week 2: Enzyme function and control Flashcards
what are the components that make up a functional enzyme?
- **Apoenzyme = ** protein components and provides a 3D structure.
- **cofactors = ** non-protein molecules. 2 types: inorganic factors (metal ions), and coenzymes (organic molecules that bind to enzyme temporarily, e.g. vitamins)
- **prosthetic groups = ** tightly bound cofactors remain associated with the enzyme through catalytic phase.
- **active site = ** region where substrate bind to be catalysed.
what is the interaction between enzyme and its substrate?
- enxyme binds with substrate = enzyme-substrate complex
- ## weak non-covalent interactions (e.g. hydrogen bonds)
what is a non-regulated enzyme?
- not controlled by regulators produced by cells.
- depend on substrate conc.
- follows Michaelis-Menten Kinetics.
- have Km and Vmax
- activity can be controlled by drugs (e.g. pain killers, blood pressure, antibiotics, chemo)
what is a regulated enzyme?
- activity changes depending on the presence of a regulator.
which kinetics do regulated enzymes follow?
- they contain 2 subunits and an active site therefore, follow Signmoidal kinetics.
what is feedback inhibition?
- mechanism used by cells to control enzyme activity.
- inhibition of an enzyme in a pathway by the end product of that pathway.
- regulate the rate of a metabolic pathway and maintain homeostasis by preventing the overproduction of certain substances.
3 types of regulations which affect regulated enzyme activity?
1. covalent modification = formation of a covalent bond via adding an atom/molecule to enzyme (PTM - post translational modification)
2. Zymogens = removing a small piece of proteins activates the enzyme.
3. isozymes = enzymes that catalyse the same reaction but have different tertiary or quaternary structures.
can zymogens be controlled after activation?
- zymogens involves irreversible regulations but can be controlled by cellular inhibitors.
- irreversible inhibition of the actovated zymogen can only occur by binding an inhibitor to enzyme active site.
where are isozymes found?
heart, liver, skeletal muscles.
what is covalent modification and is it reversible?
- type of PTM
- addition or removal of a hydroxile or phosphate group via covalent attachement or removal (e.g. phosphorylation)
- can result in enzyme activation or inhibition
- in activation –> change enzyme structure –> alteration in catalytic activity.
- reversibility depends on the specific modification and the availability of the enzyme responsible for adding or removing the modifying group.
which isozyme appears in the blood after a heart attack
- following a heart attack, the damaged heart muscles secrete lactate dehydrogenase (LDH) isozyme into the blood stream. LDH-1 and LDH-2.
- LDH isozymes are diff forms of LDH enzyme –> structurally diffeerent.
- therefore detection of elevated LDH-1 and LDH-2 can clinically serve as an indication of myocardial damage - :. diagnosis of heart attack.
how does the appearence of LDH isozymes in the blood indicate acute hepatitis?
LDH-5 (specific to the liver) are released into bloodstream when liver cells are damaged due to acute hepatitis.
- but important to consider other clinical laboratory findings to confirm diagnosis.
what is the role penicillin
- penicillin is a mechanism based inactivator, an irriversible suicide inhibitor.
- inhibits transpeptidase (enzyme) –> transpeptidase is a bacterial enzyme, essential in the synthesis of bacterial cell wall.
how does penicillin inhibit transpeptidase?
- penicillin has a reactive peptide bond between 2 amino acids which causes it to bind/destroy a functional group on the transpeptidase
- :. complementary substrate cannot bind to transpeptidase as the enzyme is destroyed.
- if bacterial cell was can’t be synthesised, bacteria cannot reproduce or maintain their cell wall –> :. bacterial death
- :. penicillin is an antibiotic.
what are 2 exmples of suicide inhibitors?
- penicillin
- some chemotherapy drugs
