Biological Molecules & Transport in Cells

Enzymes

An enzyme is a biological catalyst

<<A catalyst is a substance which increases the speed of a reaction without being changed or used up in the reaction.<<

Enzymes have active sites

Substrates will bind to these active sites and form enzyme-substrate complexes

When enzymes are denatured, their active sites will change shape and the enzyme will no longer be able to form enzyme-substrate complexes

<<Enzymes have optimum conditions that can be affected by 3 factors<<

Temperature:

As temperature increases so does rate of reaction
Once the temperature has reached the optimum the rate of reaction will be at its maximum
After the optimum the rate of reaction will decrease because the enzymes are being denatured
When the rate of reaction is 0 all the enzymes have denatured

pH:

Enzymes can work best at different pH’s
Once the pH has reached the optimum the rate of reaction will be at its maximum
Before & after the optimum the rate of reaction will be low because the enzymes are being denatured (by extreme pH’s)
When the rate of reaction is 0 all the enzymes have denatured

Concentration:

As substrate concentration increases, so does the rate of reaction
At a certain point the rate of reaction plateaus even as substrate concentration increases
This is because all the active sites would be full

Investigating Enzymatic Reactions

CP2

Add a drop of iodine solution to each well of a spotting tile
Add amylase solution and a buffer solution with pH 5 into a boiling tube
Add the boiling tube to a water bath
Add starch solution to the boiling tube
Mix the contents of the boiling tube and start timing
Every thirty seconds drop some of the solution into a well
When the iodine solution no longer changes colour to blue/black the starch is no longer present
Repeat the experiment with different pH’s to find the optimum for amylase

Enzymes in Breakdown and Synthesis

<<Enzymes break down large insoluble molecules into small soluble ones.<<

Carbohydrase

Converts carbohydrates into simple sugars

E.g - Amylase converts starch into maltose

Protease

Converts proteins into amino acids

Lipase

Converts lipids into glycerol and fatty acids

<<Enzymes can also join molecules together to synthesise proteins, carbohydrates and other long chain molecules<<

Food Tests

Reducing sugars

Benedict’s solution
Water bath
Blue → Brick red

Starch

Iodine solution
Orange → blue/black

Protein

Biuret’s reagent
Blue → purple

Lipids

Ethanol emulsion
Add ethanol
Add water
If a milky white emulsion forms there are lipids

Calorimetry

Weigh a sample of food & skewer on a mounted needle
Add water to a boiling tube
Measure the initial temperature of the water
Set fire to the food using a bunsen burner & relight until the food no longer catches fire
Measure the temperature of the water again & calculate temperature change

<<Heat is lost to the surroundings so the energy calculated is lower than expected<<

Transport in Cells

<<Diffusion : the spreading out of particles from an area of high concentration to an area of low concentration<<

Diffusion is a passive process as it acts with the concentration gradient.

<<Osmosis : the net movement of water molecules across a partially permeable membrane from a high concentration of water to a lower concentration of water<<

Osmosis is a type of diffusion - but only for water molecules

<<Active Transport : the movement of particles against a concentration gradient (from a low to high concentration)<< Active transport requires energy from respiration

Investigating Osmosis in plant cells

CP3

Prepare sucrose solutions of different concentrations
Use a cork borer to cut a potato into same sized pieces
Divide cylinders into groups of three and use a mass balance to measure the mass of each group
Place one group in each solution
Leave the potatoes
Remove the cylinders after a set time and pat them dry gently with a paper towel - to remove excess water
Weigh the groups again and record the results