AQA Biology AS Unit 1 Revision Notes

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Biology Revision Notes

 

Biochemical Tests:

Proteins - add biurettes reagent to the sample. If protein is present, clear colour change from blue to purple.

Reducing Sugars – add Benedict’s reagent to the sample. Heat in Bunsen or water bath. If reducing sugars are present, clear colour changes from blue -> orange red precipitate.

Lipidsdissolve sample in ethanol. Slowly pour the solution into the water slowly. If lipids are present a white emulation forms on the surface.

Starchadd iodine solution to the sample. If starch is present clear colour change from orange red to blue black.

Non reducing sugars – do the reducing sugars test. Add Benedict's to the sample & heat. You get a negative result. Take a fresh sample and add heat with dilute acid. Bring to the boil. This hydrolyses it! Then, neutralise it with an alkali and test with pH paper. Add Benedict's and heat again. If non reducing sugars are present, clear colour change from blue to an orange red precipitate.

 

Enzymes

 

Enzymes are protein molecules that act as biological catalysts. An enzyme catalyses a specific reaction. They have an active site… Substrate ®ENZYME® Products. Maltose is broken down by the enzyme maltase to glucose and glucose. The reactions enzymes catalyse can be anabolic or catabolic - Anabolic meaning building, catabolic meaning breaking down. They do not die. They are simply denatured. They are affected by temperature, pH and concentration of enzyme and/or substrate. They can be affected by inhibitors. NON COMPETETIVE ARE THINGS THAT STICK IN THE SIDE. COMPETETIVE FIT IN ACTIVE SITE AND ARE COMPLIMETRY IN SHAPE

The structure of an enzyme

Enzyme molecules tend to be 100’s of amino acid long. They are named ‘globular proteins’. They are arranged with charged ‘R’ groups pointing outwards so they dissolve in water. They have a complex tertiary structure. One region of this is where the substrate fits. This is called the active site.

The active site is complimentary in shape to the substrate plus it is similar in charge too.

 How do they work?

 

Reactions need energy to proceed. To start the reaction, you need to add some energy at the start of the reaction, to ‘kick start’ it. But remember, don’t say that! This is named the activation energy. When an enzyme is catalysing a specific reaction, it lowers this activation energy, therefore speeding it up, or increasing the rate of reaction.

Theories of enzyme action

 

 The lock and key model:

This theory suggests that the substrate is able to fit into the active site like a key fits into a lock. It states that the active site is complimentary in shape to the substrate. The substrate then fits into the active site and binds forming an ENZYME SUBSTRATE COMPLEX.

The induced fit model:

 

This theory states that when the substrate molecule enters and binds to the active site, it causes the enzymes active site to alter slightly, improving the fit. The…

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