Edexcel IGCSE Biology - Biological Molecules

are carbohydrates monomers or polymers?

polymers

what types of carbohydrate are there?

glycogen, starch, sucrose

what are carbohydrate monomers?

simple sugars

what types of carbohydrate monomers are there?

glucose, fructose, ribose

what elements are carbohydrates made up of?

carbon, hydrogen, oxygen

are proteins polymers or monomers?

polymers

what monomers make up proteins?

amino acids

what elements make up proteins?

carbon, hydrogen, oxygen, nitrogen

are lipids polymers?

no

what elements make up lipids?

carbon, hydrogen, oxygen

what sub-units make up lipids?

fatty acids and glycerol

what is an enzyme?

a biological catalyst, present in metabolic reactions

what kind of biological molecules are enzymes?

proteins

what is the molecule that is changed in a chemical reaction called?

substrate

what is the part of the enzyme where the substrate joins to it called?

active site

what feature of the active site is very important?

its unique shape - each enzyme can normally only catalyse one type of reaction

what model is used to describe enzyme-substrate reactions?

lock and key model

what is the lock and key model composed of?

• lock - enzyme

• key - substrate

• combine to form enzyme-substrate complex

what aspect of enzymes does the lock-and-key model stress?

the fact that the active site of the enzyme must be complementary to the substrate for the reaction to take place

which factors affect enzymes + rate of reaction?

• temperature

• pH

• substrate concentration

• enzyme concentration

how does enzyme concentration affect rate of reaction?

• directly proportional relationship

• as long as the substrate concentration is constant, the ROR will increase proportionally as more active sites become available, as long as sufficient substrates are available - stops when something else is limiting factor

how does substrate concentration affect rate of reaction?

• directly proportional relationship

• increasing concentration increases rate of reaction because there are more particles available to collide with active sites so more enzyme-substrate complexes are formed

• at some point, it will stop increasing ROR as something else becomes the limiting factor like enzyme concentration

how does temperature affect enzyme rate of reaction?

• as temperature increases to the optimum, rate of reaction increases as particles have more kinetic energy and so collide more frequently forming more complexes

• as temperature increases past the optimum, rate of reaction increases as enzymes begin to denature, meaning their active sites disfigure and so a complex cannot form - this is irreversible

• at low temperatures, enzymes do not have much kinetic energy so rate also decreases

how does pH affect the rate of reaction?

• as pH increases or decreases to the optimum, rate of reaction increases as the active site becomes more complementary to the substrate

• as pH increases or decreases (too high/low) past the optimum, rate of reaction increases as enzymes begin to denature, meaning their active sites disfigure and so a complex cannot form - this is irreversible

describe how to perform an experiment to investigate how enzyme activity is altered by temperature by measuring how fast a product appears

1. the enzyme catalase catalyses the breakdown of hydrogen peroxide into water and oxygen.

2. You can collect the oxygen and measure how much is produced in a set time

3. use a pipette to add a set amount of hydrogen peroxide to a boiling tube

4. put it in a water bath at 10C

5. set up the apparatus with an upturned measuring cylinder with a delivery tube going into it attached to the test tube, in a trough of water - record starting water volume

6. add a source of catalase - potato - to the hydrogen peroxide and attach the bung quickly

7. record how much oxygen is produced in the first minute, repeat 3x and calculate mean

8. repeat at 20,30,40,50 degrees

9. control variables

describe how to perform an experiment to investigate how enzyme activity is altered by temperature by measuring how fast a substrate disappears

1. amylase catalyses the breakdown of starch to maltose

2. starch can be detected using iodine solution: orange → blue-black

3. set up a spotting tile with a drop of iodine solution in each dimple

4. add some amylase to some starch solution and place in a water bath at 10C

5. start a timer and place a drop of solution in the spotting tile every 10 secs until the solution stops changing colour - remains orange - stop the timer

6. repeat with different temperatures

how would you alter the temperature-enzyme activity experiments to measure the effect of pH?

instead of using water baths at different temperatures, add different pH buffer solutions to the test tubes