Enzymes
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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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Enzymes

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Enzymes

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


Enzymes

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?

Timeline:

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


Enzymes

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

Enzymes, substrates and active sites

Substrate: reactant in a biochemical reaction.

Enzyme: globular protein which acts as a catalyst for biochemical reactions.

Polar regions of amino acids attract substrate & active site of the enzyme.

Active site: region on the surface of an enzyme to which substrates bind and which catalyzes the reactions.

Once a substrate has been locked into the active site, the reaction is catalyzed.

The products are released and the enzyme is used again. It is NOT consumed in the reaction.

http://i-biology.net/


Enzymes

http://www.northland.cc.mn.us/biology/biology1111/animations/enzyme.swf

http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/


Enzymes

Enzymes are specific to their substrate!

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

Structurally – the 3D structure of the active site will only fit the substrate. No fit, no Rxn.

Chemically – substrates that are not chemically attracted to the active site won’t be able to react.

http://www.youtube.com/watch?v=AKyyvuOmXq0

http://i-biology.net/


Enzymes

The induced –fit model better explains enzyme activity

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

As the substrate approaches the enzyme, it induces a conformational change in the active site- it changes shape to fit the substrate.

This stresses the substrate, reducing the activation energy of the reaction.

Conformational

change

Enzyme reverts

to original shape

http://www.stolaf.edu/people/giannini/flashanimat/enzymes/enzyme.swf


Enzymes

Enzymes lower the activation energy of a reaction!!

http://www.biology.arizona.edu/biochemistry/problem_sets/energy_enzymes_catalysis/01t.html

Activation energy is the amount of energy that must be put into a reaction to make it occur. Click on the graph to link to the Univ. of Arizona site.


Enzymes

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

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


Enzymes

Denaturation

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.

http://highered.mcgraw-hill.com/sites/0072943696/student_view0/chapter2/animation__protein_denaturation.html


Enzymes

Denaturation

  • High temperatures cause denaturation as the extra energy leads to increased vibration, breaking intra-molecular bonds.

  • Changes in pH cause denaturation as hydrogen bonds are broken.

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

http://www.youtube.com/watch?v=3IL_Df5ouUc


Enzymes

Factors affecting enzyme activity:

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

Temperature

pH

Substrate

concentration

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

http://www.kscience.co.uk/animations/model.swf


Enzymes

The Effect of Temperature on Enzyme Activity

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.


Enzymes

The Effect of Temperature on Enzyme Activity

Try this virtual lab:


Enzymes

The Effect of Temperature on Enzyme Activity

Enzymes only operate within a narrow pH range. This is called the optimum pH.

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 result is the loss of shape of the active site of the enzyme, so it does not function. This is usually a permanent change.


Enzymes

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


Enzymes

The effect of substrate concentration on enzyme activity

At the optimum concentration of substrate molecules, all active sites are full and working at maximum efficiency.

Increasing substrate concentration

increases the rate of reaction

Any increase in concentration beyond the optimum will nave no added effect as there are no extra active sites to be used.


Enzymes

Lactose

intolerance

http://i-biology.net/

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!

http://www.cartoonstock.com/directory/l/lactose.asp


Enzymes

Most people produce 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.


Enzymes

How do those who are lactose intolerance cope?

Take a lactase supplement – these are produced from a fungus called Aspergillusniger

Drink lactose free milk – milk treated with lactase (produced by A. niger)

  • 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


Enzymes

Try this: by changing just one letter at a time, get from ‘Tread’ to ‘Blink’. All intermediates must be real English words.


Enzymes

Metabolic pathways* are chains of enzyme catalyzed reactions. The product of one reaction is a reactant in the next.

*or biochemical pathways

Initial substrate

Intermediates

End

product

http://highered.mcgraw-hill.com/sites/0072943696/student_view0/chapter2/animation__a_biochemical_pathway.html


Enzymes

http://www.footprints-science.co.uk/Bloodclotting.htm


Enzymes

The Krebs Cycle (cell respiration) and Calvin Cycle (photosynthesis) are examples of enzyme catalyzed, metabolic pathways.

http://www.sparknotes.com/health/carbohydrates/section3.rhtml

http://library.thinkquest.org/C004535/calvin_cycle.html


Enzymes

Enzymes can be inhibited by other molecules

Inhibition can be competitive or non-competitive

Won’t

Fit!

Blocked!

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


Enzymes

Competitive Inhibition

A competitive inhibitor blocks the active site, preventing the substrate from entering.

The higher the concentration of inhibitor, the slower the rate of reaction

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.


Enzymes

Overcoming alcoholism: 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.


Enzymes

Non-competitive Inhibition – inhibitors bind to an allosteric (other) site on the enzyme. This binding alters the active enzyme site and substrates can no longer bind.

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


Enzymes

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

http://www.stolaf.edu/people/giannini/flashanimat/enzymes/allosteric.swf


Enzymes

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

http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120070/bio10.swf::


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