2c Biological Molecules

Question 1

What is the test for starch?

Answer 1

1) Place food sample in a dimple dish
2) Using a pipette add 2 or 3 drops of dilute iodine to the food
If a blue-black colour develops, starch is present

Question 2

What is the test for glucose?

Answer 2

1) If the food is not already in a liquid form, place a sample (1cm3) into a test tube
2) Add about 2cm3 of distilled water into the test tube
3) Add about 1cm3 of Benedict’s solution to the test tube and shake to mix
4) Using a test tube holder put the test tube in a hot water bath and place for 2 mins

If glucose is present then it will turn green, then yellow and then orange. A red brown precipitate will form if lots of glucose is present.

Question 3

What is the test for protein?

Answer 3

1) If the food is not already in a liquid form, place a sample 1cm3 into a test tube
2) Add about 2cm3 of the distilled water into a test tube to make a suspension
3) Add a little sodium or potassium hydroxide until the solution clears
4) Add a few drops of dilute copper sulfate solution and shake

If the solution goes purple then protein is present

Question 4

What is the test for fat?

Answer 4

1) Place a small sample of solid food (1cm3) into a test tube
2) Measure 3cm3 of ethanol and pour into the test tube
3) Gently shake the tube and leave to stand for 1 minute
4) Measure 3cm3 of water and pour into a new test tube
5) Decant the ethanol into the second test tube of water
6) Record observations

Question 5

What is the order for digestion?

Answer 5

Mouth - Mixes with saliva mechanical digestion

Oesophagus - peristalsis
Stomach - gets mixed with stomach acids
Small intestine - villi, nutrients are absorbed into the bloodstream
Large intestine - water is then absorbed
Rectum - The feces is stored there
Anus - Where the feces come out

Question 6

What is a polymer?

Answer 6

Long chained molecule made up of lots (poly) small units called monomer

Question 7

What is a monomer?

Answer 7

Is one/single (mono) come together to make a polymer

Question 8

What is a primary protein?

Answer 8

Amino acids can join together to make simple polymers e.g.. in a single chain. They’re called primary proteins - simplest types of proteins

Question 9

What is a secondary protein?

Answer 9

The amino acids can also fold together to make a slightly more complicated structure, might make a simple bond with another amino acid, twisted chain. They’re called secondary proteins

Question 10

What is a tertiary protein?

Answer 10

Some amino acids can form really complex structures (3D). They’re called tertiary proteins

Question 11

How many essential amino acids are there and what are they?

Answer 11

Nine essential amino acids
Histidine
Isoleucine
Leucine
Lysine
Methionine
Phenylalanine
Threonine
Tryptophan
Valine

Question 12

What are some factors that affect enzyme activity?

Answer 12

High temperatures and pH levels

Question 13

How do high temperatures affect enzyme activity?

Answer 13

• Raising temperatures generally speeds up a reaction and lowering temperatures slows down a reaction
• Extremely high temperatures can cause an enzyme to lose its shape (denature) and stop working
• As temperature increases to the optimum, the kinetic energy of the enzyme and substrate increases, causing more collisions between enzyme and substrate
• When the active site becomes denatured it means the active sight loses its important shape and can no longer form enzyme-substrate complexes, leading to a decrease in enzyme activity
• Denaturation is a permanent change
• Some enzymes (e.g in biological washing powders are thermostable, meaning they can work at a wide range of temperatures

Question 14

How does pH level affect enzyme activity?

Answer 14

• Enzyme activity has an optimum pH level
• If the pH is very acidic or alkaline the pH changes the shape of the enzyme so that it no longer works
• This effect is called denaturation and can be irreversible
• Each enzyme has an optimum pH, but also a working range of pH values, depending on the type of enzyme
• The working range of pH will work but not as well

Question 15

How do enzymes work?

Answer 15

• Enzymes are biological catalysts because they are made out of proteins
• They are complicated structures because the amino acids in the chain are folded and long around each other
• Enzymes (all catalysts) speed up chemical reactions
• Adding a catalyst lowers the activation energy of a reaction
• The activation energy is the minimum amount of energy the reactants have to have before they can collide to form products
• Lowering the activation energy makes the reaction faster
• Adding a catalyst provides an alternative and quicker pathway for the reaction to take
• A catalyst does not get used up in a reaction
• Enzymes are specific. This means they will only catalyse one reaction because of their structure