EnYems And Flashcards
Why must metabolism be accelerated by enzymes?
To operate on a time scale relevant to life
What does thermodynamics NOT a tell you
Speed of a reaction
What does he say (3 things) about this reaction:
ATP ADP + Pi
- Thermodynamically favourable so it’s spontaneous (-🔺G)
- Incredibly slow in absence of catalyst
- However in the context of ATP this is also a good thing because we don’t want to deplete energy store really quickly
How much does Triose Phosphate Isomerase (TPI), an enzyme in glycolysis speed up the reaction
- what’s the rate of the uncatalysed reaction
- catalysed reaction
- rate enhancement
Uncatalysed: one product/day
Catalysed: 4300 products/second
Rate enhancement: 1000 million fold
Slowest uncatalysed reaction
Synthesis of UMP (a pyramiding nucleotide)
1 reaction per 45 million years
When the synthesis of UMP is catalysed
Catalysed
Reaction enhancement
Catalysed - 39 products/ second
Rate enhancement: 1.4x10^17 fold
What is the synthesis of UMP catalysed by
OMP decarboxylase (decarboxylates orotidine monophosphate to UMP)
Why are uncatalysed reactions so slow
Because they go from a substrate to product via an intermediary state (the transition state)
Transition state
Transitory molecular structure that is no longer the substrate but not yet the product
What’s the least stable species in a reaction?
The transition state
What has the highest free energy in a reaction?
The transition state
What will free energy be like in a spontaneous reaction
Free energy of products will be lower than free energy of reactants
What does an enzyme do in terms of free energy?
It reduces the free energy of the transition state
How do enzymes accelerate a reaction in terms of transition state and activation energy?
They stabilise the transition state , reducing the activation energy required to reach it
Enzymes affect the ___ NOT the ___
Enzymes affect the KINETICS not the THERMODYNAMICS
Delta G remains the same
Two unaltered things when an enzymes acts
- 🔺G
2. Equilibrium position
What does an enzyme do in terms of equilibrium
Accelerates how long it takes to reach equilibrium
Simplistic analogy of how enzymes stabilise transition state
Enzyme complementary to transition state
But leaving enough room so that once the conformational change occurs the substrate is completely complementary to the enzyme (magnets arranged so they anticipate the shape of the broken sticks)
Because then by being completely complementary and snug with the transition state it makes the transition state more stable which reduces free energy required to reach it
What part of an enzyme shares similar features in all enzymes
The active site
General features of the active site
- Crevice in the enzyme structure
- AA side chain catalytic groups
- Water excluded
- Hydrophilic side chains
What are catalytic groups on enzymes
Within active site key AA side chains known as catalytic groups are precisely orientated and around the bound substrate
What is meant by water is excluded in the active site of an enzyme
Crevice is mainly lined with hydrophobic amino acids so water excluded unless it’s a reactant
What is meant by there are SOME amino acids with hydrophilic side chains in the enzyme active site?
There are a few and these polar residues acquire special properties essential for substrate binding or catalysis
What is meant by some hydrophilic residues in active site of enzyme
Some but they acquire special properties essential for substrate binding or catalysis
