Biology 2b - Enzymes and genetics

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  • Created by: ryyansb
  • Created on: 30-03-15 10:57


Enzymes are catalysts produced by living things

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

  • Enzymes have special shapes so they can catalyse reactions
  • Enzymes usually only catalyse one type of reaction because of the shape of the active site
  • Enzymes usually split or join substances
  • Enzymes need the right temperature and pH
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Enzymes and digestion

Digestive enzymes break down big molecules into smaller ones

Amylase converts starch into sugars - produced in:

  • Salivary glands
  • Pancreas
  • Small intestine

Protease converts proteins into amino acids - produced in:

  • Pancreas
  • Small intestine
  • Stomach

Lipase converts lipids into glycerol and fatty acids - found in:

  • Pancreas
  • Small intestine
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Enzymes and digestion (continued)

Bile neutralises the stomach acid and emulsifies fats

Bile is produced in the liver, it's stored in the gall bladder before it's released into the small intestine

The breakdown of food is catalysed by enzymes:

  • Enzymes used in the digestive system are produced by specialised cells in glands and in the gut lining
  • Different enzymes catalyse the breakdown of food molecules
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Digestive system

  • Salivary glands - these produce amylase enzyme in the saliva
  • Liver - where bile is produced
  • Large intestine - where excess water is absorbed from the good
  • Stomach:
    • Pummels the food with it's muscular walls
    • Produces the protease enzyme, pepsin
    • Produces hydrochloric acid to kill bacteria and right pH for protease
  • Pancreas - produces protease, lipase and amylase enzymes - releases into small intestine
  • Small intestine - produces protease and amylase enzymes to complete digestion - where digested food is absorbed into blood
  • Rectum - where faeces are stored
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Respiration is the process of releasing energy from glucose which goes on in every cell

Aerobic respiration is respiration using oxygen - it's the most efficient way to release energy from glucose

Glucose  +  oxygen  ->  carbon dioxide  + water  +  ENERGY

Energy release by aerobic respiration is used for:

  • Build up larger molecules from smaller ones
  • In animals, to allow muscles to contract
  • In mammals and birds the energy is used to keep their body temperature steady
  • In plants, to build sugars, nitrates and other nutrients into amino acids, which are then built up into proteins
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Respiration (continued)

Exercise increases the heart rate

An increase in muscle activity requires more glucose and oxygen to be supplied to the muscle cells - extra carbon dioxide needs to be removed

Physical activity:

  • increases your breathing rate and makes you breathe more deeply to meet the demand for extra oxygen
  • increases the speed the heart pumps

Glucose is used during exercise:

  • Some glucose from food is stored as glycogen
  • Glycogen's mainly stored in the liver but each muscle has it's own little store
  • During vigorous exercise muscles use glucose rapidly so some glycogen is converted back to glucose
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Anaerobic respiration

Anaerobic respiration is used if there's not enough oxygen

  • When you do vigorous exercise and your body can't supply enough oxygen to your muscles then anaerobic respiration is used
  • Glucose  ->  ENERGY  +  Lactic Acid
  • It's not the best way to convert glucose into energy because it build up lactic acid which is painful and it causes muscle fatigue which makes the muscles tired and stop contracting efficiently
  • It does not release as much energy as aerobic

Anaerobic respiration leads to oxygen debt

  • Need to keep breathing hard for a while after you stop to get more oxygen into your blood - blood flows through muscles to remove the lactic acid by oxidising it to harmless carbon dioxide and water
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Uses of enzymes

Enzymes are used in biological detergents and washing powder

Enzymes are used to change foods

Using enzymes in industry takes a lot of control


  • They're specific so they only catalyse the reaction you want them to
  • Using lower pressurre and temperatures means a lower cost and saves energy
  • Enzymes work for a very long time so you can continually use them
  • They are biodegradable so they cause less environmental pollution


  • Some people develop allergies to enzymes
  • Enzymes can be denatured by even a small increase in temperature so conditions they work in 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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Chromosomes are really long molecules of DNA

DNA stands for deoxyribonucleic acid

It contains instructions to put an organism together and make it work

Nucleus  ->  Single  Chromosome  ->  DNA

Everyone has unique DNA

DNA fingerprinting is used in forensic science and paternity testing

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Cell division - mitosis

Mitosis makes new cells for growth and repair

Mitosis is when a cell reproduces itself by splitting to form two identical offspring

  • In a cell that's not dividing, the DNA is spread out in long strings
  • If the cell is going to divide it duplicates the chromosomes and forms X shaped chromosomes
  • The chromosomes line up at the centre of the cell and cell fibres pull them to opposite ends
  • Membranes form around each of the new sets of chromosomes. These become the nuclei of the new cell. The cytoplasm then divides

Asexual reproduction also uses mitosis


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Cell division - meiosis

Gametes have half the usual number of chromosomes

During sexual reproduction, two cells called gametes join to form a new individual

Gametes only have one copy of each chromosome. This is so that you can combine one sex cell from the mother and one from the father and still end up with the right number of chromosomes

Meiosis involves two divisions 

  • As with mitosis, before the cell divides it duplicates its DNA
  • In the first division the pairs line up in the centre
  • The pairs are pulled apart so each new cell only has one copy of each chromosome. Half the fathers and half the mothers chromosomes go into each new cell
  • In the second division the chromosomes line up in the centre again
  • You get four gametes with a single set of chromosomes in each 

Stem cells
Embryonic stem cells can turn into any type of cell
Stem cells may be able to cure diseases
Some people are against stem cell research because each embryo is a potential human life

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Cell division - meiosis diagram


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X and Y chromosomes

Your chromosomes control whether you're male of female

There are 22 matched pairs of chromosomes in every human body cell. The 23rd pair is labelled ** or XY

All males have X and Y chromosomes (XY) - the Y chromosome causes male characteristics

All women have two X chromosomes - the ** combination allow female characteristics to develop

When making sperm there is a 50% chance each sperm will get an X or Y chromosome

Genetic diagrams show possible combinations of gametes


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The work of Mendel

Mendel did genetic experiments with pea plants

Mendel 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 dwarf plants, t. 


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The work of Mendel (continued)

Mendel reached 3 important conclusions:

  • 1. Characteristics in plants are determined by "hereditary units"
  • 2. Hereditary units are passed down from both parents, 1 unit from each parent
  • 3. Hereditary units are dominant or recessive - if an individual has both the dominant and recessive unit, the dominant characteristic is displayed.

"Hereditary units" are now known as genes

Genetic disorders:

  • Cystic fibrosis - recessive allele - needs 2 recessive alleles for patient to suffer
  • Polydactyl  - dominant allele - only 1 dominant required for patient to suffer
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In Vitro Fertilisation (IVF)

Embryos can be scanned for genetic disorders

During in vitro fertilisation embryos are fertilised in a laboratory and then implanted into the mothers womb

Against screening:

  • There may become a point where everyone will pick the most "desirable" one
  • The rejected embryos are destroyed - they could have developed into humans
  • It implies people with genetic problems are "undesirable"
  • Screening is expensive

For screening:

  • Help stop people suffering
  • There are laws to stop it going too far such as choosing sex
  • Treating disorders costs the government a lot of money
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Fossils are remains of plants and animals

Fossils form in rocks in 1 of 3 ways:

  • 1. From gradual replacement by minerals
    • Things like teeth, bones which don't decay easily can last a long time buried 
    • Replaced by minerals as they decay forming a rock like substance
  • 2. From cats and impressions
    • Sometimes fossils are formed when an organism is buried in soft material
    • Things like footprints can be pressed into it when soft leaving an impression when it hardens
  • 3. From preservation in places where decay doesn't occur
    • In amber and tar pits there is no oxygen or moisture so decay can't survive 
    • In glaciers it's too cold for decay
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Extinction and speciation

Extinction happens when you can't evolve quickly enough

Species become extinct for these reasons:

  • 1. Environmental changes too quickly (destruction of habitat)
  • 2. New predator kills them all (human hunting)
  • 3. New disease kills them all
  • 4. Can't compete with a new species for food
  • 5. A catastrophic event happens which kills them all
  • 6. A new species develops

Speciation is the development of a new species

Isolation and natural selection lead to speciation

2 populations of same species -> physical barrier separates the populations -> populations adapt to new environments -> development of a new species

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