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Enzymes. Topic 3.6 and AHL 7.6. http://www.livingscience.co.uk/joomla/index.php?option=com_content&view=article&id=57:enzymes&catid=42:enzymes&Itemid=54. I.A. Investigation: Factors affecting enzyme activity investigations.

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Topic 3.6 and AHL 7.6


I.A. Investigation:

Factors affecting enzyme activity investigations

You will be looking at the decomposition of H2O2 by catalase in yeast. How could you get catalase? What is catalase?


Two periods to investigate different lab protocols.

Your ORIGINAL lab design will be due the following day.

Class period to work on lab design with students using a similar design (I’ll explain).

Two lab periods for YOUR INDIVIDUAL data collection.

Due one week later

This is how you will be graded.

Remember to use the report format you have used before.

I’ll put a link here to it in the future on the website I haven’t set up.



Enzymes are http://www.northland.cc.mn.us/biology/biology1111/animations/enzyme.swfspecific to their substrate!

The Lock-and Key hypothesis: the substrate and the active site match each other in two ways:



The induced –fit model better explains enzyme activityhttp://www.northland.cc.mn.us/biology/biology1111/animations/enzyme.swf

If the lock-and-key model were true, one enzyme would only catalyze one reaction. In reality, some enzymes can catalyze multiple reactions.



Enzyme reverts

to original shape


Enzymes lower the activation energy of a reaction!!http://www.northland.cc.mn.us/biology/biology1111/animations/enzyme.swf



An enzyme stresses the bonds in the substrates, reducing the activation energy required for a reaction to occur.


Enzymes are globular proteins. Their structure can be altered by changes in pH or temperature – if the shape of the active site is changed substantially, they will not function.



  • Both methods result in an altered 3D structure of the active site, and this change is irreversible.


Factors affecting enzyme activity:http://www.stolaf.edu/people/giannini/flashanimat/enzymes/transition%20state.swf

Use this animation to test the affect of the following factors on enzyme activity:





When you have finished this, complete the enzyme activity sheet.


The Effect of Temperature on Enzyme Activityhttp://www.stolaf.edu/people/giannini/flashanimat/enzymes/transition%20state.swf

As temperature increases, rate of reaction increases as molecules have more energy, move faster and therefore collide and react more frequently.

Above optimal temperature any more increase denatures the protein. The active site changes, and the enzyme is non-functional.

A thermophile, such as bacteria in boiling pools (think Yellowstone National Park) can withstand MUCH higher temps before it denatures.

The Effect of Temperature on Enzyme Activityhttp://www.stolaf.edu/people/giannini/flashanimat/enzymes/transition%20state.swf

Try this virtual lab:

The Effect of Temperature on Enzyme Activityhttp://www.stolaf.edu/people/giannini/flashanimat/enzymes/transition%20state.swf

Look at this example of two digestive enzymes. If there is a deviation from the optimum pH, the hydrogen bonds between the amino acids in the structure of the enzyme are broken.


The effect of substrate concentration on enzyme activityhttp://users.rcn.com/jkimball.ma.ultranet/BiologyPages/D/DenaturingProtein.html




Lactose (milk sugar) can cause allergies in some people. This is usually because they can’t produce the enzyme lactase in quantity.

No ice cream for YOU!


Most people http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/D/DenaturingProtein.htmlproduce less lactase as they get older. Think about it…we don’t live off milk after we are weaned from mom. In some regions, such as Europe, a mutation has allowed lactase production to continue into adulthood. Those who are lactose intolerant don’t have this mutation.

How do those who are lactose intolerance cope?http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/D/DenaturingProtein.html

  • Lactose-free milk is made by different methods:

  • Add lactase to milk

  • Run milk though apparatus with immobilize lactase. Uses alginate beads, no enzyme in final product.

A. niger

Try this: by http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/D/DenaturingProtein.htmlchanging just one letter at a time, get from ‘Tread’ to ‘Blink’. All intermediates must be real English words.

Metabolic pathways* http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/D/DenaturingProtein.htmlare chains of enzyme catalyzed reactions. The product of one reaction is a reactant in the next.

*or biochemical pathways

Initial substrate






The http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/D/DenaturingProtein.htmlKrebs Cycle (cell respiration) and Calvin Cycle (photosynthesis) are examples of enzyme catalyzed, metabolic pathways.



Enzymes can be http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/D/DenaturingProtein.htmlinhibited by other molecules

Inhibition can be competitive or non-competitive




Inhibitor fits into the allosteric site* causing a conformational change in the active site. The substrate cannot attach to react.

Inhibitor fits the active site and prevents the substrate from entering.

*allosteric site = Other site

Competitive Inhibitionhttp://users.rcn.com/jkimball.ma.ultranet/BiologyPages/D/DenaturingProtein.html

Even with competitive inhibition, the same maximum rate of reaction will be achieved if more substrate is added because we have not change the number of enzymes available.

Overcoming alcoholismhttp://users.rcn.com/jkimball.ma.ultranet/BiologyPages/D/DenaturingProtein.html: An example of competitive inhibition

Normal metabolism of ethanol (alcohol):

Antabuse (disulfiram) competes with the aldehyde oxidase and prevents the acetaldehyde from being converted to acetic acid.

A build up a acetaldehyde follows, resulting in a strong feeling of nausea and other hang over symptoms. A great deterrent from drinking!!

Antabuse is administered as a daily pill, so how well it works depends on how much a person is motivated! If they stop taking it they can drink again.

As the concentration of inhibitor increases, the rate of reaction decreases, because there are fewer active sites available for the reaction.

Let’s take a look at how non-competitive inhibition would look.


Let’s take a look at how inhibition disturbs the final product of biochemical pathways.