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All enzymes are similar in that they: (5)
- Are globular proteins - generally soluble in water.
- Act as catalysts - speeding up reactions but not being used up as part of reaction.
- Are specific - catalysing reaction involving only 1 type of substrate.
- Contain an active site where the substrate binds to.
- Activity is affected by temperature and pH.
Enzymes are _______ proteins and have specific _______ structure. The _____ of the enzyme, like any protein is _____ to its function. The shape comes from protein's _______ structure and ________ structure. In ______ proteins, the final 3D shape usually has _______ amino acid ________ in the ______ of the "ball", and _______ amino acid ________ around the _____.
Enzymes are globular proteins and have specific tertiary structure. The shape of the enzyme, like any protein is vital to its function. The shape comes from protein's primary structure and secondary structure. In globular proteins, the final 3D shape usually has hydrophobic amino acid R-groups in the centre of the "ball", and hydrophilic amino acid R-groups around the outisde.
How many amino acids usually dictate the specific shape of the active site?
Usually fewer than 10
Give some examples of metabolic processes that enzymes catalyse.
- Formation and breakage of glycosidic bonds, peptide bonds, ester bonds - each require at least one specific enzyme.
- Protein synthesis, digestion, respiration & photosynthesis - each require a number of different enzymes.
- Each catalyses a specific reaction in the sequence of events that make up the process.
How are enzymes usually named?
- Name usually derived from substrate of reaction that is being catalysed, with the suffix "-ase".
- eg. Maltose catalysed by maltase
A molecule (or element) that speeds up a chemical reaction but does not get used up in the reaction. At the end of reaction, catalyst remains unchanged.
What do you call enzymes that catalyse reactions outside the cell? What about inside the cell?
- Outside - extracellular enzymes
- Inside - intracellular enzymes
What types of animals are birds and mammals? What are the advantages and disadvantages of this?
- Endothermic animals - maintain their internal body temperature, independently of the environment.
- Advantage - Enzymes in the body can function at near-optimum temperature continuously. Also means they can live in different environments.
- Disadvantage - need greater food supply (than similarly sized reptiles)
What is the name of organisms that consume other organisms?
What does digestion involve?
- Breaking down larger molecules into their subunits.
- eg. requires breaking of peptide, glycosidic & ester bonds.
- Catalysed by different types of enzymes.
How do extracellular enzymes in digestive system work?
They are secreted/ released from cells that make them, onto food within the digestive system spaces.
If enzymes are intracellular, in which part(s) of the cell are they usually found?
- Embedded/attached to cell membranes.
Give an example of how enzymes are used for protection.
Enzymes in lysosomes in phagocytes that take in and digest bacteria. (The endocytosed vesicle is fused with one of many lysosomes).
Suggest advantages of having an internal digestive system compared with secreting enzymes outside organism.
- Enzymes produced are not lost to the environment, and thus can be retained and recycled/reused.
- Environment of internal system can be regulated to give optimum conditions for enzymes' activity.
What is activation energy?
The amount of energy that is required initially that must be applied for a reaction to proceed. Different reactions require different levels of activation energy. Enzymes reduce the amount of activation energy needed to allow a reaction to proceed.
Why can't covalently bonded molecules simply assemble or break up?
- Because they are far too stable.
- They need the required activation energy (eg. boiling in acid, or using catalyst) in order for bonds to break and to form.
How does an enzyme work to catalyse reactions?
They work by reducing the amount of activation energy required. This means reactions can still take place speedily without boiling temperature or presence of acid.
- The enzyme's shape is not complimentary to the substrate, the shape of the enzyme's active site is complementary to the shape of the substrate molecule. Also remember that substrates never have active sites.
An enzyme has a ________ shaped active site. Shape of active site is ________ to the shape of the substrate molecule(s). Because the substrate fits into the enzyme, the term ___________ is sometimes used to describe how enzymes work.
- specifically shaped active site
- active site is complimentary to shape of substrate
Describe the induced-fit hypotheses.
- As substrate molecule collides with active site, the enzyme changes shape slightly.
- This makes active site fit more closely around substrate.
- Substrate also fits into place because oppositely charged groups on substrate and active site are found near each other. Creates an enzyme-substrate complex.
- Changes in enzyme shape also place strain on substrate molecule which destablises substrate molecule.
- Product formed - now called enzyme-product complex.
- Product formed is different shape - doesn't fit, so move away.
Explain how enzymes reduce activation energy.
By holding the substrate molecules in such a way that reaction proceeds more easily.
Explain why reduction in activation energy provided by enzymes is essential to living organisms.
Because most metabolic reactions in living organisms do not happen at a rate sufficient to maintain life without enzymes.
How does an increased kinetic energy increase the rate of reaction?
- Molecules move around more and thus
- more collisions
- collisions with greater force
How does high temperature lead to enzymes denaturing?
- Molecules vibrate as kinetic energy increases
- This put strain on bonds and breaks weaker bonds like hydrogen bonds and ionic bonds.These occur in large numbers to keep the tertiary structure in place, and especially the shape of the active site.
- As enzymes denature, they do not have the right shape to catalyse reactions and therefore rate of reaction decreases rapidly.
- This is not reversible - once enzymes denature, they cannot work againNote also that primary structure (ie covalent peptide bonds between amino acids) would not be affected.
Suggest why normal body temp of mammals is slightly below optimum temp of most enzymes in organism.
- If body temp was too near the optimum temp, then in situations of increased temperature (eg. exercising and fever) many enzymes would be denatured.
- Also, higher body temp requires more energy and might denature other proteins.
Why can changes in pH affect the enzyme activity?
- Because it causes changes to the shape of the active site.
- The hydrogen ions (positively charged) interfere with hydrogen and ionic bonds holding the tertiary structure in place.
- Positive charge of hydrogen ions attracted to negative charges on alpha-helix and so "replace" hydrogen bonds.
How else can pH affect enzyme activity? (In terms of induced-fit hypothesis)
- Induced-fit hypothesis states that active site relies on charged groups on the R-group of amino acids in order to bind to the substrate.
- Hydrogen ions interfere with these charges.
Give examples of how optimum pH of enzymes vary depending on their location and environment.
- Enzyme pepsin in stomach has optimum pH 2. (stomach acidic conditions)
- Enzyme trypsin in small intestine has optimum pH 7. (food leaving stomach gets neutralised)
What are protease enzymes?
Those that break peptide bonds.
Then what are enzymes that break glycosidic bonds and those breaking ester bonds?
- Glycosidic - carbohydrases
- Ester - lipases