Enzymes Flashcards
What is activation energy?
The amount of energy a reaction needs to occur
How do enzymes lower activation energy?
They provide an alternative pathway for a reaction, one with a lower activation energy,
What does lowering activation energy mean in terms of temperature?
Reactions can occur at lower temperatures than they would normally, this speeds up the rate of reaction.
What are cofactors?
They are additional non-protein molecules that are attached to or within enzymes which allows them to function
What are prosthetic groups?
They are cofactors that form part of an enzymes structure
What is the lock and key model?
The active site of an enzyme is rigid and only works with substrates that are the exact fit
- A substrate with the right shape binds to form the enzyme-substrate complex
- The reaction occurs and the enzyme-product complex forms
- The products separate from the enzyme and the enzyme remains unchanged.
- This is what scientists thought when first studying enzymes
What is the induced fit model?
The active site of an enzyme is not rigid, it can change shape
- A substrate that can change the shape of the active site in the right way binds
- The enzyme-substrate complex is catalysed to an enzyme-product complex by the active site
- The products leave the site and the shape of the active site returns to its original shape.
- This is the modern, accurate view on enzyme function
Why are enzymes described as biological catalysts?
They speed up metabolic reactions. (Takes place in a living things) They aren’ t used up in the reaction
What do anabolic enzymes do?
They build more complex molecules by combining several/lots of smaller ones
What do catabolic enzymes do?
They breakdown bigger molecules into smaller ones
Give examples of how enzymes can affect structure
Enzymes can affect structures such as in the production of collagen or keratin
Give examples of how enzymes can affect functions
Enzymes can affect functions in a cell such as respiration, photosynthesis and DNA
replication.
Describe the structure of enzymes
- Globular proteins
- Enzymes have an active site with a specific shape that substrate molecules bind to
- The tertiary structure dictates the shape of the active site
- The shape of the substrate is complementary to the active site
Give an example of an enzyme that catalyses intracellular reactions
- Catalase - breaks down hydrogen peroxide into water and oxygen.
- Hydrogen peroxide is a toxic by-product of several metabolic processes. If it builds up it can kill
cells and tissues.
Give two examples of enzymes that catalyse cellular reactions
- Amylase catalyses breakdown of starch into maltose.. its found in saliva, secreted into the mouth by the salivary glands, as the first chemical step of digestion.
it can also be secreted by the pancreas into the small intestine - Trypsin catalyses the breakdown of peptide bonds. its produced by the pancreas and secreted into the small intestine to help digest proteins.
Give an example of a cofactor for an enzyme
Cl- is a cofactor for the enzyme amylase which is involved in the breakdown of starch
Give an example of a prosthetic group for an enzyme
Zn2+ for carbonic anhydrase which turns carbon dioxide into carbonic acid in the blood
Give an example of a source of coenzymes
vitamins
What are coenzymes?
A type of cofactor that form temporary associations with the enzyme
What is the effect of temperature on enzyme activity?
- The rate increases because there is more kinetic energy in the molecules so they move
faster. - Enzymes are more likely to collide with substrates and with more force/energy so enzyme substrate complexes are more likely to form
- If temperature gets too high the reaction stops because the enzymes denature.
What is the effect of pH on enzyme activity?
- Enzymes have an optimum pH value that they operate fastest at.
The closer pH is to the optimum the faster the rate of reaction - Enzymes will denature at pH values that are significantly different from their optimum pH.
What pH does pepsin work best at and why?
pH 2 because it is used in the stomach to digest protein
What is the effect of substrate concentration on enzyme activity?
High substrate concentration = fast rate of reaction because there is a greater chance of a collision that form enzyme-substrate complexes.
- A saturation point will be reached at which all the enzymes are operating at full capacity – their active sites are full.
- As substrate concentration decreases over time (as they get used up), the rate of reaction decreases over time unless more is added.
What is the effect of enzyme concentration on enzyme activity?
The higher the enzyme concentration, the greater the chances of a substrate colliding with an enzyme and forming a enzyme-substrate complex, so the rate of reaction will increase.
- If the amount of substrate is low then there will be a saturation point where the rate of reaction no longer increases with enzyme concentration.
What are competitive inhibitors?
inhibitiors which compete with the substrate to bind with the enzyme. When they bind, no reaction takes place.
What are non competitive inhibitors?
Inhibitors which don’t compete with the substrate to bind to the enzyme. They bind to the allosteric site of an enzyme causing the active site to change shape so that no substrate can bind to it. The effect of this type of inhibition is much stronger than that of competitive inhibitors.
what happens when inhibitors form covalent bonds with the enzyme?
covalent bonds are strong so this makes the reaction irreversible
How can inhibitors be useful
They can be used for regulating metabolic reactions
What happens when inhibitors form hydrogen bonds with the enzyme
If an inhibitor forms hydrogen bonds with an enzyme, then the reaction is reversible.
- hydrogen bonds are weaker
Give examples of inhibitors in poisons
Cyanide irreversibly inhibits cytochrome c oxidase, an enzyme that catalyses reactions during respiration.
• Arsenic inhibits pyruvate dehydrogenase,
another respiratory enzyme
Give examples of medicinal inhibitors
Antivirals
• Inhibitors of viral enzyme reverse transcriptase prevent viruses from replication, used in HIV treatment Antibiotics
• Penicillin inhibits transpeptidase, preventing
bacteria from growing their cell walls and
ultimately killing them.
