ENZYMES. http://www.kscience.co.uk/animations/model.swf. http://www.kscience.co.uk/animations/ectopeptidase.swf. http://www.kscience.co.uk/animations/enzyme.swf http://www.youtube.com/watch?v=XTUm-75-PL4.
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In all metabolic activities of our body and cells, lots of small molecules called ENZYMES work.
If we destroy enzymes in the body, all reactions will slow down and stop.
Because enzymes reduce activation energy of the reactions.
The minimum amount of energy that is needed to start the reaction is called ‘ ACTIVATION ENERGY ’
Substance which is used to decrease the activation energy of a reaction is called ‘ CATALYSTS ’ . Enzyme is a catalyst which is found in living organisms ; It REDUCES the activation energy and makes reaction FAST and EASY
Heat can also decrease activation energy, but in cells heat can harm/denature molecules, so instead of heat enzymes speed up reactions.
Usually they are named as:
Enzyme that breaks down sucrose : SUCRASE
Enzyme that breaks down lipid : LIPASE
Sometimes they have special names .
For example : The enzyme that breaks down starch is called amylase.
STRUCTURE OF ENZYMES
COFACTOR( mineral )
Activated enzymeAPOENZYME + or
( HOLOENZYME ) COENZYME( vitamin )
1. Enzymes acts on their SUBSTRATES. A SUBSTRATE is the molecule that is affected by enzymes.
Enzyme+Substrate→ Enzyme-Substrate Complex → Enzyme + Products
Properties of enzymes:
1. Each enzyme has a specific substrate .
2. The site that binds to substrate is called as ACTIVE SITE . The relation between an enzyme and its substrate is called LOCK AND KEY MODEL
3. The enzyme isn’t SPENT during reaction(only used), So it can be used MANY TIMES. (never changed)
4. Reactions of Enzymes are Reversible.(not digestive ones)
Starch+ amylase enzymeglucose+ enzyme
5. Enzymes can’t work unless being water less than %15
6. Enzymes can work as a team. (ex.in digestion)
7. Enzymes are produced inside the cell but they can work inside OR outside of the cell.
8.Enzymes start their action from the outer surface of the substrate.
At lower temperature ;the reactions slows down or stops but as the temperature increases the rate of the reaction increases until optimum. But denatures after 60 C.
The factors that affect enzyme activity
Each enzyme works best at a certain pH ,that is called optimum pH.
( Ex: Optimum pH=2 in the stomach for digestion )
Enzymes are (denatured) broken down above or below the optimal pH.
1 2 3
Enzymes can’t work unless being water less than %15.
Ex : Dry plant seeds can’t germinate
Increasing the enzyme concentration increases the rate of reaction.
But after all substrate molecules are used and no change will be in the rate of reaction
If we increase the concentration of substrate, the rate of the reaction increases. But after all enzyme molecules are full, they can not change the rate of reaction.
increasing the surface area of substrate,increases the activity of enzymes
For example ; if we cut meat into pieces to make the surface bigger. Minced meat is digested easier than a piece of meat.
Some chemicals like Mercury (Hg) slows or completely stops the activity of enzymes . These molecules are inhibitors .
Some chemicals increase the activity of enzyme and they are called activators
Rate of the reaction
K + M N + O + M
By looking at the reaction above, answer the questions.
a. What kind of a reaction is I and II ?
b. Which of them is the enzyme?WHY?
c. Which of them is the product and substrate?
Fresh liver Liver grounded Liver boiled
pieces in mortar in water
2 ml of H202 solution is placed in each tube. Fresh , grounded and boiled liver are placed in the tubes as shown in the figure.
a. Write the reaction of equation?
b. Write the correct order of reaction rates from the fastest to the slowest ?
Explain the reasons