KEGS Biology Blog


Wednesday 14th November Section 2
November 15, 2012, 9:44 am
Filed under: Uncategorized

Enzymes

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In todays lesson we learnt how various factors can affect an enzymes rate of reaction, whether this be due to unsuitable conditions, sometimes known as denaturing, or factors limiting it in terms of a lack of materials.

Enzymes and the rate at which they convert substrates to products is very important, especially inside us humans. An example of why enzymes are so important in catalysing reactions is urease. It has been calculated that the enzyme urease can break down in one second an amount of urea that would otherwise take 3 million years to be broken down without the presence of the enzyme.

The four factors which concern us that limit or stop an enzyme from working are:
-Temperature
-pH
-Concentration of substrate
-Concentration of enzyme

Temperature:
Each enzyme has it’s own optimum temperature, so for example the enzymes within humans have an optimum temperature of around 37 degrees celsius although other enzymes may have optimum temperatures up to 90 degrees celsius and more. As the temperature increases so does the rate of reaction, to an extent, because the enzyme molecules along with the substrate’s move around quicker and so there’s a higher chance of a random collision. However, should the temperature get too high the enzymes will start to vibrate which causes stress on the bonds holding the protein together and will result in what is known as denaturing of the enzyme, in which the bonds within the tertiary strucure break and the active site changes shape. The same does not apply for lowering the temperature below the optimum, which only slows the rate of reaction as the enzymes move around less, but does not cause denaturation.

pH:
pH is the measure of hydrogen ions and is measured in a range of 1-14. The higher the concentration of hydrogen, or H the lower the pH (acidic), and the lower the concentration of H the higher the pH (alkaline). Similarly to temperature, all enzymes have their own optimum pH with only a narrow range either side in which they can operate.Altering of the pH levels slightly affects the rate of reaction because the charged ions alter the shape of the active site.

Increasing the substrate concentration:
The substrate concentration directly affects the rate of reaction of the enzymes because without any substrate, enzyme-substrate complexes cannot form.As the level of substrates is increase so does the rate of reaction up until the substrate ceases to be the limiting factor and instead the enzyme is. This is because the reaction reaches a rate where all the enzymes are working at full rate and all the active sites are occupied .

Increasing the enzyme concentration:
As the number of enzymes increase the number of active sites obviously does aswell. This of course means that more enzyme-substrate complexes are formed and therefore more products, increasing the rate of reaction. Increasing the levels of enzymes will eventually cause you to reach a point where all of the substrate molecules are being catalysed by enzymes and so a maximum rate has been reached.

Key words:
Temperature
pH
Enzyme
Enzyme-substrate complex
Active site
Denaturation
Substrate concentration
Enzyme concentration
Limiting factors
Rate of reaction
Random collisions

Thank you to the websites from which the graphs are sourced.

Comment by elliswhyte

Here are 2 links for good websites about enzymes and their limiting factors:

http://www.s-cool.co.uk/a-level/biology/biological-molecules-and-enzymes/revise-it/enzymes

http://alevelnotes.com/Factors-affecting-Enzyme-Activity/146

Comment by sarahroche12

Youtube video on the factors affecting enzymes:

Comment by meganbpotter




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