B2b- Enzymes and Genetics

  • Created by: Miahtd13
  • Created on: 10-05-14 12:19


Enzymes are Catalysts produced by living things 

  • Living things have thousands of different chemical reactions going on inside them all the time. These reactions need to be carefully controlled- to get the right amounts of substances
  • You can usually make the reaction happen more rapidly by raising the temperature. This would speed up the useful but also the unwanted reactions which isn't a good thing. There's also a limit to how far you can raise the temperature inside a living creature before its cells start getting damaged 
  • So organisms produce enzymes that act as biological catalysts that reduce the need for high temperatures and we only have enzymes to speed up the useful chemical reactions in the body 

A catalyst is a substance which INCREASES the speed of a reaction without being changed or used up in the reaction

  • Enzymes are all proteins which are made up of chains of amino acids. They are folded into unique shapes to help them do their jobs. As well as catalysts, proteins act as structural components of tissues (e.g. muscles), hormones and antibodies.
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Enzymes have special shapes so they can catalyse reactions

  • Chemical reactions usually involve things either being split apart or joined together
  • Every enzyme has a unique shape that fits onto the substance involved in a reaction
  • Enzymes usually only catalyse one reaction. This is because for the enzyme to work, the substance has to fit its special shape. If the substance doesn't match the enzyme's shape, then the reaction won't be catalysed

Enzymes need the right temperature and pH

  • Changing the temperature changes the rate of an enzyme-catalysed reaction. Like with any reaction, a higher temperature increases the rate at first. But if it gets too hot, some of the bonds holding the enzyme together break. This destroys the enzyme's special shape and so it won't work anymore- it will become denatured. Human body enzymes work best at 37 degrees. The pH also affects enzymes. If its too high or too low it interferes with the bonds holding the enzyme together- the shape is changed and the enzymes is now denatured.
  • All enzymes have an optimum pH- its usually neutral 7 but not always e.g. pepsin breaks down proteins in the stomach and works best at pH 2 so its well suited to the acidic conditions there
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Enzymes and Digestion

Digestive Enzymes break down Big Molecules into Smaller Ones

  • Starch, proteins and fats are too big to pass through the walls of the digestive system
  • Sugars, amino acids, glycerol and fatty acids are much smaller molecules and so can pass through the walls of the digestive system.

Amylase Converts Starch into Sugars ( Maltose)

  • Its made in the Salivary Glands, the Pancreas and the Small Intestine

Protease Converts Proteins into Amino Acids

  • Its made in the Stomach (its called pepsin there), the Pancreas, and the Small Intestine

Lipase Converts Lipids into Glycerol and Fatty Acids

  • Its made in the Pancreas and the Small Intestine

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Enzymes and Digestion.2

Bile Neutralises the Stomach Acid and Emulsifies Fats

  • Bile is produced in the liver. It is stores in the gall bladder before being released into the small intestine. The hydrochloric acid in the stomach makes the pH too acidic for enzymes in the small intestine to work properly. Bile is alkaline- it neutralises the acid and makes conditions alkaline. The enzymes in the small intestine work best in these alkaline conditions
  • Bile emulsifies fats. It breaks the fat into tiny droplets giving a much bigger surface area of fat for the lipase to work on- making the digestion faster

The Breakdown of Food is Catalysed by Enzymes                                                    Enzymes used in the digestive system are produced by specialised cells in glands and in the stomach lining.

  • Salivary glands: these produce amylase in the saliva
  • Liver: produces bile which neutralises stomach acid and emulsifies fats
  • Gall bladder: bile is stored here before its released into the small intestine
  • Large Intestine: where excess water is absorbed from food leaving faeces
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Enzymes and Digestion.3


  • It pummels the food with the muscular walls. It produces pepsin, the protease enzyme
  • It produces hydrochloric acid to kill bacteria and provide the right pH (pH 2- acidic) for the protease to work


  • Produces protease, amylase and lipase which are then released into the small intestine

Small Intestine: 

  • Produces protease, amylase and lipase to complete digestion. 
  • This is also where the digested food is absorbed out of the digestive system into the blood


  • Where the faeces (made up of mainly indigestible food) is stored before it exits through the anus 
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Enzymes and Respiration

Respiration involves many reactions all of which are catalysed by enzymes. These are very important as respiration releases the energy the cell need to complete all their function  

Respiration is the process of releasing energy from the breakdown of glucose which goes on in every cell in the human body

It happens in plants too. It is how they release energy from food

Aerobic Respiration Needs Plenty of Oxygen

  • Aerobic Respiration is respiration using oxygen. It is the most efficient way to release energy from glucose. It goes on all the tome in plants and animals
  • Most of the aerobic respiration reactions happen inside mitochondria 

Glucose + oxygen = carbon dioxide + water +energy 

Respiration releases energy to build smaller molecules into bigger ones. To allow muscles to contract. In mammals and birds to keep a steady body temperature. In plants to build sugars, nitrates an other nutrients into amino acids which are then built up into proteins

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Exercise increases heart rate

  • Muscle cells use oxygen to release energy from glucose which is used to contract the muscles
  • An increase in muscle activity requires more glucose and oxygen to be supplied to the muscle cells. Extra carbon dioxide needs to be removed from the muscle cells. For this to happen, the blood has to flow at a faster rate
  • This is why physical activity increases the breathing rate and makes you breathe deeper to meet the demand for extra oxygen. It also increases the speed at which the heart pumps.

Glycogen is used during exercise 

  • Some glucose from food is stored as glycogen which is mainly stored in the liver but each muscle has its own store
  • During vigorous exercise muscles use glucose rapidly, so some of the stored glycogen is converter back to glucose to provide more energy
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Anaerobic Respiration is Used if There's Not Enough Oxygen

  • If you start doing vigorous exercise and your body can't supply enough oxygen to your muscles they start doing anaerobic respiration- without oxygen. It is the incomplete breakdown of glucose : Glucose= energy + lactic acid. 
  • This isn't the best way to convert glucose into energy because lactic acid builds up in the muscles which gets painful. It also causes muscle fatigue- the muscles get tired and then stop contracting efficiently. Anaerobic respiration also doesn't release as much energy but it's useful for emergencies and you can use your muscles for a while longer.

Anaerobic Respiration Leads to an Oxygen Debt

  • After doing anaerobic respiration, you are in oxygen debt and so you have to repay the oxygen that you couldn't get your muscles on time because your heart lungs and blood couldn't keep up with the demand. This means you keep breathing while after you stop exercising to get more oxygen into the blood which flows through muscles to remove the lactic acid by oxidising it to carbon dioxide and water. While high CO2 levels and lactic acid are detected by the brain, the pulse and breathing rate stay the same
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Uses of Enzymes

Enzymes are used in Biological Detergents

  • Enzymes are the biological ingredients in biological detergents and washing powders
  • They are mainly proteases and lipases
  • Because the enzymes break down animal and plant matter, they're ideal for removing stains like food and blood. 
  • Biological Detergents are also more effective at working at low temperatures (e.g. 30 degrees) than other types of detergents

Enzymes are used to change foods

  • The proteins in some baby foods are "pre-digested" using proteases so they're easier for the baby to digest 
  • Carbohydrases can be used to turn starch syrup into sugar syrup
  • Glucose syrup can be turned into fructose syrup using an isomerase. Fructose is sweeter so you can use less of it which is good for slimming foods and drinks
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Uses of Enzymes In Industry


  • They're specific, so they only catalyse the reaction you want them to
  • Using lower temperatures and pressures means a lower cost as it saves energy
  • Enzymes work for a long time, so after the initial cost of buying them, you can continually use them
  • They are biodegradable and therefore cause less environmental pollution


  • Some people can develop allergies to the enzymes e.g. in biological washing powders
  • Enzymes can be denatured by even a small increase in temperature. They're also susceptible to poisons and changes in pH. This means the conditions in which they work must be tightly controlled
  • Enzymes can be expensive to produce
  • Contamination of the enzyme with other substances can affect the reaction
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Stem Cell Research

  • Some people are against it because they feel human embryos shouldn't be used for experiments since each one is a potential human life
  • Others think that curing patients who already exist and who are suffering is more important than the rights of embryos
  • The embryos used in this research are usually unwanted ones from fertility clinics, which if weren't used would have otherwise been destroyed. 
  • However campaigners want this banned, and they feel scientists should concentrate more on finding and developing other sources of stem cells, so that people could be helped with out using embryos
  • In some countries, stem cell research is banned but it is allowed in the UK as long as it follows strict guidelines 
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X and Y Chromosomes

Your chromosomes control whether you're male or female

  • There are 22 matched pairs of chromosomes in every human body cell. The 23rd pair are labelled ** or XY. They're the two chromosomes that decide whether you turn out male or female.
  • All men have XY, the Y causes male characteristics
  • All women have **, the combination ** causes female characteristics
  • When making sperm, the X and Y chromosomes are drawn apart in the first division of meiosis. There's a 50% chance each sperm gets an X chromosome and a 50% chance it gets a Y chromosome. This is similar when making eggs, but the original cell has two X chromosomes so all the eggs have one X chromosome.
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Genetic Diagrams

They show the possible combinations of gametes

  • To find the probability of getting a boy or a girl, you can draw a genetic diagram. 
  • You put the possible gametes from one parent down the side, and those of the other parent along the top.
  • There are two ** results and two XY results so there's the same probability of getting a boy or a girl. This 50:50 ratio is only a probability at each pregnancy.

Another genetic diagram is the use of circles and lines.

  • At the top are the parents then each chromosome is split up so there would be an X another X (for female), then an X and a Y (for male)
  • In the middle the circles would show the possible gametes that are formed. One gamete from the female combination joins with one gamete from the male combination (during fertilisation)
  • The criss-cross lines show all the possible ways the X and Y chromosomes could combine. The possible combinations of the offspring are shown in the bottom 4 circles. 
  • Only one of these possibilities will actually happen for any one offspring.
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The Work of Mendel

  • Mendel did genetic experiments with Pea Plants
  • Gregor Mendel was an Austrian monk who trained in maths and natural history. On his garden plot in the monastery, he noted how characteristics in plants were passed on from one generation to the next. 
  • The results of his research then became the foundation of modern genetics.
  • He had shown that the height characteristics in pea plants was determined by separately inherited "hereditary units" passed on from each parent. The ratios of tall and dwarf plants in the offspring showed that the unit for tall plants :T was dominant over the unit for dwarf plants :t

Mendel's 3 Important Conclusions

  • Characteristics in plants are determined by "hereditary units"
  • "Hereditary units" are passed on from both parents, one unit form each parent
  • "Hereditary units" can be dominant or recessive- if an individual has both the dominant and the recessive unit for a characteristic, the dominant unit will be expressed
  • These "hereditary units" are genes
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Genetic Diagrams.2

Alleles are different versions of the same gene.

  • In genetic diagrams, letters are usually used to represent alleles
  • If an organism has two alleles for a particular gene that are the same, then its homozygous
  • If its two alleles for a particular gene are different, then its heterozygous
  • If the two alleles are different, only one can determine what characteristic is present. The allele for the characteristic that is shown is called the dominant allele shown with a capital letter. The other one is called recessive and it is shown with a lower-case letter.
  • For an organism to display a recessive characteristic, both alleles must be recessive. But to display a dominant characteristic, the organism can be either Cc or CC because the dominant allele overrules the recessive one if the organism is heterozygous
  • Genotype: the alleles that you have
  • Phenotype: the actual characteristic
  • When you cross-breed two parents and look at only one characteristic it is called a monohybrid cross
  • These results are also only probabilities
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Genetic Disorders

Cystic Fibrosis is caused by a recessive allele

  • It is a genetic disorder of the cell membranes. It results in the body producing a lot of thick mucus in the air passages and in the pancreas. The allele which causes cystic fibrosis is a recessive allele "f" carried by about 1 person out of 25. 
  • Because it is recessive only people with two recessive alleles will be sufferers.
  • Sufferers must have both parents as carriers or sufferers
  • People with only one copy of the allele won't have the disorder, they will only be carriers

Polydactyly is caused by a dominant allele

  • It is when a baby is born with extra fingers or toes. 
  • It is caused by the dominant allele "D" so it can be inherited if even one parent carries the defective allele. The parent that has the allele will also be a sufferer as the allele is dominant.
  • If one parent has the disorder, there is a 50% chance of a child having it too.
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Embryos can be screened for Genetic Disorders

During IVF, before the ovum is implanted into the mother's uterus, its possible to remove a cell from each embryo and analyse its genes.

  • Many genetic disorders could be detected in this way such as cystic fibrosis
  • Embryos with good alleles will be implanted and the ones with bad alleles will be destroyed.


  • There may come a time when everyone wants to pick and choose the more "desirable" embryo
  • The rejected embryos are destroyed- they could have developed into humans
  • It implies that people with genetic disorders are "undesirable"- which could increase prejudice
  • Screening is expensive


  • It will help to stop people from suffering. There are laws to stop it going too far- at the moment parents can't even choose the gender of the baby. During IVF most embryos are destroyed anyway-screening allows the selected one to be healthy. Less money is spent by the government on treating disorders.
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