1.1 & 1.2 - Carbohydrates & lipids

What are the four types of organic molecules found in living organisms?

• Carbohydrates

• Lipids

• Proteins

• Nucleic acids (DNA)

What elements do carbohydrates only contain?

Carbon, hydrogen & oxygen

• (they are polar)

What are 3 examples of monosaccharides?

• Glucose

• Fructose

• Galactose

What are 3 examples of disaccharides?

• Sucrose

• Maltose

• Lactose

What are 3 examples of polysaccharides?

• Starch

• Cellulose

• Glycogen

What is the definition of a monosaccharide?

An organic monomer that cannot be hydrolysed to a simpler sugar

Draw the structure of alpha glucose

Draw the structure of beta glucose

Draw the structure of the pentose, ribose

What is a condensation reaction?

Joining two molecules together, creating a chemical bond & removing a molecule of water

How to work out how many bonds are required to join monomers together in a condensation reaction?

If there are ‘n’ number of monomers, then the number of bonds required to join the monomers together is ‘n-1’

Draw the condensation reaction to form maltose

How are disaccharides formed?

When two monosaccharides are joined together by a glycosidic bond via a condensation reaction

What is the reverse process of a condensation reaction?

Hydrolysis reaction: breaking a chemical bond between two molecules using water

How is maltose formed?

Glucose + glucose → maltose + water

How is sucrose formed?

Glucose + fructose → sucrose + water

How is lactose formed?

Glucose + galactose → lactose + water

What are polysaccharides?

Chains of many monosaccharides joined together by glycosidic bonds

What is starch?

• Plant storage polysaccharide

• Insoluble & forms starch granules inside many plant cells

• Mixture of amylose & amylopectin

What is the difference between amylose & amylopectin?

Amylose:

• 1,4 glycosidic bonds

• long glucose chain that coils up into a helix held together by hydrogen bonds

Amylopectin:

• 1,4 & 1,6 glycosidic bonds

• highly branched, so can be broken down (hydrolysed) quicker than amylose by amylase enzymes

  • how to remember → think amyloPECtin = chicken pecking to hydrolyse quickly

What is glycogen?

• The animal storage polysaccharide, mainly found in muscle & liver cells

• Contains 1,4 & 1,6 glycosidic bonds

• Highly branched, so can be broken down (hydrolysed) into glucose very quickly for energy

What is cellulose?

• Only found in plants & is the main component of cell walls

• Contains 1,4 glycosidic bonds & beta-glucose molecules → alternate glucose molecules are flipped

  • (starch & glycogen only contain alpha-glucose)

What is the structure of cellulose?

• Beta-glucose bond is rigid, so cellulose molecules form straight chains

• Hundreds of these chains are linked together by hydrogen bonds between the chains to form cellulose microfibrils

• These microfibrils are very strong & rigid, giving strength to plant cell walls

What elements do lipids contain & what are the most common?

• Carbon, hydrogen, oxygen & sometimes phosphorus

• Most common lipids are triglycerides & phospholipids

How are triglycerides formed?

Condensation reaction between 1 molecule of glycerol & 3 fatty acid molecules, joined by ester bonds → results in 3 water molecules

• (they are non-polar)

What are the purposes of triglycerides?

• Energy storage: due to large ratio of energy-storing hydrocarbon bonds

• Insulation: fatty tissue under the skin is used to insulate warm-blooded mammals against heat loss

• Waterproofing: mammals’ fur & birds’ feathers contain the lipid lanolin for waterproofing → plants have a lipid waxy cuticle to reduce water loss

What is the difference between a saturated & unsaturated fatty acid?

Saturated fatty acid:

• fatty acid chains in a triglyceride have no C=C double bond

• tend to be found in warm-blooded animals

• high melting point & solid at room temperature

Unsaturated fatty acid:

• fatty acid chain in a triglyceride do have C=C double bond

• tend to be found in cold-blooded animals & plants

• low melting point & liquid at room temperature

How do phospholipids differ from triglycerides?

Phospholipids have a glycerol attached to 2 fatty acids & 1 phosphate attached to the glycerol

What is the function of phospholipids?

Main components of cell membranes:

• when mixed with water, they form a phospholipid bilayer

• the hydrophilic, polar phosphate heads interact with the water & the hydrophobic, non-polar fatty acid tails face inwards towards each other

What is the biochemical test for reducing sugars?

Benedict’s test:

• add Benedict's reagent to the sample & heat on a Bunsen burner/water bath

• if reducing sugars are present, the sample will change from blue to brick red precipitate

What is the biochemical test for lipids?

Emulsion test:

• add ethanol to the sample, shake & pour into water

• if lipids are present, a cloudy, white emulsion will form on the surface

What is the biochemical test for starch?

Iodine test:

• add iodine solution to the sample

• if starch is present, the solution will immediately change from orange/brown to blue/black colour

What is the biochemical test non-reducing sugars (e.g. sucrose) ?

1. Test for reducing sugars first, using Benedict’s test → result will be negative

2. Take a fresh sample & heat with dilute HCl

3. Neutralise with sodium hydrogencarbonate (check against pH paper). Add Benedict's reagent & heat again

4. If non-reducing sugars are present, the solution will change from blue to brick red precipitate

What is the biochemical test for proteins?

Biuret test:

• add few drops of sodium/potassium hydroxide, then add copper sulphate

• if proteins are present, solution will change from blue to purple