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Flashcards in L.3 Enzyme Kinetics Deck (27)
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What is Saturation Kinetics?

As subtrate [S] levels increase, so does the rate of the reaction, until a maximum value is reached.



What does the Michael-Menten Equation describe?


It describes how the rate of the reaction (v),

depends on the concentration of both

the enzyme (E) and substrate (S). 

These form the product (P).


What is the Michaelis-Menten equation?


What is the equation for V?

V = kcat / Km [E] [S]


What is Kcat?

Is the rate of E + P formation.


What is Km?

Km is the Michaelis Constant.

  • The concentration of substrate when 1/2 of active sites are full, on an enzyme
  • An intrinsic property of the enzyme-substrate system and cannot be altered by changing the concentration of substrate or enzyme.
  • It is often used to compare enzymes
  • Under certain measures, it is used to measure the affinity of the enzyme for its substrate
  • High Km = lower affinity for substrate


Turn over equation?


what does Vmax equal to?

Vmax = [E] Kcat


What is catalytic efficiency?

The ratio of Kcat/Km.

A large Kcat (hight turnover rate) or a small Km (high substrate affinity) will result in higher catalytic efficiency.


What is the Lineweaver-Burk Plot?

Is a double reciprocal graph of the M-M equation. 

X-axis = - 1 / km

Y-axix = 1 / Vmax

Slope = km/ Vmax


What is cooperativity and how is the graph different?

Cooperativity enzymes have multiple subunits and multiple active sites. May exist in one of two states.

Low-affinity Tense state T

High-affinity Relaxed state R


Sigmoidal S shape on Graph



What is Hills coefficient?


A way to quantify cooperativity.

Coefficient > 1       Positive cooperation (more and more binding)

Coefficient < 1       Negative copperation 

Coefficint = 1          No Cooperation


What are the effects of increasing concentration of S? and E?

Increasing S

In early binding increasing S will increate the rate of V

At late binding increasing S does not have an effect

Increasing E

Will increase Vmax, there are more enzymes that can bind to the substrate.


Environmental factors affecting enzymes activity

  1. pH
  2. Temperature
  3. Salinity 


The ideal temperature for the body enzymes?

What is the effect of temperature on enzymes?




Enzymes increase their efficiency x2 for every 10-degree increase until reaching optimal temperature.


Ideal pH (most enzymes)?

Ideal pH (gastric)?

Ideal pH (Pancreatic)?

  • 7.35
  • 2
  • 8.5


What is feedback regulation?

When enzymes are subject to regulation by their own products down their given metabolic pathway.


What is feed-forward regulation?

When enzymes are regulated by their intermidiates instead of their products.


What is negative feedback?

or also known as feedback inhibition?

When product binds to the active site of the enzyme/s , competing with inhibitor and making them unavailable fo use.

Stopping the metabolic pathway.


What are the 4 types of reversible inhibition?

  1. Competitive
  2. Non-competitive
  3. Mixed
  4. Uncompetitive


Four characteristics of a Competitive inhibitor.

  1. Occupancy of the active site
  2. Can be overcome by adding more substrate
  3. Does not alter Vmax, if enough substate added it will outcompete inhibitor
  4. Increases Km, the concentration of S has to be increased to reach 1/2 max vel


Four characteristics of Noncompetitive inhibitor.

  1. Binds to an allosteric site on the enzyme, inducing conformation change.
  2. Binds equally to E and ES
  3. Cannot be overcome by adding more substrate
  4. Decreases Vmax, there is less enzyme available to react


Five characteristics of Mixed inhibitors

  1. Binds to E or ES, at an allosteric site.
  2. Different affinity for E and ES.
  3. Alters Km, depending on the preference of the inhibitor.
  4. Preference for E, then increases Km (lowers affinity). Preference for ES, the lowers Km (increases affinity).
  5. In either case Vmax is decreased. 


Four characteristics of Uncompetitive inhibitor.

  1. Binds allosterically
  2. Binds only to ES, locking substrate in place
  3. Lowers Km, (increased affinity)
  4. Lowers Vmax, less reaction to completion.


What is irreversible inhibition?

RI alters the enzyme so that the active site is unavailable for a prolonged period of time or even permanently.


New enzyme molecules must be made for

reaction to occur again.


Eg Aspirin & prostaglandins 


What is an allosteric enzyme?

Allosteric enzymes alternate between active and inactive forms, molecules that bind these enzymes, can be either allosteric activators or inhibitors.


What are the 2 types of covalently modified enzymes?

  1. Enzymes can be activated or deactivated by phosphorylation or dephosphorelation.
  2. Glycosylation


What are zymogens?

Zymogens are enzymes secreted in an inactive form

and are activated by cleavage