This document discusses enzyme affinity and the Michaelis-Menten model. It defines enzymes as biological catalysts and explains how they increase reaction rates. It then describes how enzymes convert substrates to products, noting the high turnover rates of some enzymes. The document discusses measuring the initial rate of reaction and how the rate depends on substrate concentration. It defines Vmax as the maximum rate an enzyme can catalyze a reaction and Km as the substrate concentration when the reaction rate is half of Vmax, representing the enzyme's affinity for the substrate.

1. Comparing Enzyme
Affinity
CHAPTER 3: ENZYME
AFFINITY- THE MEASURE TO WHICH A SUBSTANCE
TENDS TO COMBINE WITH ANOTHER

2. What are enzymes
• Biological Catalyst
• Specific a certain substrate by its R group
• Globular protein- water soluble
• Remain unchanged after the reactions
• Enzymes can break and bond
• Nearly all metabolic reaction are enzymes catalyzed
• Enzymes reduces activation energy- increase rate constant

3. How the enzyme convert substrate into
product
• A typical enzymes molecules can convert around one thousand substrate
molecules into product per second, this is known as turnover rate
• The fastest enzymes( carbonic anhydrase ) can remove 600000 molecules of
carbon dioxide from respiring tissue per second.
• Speed such as these can only possible because
1. molecules within cells move about very quickly by diffusion over short
distance
2. With tens or hundreds of thousand of collision per second occurring
between enzymes and substrate molecules.

4. Course of an Enzyme reaction
• Usually starts out quickly before going out on a gentle
curve
• At first every enzymes Is paired up- this rate depend on
how quickly an enzyme can catalyze, then released- this
IS the rate
• Because after this point, the measure is influenced by the
amount of the substrate left although the rate is
supposed to only measure how fast an enzyme work.

5. • Imagine the enzyme as a factory worker
• You want to measure how fast she/he can finish the
work
• Now, you have a 50 toys that you want him/her to piece
together(the Substrate)
• But also imagine – as in a cell – you didn’t put the toys
on her desk, you leave them all over the room
• At the beginning, she/he’s quick to find the toys – in
fact she/he’ll randomly bump into(pick) those ones
lying around

6. • So if you time at the beginning, you’ll actually get the
speed of her work
• But after she’s done, say, 25 of them. The other 25 are
hidden very well. Now she has to look around for them.
• So if you time her now, you won’t actually get the speed
of her work – you will get the speed of her looking for
things.
• This applies similarly to enzymes

7. • At the beginning of the reactions, there are enough substrates for the
enzymes to work with- so they’re working at the real speed
• Soon there are fewer substrates- enzymes are waiting to be filled up – soon it
stops
• Therefore the first 30 seconds usually gives us The initial rate of reaction

8. • As substrate concentration (number of
toys) increases, the initial rate of reaction
(the speed of worker’s work) increases….
• Until there are too many things to do …
the enzymes (workers) cannot be any
faster- reached the V max

9. V max
• The theoretical maximum rate that an enzyme can perform
• Measured at the point of saturation- every enzymes has a
substrate
• Measures by increasing substrate concentration while leaving
the enzymes concentration constant
The key steps towards understanding of how well an enzyme
performs is to measure

10. Michaelis Menten Model
• When the Enzymes are working at the hardest, and they cannot go any
faster – Enzyme saturation
• This is the Vmax – a maximum rate in which an enzyme can work at
Michaelis Menten constant
o Is the substrate concentration at which an enzyme works at half its
maximum rate( ½ V max).
o IS a measure of the affinity of the enzyme for its substrate
o The higher the affinity, the lower the Michaelis- Menten constant and
the faster the reaction will proceed to its maximum rate

11. Km
• V max/2 is Km
• Km measures the affinity/ efficiency of an enzyme- how quickly an enzyme
reaches V max
• It only points to when substrate is already in an enzyme
• Kinda like acceleration- how quickly it reaches the maximum speed
• The value of Km can vary, identity of substrate, temperature, ph ,
presence of particular ions ,overall ion concentration, and the presence of
poisons, pollutants or inhibitors.

12. The Double Reciprocal (inverse) Plot
• In reality, the enzyme continues to work, so the rate increases little by little and
would only flatten at infinity
• Because infinity is not on the graph- we can’t accurately read off the V max – we can
guess the best
• Solution: Since 1/ infinity = 0 if n tends to infinity but if an infinity value is fived ,
then it is 1)
• Therefore, by plotting a graph of 1/ (Substrate concentration) against a graph of 1/
(velocity)- we receives a reciprocal graph that at which ever point that it reaches the
0 substrate concentration- the point when it touches the y – axis ( because that is
the infinity substrate concentration in reciprocal term) – will be equal to 1/ V max.
• -1/Km ( because we can’t have negative Km) can be found at the point of x- axis
interception

14. Relationship in retrospect
• First: Rate of reaction at 30 seconds is INITIAL RETE OF
REACTION
• INITIAL RATE OF REACTION is the VELOCITY in Michaelis-
Menten model which tries to calculate the Vmax ( a theoretical
maximum velocity of a certain enzyme) and how quickly the
enzyme can reach that, expressed in terms of Km
• Km= ½ of Vmax – calculated by the reciprocal plot or a
hyperbolic normal plot