A-level Biology Biological Molecules unit 1

Monosaccharide

single sugar monomers, all are reducing sugars

Disaccharide

formed from 2 monosaccharides joined by a glycosidic bond in condensation reaction

Polysaccharides

Polymers formed by many monosaccharides joined by glycosidic bonds in a condensation reaction

Condensation reaction

when monomers combine together by covalent bonds to form polymers or macromolecules, water is removed

Hydrolysis reaction

when covalent bonds are broken when water is added

What are reducing sugars

it donates electrons, the sugars become the reducing agent

What are some examples of reducing sugars

glucose, fructose, galactose

what are non-reducing sugars

it cannot donate electrons, therefore cant become reducing agent

What is an example of a non-reducing sugar

sucrose

What is glucose

most common monosaccharide and is of central importance to most forms of life

What are the 2 types of glucoses

alpha and beta

What are alpha glucose molecules

The -OH bond is below the ring

It has starch and glycogen but not cellulose

What are beta glucose molecules

The -OH bond is above the ring

It doesnt have starch and glycogen but has cellulose

What are glycosidic bonds

they are to make monosaccharides more suitable for transport, storage and to have less influence on a cell’s osmolarity

used to form disaccharides and polysaccharides

How can a glycosidic bond be broken

When water is added in a hydrolysis reaction

Example: digestion of food

Starch and glycogen are what form of saccharides

Polysaccharides

What bond type do starch and glycogen have

Glycosidic bond

What are the 3 chain types

1. Branched or unbranched

2. Folded

3. Straight or coiled

What is glycogen

the storage polysaccharide of animals and fungi

branched

Why are starch and glycogen storage polysaccharides

1. Compact (large quantities can be stored)

2. Insoluble (no osmotic effect)

Why is glycogen more compact than amylopectin

It is more branched

What does the branching enable

more free ends where glucose molecules can either be added or removed allowing for condensation and hydrolysis reactions to occur more rapidly.

What is the function of a polysaccharide

main structural component of cell walls due to its strength

high tensile strength of cellulose allows it to be stretched without breaking

cellulose fibres are freely permeable

What are the characteristics of polysaccharides

polymers formed by many monosaccharides joined by glycosidic bonds in a condensation reaction

insoluble in water

folded

Describe the Benedict’s test for reducing sugars

1. add benedict’s solution in excess

2. heat the test tube under a warm water bath

3. if a reducing sugar is present, a coloured precipitate will form

Describe the results for Benedict’s test for reducing sugars

Blue to green= none

yellow to orange= low to medium

brown to red= high

Which two monosaccharides make up maltose

glucose and glucose

Which two monosaccharides make up sucrose

glucose and fructose

Which two monosaccharides make up lactose

glucose and galactose

Describe the test for non-reducing sugar

First you have to hydrolyze into its monosaccharide components by hydrolysis.

Describe the characteristics of starch

1. main role is energy storage

2. insoluble so do not affect water potential

3. it does not diffuse out of cells

4. compact, so a lot of it can be stored

5. when its hydrolyzed it forms alpha glucose, which is both easily transported and readily used in respiration

Describe the characteristics of glycogen

1. insoluble therefore does not affect water potential

2. does not diffuse

3. compact

4. more highly branched than starch, and has more ends that can be acted on simultaneously by enzymes.

Describe the characteristics of cellulose

1. monomers of beta glucose

2. straight unbranched chains

3. chains run parallel to one another and are cross linked by hydrogen bonds

What are microfibrils

When cellulose molecules are grouped together

What are the 2 forms of lipids

1. triglyceride

2. phospholipid

Describe the characteristics of triglycerides

1. three fatty acids with one glycerol

2. each fatty acid forms an ester bond with glycerol in a condensation reaction

What is esterification

When glycerol and fatty acids form an ester bond

What is the solid form of triglyceride

fat (butter, animal fats)

What is the liquid form of triglyceride

oil (cooking oil)

What can the long chained hydrocarbon be simplified as in a triglyceride molecule

R

Are triglycerides hydrophobic or hydrophilic

hydrophobic

Are phospholipids hydrophobic or hydrophilic

both

Are triglycerides polar or nonpolar

nonpolar

Are phospholipids polar or nonpolar

polar

What is the difference between a saturated fatty acid and an unsaturated fatty acid

saturated- only single covalent bond, no double bonds in the long hydrocarbon chain

unsaturated- one or more double bonds

Describe the characteristics of saturated fats

The hydrocarbon chains of their hydrocarbons lack double bonds, and their flexibility allows fat molecules to be packed close together

Describe the characteristics of unsaturated fats

The molecules of an unsaturated fat such as olive oil cannot pack close enough to solidify because of the kinks in some of their fatty acid hydrocarbon chains.

Describe the characteristics of a phospholipid molecule

1. 2 fatty acids attached to glycerol and a phosphate group

2. Has two ends- heads and tail

3. Tails are hydrophobic

4. Heads are hydrophilic

What happens when water is added into phospholipids and what is this structure called

They self arrange into aggregates with the hydrophobic tails pointing towards the center and hydrophilic heads pointing towards the outside

The structure is called micelle

What is a bilayer?

It is when hydrophilic heads are on the outside of the bilayer, in contact with the aqueous solutions inside and outside of the cell

Hydrophobic tail points towards the interior of the bilayer, away from water

What are the two structures phospholipid form?

1. micelle

2. bilayer

What are the roles of lipids?

1. Energy storage

2. Component of cell membrane

3. Waterproofing

4. Insulation

5. Transports of fat-soluble vitamins

Why do animals store fats instead of carbohydrates in their body?

1. Fats contain more carbon-hydrogen bonds compared to carbohydrates

2. Therefore it has less than half the mass of carbohydrate for a similar quantity of energy stored

3. Fats also protect the body’s organs, acting as an insulator

Describe the emulsion test.

1. Add ethanol and water to sample lipid then shake/mix

2. white emulsion