Enzymes Flashcards
What are the characteristics of enzymes?
- Specific
- Proteins with large molecular weights
- Labile
- Catalytic efficiency
- Does not alter the equilibrium
- Their activity can be regulated
- They have an active site
What are the two types of ‘substrate specificity’?
- Abosolute specificity
- Broad specificity
What are the two types of specificity related to enzymes?
- Substrate specificty
- Reaction specificity
- Stereospecificity
What are the proteins with large molecular weights with secondary and tertiary structure?
- Simple proteins
- Conjugated proteins
- Protein + co - factor component
What is a Holo enzyme?
An Apo-enzyme + non-protein
What are the two classification sof enzymes based on thenumber of polypeptide chains?
- Monomeric - One chain
- Multimeric - more thna one chain
What is a Multienzyme complex?
- Many reaction catalyzing sites in same macro-molecule at different sites
- Becomes inactive when units each with enzyme activity is fractionated.
Examples of multienzyme complexes?
Eg: Fatty acid synthetase , Pyruvate dehydrogenase
What does it mean to say that an enzyme is “Labile”?
Unstable – enzymes are proteins & are subjected to denaturation by all agents causing denaturation of proteins.
What is the catalytic efficiency of enzymes?
Accelerate specific chemical reactions by decreasing activation energy
How can the activity fo an enzyme be regulated?
- Activated
- Inhibited
Describe the role of enzymes in compartmentalization.
Isolate the substrate and products from other competing reactions providing a favourable environment for the reactions or pathways.
Describe the active site of an enzyme
Is made up of several amino acids that come together as a result of specific folding of IIry and III ry structure of enzymes
- globular proteins
- hydrophilic side chains on outer parts
- has specific 3D structure, shape & specific charges.
- forms a cleft or pocket on the enzyme surface
that accepts & binds substrate.
Importance of active site?
• within the active site the substrates are brought close to one another in optimal alignment with cofactors & prosthetic gps and amino acid side chains responsible for chemical transformation in to products.
•Active site shield substrates from water and generate an environment (polar, acid, hydrophobic or alkaline) that can differ from the surrounding cytoplasm.
What are the ‘Mechanisms that facilitate Catalysis’ ?
- Proximity - bond forming distance (conc)
- Acid –base catalysis – prosthetic groups and side chains of amino acids of enz help catalysis by acting as acids and bases etc
- Catalysis by strain - ‘Enz’ that break bonds bind substrates in an unfavourable conformation that will help break the bond
- Covalent catalysis – formation of a covalent bond between ‘Enz’ and a substrate (s). Introduces a new reaction path whose activation energy is lower hence the re becomes faster. Enz modification is transient (temporary)
How do enzymes lower the EA?
- Acting as a template for susbtrate orientation
- Stressing the susbtrates and stabilizing the transition state
- Providing a favorable microenvironment
- Partticipating in the catalytic reaction.
Enzymes are classed in to 6 groups depending on reactions catalysed?
- Oxidoreductase
- Transferases
- Hydrolases
- Lyases
- Isomerases
- Ligases
Oxidoreductase?q
Oxidize or reduce substrates by transfer of hydrogens, electrons or oxygen
Oxidation & reduction take place in the same reaction
remove groups (not H) from substrates & transfer them to acceptor molecules (not H2O)
ATP + glucose —(hexonkinase)—-> glucose-6-P + ADP
Hydrolases?
water participates in the breakage of covalent bonds (C-C, C-N, C-O etc) of substrate with concurrent addition of elements of water to the those bonds.
Ester + H20 —(esterases)—-> acic + alcohol
Lyases?
remove atoms/small groups (elimination) from large substrates to leave a double bond (other than hydrolysis or oxidation) or a ring st.
Isomerases?
Rearrange functional groups / isomerization of substrate
Glyceraldehede-3-phosphate <—(Triose phosphate/isomerase)—> DHAP (Ketose)
Ligases?
Joins 2 molecules
Covalently links 2 molecules with subsequent breakage of a high energy bond.
- forms C-C, C-N, C-O, C-S bonds
ATP + aspartate + NH3 —(Aspartate:NH3 Ligase)—> AMP + pp + asparagine.
HI
HI
What is covalent modification?
Responds to hormonal regulaation
(Eg; Insulin and glucagon)
Covalent might help allostery
Carries out SIGNAL AMPLIFICATION
Examples of Allosteric enzymes?
- Glycogen synthase - need to get phosphorylated to become active
- Glycogen phosphorylated
Regulation of Glycogen Sythase after a meal?
“Reciprocal regulation”
The activity is high
Hexokinase
[Need to add more points]
Activity changes based on glucose levels
Action of Glucagon and Insulin on Glycogen Phosphylase based on glucose concentration?
- Glucagon activates Kinase to phsophorylase
What is a signal cascade?
For cells that cannot pass through the plasma membrane and to amplify the signal
ligand binds to the gate
receptor changes conformation
Adenylate Cyclase —-(glucagon)—-> Ad Cyclase
ATP -> cAMP
activate the protein kinase
Enzyme a -> Enzyme b
Differenttiate between active and apssive regulation of enzyme activity
Active - Enzyme regulation
Passive - Substrate regulation
Differentiate between Induction and Repression of enzymes
Regulates the number of active enzymes
What are isozymes?
Multiple forms of the same enzyme
structure, ionic charge, physical, electrophoreticsal and immunological - all different
they catalyse the same reaction
Maybe in different organs but catalyse the same reaction
[sometimes protein used]
isozyme used in clinical diagnmosis?
Enzymes for diagnosis?
during disease, enzymes spill into blood
enzyme level will be very high
idenitify the enzyme to see where and the extent of the tissue damage
“Cell Necrosis”
isozyme for liver damage?
Alanine aminotransferase
creatine kinase as isoenzyme?
creatine phosphate - very high energy molecule
increased maount in skeletal muscle, mycardium and brain (All has different isozymes)
-> can measure the concentration and help identify which is damaged
2 subunits - M & B
-> combinations? 3
isozymes of creatine kinase in skeletal muscle, cardiac muscle and brain?
SM - MM (CK3 CK MM)
-> will be high in the blood (usually very low)
CM - MB (CK MB)
-> After heart attack (MI) MB CK level is high
-> Trop - I level can be high
how to identify the isozymes?
electrophoresis
migration of CK? CK 1, CK 2 and CK 3
Enzymes used in diagnosis examples. list.
ALT - viral hapatitis
Acid phospate - prostate cancer
Alkaline phosphate - bone and liver
amylase - pnacreatitis, pancreatic cancer
LDH, CK - myocardial infarction
Myocardial markers
eznymes as laboratory agents?
Enzymes for therapaeutic use?
Therapy in pancreatic insufficientcy - Amylase, Lipase, Protease
Hyaalurodinase - depolymerise ground susbtance
[Look into other examples]
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