Enzymes 1 Flashcards
What are enzymes?
Biological catalysts that increases the rate of a chemical reaction of a chemical reaction without itself undergoing any permanent chemical change
- enzymes are specific
- they are located inside of cells, in the extracellular space or in the blood plasma
- they can be regulated
What are the functions of enzymes?
- Breakdown of nutrients
- Production of high energy molecule
- synthesis and assembly of cellular building blocks
What are substrates?
The reactants that are activated by the enzyme
What are apoenzymes?
Enzyme without its nonprotein component
What are holoenzymes?
An active enzyme with its nonprotein component
Differentiate Cofactors and Coenzymes?
Cofactors- a metallic nonprotein component e.g, Zinc (Zn2+)
Coenzymes- nonmetallic small organic molecule divided into co-substrates and prosthetic group
Define the category’s of Coenzymes
Co-substrates- transient association with the enzyme and dissociates into an altered form e.g. NAD+
Prosthetic groups- permanent association with an enzymes and the form is not changed at the end of the reaction
What is an active site?
Special pocket where substrate binds
What is the turnover number?
The number of substrate molecules converted to product per enzyme molecule per second
Describe the specifier of enzymes
Specificity:
- Enzymes are specific for a single molecule or a structurally related group of substrates
- Usually only 1 enzyme per reaction type
What are the c,asses of enzymes?
- Oxidoreductases
- Transferases
- Hydrolases
- Lyases
- Isomerases
- Ligases
What type of enzyme are oxidoreductases?
Catalyze oxidation-reduction reactions
What type of enzyme are transferases?
Catalyze transfer of C-, N- or P- containing groups
What kind of enzymes are hydrolases?
Catalyze cleavage of bonds by addition of water
What kind of enzyme are lyases?
Catalyze cleavage of C-C, C-S and certain C-N bonds
What kind of enzymes are isomerases?
Catalyze racemization of optical or geometric isomers
What kind of enzymes are Ligases?
Catalyze formation of bonds between carbon and O, S, N, coupled to hydrolysis of high-energy phosphates
What are 2 minor enzyme Groups?
Kinases
Phosphatase
What are the steps in an enzymatic reaction?
- Enzyme and substrate combine to form a complex E+S = ES complex
- The complex goes through a transition state- not quite substrate or product. ES=ES*
- A complex of enzyme and product is produced
- The product is released
EP= E+P
What are the 2 basic components of the active site ?
- catalytic site
- Binding site
What is the catalytic site of an enzyme?
Where the reaction occurs
What is the binding site of an enzyme?
Area that holds the substrate in proper place
Describe the shape of enzymes
Shape are complementary to the substrate and determines the specificity of the enzyme
Describe the interactions of enzymes
Enzymes use weak, non-covalent interactions to hold the substrate in place based on R groups of amino acids
How are enzyme sutes shaped?
These are clefts or pockets on the enzyme surface
Describe the lock and key model
The lock and key model-1890
Assumes only a substrate of the proper shape could fit with the enzyme
Describe the induced fit model
Induced-fit model -1958
- assumes continuous changes in active site structure as a substrate binds
- more widely-accepted
What are factors that influence enzyme activity?
Environmental factors
-temperature,pH
Cofactors
-metal ions
Effectors
-species that alter enzyme activity
Explain the effect of temperature on enzyme activity
- exceeding normal temperature ranges always reduces enzyme reaction rates
- optimum temperature is usually 25-40 degrees celsius(but not always)
What is enzyme regulation?
Proteolytic cleavage to activate : enzyme exists in inactive form(zymogen) that is activated by removal of a shirt peptide segment(truncation)
What is covalent modification?
This is achieved by the addition(phosphorylation) or removal (dephosphorylation) of phosphate groups from specific serine, threonine and tyrosine residues of the enzyme
What is the purpose of covalent modification?
Phosphorylation May make an enzyme more active or less active depending on the specific enzyme
What is an example of covalent modification?
Glycogen phosphorylase increases increases with phosphorylation whereas that of glycogen synthase decreases
What are the 5 types of covalent modification?
Phosphorylation
Adenylylation
Uridylylation
ADP-ribosylation
Methylation
What is enzyme repression-downregulation?
Decrease gene expression, decrease synthesis of enzyme molecules
What is enzyme degradation?t
Achieved by specific changes in the protein structure that is recognized for degradation by the ubiquitin-proteasome
What is allosteric regulation?
“Other site” regulation, both. Positive and negative effectors(homotropic, heterotropic)
What are homotropic effectors?
Substrate acts as the effector, most Often a positive effector.
Exhibits cooperativity analogous to the binding of oxygen to hemoglobin
What are heterotropic effectors?
Effector may be different from the substrate. Feedback inhibition in some reactions can serve as an example (phosphofructokinase-1 and citrate in glycolysis)
What is enzyme induction/upregulation?
Increase gene expression, synthesis of more enzyme molecules
Examples: steroid receptor mechanism of signal transduction
Highlight the mechanism to form active Trypsin
- Chymotrypsin converted to pi-chymotrypsin by cleaving Arg, leaving Ile on the tail
- pi-chymotrypsin converted to a-chymotrypsin by adding another peptide chain to Ile and cleaving iff a poetics chain on the opposite end between Tyr and ALS
- trypsinogen is converted to trypsin(active form) by enteropeotidase
What is a binary complex?
One substrate and one enzyme
What is a tertiary complex?
Two substrates and one enzyme
What is activation energy?
The energy difference between that of the reactants and a high-energy intermediate, the Transition state(T), which is form during the conversion of reactant to product
What is the job of the kinase?
Uses ATP to add phosphate
What is the job of a phosphatase?
To remove a phosphate group
