Chapter 2.4 ENZYMES Flashcards
Why are enzymes thought of as catalysts ? (3)
- remain unchanged at the end of reaction
- small amount can catalyse the conversion of a large number of substrate molecules
- reduces activation energy
How to you alter the shape of the active site ?
2
- change in Ph
- change in temperature
What kind of enzymes are there ?
2
- Catabolic - big broken to small
- Anabolic -small made to big
Outline the structure of catalase ?
- chains
- prosthetic group
- 4polypeptide chains
- Haem group with iron
Where is catalase found ?
- lysosomes Called peroxisomes
What could changes in the DNA sequence do to the enzyme ?
Start from mRNA
( 5)
1-changes in protein coded hence change in MRNA 2-change of primary structure 3-tertiary structure changes shape 4-active site changes shape 5-enzyme can’t catalyse reaction
What is a cofactor ?
A substance that has to be present to ensure enzyme catalysed reaction takes place at an appropriate rate .
What’s a prosthetic group?
3
- permanent attached cofactor
- covalently bonded
- examples : Haem group ( Fe2+)
Other cofactor examples ?
3
- mineral ions
-organic coenzymes example : B12 , folic acid etc
= temporary associations with enzyme
What are the two scenarios of cofactors ?
4
1-co substrates to make correct shape to bind to active site
2- charge distribution on surface of enzymes active site changes
What bonds are present in prosthetic groups ?
1
Covalent
What bonds are present in Metallic ions?
1
Ionic bonds
What bonds are present in coenzyme /enzyme substrate molecule ?
(2)
Ionic /hydrogen bonds
What does the lock and key model say ?
(5)
-complexes
-collision
- if a substrate = successful collision with enzyme = ESC
- EPC
- product molecules leave site
- enzyme makes another ES complex
- shapes of substrate and enzyme = complementary !
What does the induced fit hypothesis say?
2
- active site = complementary shape to substrate molecule but R groups change a little so active sites are more precise
- fits like glove
How do enzymes lower activation energy ?
1
- bring molecules close together to react
What happens when you increase temp to enzymes ?
3
- ke causes particles to move faster
- rate if collision increases
- force of collisions increases
What does over heating the enzyme do ?
5
- molecules vibrate
- hydrogen bonds break
- tertiary structure unfolds
- substrate no longer fills active site
- enzyme is denatured
What’s the effect of altering PH ?
4
- H+ ions attracted to negative parts
- excess H+ ions interfere with hydrogen bonds and ionic forces
- active site hanged shape
- enzyme denatures
What happens if you increase substrate concentration?
2
- rate increases up to a point then plateaux as all active sites are filled ! What
What’s Q10?
(2)
Equation ?
- temperature coefficient
- rate of reaction at T+10 / rate of reaction at T
What’s enzyme synthesis ?
1
- particular enzymes switched on/ off
Why do cells go through enzyme degradation ?
2
- elimination of abnormal shaped proteins
- regulation of metabolism ( eliminate surplus enzymes )
What’s competitive inhibition.
3
- when inhibitor has similar shape to substrate
- blocks active site ( no binding required )
- substrate can’t bond
What’s non competitive inhibition ?
2
- bonds to allosteric site
- active site shape changes
What kind of bond makes a irreversible inhibitor ?
1
Strong covalent bonds
What kinds of bond make reversible inhibitors ?
3
- weak hydrogen bonds
- weak ionic bonds
- inhibitor can be removed !
How are enzymes in organisms which live in hot conditions different ?
(1)
- more disulfide bridges ( heat stable )
What’s a buffer solution ?
1
Resists ph changes by accepting or donating protons .
What does cyanide do ?
3
CN- ions bind irreversibly to enzyme found in mitochondria - inhibit final stage of respiration
- paralyses
- Inhibits AChE ( found in neuromuscular synapses )
Name some examples of enzyme inhibition drugs and poisons ?
Name 3
- snake venom
- Cyanide
- Aspirin
- ATPase
- ACE inbitor
- antiretroviral drugs
