2.4)Enzymes Flashcards
what are enzymes?
biological catalysts that speed up the rate of metabolic reactions without being used up
what type of proteins are enzymes?
globular
how do enzymes work?
interact with substrate mol. to form enzyme substrate complex (ES)
what is the turnover number?
number of reactions that an enzyme can catalyse in one second
what is a difference between chemical catalysts and enzymes?
-they can work at lower temp, neutral pH + lower press
-more specific than chemical catalysts
what effects do gene mutations have on enzymes?
-alter the AA sequence of a protein
-alter the enzymes tertiary structure
-prevent enzyme from functioning
what can a deficiency in enzymes cause?
metabolic disorder
what is an active sight?
indentation or cleft on the surface of the enzyme consisting of about 6~10 AA
what structure does the active sight have?
tertiary
why is the tertiary structure of the active sight crucial?
-shape is complementary to the shape of the substrate binding to it
why are enzymes specific?
the active sight is complementary to the substrate
how to enzymes affect the activation energy ?
lowers the activation energy to get the reaction started
what is the activation energy?
minimum energy to start a reaction
what are intracellular enzymes?
-act within cells
-structure and function of cells
what are the 3 pathways that intracellular enzymes take?
-metabolic
-anabolic
-catabolic
what is the metabolic pathway?
each step catalysed by a different enzyme
what is the anabolic pathway?
large mol. synthesised from small mol.
what is the catabolic pathway?
large mol. broken down into smaller mol.
what is one product of metabolic pathways?
hydrogen peroxide
which enzyme breaks down hydrogen peroxide?
catalase
how does catalase protect the cell from damage from reactive oxygen?
breaks it down into water + oxygen
what are extracellular enzymes?
work outside the cell
what is one type of the extracellular enzymes?
-digestive enzymes secreted from the cells lining the alimentary canal in the lumen of the gut
-digest large mol. (fat,protein + starch)
-absorbed into the bloodstream
what are 2 types of digestive enzymes?
-amylase
-trypsin
how do enzymes that work outside of the body work?
-release enzymes into their immediate surroundings
-breakdown large mol. into smaller mol.
-absorbed by cell
what is a cofactor?
small non protein mol. that attaches to an enzyme
what are cofactors for?
ensure that an enzyme catalysed reaction takes place at an appropriate rate
what is a prosthetic group?
cofactor that is permanently bound with covalent bonds to an enzyme
what is the prosthetic group in carbonic anhydrase?
zinc ion
where is carbonic anhydrase found?
erythrocytes
what reaction does carbonic anhydrase catalyse?
interconvention of CO2 + H2O to carbonic acid
why is the catalytic reaction of carbonic anhydrase imporatant?
allows CO2 to be carried in the blood from respiring tissue to the lungs
what hormone is zinc an important cofactor for?
polypeptide hormone into insulin
can cofactors also be ions?
yes
what type of bond is there between cofactors and substrate?
temporarily bound
what effect do cofactors have on substrate on substrate mol.?
-ease the formation of the ES
-increase the rate of the enzyme catalysed reaction
chloride ion is a cofactor for which enzyme?
amylase
what are coenzymes?
small organic non proteins that bind temporarily to the AS
what happens to coenzymes during chemical reaction?
chemically changed and need to be recycled to their original state
what is the difference between a prosthetic group and a coenzyme?
prosthetic group bind permanently to enzyme, a coenzyme binds temporarily
what effects can increased temperatures have on enzymes?
denature them
what happens to the Ea when the substrate binds to the active sight?
-lowers the Ea
what happens when there is a low Ea?
-⬆️ number of collisions
-speed up metabolic reactions
what are the 2 hypothesis’ of the formation of an ES-complex?
1) lock & key
2) induced fit
explain the lock & key hypothesis
-substrate fits into the AS like a key into a lock
-substrate held in way that the right atom groups are close enough to react
-R-groups react= form H bonds= ES-complex
-substrate mol. broken into smaller product mol. –> leave AS
what type of energy do the enzyme + substrate have?
kinetic energy
as the enzyme + substrate have KE, what does this cause?
-constantly moving
-2 mol. collide= ES-complex
-substrate mol. broken or built up to form= enzyme product complex
-product leaves AS = enzyme binds to another substrate mol.
-form another ES-complex
who introduced the induced fit hypothesis?
Daniel Koshland
what did the induced fit hypothesis suggest?
-substrate enters the AS
-induces a slight change in shape
-AS moulds itself around the substrate =good fit
-R-groups change shape slightly
in an induced fit why is the conformation more precise?
R-groups change shape
where is the ES-complex formed?
where the H bonds, ionic bonds, hydrophobic interactions + van der waals forces bind the substrate to the AS
what happens when the product is released from the induced fit?
-has a slightly diff shape to the substrate
-detaches from the AS
-enzyme is free to bind to another substrate mol.
what happens when a mixture of enzyme + substrate is heated?
-both mol. gain KE
-⬆️ number of collisions
-⬆️ rate of ES-complexes
-until the optimum temp
what does increasing the temp cause to the bonds?
-mol. vibrate faster
-weaker bonds break
-H bonds + ionic bonds hold the tertiary structure together
-vibrations ⬆️= AS begins to change shape
-⬆️ temp even more= AS has irreversibly changed shape= no longer complementary
-denatured
what does it mean when the enzyme has denatured?
-AS has completely changed shape
-no longer complementary
which bonds break when the enzyme becomes denatured?
-tertiary bonds BREAK
-peptide bonds DO NOT break= primary structure is not altered
what does the optimum temp mean?
temp at which the ROR is the highest
why are some enzymes stable at really high temps?
-more disulphide bonds
-dont break with heat
-keep the shape of the tertiary structure
how to calculate rate of reaction?
1/ time taken to reach end point
what is the temperature coefficient Q10/
measure of how much the R.O.R increases with a 10C rise in temp
what is the equation for Q10?
R.O.R at (T + 10C) / R.O.R at TC
