Carbs & Lipids

Question 1

Monomer Definiton

Answer 1

Monomers are small identical or similar molecules which can be condensed to make polymers

Question 2

Polymer Defintion

Answer 2

Polymers are large molecules made from joining many identical or similar monomers together.

Question 3

Condensation reaction

Answer 3

joins two monomer units together with the removal of one water molecule.

Question 4

Hydrolysis reaction

Answer 4

adding one molecule of water to break the bond between two monomers.

Question 5

Types of monomers and polymers

Answer 5

Monomer, Polymer, Bond, Example

Monosaccharides e.g. α glucose, Disaccharides, Glycosidic Maltose, Lactose

Monosaccharides e.g. α/β glucose, Polysaccharides, Glycosidic Starch, glycogen, cellulose

Amino acids, Polypeptide or protein, Peptide, haemoglobin

Nucleotides,Nucleic acids, Phosphodiester DNA, RNA

Question 6

Monosaccharides

Answer 6

Glucose (alpha)
Galactose
Fructose

Question 7

Forming Disaccharides

Answer 7

Glucose+Glucose→Maltose (enzyme=maltase)

Galactose+Glucose→Lactose (enzyme=lactase)

Glucose+Fructose→Sucrose (enzyme=sucrase)

Question 8

Describe how lactose is formed and where in the cell it would be attached to a polypeptide to form a glycoprotein

Answer 8

• Glucose and galactose
• Joined by condensation
• Joined by glycosidic bond
• Added to polypeptide in Golgi

Question 9

Starch

Answer 9

• energy storage in plants
• amylase= helical
• amylopectin= branched
• insoluble
• a (1-4)(1-6) glycosidic bonds
• large surface area- Does not diffuse out of cells

Question 10

Cellulose

Answer 10

• cell wall structure in plants
• long, straight, unbranched chains
• insoluble
• B (1-4) glycosidic bonds
• many weak hydrogen bonds cross linked
• chains form microfibrils
• provides strength/ rigidity

Question 11

Glycogen

Answer 11

• energy storage in animals
• highly branched
• shorter chains
• insoluble
• a (1-4)(1-6) glycosidic bonds

Question 12

A starch molecule has a spiral shape. Explain why this shape is important to its function in cells

Answer 12

Compact

Question 13

Give one feature of starch and explain how this feature enables it to act as a storage
substance.

Answer 13

• Helical So compact
• Branched chains So rapid hydrolysis to remove glucose for respiration

Question 14

Describe how the student would show that reducing sugars were present in a solution.

Answer 14

1. Add equal volumes of Benedict’s solution;
2. Heat to 95 ⁰C;
3. Red precipitate (shows reducing sugar present);

Question 15

A student carried out the Benedict’s test. Suggest a method, other than using a colorimeter, that this student could use to measure the quantity of reducing sugar in a solution.

Answer 15

Filter
Dry
Weigh

Question 16

Describe how the student would show that a non-reducing sugar was present in a solution

Answer 16

1. Complete Benedict’s test and observe negative result
2. Add acid to sugar solution. Heat to 95℃
3. Neutralise with alkali
4. Add equal volume Benedict’s
5. Heat again to 95℃
6. Red ppt
   - only for sucrose

Question 17

Producing a calibration curve

Answer 17

1. Make up several known concentrations of maltose/glucose/lactose/galactose/ fructose;
2. Carry out the Benedict’s test on each sample;
3. Use a colorimeter to measure the colour of each solution and plot a calibration curve; Conc on X axis and absorbance on Y.
4. Find the concentration of the unknown sample using the calibration curve;

Question 18

Describe how you would test a sample of food for the presence of starch

Answer 18

1. Add potassium iodide solution to the food sample;
2. Blue/black indicates starch is present;

Question 19

Amylase test

Answer 19

1. Add biuret (reagent) and becomes purple
2. Add starch, test for reducing sugar

Question 20

Describe how you would test a liquid sample for the presence of lipid box and how you would recognise a positive result.

Answer 20

1. Crush
2. Mix with ethanol and shake
3. Add water and shake
4. forms cloudy white emulsion

Question 21

Lipid Formation

Answer 21

Lipids are formed by joining three fatty acid molecules to a glycerol molecule by condensation reactions, forming Ester bonds.

Question 22

Triglyceride Formation

Answer 22

one molecule of glycerol joined by Ester bonds to three fatty acids.

Question 23

Saturated Vs Unsaturated Fatty Acid

Answer 23

Saturated fatty acids do not have any double bonds between carbons within the hydrocarbon chain.

Unsaturated fatty acids do have double bonds between the carbon atoms within the hydrocarbon chain.

Question 24

Describe how an ester bond is formed in a phospholipid molecule.

Answer 24

1. Condensation (reaction)
2. Between glycerol and fatty acid;

Question 25

What are the differences between a triglyceride and a phospholipid?

Answer 25

1. Fatty acid removed;
2. Replaced with a phosphate group;

Question 26

Compare and contrast the structure and properties of triglycerides and phospholipids

Answer 26

• Both contain ester bonds
• Both contain glycerol
• Both are insoluble in water
• Both contain C, H and O but phospholipids are also contain P
• Triglyceride has three fatty acids and phospholipids have two fatty acids plus phosphate group
• Triglycerides are hydrophobic/non-polar and phospholipids have hydrophilic and hydrophobic region
• Phospholipids form bilayer but triglycerides don’t.