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Enzymes
What, how, why, what
Prior Learning
• From GCSE what can you remember about Enzymes
• Hopefully you got
• Biological catalysts, proteins, specific shape, active site,
substrate,
What are ENZYMES
• Biological catalysts – so they speed up the reaction whilst
not being used up themselves.
• They are made of PROTEIN and are GLOBULAR (so are
folded and have a 3d shape)
• Folding is due to two things
• Sequence – what Amino Acid is where
• Bonding – there are four types, ionic, disulphide,
hydrophobic/hydrophilic interactions, hydrogen bonds
• Look at the white board!
Enzyme Facts
• There are two types of two types!
• Simple GCSE types – Catabolic, anabolic enzymes one breaks
and one breaks can you guess which is which?
• Correct Anabolic makes catabolic makes….
• Now AS level types –
• Intracellular (inside cells) so for example catalase (more
about that next week)
• Extracellular (outside cells) for example digestive enzymes
like trypsin, pepsin or amylase.
Why does they work?
• First GCSE revision – what affects the rate of reaction?
• Temperature
• Concentration
• Surface area
• Catalyst
• Does anyone know why catalysts work?
• They lower activation energy!
A Bit of Detail
• So, so far we know the following
• Biological catalysts, Protein, Specific shape, Lowers
activation energy
• But how they do what do they do?
• Simple
• If joining the enzyme holds the two bits (molecules)
together to overcome any repulsion
• If splitting it puts a strain on the bonds and they break
easily (see hydrolysis reactions)
Shape matters
• Indeed it does – the enzyme and substrate have to match to
start with.
• So if the protein strand is not right then the shape isn’t
right then the substrate won’t bind
• Example – Fabrys disease – lipases are not made properly
and they build up in the kidney heart and other organs.
• All because the enzyme can’t do this
Two models
• First lock and key model – substrate fits like a hand in a
glove – look at white board!!
• Second model – like the first but a bit different
• Induced fit – a bit like tight jeans! A little bit of movement
is needed makes the enzyme substrate relationship even
more specific!
SO
Quick Recap
• So far we have covered the following:
• Enzyme structure – 1, 2, 3, 4
• Enzyme action – lock and key and induced fit (more useful
and accurate)
• Types of enzymes (intra and extra)
• And factors affecting their action conc of enzyme and
substrate
• What enzymes actually do!
SO
Factors affecting enzymes
• First rate of reaction revision:
• Temperature
• Concentration
• Surface area
• Catalysts
Factors affecting enzyme performance
• Temperature
• Concentration
• pH
• Enzyme structure
Graphs and limiting factors
• Temperature – increases rate due to increased collisions
then after optimum the enzyme structure breaks down
• pH – Either side of optimum pH the H+ and OH- ions
interrupt the tertiary structure and this changes the active
site
• Concentration of enzyme and substrate – Both increase until
a plateau is reached then the reaction is limited due to not
enough substrate or the active sites being Occupied
Denaturation and occupied sites
• IMPORTANT
• Enzyme structure breaking down leads to DENATURING,
not breaking – it is a specific thing that needs to be
explained specifically!!!
• Additionally – when an enzyme controlled reaction hits a
limiting factor that is the enzyme it is because the active
sites are OCCUPIED not USED UP – think of it like seats on
a bus
IMPORTANT!!!!
• Temperature – increasing it increases rate of reaction
• Temperature coefficient or Q10 is a value for the reaction
that shows how much the rate increases when you increase
the temperature by 10oC
• At temperatures before optimum if the Q10 is 2 then the
rate doubles for 10oC increase
• A value of 3 will triple the rate
• Most enzymes are at 2
Calculate Tangent
• Worksheet!
• Practice Questions
Cofactors and inhibition
• These are two different things
• One stops and one makes it work, can you figure out which is
which?!?!?!?
• Correct cofactors – help
• Inhibitors – no help
Cofactors
• Two types
• Inorganic – the help the substrate and enzyme bond but are not
changed or used in any way
• Example Cl- for amylase
• Organic – They are called coenzymes and participate in the reaction
and are changed by it (second substrate) they also recycle
• Example Vitamins e.g. NAD is derived from vitamin B3
• When a cofactor is bound to the enzyme it is known as a prosthetic
group e.g. Zn ions on carbonic anhydrase
Inhibition
Again two types
Competitive and Non competitive
On white boards draw what you think this means.
Correct
• Competitive – hit the active site
• Non competitive hit somewhere else (allosteric site)
• We then move into permanent (non reversible) and non permanent
(reversible)
• That is all to do with the bonding – if it is strong covalent bonds
no removal, if ionic or H then they can be removed
Try the questions on page 110 of text book
Special inhibition
• End product inhibition
• E.g. phospofructokinase an enzyme used in production of
ATP lots of ATP inhibit it’s production – makes sense really
• Enzyme inhibition – inactive precursors e.g.
pepsin/pensinogen
Questions
• Can you explain the structure of enzymes
• Explain how enzymes work
• Outline all the factors that can affect enzyme function
• Describe what a cofactor is and how they influence enzyme
action
• Outline an example of when an enzyme is inhibited in the body