Enzymes Flashcards
What are enzymes?
Biological catalysts that speed up the rate of reaction. They catalyse at cellular cells (e.g respiration) and for the organism as a whole (digestion in mammals) but are not used up.
How can enzymes affect the structure in an organism?
They’re involved in the production of collagen
How can enzymes affect the functions of organisms?
Through processes e.g respiration and photosynthesis
What is the definition of metabolism?
The total sum of chemical reactions which can be described as enzyme driven, this includes:
- respiration
- protein synthesis
- digestion
- photosynthesis
- DNA replication
Why must enzymes be in an aqueous environment?
It allows both the enzyme and the substrate the ability to move and therefore collide with one another allowing for enzyme-substrate complexes
What does it mean if an enzyme action is intracellular?
Provide an example
-made and retained inside the cell
Example of this include: -catalase enzyme breaks down hydrogen peroxide into harmless oxygen and water so that cells aren’t killed
What does it mean if an enzyme action is extracellular?
Provide an example
-carries out function outside the cell
An example includes: -amylase works outside the cells in saliva to catalyse the hydrolysis of starch
-Trypsin is produced by pancreatic cells and released into the small intestine
What is the structure of an enzyme?
- Globular protein: has a 3D, almost spherical shape + water soluble due to positioning of hydrophilic R group
- Has an active site: which has a very specific shape where the complementary substrate binds to
Describe and explain the lock and key model as a mechanism of enzyme action
-lock and key suggests that the substrate fits perfectly into the active site as they have a specific and complementary shape to one another. When the substrate bonds to the active site, and enzyme substrate complex is formed. The products of the reaction are then released and it is now an enzyme-product complex. The enzyme is now free to bind with another substrate molecule.
Describe and explain the induced fit model as a mechanism of enzyme action
(This is the new model)
The active site on the enzyme is initially not the correct shape in which to fit the substrate. As the substrate approaches the active site, the site changes and results in being the perfect fit, forming an enzyme substrate complex. After the reaction has taken place and the products have been released (enzyme-product complex) the active site returns to its normal shape.
What effect does an increase in temperature (from 10 to 30 c) have on the rate of a reaction?
Kinetic energy is increased which increases the number of successful collisions, therefore more enzyme-substrate complexes are formed and the rate of reaction increases
What is meant by optimum temperature?
When enzyme activity is at its highest
What happens when the temperature is raised too high (40 to 60 c) on the rate of a reaction?
The increase of energy means vibrations are produced which break the bonds that hold the enzyme together. This means the enzyme denatures, meaning there is now an irreversible change to the shape of the active site, and so enzyme activity and rate of reaction decreases
What does the temperature coefficient show in a reaction?
It shows how much the rate of the reaction changes when the temperature is raised by 10 degrees
What is the formula for the temperature coefficient?
Q10 = rate at higher temperature / rate at lower temperature
What is meant by optimum pH?
The pH the enzyme works best at
What happens as you move away from the optimum pH on a graph?
The enzyme begins to denature (the H+ and OH- ions found in acids and alkalis break the ionic and hydrogen bonds that hold the enzymes tertiary structure together, resulting in it changing shape. Therefore enzyme activity decreases.
Explain the effect of having few substrate molecules on rate of reaction.
Few substrate molecules mean there are many active sites free and able to be reacted, and so an increase in substrate concentration will increase the rate of reaction
Explain the effect of having more substrate molecules on rate of reaction.
When there are more substrate molecules, all the active sites are engaged in catalysts. This therefore produces the maximum rate of reaction
Explain the effect of having an excess of substrate molecules on rate of reaction.
An excess of substrate molecules means all active sites are engaged in catalysis and so an increase in substrate concentration will not change the rate of reaction
What is an inhibitor?
A substance which slows the rate of reaction down on an enzyme- controlled reaction
What is a competitive inhibitor?
A molecule which has a similar shape to the substrate of an enzyme, allowing for it to bind to the active site and block it and therefore stop the reaction. This is called an enzyme-inhibitor complex
What is a non-competitive inhibitor?
An inhibitor which binds to another site on the enzyme called the allosteric site. This still causes the active site to change shape so that the substrate molecule can no longer fit, but it does not compete with the substrate.
What is end product inhibition?
- A process whereby the final end product in a metabolic pathway acts as a regulator.
- when the amount of end product is high, it binds non-competitively to an enzyme in the pathway, blocking further production of itself.
- When the amount of end product fails, inhibition ends and the pathway restarts
Why are some medical drugs classed as enzyme inhibitors?
- An antiviral drug uses a reverse transcriptase inhibitor to prevent viral DNA from replicating
- penicillin inhibits transpeptidase which forms the protein to synthesis bacterial cell walls
What does a metabolic poison does and give an example of an inhibitor involved in respiration?
- they interfere with metabolic reactions in cells
- an example is cyanide which is a non competitive inhibitor of cytochrome C oxidase
What is an organic cofactor (coenzyme) and what is it’s purpose?
- an organic, non-protein molecule which binds to certain enzyme in order to make them work
- the presence of cofactors may help the formation of the enzyme substrate complex (e.g certain ions)
- some cofactors change the charge distribution on the surface of the substrate or enzyme. This makes the temporary bonds in the enzyme substrate complex easier to form
- they may act as carriers moving chemical groups between enzymes
- an example are vitamins
-e.g chloride ions are cofactors for the enzyme amylase
What are prosthetic groups?
- the name given to a cofactor when it’s tightly bound to an enzyme
- they’re a permanent part of the enzymes active site and contribute to the final 3D shape and other properties of proteins e.g charge
-e.g zinc ions are the prosthetic group for carbonic anhydrase
Why are some enzymes released in an inactive form?
the active enzyme could cause damage to the cells producing them or the tissues where they are released + allows the location and conditions where the enzyme is active to be tightly regulated
