enzymes an introduction to metabolism. the purpose of an enzyme in a cell is to allow the cell to...
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EnzymesAn introduction to metabolism
The purpose of an enzyme in a cell is to allow the cell to carry out chemical reactions very quickly. These reactions allow the cell to
build things or take things apart as needed. This is how a cell grows and reproduces.
What are enzymes?
affected by some factorsThey speed up
chemical reactions.
they’re substrate specific.
They have (the active
site).
Frist: speeding up chemical reactionse.g. hydrolyzing sucrose
H2O
H2O
Activation energy
It’s the amount of energy necessary to push the reactants over an energy barrier.
The energy barrier
Amount of energy
reactants need to reach the products( without the enzyme )
Energy barrier and amount of
energy needed after the enzyme
Delta G
Enzymes in metabolic reactions
Enzyme speed reactions by lowering EEnzyme speed reactions by lowering EAA. The transition . The transition
state can then be reached even at state can then be reached even at moderate temperatures. moderate temperatures.
Substrate specific
This means that every enzyme is specific for a certain substance called the substrate. The enzyme can only identify its substrate and work on it.
http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_enzymes_work.html
Second: enzymes are substrate specific
A Substrate is a reactant which binds to an enzyme.
e.g. Sucrose (substrate) Glucose + Fructose
Catalyst(Enzyme)
products
Each enzyme works with certain substrate
(due to its active site)
Third: the active site
Gives the enzymes its specificity due to the fit that attracts the substrate.
The enzyme changes shape and bring the chemical groups in position
The cycle in which the enzyme attracts the substrate to the active site and then produce the products
Catalytic cycle of
the enzyme
Weak hydrogen bondsAfter breaking the bonds
Factors Affecting Enzyme Activity
Factors Affecting Enzyme Activity
Make the reaction fasterBut in certain
rangeOr denature the reaction above range
Digestive enzymes work best at PH 2
intestine enzymes work best at PH 8
Other factors
Cofactors
Non-protein helpers.
Attach permanently to the enzyme
They are two types:
Inhibitors
They prevent enzymes from catalyzing.
The inhibition could be irreversible (when covalently bind) or reversible (when binding weakly)
There are two types of inhibitors.
Inorganice.g.
Zinc, iron and copper
Organice.g.
vitamins
Types of inhibitors
They bind to the same site as the substrate
They block the active site.
They bind somewhere other than the active site.
They change the enzyme shape and deactivate the active site.
Conclusions
What we know about enzymes
A single enzyme can catalyze 1000s of reactions in seconds.
Enzymes are reusable. Most of them catalyze reactions in both ways. They are affected by reactant concentration:
A. The concentration directs the reaction to equilibrium.
B. Some concentration cause enzyme saturation.
-
Q1: Write whether each of the following statements is True (T) or False (F):
1-The non-competitive inhibitor reduces the activity of an enzyme by changing the shape of the
enzyme………………………………………………………………………………2-The activity of an enzyme is affected by
temperature and pH.3- Enzymes are substrate-specific …
4-The active site of enzyme is the region at which the competitive inhibitor is bound
5- The changes in temperature will not affect the activity of enzymes.
Q 2: Choose the correct answer (one answer only): Which of the following is true about enzymes:
a)- decrease the free energy change of a reaction b)- increase the rate of the
reactionc)- change the direction of the reaction
d)- are altered by the reactions they catalyse
2-The non-competitive inhibitor inhibits the enzyme activity by:
a)- binding at the active site of the enzyme b)- changing the shape of the enzyme
c)- changing the free energy of the reaction d)- acting as a co-enzyme
3-The active site of the enzyme is the region that:
a)- binds allosteric regulators of the enzyme b)- binds to the substrate and involved
in the catalytic reactionc)- binds the products of the catalytic reaction d)- is inhibited by the presence of a co-
enzyme or a co-factor
4-All of the following are factors that affect enzyme activity except:
a)- temperature b)- cofactors c)- pH d)- ADP
5-- Enzymes work by
a- Decreasing EA b- Increasing EA c- Stabilizing EA
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