Biology a level biological molecules

water dipole nature

water dipole nature

• a weak negatively charged region on the oxygen atom (δ-) and a weak positively charged region on the hydrogen atoms (δ+)

• This separation of charge due to the electrons in the covalent bonds being unevenly shared is called a dipole

what is a polar molecule

When a molecule has one end that is negatively charged and one end that is positively charged

why is water good at transporting substances

its dipole nature

cohesion

Hydrogen bonds between water molecules allow for strong cohesion between water molecules

adhesion

Water is also able to form hydrogen bonds with other molecules

why is water a good solvent

• Water molecules surround charged particles; the positive parts of water are attracted to negatively charged particles and the negative parts of water are attracted to positively charged particles

what are monosaccharides

the monomers of carbohydrate

are simple carbohydrates

are sugars

what are Disaccharides

Two monosaccharides can join together via condensation reactions to form disaccharides

glycosidic bond is formed

what are polysaccharides

• Polysaccharides are carbohydrate polymers; repeated chains of many monosaccharides joined by glycosidic bonds in a condensation reaction

starch (polysaccharide)

the storage polysaccharide of plants

• Starch is constructed from two different polysaccharides

  • Amylose and amylopectin

glycogen (polysaccharide)

he storage polysaccharide of animals and fungi

• It is highly branched and not coiled

• compact so can be stored in a small space

function of monosaccharides

to store energy within their bonds

structure:

• It is soluble so can be transported easily

• It has many covalent bonds which store energy

formation of disaccharides ( condensation)

glucose + glucose → maltose + water

glucose + fructose → sucrose + water

glucose + galactose → lactose + water

structure of disaccharides

maltose - 1,4 glycosidic bond

sucrose - 1.2 glycosidic bond

lactose - 1,4 glycosidic

disaccharides are easily soluble in water and sweet in taste

function of disaccharides

to provide the body with a quick-release source of energy

structure of polysaccharides

• Branched or unbranched

  • Being branched increases the rate at which a polysaccharide can be broken down

• Straight or coiled

  • Being straight makes the molecules suitable for constructing cellular structures e

  • Being coiled makes a molecule more compact and suitable for storage

why are starch and glycogen useful as storage polysaccharides?

• Compact; large quantities can be stored

• Insoluble; they will have no osmotic effect

structure of starch

Amylose

• Unbranched helix-shaped chain with 1,4 glycosidic bonds

• Amylopectin

  • A branched molecule containing 1,4 and 1,6 glycosidic bonds

  • The branches result in many terminal glucose molecules that can be easily hydrolysed

structure of glycogen

• highly branched and not coiled

• It contains both 1,4 and 1,6 glycosidic bonds

• Glycogen is more branched than amylopectin

• compact

how are disaccharides and polysaccharides formed?

two hydroxyl (OH) groups on different monosaccharides interact to form a strong glycosidic covalent bond (condensation)

how a triglyceride is synthesised

the formation of ester bonds during condensation reactions between glycerol and three fatty acids

Forming an ester bond

An ester bond forms when the hydroxyl (-OH) group of the glycerol bonds with the carboxyl group (-COOH) of the fatty acid

Saturated fatty acids

contain no carbon-carbon double bonds

Unsaturated fatty acids

contain carbon-carbon double bonds