; mitochondria provide the ATP (from aerobic respiration) to allow active uptake (and / or active secretion of glucose to maintain the concentration gradient into the cell).

3. a

Since the concentration of urea in the solution in the artificial kidney is virtually zero, urea will leave the blood by diffusion and be carried away.

The concentration of ions in the kidney machine is set at the optimum level for the body; ions will thus leave the blood until they reach equilibrium, i.e. the optimum level

Because the Visking tubing (or its equivalent) has pore that are too small to allow proteins and RBC’s to pass through it., whilst still allowing small molecules such as urea, water and ions such as Na⁺ to pass across.

This will give a larger surface area and so, by Fick’s Law, the rate of diffusion will be faster and so the time for complete dialysis reduced.

‘continuous’ = goes on all the time
‘ambulatory’ = the patient can walk around
‘peritoneal’ = uses the peritoneum as the dialysis membrane
‘dialysis’ = the process by which excess chemicals are removed from the blood

If the concentration in the dialysis fluid is greater than that in the blood, then water will flow into the fluid, from the blood, by osmosis

Chapter 3 - Biological Molecules

In Chapter Questions [back to top]

1. a

Glucose; amino acids (all 20 of them);

Starch and protein

Starch, proteins and fats (the latter depending on the length of the fatty acid chains – waxes yes, oils no)

Maltose = glucose (C6) + glucose (C6) – water, so 12 carbons in all.

C₁₂H₂₂O₁₁ This comes up a lot, so learn it (same formula for sucrose and lactose too!)

The proportions of amylose and amylopectin will vary; the position of the 1: 6 branches within the amylopectin will vary; the lengths of the individual molecular chains will vary. All are only made of one monomer - a glucose - and so we usually say there is only one sort of starch.

Women are lighter so eat less in total; they worry more about their weight, so eat less when dieting; they like chocolate more! Men eat more sandwiches and chips!

Very strange cell – particularly as bacterial cell walls contain several polysaccharides! However, there are 20 different amino acids and the sequence in which they are arranged makes each protein different (like the 26 letters in our alphabet can make many words and an infinite number of different sentences). This is known as the protein’s primary structure and is determined by the order of the bases in the gene (DNA and mRNA) which coded for it. Since neither DNA nor RNA are branched molecules, nor are proteins (our sentences are linear too!). Since polysaccharides are made of only one monomer (usually a glucose), there is usually considered to be only one polysaccharide.

One between each pair, so 8 in all

N- terminus means the amino-acid at one end of the chain with a free amine group
C- terminus means the amino acid at the other end of the chain with a free carboxyl group. This is important in protein sequencing in the laboratory and in digestion in the small intestine, both of which use enzymes (exopeptidases) which can only attack one end or the other of the peptide chain

d -only – the others all involve covalent bonds, formed by condensation reactions.

10.

Influenza (‘flu) is an RNA virus and so mutates rapidly. Similar viruses are also common in other animals, particularly pigs. Thus new mutants and new hybrids with the animal viruses are constantly being produced. Each has different antigens, so each will need different antibodies to react with it. ‘Flu vaccines therefore need to be given each year and are designed to target the scientists’ best guess as to what will be the current strains a year or so ahead.

11.

An unsaturated fatty acid is one containing C=C double bonds (this has the effect of putting a ‘kink’ in the tail of the fatty acid and so makes the membrane more fluid. Hence they are found in fish and plant oils, where the organisms’ operating temperature needs fluid membranes at 10- 20^oC. ‘Poly’ = many; in this case more than one C=C bond. Given the (largely misleading) advertising messages we see daily, cholesterol is also a polyunsaturated fat!

12.

A phospholipid has two fatty acid chains, a triglyceride has three; a phospholipid has a phosphate group, a triglyceride does not. This means that phospholipids are polar molecules, whilst triglycerides are not.

13.

One C=C double bond, so it is monounsaturated.

14.

The fastest a substance can move is to be level with the solvent front, so the top number ( numerator) is always smaller than the bottom number (denominator)!

Chapter 3 - Biological Molecules

Answers to Exam Questions [back to top]

1. a

Glycerol = 3; glucose = 6

i. There are 20 different amino acids, each with a different ‘R’ group. The ‘core’ of the amino acid has just 2 carbons; the balance (0 to 9) are found in the side chain.

i. Starch molecules are made of varying numbers of amylose and amylopectin molecules and each of these has a variable number of glucose sub-units. Starch varies – ask any cook!

Each time a glucose molecule is joined to another (by a 1:4 glycosidic bond), a molecule of water is released. Hence a condensation reaction.

2. a

Place the spots on a line about 2 cm from one end of the paper.
Include reference substances as well as the unknown(s).
Place in a tank of solvent and leave to run for some hours.
Examine and mark the solvent front when removed from the solvent tank.
Calculate the Rf values of the spots (and compare with the reference spots) to identify the unknown molecules.
Check the Rf values against data tables for the same solvent to confirm the identification.

i. Because this represents the total radioactivity, rather than its peak emission

ii. Since the radioactivity was introduced in the fatty acids through ¹⁴C, it follows that the more carbon atoms in the fatty acid, the more radioactive it will be.

Chapter 3 - Biological Molecules

Answers to Assignment Questions [back to top]

To allow them to be compared

2. a

All the carbon will have been oxidised to CO₂ gas and so will not be in the ash

The ash will contain minerals and vitamin residues.

Bar chart

34.4 – 10.8 x 100 = 218.5% 10.8	(i.e. their weight has more than doubled in a little over a week)

5. a

They contain only C-C bonds and no C=C bonds.

Unsaturated are in bold:
Vegan = 39 + 68 + 166 + 52 + 12 + 313 +317 + 15 = 982
Control = 33 + 80 + 276 + 108 + 36 + 353 + 69 + 8 = 963

Unsaturated concentration:
       Vegan concentration = 325 ÷ 982 x 100 = 33.1%
       Control concentration = 497 ÷ 963 x 100 = 51.6%
Saturated concentration:
       Vegan = 657 or 66.9%
      Control = 466 or 48.4%7

Control group produce roughly equal quantities of both saturated and unsaturated fats in their milk.
Vegan group produce roughly twice as much saturated fat as unsaturated fat.

Given that plant fats tend to be unsaturated, this shows that the fats produced in the breast milk are synthesised in the body and not directly related to those in the diet. There is also the recent discovery that omega-3 fatty acids are linked to a number of aspects of brain activity and development. On the basis of the information in this table, it would seem that the two groups of babies will receive very different quantities of this essential nutrient. What the effect of this on their children will be, we can only guess!

Chapter 4 - Enzymes

In Chapter Questions [back to top]

Protein synthesis (DNA ® mRNA = transcription, mRNA ® protein = translation)

Human body temperature is, of course, not constant. It varies throughout the day, rises when exercising or when ill, and a woman’s average temperature varies around the time of ovulation. By being warm-blooded, mammals are able to remain active throughout the year – though at the cost of needing a much larger energy intake than a comparably sized reptile. Crocodiles can feed weekly or less; a tiger needs to eat daily! In cold winter climates, when energy supplies are limited, some mammals hibernate to conserve energy; others migrate. A constant temperature means that enzymes (and other processes too) can be optimised for that temperature. 37^oC is a compromise. Higher temperatures mean faster reactions (good) but at the cost of faster enzyme denaturation (bad).

The hydrogen bonds within each albumen molecule (the main protein in egg white) break when heated, allowing the molecules to uncoil and become entangled. They then reform between the molecules on cooling, ensuring that the egg white remains coagulated. Since the proteins now disperse light, the cooked white is white, whilst raw albumen allows the light to pass through easily. Albumen coagulation is the principle of making sponge cakes and custard (amongst other sauces) – and custard is the basis of ice-cream (yum, yum!). A similar process happens when meat is exposed to acid – you can therefore ‘cook’ meat or fish by marinating it in acid (e.g. lemon juice). Ever eaten gravilax?

The buccal cavity (or mouth, as we scientists call it) has a pH of about 8.0 to ensure that the tooth enamel is strengthened and more calcium can be deposited between meals. On entering the stomach, gastric juice (pH 2.0) denatures it immediately (hence amylase has to work very quickly). Being a protein, amylase will then be attacked by gastric protease (or pepsin) and broken down.

Competitive – normally similar in shape to the substrate (therefore chemically related); bind to active site; complementary to the shape of the active site; normally only bind temporarily; causes inhibition proportional to the relative concentration of the inhibitor (i.e. more substrate speeds things up again).

Non-competitive – binds elsewhere on the enzyme than the active site, distorting the shape of the active site and stopping it binding with the substrate and forming an enzyme-substrate complex. Normally permanent in its effect, it has no chemical connection to the substrate. Heavy metals and many disinfectants and poisons work in this way. Inhibition is proportional to the quantity of inhibitor and so adding extra substrate has no effect.

Some allosteric enzymes have evolved to require a molecule similar to a non-competitive inhibitor before they can act i.e. the inhibitor has now become a promotor.

Chapter 5 - Gas Exchange

In Chapter Questions [back to top]

If external they would be very vulnerable to infection, physical damage or attack and becoming clogged with dust etc. In addition, the water losses from such a large area would be prohibitive.

Gas exchange is a process of diffusion, which can only take place in solution in living things.

It would steadily decrease until it reached zero. The oxygen affinity of haemoglobin varies from species to species, so the actual concentration achieved would vary too.

Because when you fainted the autonomic processes of the body would ‘resume normal service’ and you would start to breathe again.

Hyperventilation means breathing too quickly or too deeply – this is the opposite of holding one’s breath – so the question makes no sense! You feel light headed if you do this (it can happen in a panic attack) due to the very low concentration of carbon dioxide in the blood raising the pH above normal. If you breathe pure oxygen another effect happens – tunnel vision – leading to death (particularly if flying a WW II aircraft and you forgot to switch the oxygen off as you descended to land).

15 x 0.5 = 7.5 litres/min. You extract about 25% of the oxygen, so consume about 0.35 litres/min of oxygen.

Chapter 5 - Gas Exchange

Answers to Exam Questions [back to top]

3 features that increase the rate of diffusion:
      i. thin alveolar walls;
      ii. large surface area;
      iii. transport system to maintain diffusion gradient.

2. a

i. Manv small alveoli (= more surface area than a few, larger ones & walls are thin so more alveoli can be accommodated).

ii. 2 processes ensuring a difference in concentration maintained:
- a ventilation mechanism occurs;
- a transport system removes gas (removes O₂ to body; brings CO₂ to lungs).

Exhaled air from mouth to mouth resuscitation is still valuable because:
i. it contains 15% oxygen;
ii. high levels of CO₂ are present which may stimulate the inspiratory centre of the medulla.

3. a

Nerve A (intercostal and phrenic nerves) stimulates the external intercostal muscles (& diaphragm).

Nerve B (vagus nerve) → causes relaxation of the diaphragm & external intercostal muscles. (\air out of lungs).

The medulla inspiratory centre receives messages from the carotid and aortic bodies. If CO₂ levels rise - it increases the breathing rate.

i. The type of breathing for person in Column X is fast and shallow.

ii. Although Column X shows a faster breathing rate, it is delivering less oxygen to the body (& conversely removing less CO₂) as it is the tidal volume that is of most significance - as there is about 150 cm³ of 'dead' air space in the trachea and bronchi that needs to be deducted from the tidal volume before the alveolar ventilation rate can be calculated.

It is this rate that is of most significance in explaining O₂ delivery into the body. Thus it is possible to breathe less frequently (as in Column Y) but more deeply (\bigger tidal volume) and get a bigger increase in the alveolar ventilation rate than with faster, shallower breathing.

Chapter 5 - Gas Exchange

Answers to Assignment Questions [back to top]

1. a

Will be errors in finding an animal's surface area by:
i. removing skin as it may stretch and not lie entirely flat where it bulges over the body;
ii. cylinder and cones give only a rough, approximate guide.

2 a

Length of one side	Total surface area	Volume	Surface area / Volume ratio
1	6²	1³	6 : 1
2	24²	8³	3 : 1
3	54²	27³	2 : 1
4	96²	64³	1.5 : 1
5	150²	125³	1.2 : 1
6	216²	216³	1: 1

A true B not true C true D true

3 a

Log scales keep the graph size manageable (shortens 'x' axis length considerably).

i 10 cm³ ii 10^5.5 g

Elephants' ears have a large surface area for blood cooling.

Large reptiles cannot live in cooler regions because they have a relatively small external body surface area in relation to their volume - they need the surface area to absorb heat as they are ectotherms ( = "cold blooded animals").

Real size = Size of photograph
Magnification

A microvillus length is 30 mm on the photograph
(= 30,000mm), but in reality it is 3 mm, so, applying the formula:

3 = 30,000 and 3 x mag = 30,000 \ mag = 30,000 = 10,000 x
mag. 3

If a 25 mm length of small intestine is taken, it contains 6 villi, thus:

\ each microvillus has length (each side + top) of 30 + 30 + 4 = 64.
With 6 microvilli = 6 x 64 = 384 mm \ the increase in surface area = 384 ¸ 25 = 15 times more surface area

Chapter 6 - The Heart and Circulation

In Chapter Questions [back to top]

Oxygen: source = lungs, sink = muscles;

Glucose: source = small intestine, sink = muscles

Pulse points require an artery to pass over a bone near to the skin. The pressure within, and diameter of, an artery changes with each beat of the heart; that of the blood in a vein is much lower and constant.

Artery: blood spurts up to the ceiling (!), blood bright red in colour

Vein: blood pours out more slowly, dull red in colour.

Before you faint or call an ambulance, place a clean cloth over the wound and press hard; get the victim to raise their arm as high as possible. If the cloth gets saturated, just add another one, leaving the first in place. Victim should also be given hot, sweet drink (tea!) and kept warm to reduce shock.

4. a

High blood pressure will result in more fluid being squeezed out of the capillaries at the artery end and will tend to reduce absorption at the venous end of the capillary bed. Hence a build-up of tissue fluid (called odema) most obvious on the ankles of old ladies (old men, very wisely, keep their legs covered by trousers!)

This will reduce the water potential of the blood and so will reduce the reabsorption of fluid at the venous end of the capillary bed, resulting, again, in odema as above. This might occur in some types of diabetes, in particular.

Epithelium (found in all organs); smooth muscle (both longitudinal and circular); fibrous tissue (collagen)

6. a

hepatic portal vein (high after a meal, low in between)

hepatic vein (blood has been through two capillary beds in two different organs)

7. a

they have no mitochondria, which is the sole site of aerobic respiration

they have no nucleus, rough endoplasmic reticulum, 80s ribosomes and source of large quantities of ATP (i.e. mitochondria) all of which are needed for protein synthesis.

hepatic vein; (posterior) vena cava; right atrium, right ventricle; pulmonary artery; pulmonary vein; left atrium, left ventricle; aorta; renal artery.

Exactly the same. Liquids are not compressible and blood transmits the pulse uniformly and simultaneously.

10. a

A (pressure in ventricles > in atria)

C (pressure in ventricle < in aorta)

11. a

this enables the atria to fully empty before the ventricles begin to contract. It also puts an upper limit on the heart rate, thus ensuring that the heart never becomes anaerobic.

this ensures that the ventricles both contract from the bottom up, thus ensuring that they fully empty with each beat.

12.

5500 ¸ 70 = 78.57 cm³

13.

The heart responds to two types of stimulus – nerves and hormones. Adrenaline still works!

Chapter 7 - Enzyme Technology

In Chapter Questions [back to top]

Enzymes are specific, so the product(s) made by them are pure. They work best under benign conditions, so saving the cost of fuel and they are not dangerous, so extensive safety measures (such as might be needed with strong acids or high pressures) are avoided. Since enzymes are proteins, any contamination of the product is unlikely to be toxic. They are readily denatured by heat, so pasteurisation (or similar) of the end-product will prevent them continuing to work, potentially degrading the product. Because they are natural, their product is the natural form of the product, i.e. any glucose made will be 100% a-, or 100% b- glucose; synthetic glucose would be a 50:50 mixture of the two.

This is the basis of much drug-testing of athletes. If the breakdown products in their blood or urine are 100% of one form, their origin is natural; if a 50:50 split, then the chemical was produced synthetically. They could be cheating either way, of course!

Because as they are viruses and can replicate very quickly, they would rapidly kill the bacteria in the fermenter. – visit http://www.cellsalive.com/phage.htm for good animations of a bacteriophage infecting an E.coli cell

A biosensor could be used to monitor the level of glucose in the diabetic’s blood. If connected to a transducer, the electrical signal could be connected to a device which automatically injected the correct quantity of insulin into the patient. With the widespread use of ‘Humulin’ (fast-acting human insulin) it is more important to keep the levels of insulin and glucose within a narrow range. All attempts to do this with an automatic syringe have so far failed, due to infection or blockage of the canula used (in place of a needle) to inject the insulin. The modern approach is now to inject the correct amount of insulin to control the actual carbohydrate intake and activity levels of the diabetic, rather than controlling the diet to allow for fixed volumes of insulin. This makes for a more natural life-style and less variation in blood glucose levels.

A transducer or use a pH probe, attached to a read-out of some kind.

Enzymes, normally used in an industrial or laboratory process, which are trapped in some form of matrix so that they do not leach into and contaminate the product(s).

A stain of biological origin, i.e. one based on protein (needs proteases), lipid (removed by detergents anyway, but might need lipase) or carbohydrates (polysaccharides, since sugars are water-soluble ; this will need a range of carbohydrases). Thus a ‘cocktail;’ of enzymes is necessary to remove them all.

Chapter 7 - Enzyme Technology

Answers to Exam Questions [back to top]

1. a

An enzyme that is normally secreted by the organism and so works outside the cell. Such enzymes (including those of digestion) are normally more stable and robust than the much more common intracellular enzymes. They are therefore favoured for industrial use.

i. This is to enable the bacteria to grown and reproduce rapidly – for which protein is essential

ii. This is to induce the bacteria to produce large quantities of the desired extracellular protease as they attempt to make up for the lack of readily available protein

-   Other bacteria would use up the growth medium without producing any useful product.
-    They might contaminate the product and make it valueless – or even toxic.
-    They might out-compete the desired microbe and, by the ‘competitive exclusion principle’, completely replace the desired microbe in the fermenter.
-    They might be poisonous or hazardous to the employees at the factory (either directly as a pathogen, or by inducing an allergic reaction).

2. a

An enzyme that is attached to an inert material (or contained within a porous inert ‘bead’) and used in an industrial process. The advantage is that the enzyme can be re-used and is more stable; the process is therefore cheaper. In this particular case, the advantage is that the enzyme will not contaminate the milk and therefore make it unsaleable.

In any question like this the answer is always the same. “At low temperatures the molecules have less kinetic energy and so collide with each other less frequently and with insufficient force to overcome the activation energy. As a result, fewer enzyme-substrate complexes are formed and the reaction proceeds more slowly”. [On the other hand, the enzyme will denature more slowly and so last longer before it needs to be replaced – important if it is very expensive to replace.]

Chapter 7 - Enzyme Technology

Answers to Assignment Questions [back to top]

There is no prepared answer to this assignment!

Chapter 8 - DNA and Protein Synthesis

In Chapter Questions [back to top]

A nucleic acid (DNA or one of the three forms of RNA) is a long, linear molecule (a polymer). Nucleotides are the monomers from which they are built.