B1.1 Carbohydrates and Lipids

What are the 3 functions of carbohydrates?

• Energy source – released from glucose during respiration

• Energy store – e.g. starch & glycogen

• Structural – cellulose

What are monosaccharides and what are their properties?

• ‘Monomers’ of carbohydrates
  

All monosaccharides have similar properties:

• Soluble in water - why is this useful in living organisms?

• Sweet tasting

• Form crystals

• Chemically stable

• Yields high levels of energy when broken down - what important reaction uses glucose as a reactant?

Draw Alpha and Beta glucose.

Disaccharide properties:

• Soluble

• Sweet tasting

• Form crystals

Examples of disacharides

• Glucose + glucose = maltose

• Glucose + fructose = sucrose

• Glucose + galactose = lactose

What is a condensation reaction?

• Condensation reaction: two molecules are linked together and a water molecule is released. 

• Water is formed by removing a hydroxyl group (-OH) from one molecule and a hydrogen (-H) from the other. A bond is formed between the molecules as water is released. 

• Requires energy from ATP.

Formation of disaccharides (bonds)

• Formed when two monosaccharides are joined together by a glycosidic bond (covalent). 

• The reaction involves the formation of a water molecule (H₂O)

• The glycosidic bond forms at carbon 1 of the first glucose molecule, and carbon 4 of the second - called α -1,4 glycosidic bond.

• Many of these 1-4 glycosidic bonds results in an unbranched chain.

What glycosidic bonds causes branching?

1,6 glycosidic bonds

Amylose, amylopectin, glycogen and cellulose

Amylose consists of 1000’s of α -glucose molecules; all bonded together by 1,4 glycosidic bonds through condensation reactions. Unbranched, straight chains.

Consists of α –glucose molecules in a branched chain, bonded by 1,4  and 1,6 glycosidic bonds

Polymer of α –glucose molecules (1,4 & 1,6 glycosidic bonds), Similar structure to starch, but shorter chains, Lots of branches, Found in animals

Polysaccharide of b-glucose molecules bonded together by condensation reactions (1,4, links). The chains are straight and long (unlike chains of a-glucose molecules which are coiled and often branched). The chains are strong, and called cellulose. Structural function

Roles of lipids:

• Energy source

• Excellent store of energy in animals and plants seeds

• Being insoluble not leached from the cell

• Insulation 

• Protection 

• Waterproofing 

• Buoyancy 

• Cell membranes

Glycerol is one of the building blocks in lipids. Draw glycerol.

Triglycerides:

• Triglycerides are formed by condensation reactions between a glycerol and 3 fatty acids.

• These reactions form ester bonds.

• They are insoluble in water

• Completely hydrophobic.

Saturated vs Unsaturated fatty acids

• Saturated fatty acids have no double bonds. They tend to be solid at normal temperatures.

• If one double bond – mono-unsaturated 

• More than one double bond present – polyunsaturated

• Unsaturated fatty acids tend to have a low melting points and so tend to be liquid at normal temperatures.

Cis vs Trans fats

Starch test:

Starch test

Reagent: Iodine

Positive colour: blue/black

Negative colour: orange/brown

Testing for reducing sugars:

Reducing sugar

Reagent: Benedict’s reagent

Positive colour: brick red

Negative colour: blue 

Testing for non-reducing sugars:

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