Enzymes. Flashcards
What is an apoenzyme?
An enzyme protein which is not bound to a cofactor.
What is a coenzyme?
An organic molecule, that is not a protein.
What is a coenzyme also known as?
A prosthetic group.
What are coenzymes used for?
To help enzymes form their product.
Most coenzymes are what kind of molecule?
Vitamins.
What is a cofactor?
An inorganic molecule that is used to help some enzymes to produce their product.
Many cofactors are made up of that type of element?
Metallic elements.
What is a holoenzyme?
An enzyme that bound to its cofactor.
What is the induction of enzymes?
An up regulation of enzymes.
This is due to an increase in gene expression which signals for more enzymes to be synthesised.
What is kinetics?
The study of how quickly reactants are converted to products.
What are prosthetic groups?
These are organic in nature and not made of protein.
Prosthetic groups are very tightly bound (usually covalently) to the enzyme.
What is the repression of enzymes?
The down-regulation of enzymes.
It is caused by a decrease in gene expression, leading to fewer enzymes.
What is a zymogen?
An inactive form of an enzyme.
What controls and regulates metabolism?
Many different enzymes.
What are enzymes?
Biological catalysts that lower the activation energy required for a reaction to occur.
What is the active site of an enzyme?
The site to which the substrate will bind.
Can any substrate go into the active site of an enzyme?
No.
Enzymes are very specific for a certain substrate and will only work on one particular substrate.
What is enzyme specificity?
That each class of enzyme will only react with one class of substrate.
What is the substrate?
The molecule that the enzyme is working on and will eventually change into products.
What is the turnover number of an enzyme?
The number of substrate molecules that are converted to product, per enzyme per second.
Are cofactors organic or inorganic?
Inorganic.
If an enzyme requires a cofactor, will it be able to work without that cofactor?
No.
If an enzyme is bound to its cofactor, what is the complex called?
A holoenzyme.
If an enzyme is not bound to its cofactor, what is the complex called?
An apoenzyme.
Are coenzymes usually organic or inorganic?
Coenzymes are made from organic material but they are not proteins.
Can some enzymes use cofactors and coenzymes?
Yes.
Some can use both.
If a cofactor is covalently bound to the enzyme, what can it be called?
A prosthetic group.
What is a simple enzyme?
A simple enzyme is made up of only a protein.
They can be composed of single or many polypeptides.
Do simple enzymes often need prosthetic groups or cofactors?
No.
Do complex enzymes often require need prosthetic groups or cofactors?
Yes, always.
Are complex enzymes often composed of subunits?
Yes.
Of which 1 is catalytic and 1 is regulatory.
Enzymes are made of what type of organic molecule?
Proteins.
What isn enzyme classification based on?
On what an enzyme does or on the type of reaction that they catalyse.
What kind of reactions are oxidoreductases involved in?
They will catalyse oxidation and reduction reactions.
Therefore, it will transfer electrons from one atom to another which usually increases the double bonds in the molecule that lost electrons.
What is a common metabolic reaction that oxidoreductases are involved in?
A transferase will usually transfer electrons to NAD+ making it NADH + H.
Oxidoreductases are often known as what?
Dehydrogenases or oxidases.
What kind of reactions are transferases involved in?
They will move or transfer a specific group or functional group from one molecule to another.
What are transferases often known as?
As transaminase or as a kinase.
What kind of reactions are hydrolases involved in?
They catalyse the cleavage of bonds by the addition of water.
What is the name of the reaction that hydrolases use to cleave bonds?
A hydrolysis reaction.
What kind of reactions are lyases involved in?
A lyase is similar to a hydrolase as its main function is the cleavage of bonds.
The exception being that lyases do not need water to cleave bonds.
What bonds are most often cleaved by lyases?
C-C.
C-S.
C-N.
What are lyases often referred to as?
Decarboxylases and aldolases.
What kind of reactions are isomerases involved in?
They will change the molecular formula of the substrate to form an optical or a geometric isomer.
What are isomerases often referred to as?
Mutases or epimerases.
What kind of reactions are ligases involved in?
They will catalyse the formation of bonds between C, O, N and S.
What kind of reactions are kinases involved in?
A kinase is a specific type of transferase and will take a phosphate from ATP and will transfer it to an enzyme that has a hydroxyl group.
If an enzyme has a phosphate group added to it, it is said to be what?
Phosphorylated.
What kind of reactions are phosphatases involved in?
A phosphatase is the opposite of a kinase, as they will break off a phosphate group from a protein.
What is proteolytic cleavage
This is when an inactive enzyme (zymogen) is activated by the removal of a short peptide segment from the amino terminus.
When proteolytic cleavage occurs, the short peptide is removed from which part of the amino acid?
The amino terminus.
Give an example of proteolytic cleavage?
Trypsinogen is the inactive form of trypsin.
When the enzyme enteropeptidase removes the first 6 amino acids from amino end, trypsin is formed in its active state.
What is the covalent modification of an enzyme?
When a new covalent bond is added to the enzyme.
What is a common form of covalent modification?
The addition of a phosphate group to the enzyme.
What enzymes are heavily involved in covalent modification?
Kinases.
What are 2 less common forms of covalent modification?
Adenylation.
Methylation.
What effect will covalent modification have on enzyme activity?
It will either increase or decrease enzyme activity.
Kinases typically modify what localised groups within the R groups?
The hydroxyl groups on the R groups of some amino acids by removing the hydrogen and adding a phosphate group.
Which amino acids commonly undergo covalent modification from a kinase?
Serine.
Threonine.
Tyrosine.
The addition of a phosphate group will have what affect on an enzyme?
It will either activate or inactivate the enzyme.
Do phosphatases add or remove a phosphate group?
The will remove phosphate groups.
What is the sequestration of enzymes?
When some enzymes can be found in different forms, within the cell.
When the enzyme is in these different forms, it will be inactive.
What is the allosteric regulation of enzymes?
An allosteric molecule can bind to the allosteric site and this can regulate the enzyme or activate it.
How many sites do allosteric enzymes have?
Allosteric enzymes have 2 sites, an active site and a 2nd site, which is called an allosteric site.
What effect does allosteric modification have on the active site?
When the allosteric modifier binds to the allosteric site, the active site will physically change.
If an allosteric enzyme has a catalytic and regulatory subunit, where will the substrate and allosteric modifier bind on the enzyme?
The substrate will bind to the active site in the catalytic subunit.
An allosteric activator or inhibitor will bind to the allosteric site at the regulatory subunit.
What effects can allosteric modification have on an enzyme?
Allosteric modification will either increase or decrease enzyme activity.
What effect will a positive allosteric modifier have on an allosteric enzyme?
It will increase enzyme activity.
What effect will a negative allosteric modifier have on an allosteric enzyme?
It will decrease enzyme activity.
What is the process called, by which the body will create more enzymes?
Enzyme induction.
What is responsible for initiating an upregulation of enzymes?
Hormones.
How does a hormone initiate enzyme induction?
They will cross the plasma membrane.
They will find a specific receptor in the cytoplasm and will bind to it.
The active complex moves into the nucleus and will bind to a region of DNA.
It will then find a specific gene and activate it.
The gene will then make mRNA which is translated into enzymes.
What is the composition of specific receptor that hormones find in the cytoplasm?
A protein.
What is the structure called when the hormone binds to the receptor in the cytoplasm?
An active complex.
