Summary OCR A Level Biology A* Enzymes Detailed Notes
22 views 0 purchase
Course
Module 2 - Foundations in Biology
Institution
OCR
These A-Level Biology notes are designed for students aiming for top grades and a future in medicine. They are both aesthetic and detailed, offering comprehensive coverage of the syllabus while being visually engaging.
Comprehensive Coverage: Every topic is fully covered, directly aligned with t...
Enzymes Notes
1. Enzymes
Definitions
- Product = molecules produced from substrate molecules, by an enzyme-catalysed reaction
- Substrate = molecule that is altered by an enzyme-catalysed reaction
Biological catalysts – basic concept
- Enzymes are biological catalysts because: 1. Inside living organisms, 2. they speed up metabolic reactions
and remain unchanged at the end of them, able to be used again
- Small amount of catalyst can catalyse reaction of large number of substrate molecules into products
- The number of reactions that an enzyme molecule can catalyse per second = the turnover number
Enzymes vs chemical catalysts
- Catalyst = chemical that speeds up the rate of a reaction and remains unchanged and reusable at the end
of the reaction
- Chemical catalysts usually need:
a) Very high temperatures
b) Increased pressures
c) Extremes of pH
- Enzymes are able to increase metabolic reactions by up to 1012 times at lower temperatures with:
a) Lower temperature
b) Normal pressure
c) Neutral pH
(conditions that sustain life)
- Enzymes are more specific than chemical catalysts
- Enzymes don’t produce unwanted by-products
- Enzymes rarely make mistakes
- The cells where they are made/act can regulate their production/activity to fit the needs of the cell at the
time
How enzyme structure determines its function
- May need help from cofactors to catalyse some reactions
- Instructions for making enzymes are encoded in genes so if a mutation occurs in the gene which alters the
sequence of amino acids in the protein, it may alter the enzymes tertiary structure and prevent it from
functioning
- If an enzyme that catalyses a metabolic enzyme is deficient, a metabolic disorder results
- Enzymes catalyse formation of structural components e.g. collagen in bone/cartilage/blood-vessel
walls/joints so genetic problems with enzyme formation can damage these
Active site
- Active site = indented area on the surface of an enzyme molecule with a shape that is complementary to
the shape of the substrate molecule
- Only 6-10 amino acids involved in the active site
- Tertiary structure is important as its shape must be complementary to the shape of the substrate
- Each enzyme is therefore highly specific and can only catalyse a reaction involving the particular substrate
- Shape of active site, hence its ability to catalyse a reaction, can be altered by changes in temperature in
pH – as these affect the bonds that hold the tertiary structure together
Intracellular enzymes
- Intracellular = Inside the cell
- Up to 1000 metabolic reactions occurring at once in any cell, each catalysed by a different enzyme
- Some are part of a metabolic pathway (metabolism = the chemical reactions that take place inside living
cells/organisms)
- Each metabolic pathway is one of a series of consecutive reactions, every step catalysed by a specific
enzyme to produce a specific product
- Various reactants and products that become reactants act as substrates for specific enzymes
- The reactants, intermediates, and products are called metabolites
, Types of metabolic pathways
- Catabolic = metabolites are broken down to smaller molecules and release energy
- Anabolic = energy is used to synthesise larger molecules from smaller ones
- Respiration and photosynthesis are examples of complex metabolic pathways using many enzymes
Extracellular enzymes
- Extracellular = outside the cell
2. Cofactors
Definition
- A substance that has to be present to ensure that an enzyme-catalysed reaction takes place at the
appropriate rate
- Some cofactors are prosthetic groups and part of the enzyme’s structure
- Others – mineral ion cofactors and organic coenzymes – form temporary association with the enzyme
Prosthetic groups
- Prosthetic group = cofactor that is permanently bound by covalent bonds to an enzyme molecule
Carbonic anhydrase enzyme
- Found in red blood cells, zinc ion permanently bound as a prosthetic group to the active site
- Catalyses the interconversion of CO2 and H2O to carbonic acid which then breaks down to protons and
hydrogencarbonate ions
- The reaction can occur in either direction depending on the concentration of substrate or product
molecules
- Amylase digests starch to maltose and only functions if chloride ions are present
Cofactors – temporary binding
- Some enzymes work better in the presence of ions that are temporarily bound to them – also cofactors
- In enzyme-catalysed reactions, the enzyme and substrate molecules temporarily bind to form an enzyme-
substrate complex
- The presence of certain ions that may temporarily bind to either the substrate or enzyme may ease the
formation of the ES complexes, therefore increasing the rate of enzyme-catalysed reactions
- Some cofactors act as co-substrates: they and the substrate together form the correct shape to bind to
the active site
- Some cofactors change the charge distribution on the surface of the substrate or active site and make
temporary bonds in the ES complex easier to form
Coenzymes
- Small organic non-protein molecules that bind temporarily to the active site of enzyme molecules, either
just before or simultaneously with the substrate
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 alevelrevisionresources. Stuvia facilitates payment to the seller.
Will I be stuck with a subscription?
No, you only buy these notes for $9.08. You're not tied to anything after your purchase.
