Biology - Carbohydrates

The ___ of life, both past and present, is ___, but the biochemical basis of life is ___ for all living things.

The variety of life, both past and present, is extensive, but the biochemical basis of life is similar for all living things.

Carbohydrates, lipids, proteins and nucleic acids all contain what?

Carbon, Hydrogen and Oxygen in different proportions

Monomer

Small repeating units from which larger molecules called polymers are formed

Polymer

Large molecules made from a large number of/many monomers (3 or more) joined together

Polymer of Monosaccharides

Polysaccharides/Carbohydrates

Examples of Polysaccharides/Carbohydrates

• Starch

• Glycogen

• Cellulose

Monomer of Polysaccharides/Carbohydrates

Monosaccharides

Examples of Monosaccharides

• Glucose

• Fructose

• Galactose

Condensation Reaction

A reaction that joins 2 molecules together with the formation of a chemical bond and elimination of a water molecule

Hydrolysis Reaction

A reaction that breaks a chemical bond between 2 molecules and involves the use of a water molecule

Molecular formula of a monosaccharide

C₆H₁₂O₆

Molecular formula of a disaccharide

C₁₂H₂₂O₁₁

Simplified Alpha Glucose Diagram

Simplified Beta Glucose Diagram

Isomer

Molecules with the same molecular formula but different arrangement of atoms

Complete the equation:

Glucose + Glucose →

Glucose + Glucose → Maltose + Water

Maltose → Monosaccharides

(Alpha) Glucose + (Alpha) Glucose

Lactose → Monosaccharides

Glucose + Galactose

Sucrose → Monosaccharides

Glucose + Fructose

Draw a ring diagram for alpha glucose

(May ask for carbons to just be lines + ignore red box)

Food Tests → Starch

1. Add equal volume of Iodine Solution to liquid sample

2. Shake gently

3. If present colour turns to blue-black → otherwise orange-brown

Food Tests → Proteins

1. Add equal volume of Biuret Solution to liquid sample

2. Shake gently

3. If present colour turns to purple/lilac → otherwise blue

Food Tests → Lipids

1. Add ethanol and shake

2. Add distilled water and shake

3. If present white emulsion forms → otherwise clear

Food Tests → Reducing Sugars

1. Add equal volume of Benedict’s Solution to liquid sample

2. Heat

3. If present colour turns to brick-red precipitate → otherwise blue

Why is Benedict’s test semi-quantitative

Different colours allow you to approximate the concentration so is less subjective than qualitative data but the test does not give a numerical value so is not fully quantitative

Colours formed by Benedicts based on concentration

• Green/Yellow → Low

• Orange → Medium

• Brick-Red → High

Food Tests → Non-Reducing Sugars

1. Boil with dilute acid to hydrolyse the glycosidic bonds

2. Neutralise with an alkali

3. Add equal volume of Benedicts’ solution

4. Heat

5. Brick-Red precipitate forms

Precipitate

Solid particles suspended or settled in a liquid

Emulsion

Liquid droplets suspended inside another liquid

Draw Maltose

Difference between alpha and beta glucose

Hydroxyl group on Carbon-1 points downwards below the plane in Alpha Glucose whereas it points upwards above the plane in Beta Glucose

Starch → Location & Role

Storage molecule found in plants

Cellulose → Location & Role

Found in plant cell walls, providing the cell with rigidity and strength

Glycogen → Location & Role

Storage molecule found in the livers and muscles of animals

Glycogen → Structure & Properties

• Helical/Coiled → compact → can store more alpha glucose for respiration

• Polymer of alpha glucose → easily hydrolysed & provides respiratory substrate for release of energy

• Highly branched → more ends for faster hydrolysis

• Insoluble → doesn’t affect water potential

• Large → can’t cross cell surface membrane

Starch → Structure & Properties

• Helical/Coiled → compact → can store more alpha glucose for respiration

• Polymer of alpha glucose → easily hydrolysed & provides respiratory substrate for release of energy

• Branched → more ends for faster hydrolysis

• Insoluble → doesn’t affect water potential

• Large → can’t cross cell surface membrane

Cellulose → Stucture & Properties

• Straight/Linear/Unbranched chains of beta glucose

• Large

• Insoluble → doesn’t affect water potential

• Every other glucose is flipped

• Has many weak hydrogen bonds

• Can form microfibrils

Explain how the structure of cellulose is related to its function

1. Straight/unbranched chains of beta glucose

2. Joined by weak hydrogen bonds

3. Forms microfibrils

4. Providing the cell rigidity and strength

Why can cellulose form microfibrils?

1. The beta 1-4 glycosidic bonds cause every other glucose to be flipped allowing cellulose to be straight and linear

2. This allows the chains to be packed very close together parallel to one another

3. Because the chains are so close together lots and lots of cross-links/hydrogen bonds form

4. This causes the formation of a rigid structure called microfibrils

Colorimeter → Absorbance & Transmission

• Absorbance → how much light is absorbed by the sample (AU)

• Transmission → % of light passes through the sample (%)

Plotting a calibration curve → example for maltose concentration in unknown sample

1. Make maltose solutions of known concentrations

2. Carry out Benedict’s test on each solution

3. Use colorimeter to measure colorimeter value (absorbance or transmission) of each solution

4. Plot calibration curve by joining points and with colorimeter value on y axis and concentration on y axis

5. Estimate concentration by using calibration curve and colorimeter value

All reducing sugars

• Glucose

• Galactose

• Fructose

• Lactose

• Maltose

Non-reducing sugar

Sucrose