Summary
Summary CIE A level Biology notes on unit o3 - enzymes
- Course
- Institution
Everything you need to know about unit 03 of the CIE A level biology course, including diagrams and notes.
[Show more]
Seller
Follow
olivertraherne
Reviews received
Content preview
3.1 - Mode of action of enzymes:Enzymes - Globular protein molecules (tertiary structure with hydrophilic R-groups on outside) that are involved in catalysing
reactions.
• A catalyst is a molecule that speeds up a chemical reaction but remains unchanged at the end of the reaction.
• Virtually all metabolic reactions within living organisms are catalysed by an enzyme so they are crucial for life to exist.
• Intracellular - enzymes which catalyse reactions within the cell.
• Extracellular - enzymes that are secreted by the cells and catalyse reactions outside of the cell e.g. digestive enzymes in the
gut.
Mode of action...
Active site - a region, usually a cleft or depression to which another molecule or molecules can bind (the substrate).
• The shape of the active site is speci c to the substrate, so only certain substrates can bind.
• The enzyme and the substrate bind to form and enzyme substrate complex (ESC), which then forms the enzyme product
complex.
• Hydrophilic R groups on the site active site form Hydrogen bonds with the substrate, bonding them together.
Lock and key hypothesis...
• The idea that the enzyme has a particular active site shape into which the substrate ts exactly.
• The substrate is the key which ts the lock (the active site), then it is held temporarily by bonds between the two.
• CONS - Doesn’t give ideas of how the binding actually a ects reactions.
Induced t hypothesis...
• The active site is nearly the correct shape for the substrate, but after binding, the shape
is altered slightly for them to t perfectly (induced t).
• The active site alters its shape to maximise the intermolecular attractions, making the
catalysis even more e cient.
• When the reaction is complete, the product/products leave the active site and the
enzyme is unchanged, meaning it is capable of now receiving another substrate
molecule.
Activation energy...
• The energy that must be put into a chemical system in order for the reaction to occur.
• Enzymes lower the activation energy needed for reactions by holding the substrate in
such a way that the molecules react more easily.
• In many chemical reactions, the substrate will not be converted to a product unless it is
temporarily given some extra energy (the activation energy).
• Rock on the slope idea - a rock is stuck at the top of the hill and needs some force to
move it. A small gust of wind knocks it and it begins to fall, lowering the potential
energy, and once in motion it gains momentum and no more extra energy is needed.
3.2 - Factors that a ect the enzyme action:
E ect of temperature...
• If the temperature is increased then the rate of reaction increases because the
molecules have a higher kinetic energy and therefore there are more successful
collisions between the active sites and substrates, so more ESCs are formed.
• At rst, the temp increases but not signi cantly, so molecules might collide but not
successfully bind as they don’t have enough energy.
• As it rises, the rate increases up to the optimum temp which is the point at which
enzyme reaction is at its max (most human enzymes have a optimum of 40 degrees so
we try to maintain this by staying at 37 degrees).
• However, after this point, the bonds between R groups begin to break, so it is
denatured, causing the active site to lose its 3D shape and not be able to bind to any
substrates.
E ect of PH...
• Most enzymes have an optimum PH of around 7 (in fairly neutral conditions), however
some such as the protease pepsin, which is found in the stomach, have an extremely
low optimum acidic PH.
• PH is the measure of the concentration of hydrogen ions in a solution.
• Outside of the optimum PH, hydrogen ions interact with the R-groups of amino acids
which breaks the ionic bonds in the tertiary structure.
• The shape of the active site is thus permanently altered (denatured).
• When investigating PH, you can use bu er solutions which have a particular PH and
maintain this even if the reaction taking place is meant to change it.
The benefits of buying summaries with Stuvia:
Guaranteed quality through customer reviews
Stuvia customers have reviewed more than 700,000 summaries. This how you know that you are buying the best documents.
Quick and easy check-out
You can quickly pay through credit card or Stuvia-credit for the summaries. There is no membership needed.
Focus on what matters
Your fellow students write the study notes themselves, which is why the documents are always reliable and up-to-date. This ensures you quickly get to the core!
Frequently asked questions
What do I get when I buy this document?
You get a PDF, available immediately after your purchase. The purchased document is accessible anytime, anywhere and indefinitely through your profile.
Satisfaction guarantee: how does it work?
Our satisfaction guarantee ensures that you always find a study document that suits you well. You fill out a form, and our customer service team takes care of the rest.
Who am I buying these notes from?
Stuvia is a marketplace, so you are not buying this document from us, but from seller olivertraherne. Stuvia facilitates payment to the seller.
Will I be stuck with a subscription?
No, you only buy these notes for $12.33. You're not tied to anything after your purchase.
Can Stuvia be trusted?
4.6 stars on Google & Trustpilot (+1000 reviews)
73314 documents were sold in the last 30 days
Founded in 2010, the go-to place to buy study notes for 14 years now