BIOL115 - Lecture 6

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  • Created by: Katherine
  • Created on: 13-05-16 11:33
What are enzymes?
Biological catalysts
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What did Louis Pasteur discover?
That fermentation requires living cells (1850). Live yeast + sugar = alcohol. Cell free yeast extract + sugar = no alcohol.
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What did Wilhelm Kuhne do?
He proposed the term enzyme (1878) when looking at trypsin.
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What did the the Buchner brothers do?
They looked at fermentation in cell free extracts from yeast (1897).
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What did all these influential figures agree?
That cells contained a biological catalyst.
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What are the functions of biological catalysts?
Regulate the flow of molecules through all metabolic pathways, build structures of cells (and break them down again) Break down invading pathogens and parasites e.g lysozymes
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What are where are lysozymes?
They break down pathogens and they are found in tears.
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What are some uses of biological catalysts?
In washing powder, in GM rennet for cheese, in stone washed jeans, in fondant centres.
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What do enzymes do?
They increase reaction rates remaining unchanged after the reaction. It amplifies the rate of reaction considerably.
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Which enzyme is essential in the break down of CO2 in the blood?
Carbonic anhydrase. It converts H2O + CO2 -> Carbonic acid (H2C03) Bicarbonate (HCO3-) + H+
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Give an example of a low specificity enzyme?
Subtillisin - a bacterial protease that cleaves peptide bonds indiscriminately
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Give an example of a moderate specificity enzyme?
Trypsin - a digestive enzyme that cleaves peptide bonds on the carboxyl sides of Lys or Arg
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Give an example of a high specificity enzyme?
Thrombin - a blood clotting enzyme that cleaves between Arg and Gly within specific amino acid sequence motifs. It has a very specific cleavage site.
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What do enzymes end in?
Most enzymes end in 'ase" e.g. ATPase (breaks down) and ATP synthase synthesizes. Exceptions are proteolytic enzymes that end with 'in'.
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What are EC numbers?
They are Enzyme classification numbers. They take the form: 1.2.3.4.
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What does the first number describe?
It is the descriptor of what the enzyme does.
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What do the 2nd and 3rd numbers do?
They give further details for type of reaction (bonds,groups)
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What does the 4th digit describe?
It describes the substrate (generate descriptor, e.g. amino acid, nucleic acid, lipid ect.)
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What is the activity of an enzyme measured by?
By the rate of reaction: amount of product produced per unit of time.
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What is the SI unit?
Katal (kat) - The amount of an enzyme that converts 1 mol of substrate per second under standard assay conditions.
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What is the international activity unit?
An amount of enzyme that will caatalyse the transformation of 1 micromole of the substrate per minute under standard assay conditions.
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What is Kfor and what is Krev
Kfor is the rate constant for forward reaction, and Krev is the rate constant for the backwards reaction.
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What happens if the forward rate is greater than the reverse?
If the forward rate is greater than the reverse, when we hit equilibrium, we'll have more product than substrates.
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What is it called when reactions release energy to the surroundings?
Exergonic - this will occur spontaneously.
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What is it called when reactions require overall input of energy?
Endogonic - breaking bnds requires energy. Forming bonds releases energy.
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In an exergonic reaction, the reactants must what?
They must absorb energy from their surroundings to break bonds before new bonds can form and release energy.
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What is the initial input of energy needed to start the reaction called?
Activation energy (Ea) or Gibbs free energy of activation.
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What does the activation energy do?
This energy increases the speed of the reactant molecules, creates more powerful collisions, and thus makes the reactants unstable.
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The difference between free energy of the products and the free energy of the reactants is the..
total reaction change in free energy - Delta G
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The difference between the free energy of the reactants and the transition state is the...
Activation energy
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Is activation energy limiting?
Yes
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In most cases, is the activation energy higher than the thermal energy of the room?
Yes, this means that a significant input of energy is required.
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How do enzymes increase reaction rates?
If the activation energy is significantly high, an input of energy is required to drive the reaction forward to approach equilibrium at a significant rate. Enzymes work by reducing the amount of activation energy required.
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What does the enzyme do?
It doesn't alter delta G, but activation energy. It reduces the activation energy so less energy is required to start the reaction.
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How do enzymes reduce activation energy?
By helping to form the transition state. Before they can interact with each other, you have to break the bonds within the molecules.
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What is the metal stick analogy?
To break a metal stick, you bend it and weaken it. This is the same as the transition state, for an enzyme substrate. Eventually it'll break.
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Which theory is incorrect regarding enzymes and the metal stick theory?
The incorrect theory involves the enzyme being complementary to the substrate.
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Why is this theory incorrect?
Because if the enzyme binds to the substrate it will be even more stable than the stick alone and will need even more energy input to break it.
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What is the correct theory?
The enzyme is complementary to the transition state. The active site of the enzyme is shaped like the transition state (bent). It binds to substrate then magnets start to pull middle of stick upwards to form transition state.
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Binding between enzyme and transition state...
contributes energy
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Card 2

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What did Louis Pasteur discover?

Back

That fermentation requires living cells (1850). Live yeast + sugar = alcohol. Cell free yeast extract + sugar = no alcohol.

Card 3

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What did Wilhelm Kuhne do?

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Card 4

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What did the the Buchner brothers do?

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Card 5

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What did all these influential figures agree?

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