Enzymes

They are biological catalysts and globular proteins.
Each type of enzyme catalyses a specific reaction.

Enzymes can be re-used.

Metabolism consists of many enzyme reactions.

The reactions are either anabolic (builds up) or catabolic (breaks down).

To increase the rate of a reaction you could:

• Increase the temperature. (More kinetic energy = more collisions.
• Increase the concentration of reactants.
• Increase the surface area : volume ratio.
• Add a catalyst (like an enzyme).

All of these factors allow a larger number of successful collisions per unit time.

Enzyme/Substrate Complexes.

This is when a substrate combines with an enzyme. When more of these occur, the rate of reaction increases. In this complex, the chance of a reaction happening is larger than normal.

Collisions need to occur in a specific orientation for them to be successful. Enzymes have a specific shape which can "hold on" to the substrate and then changes its shape slightly to combine the two substances together in a specific orientation.

Activation Energy

This is the minimum amount of energy required for substrates to react. The higher the activation energy, the harder it is for the substrates to react. Enzymes lower the activation energy which makes it easier for reactions to occur. Enzymes don't change the energy level of a substrate.

Lock and Key (Fischer 1890)

The substrate binds into the enzyme's active site (3-12 amino acids) and the shape of the active site fits the substrate, so they are complementary. The shape of the enzyme is dependent on the specific R groups of the amino acids. These may bond with the substrate.

Induced Fit (Koshland 1959)

The substrate causes a change in the shape of the enzyme, and the amino acids in the active site form a specific arrangement for the enzyme to carry out its catalytic function.

Measuring Enzyme Activity

To measure enzyme activity, you can use the amount of substrate used against time or the amount of product made in time. Being measured over time, it identifies the changes in the rate of reaction. To measure the activity, the initial rate of reaction needs to be calculated.

Enzyme activity is affected by:

• Temperature
• Enzyme Concentration
• Substrate Concentration
• pH

Temperature
The optimum temperature on this graph is 40 ˚C

When you increase the temperature, there is more kinetic energy so there are more successful collisions per unit time. This means more enzyme/substrate complexes.

When the temperature goes past it's optimum point, there is still more kinetic energy, but H bonds break as well as other bonds causing the enzyme to lose it's shape, becoming denatured.

Enzyme Concentration

More enzymes = more collisions per unit time.

This means more enzyme/substrate complexes

It reaches a maximum rate of reaction because of limiting factors. In this case, the concentration of the substrate.

Substrate Concentration

More substrate = more collisions per unit time.

This means more enzyme/substrate complexes which means a faster rate of reaction.

It reaches a maximum rate because of limiting factors. In this case, the concentration of enzymes. Active sites are saturated with substrates so the reaction can't occur any faster.

pH

Above or below the optimum pH, the enzyme loses it's shape and denatures. This is because ionic bonds break due to changes in pH.

Denatured enzymes mean no enzyme/substrate complexes which lowers the rate of reaction dramatically.

The Practical Write Up

Hello 12B :o)

Hope you are all getting on well with the practical write up, you all carried out the experiment exceptionally well regardless of whether or not it worked! Remember graphs, conclusions and evaluations!! Enjoy!

Friday 17th October

Amino Acids

R- group changes to make all the different amino acids

carboxyl group makes it acidic

amine group is the base and it accpets H+ ions

amphoteric - has both acidic and basic properties

they act as pH buffers, they regulate the pH by changing their charge

isoelectric point - ph at which the charge on amino acids is neutral

R-group determines the properties

1.2nd amino group (positively charged, basic)

2. 2nd carboxyl group (negatively charged, acidic)

3. simple hydrocarbon chain (hydrophobic, non-polar)

4. polar hydrocarbon chain (hydorphylic)

protein is determined by the 3D shape

joined together by peptide bonds - requires an enzyme and energy

ionic bond - between charged R-groups

disulphide bond - only between the sulphyl groups of 2 cysteine amino acids

hydrogen bond

Protein Structure

1.Primary (peptide bonds)

2.Secondary (hydrogen bonds)

3.Tertiary (hydrophylic amino acids, hydrogen/ionic/disulphide bonds)

4.Quaternary

Fibrous protein - long chains, strong

Globular protein - irregular structure

Common Assessment One Test

One way in which I would like you to use this blog is to help you be reflective learners. I would like your comments about your test result and what actions you are going to take to help your progress in the subject.

The class average mark was 18/28 (64%)

Think about the following questions:

1) How much background reading have you done to support your lesson notes?
2) How much revision did you do for the test?
3) Did you find it difficult to recall facts, demonstrate understanding or apply your understanding to a new situation?
4) Have you underestimated the challenge and expectations of A Level?

Sharing your comments and ideas on this blog will help each other! I look forward to your comments.

Welcome to your blog

Hello everybody.

I thought it might be useful and fun to have a class blog.

Here we can keep a diary of what we have learnt and I hope to use it for your learning in the future.

If you have any ideas, hints, help, links then post them here, share them with the class. If you want to have a moan, complain, share your worries about the course then post them here (but try to be constructive)

I'll introduce the blog in a lesson soon.