This set of notes contains all you need to know about enzymes for the OCR exam.
Including the basics, activation enthalpy as well as inhibition both competitive and non-competitive as well as poisons.
Biological catalysts that speed up metabolic reactions
- They speed up chemical reactions and remain unchanged and are able to be used again
- Some catalysts can catalyse the conversion of a large number of substrate molecules
into product molecules
- Number of reactions that an enzyme molecule can
catalyse per second is known as its turnover
number.
Enzymes speed up reactions at low temperatures, often
neutral ph and at normal pressures - able to function
inside us.
They are highly specific, do not produce unwanted products and can regulate their activity.
- Instructions for the enzyme is encoded in its genes
- If an enzyme is deficient, then a metabolic disorder results
Active site:
The specific area, with an indentation on the surface of the molecule. (6-10 amino acids)
- Tertiary structure is crucial, shapes the complementary substrate molecule
- Highly specific to its function, as can only catalyse a reaction involving the particular
substrate.
- It can be altered by changes in temp or ph, which affects the bonding in their tertiary
structure.
Intracellular enzymes:
- Each metabolic pathway in a cell is one of a series of reactions, catalysed by enzymes
that make a specific products
- Various reactants and intermediates act as substrates for specific enzymes
- Reactants intermediates and products are called metabolites
- In some pathways, catabolic, metabolites are broken down to smaller molecules and
release energy
- In others, anabolic, energy is used to make larger molecules from smaller ones
- Respiration and photosynthesis are examples of complex metabolic pathways, with
many enzymes involved.
Intracellular enzyme example:
Catalase is found in nearly all living organisms - it breaks down the toxic by product, hydrogen
peroxide, which if left to build can kill cells. Breaks it down into harmless oxygen and water.
- Consists of four polypeptide chains and contains a heme groups with iron
- Fastest acting enzyme, highest turnover number
- White blood cells use catalase to kill microbes.
- Optimum ph for human is ph7, and temp is 45degrees, this can very depending on
organism.
Extracellular Enzymes
, Some enzymes are secreted out of cells, this is especially active in our digestive system,
secreted from the alimentary canal, into the lumen. Where they digest large molecules eg.
proteins, fats, found in food. Break them down into smaller products which can then be used.
Extracellular Enzyme example:
- Amylase (human digestive system) is produces in the salivary glands, digests
polysaccharide starch into disaccharides maltose (sugar), ade in the pancreas.
- Trypsin (human digestive system) is made in the pancreas, acts in the lumen of the
small intestine to break large proteins into smaller peptides by hydrolysing (breaking
down) peptide bonds. optimum ph 7.5-8.5
Enzymes can be involved in anabolic (building up ie.DNA polymerase) reactions
Or they can also be involved in Catabolic (breaking down) ie.Amylase) reactions
Lowering activation energy:
- Chemical reactions need energy to begin them, normally this is done by increasing
temperature to move the molecules
- However this cannot be done inside a body, as enzymes
would denature.
- Due to the active site, enzymes bring molecules close
enough together to react, without the need for excessive
heat
- Therefore they lower the activation energy and hece
speed up reactions
- They create a TRANSITION STATE between the
enzyme and substrate that is more stable (it has less
energy) than usual.
This means that enzymes are biological catalysts - they speed
up reactions, they lower the activation energy by bringing substrate molecules close enough
together to react, reducing repulsion between the molecules so they can bond more easily.
Fitting a substrate into an active site puts a strain on bonds in the substrate. This strain means
the substrate molecule breaks up more easily. This enables the reaction to have enough energy
to start the reaction without needing to add heat - they hold the substrate molecules long
enough to react.
STRUCTURE
- Globular proteins, soluble in water due to hydrophilic R groups
- Active site is v.small (6-10) amino acids
- Rest of the amino acids within the enzyme maintain the active sites shape - which is
highly specific to one substrate (has a complementary shape)
Action of Enzymes:
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