Carbohydrates

This deck contains content from 3.1.2 Carbohydrates.

What is the biological name for carbohydrates?

Polysaccharides

What are the monomers for polysaccharides?

Monosaccharides

What bonds join monosaccharides together?

Glycosidic bonds

What elements are within carbohydrates?

• Carbon

• Hydrogen

• Oxygen

What is the general formula of a monosaccharide?

(CH₂O)_n

What are two properties of monosaccharides?

1. Sweet-tasting

2. Soluble

What are 3 examples of monosaccharides?

1. Glucose

2. Galactose

3. Fructose

What is the difference between hexose & pentose?

A hexose is a 6-carbon sugar, a pentose is a 5-carbon sugar

What is an isomer?

Molecules with the same molecular formula but with a different arrangement of atoms

What is an example of 2 isomers?

a - glucose & B - glucose

What is the main difference between alpha & beta glucose?

The hydroxyl group on each is swapped, so on alpha, it is on the bottom and on beta, it is on the top

What is a disaccharide & how are they formed?

Two monosaccharides joined by a glycosidic bond, and they are formed by the condensation of two monosaccharides

What is maltose made of?

Glucose + Glucose

What is Sucrose made of?

Glucose + Fructose

What is lactose made of?

Glucose + Galactose

What is the test for reducing sugars called?

Benedict’s Test

What are some examples of reducing sugars?

• All monosaccharides

• Some disaccharides(maltose)

What is reduction?

A chemical reaction that involves the gain of electrons/hydrogen

What is a reducing sugar?

A sugar that can donate electrons to another chemical( e.g. Benedict’s reagent)

What is Benedict’s Reagent?

An alkaline solution of copper(II)sulphate (CuSO₄)

What is the method for the test for reducing sugars?

1. Add 2cm³ of the food sample to a test tube

2. Add an equal volume of Benedict’s

3. Heat the mixture gently in a water bath for 5 min

What is the positive result for the test for reducing sugars?

A colour change from blue to green/yellow/orange/red

What type of test is Benedict’s test?

Semi-quantitative

What is an example of a non-reducing sugar?

The rest of the disaccharides, such as sucrose

What is the method for the test for non-reducing sugars?

1. Perform Benedict’s test & obtain a negative result

2. Boil with HCl & neutralise with NaHCO₃ alkali

3. Heat with Benedict’s again & obtain a red precipitate.

Give 3 examples of polysaccharides…

1. Starch

2. Cellulose

3. Glycogen

What is starch made up of?

Chains of alpha-glucose

What bonds link the monomers in starch?

1,4 and some 1,6 glycosidic bonds

What are 1,6 glycosidic bonds responsible for?

Branching of polysaccharides

Where is starch found?

In plants as small grains

What are the chains in starch?

• Branched

• Unbranched

  So is a tight coil, making it highly compact

Where is starch never found?

Animal cells

What does starch look like?

What are the 5 features of starch that make it a good storage molecule?

1. Insoluble, so does NOT affect water potential

2. Branched, so molecule is compact

3. Polymer of glucose, so provides glucose for respiration

4. Branched, so more ends for fast hydrolysis

5. Large molecule, so CANNOT cross the cell membrane

How do we test for starch?

1. Add 2cm³ of food sample into a test tube and add 2 drops of iodine.

2. Shake/stir.

3. The positive result is a colour change from orange to blue/black.

What is glycogen made up of?

Chains of alpha glucose molecules

What bonds link the monomers in glycogen?

1,4 & 1,6 glycosidic bonds

Where is glycogen found?

In animal and bacterial cells

What is the main difference between starch & glycogen?

Starch is a longer molecule and less branched than glycogen

What is glycogen stored as?

Small granules in the muscles and liver

What are the 5 points where the structure of glycogen relates to its function?

• Helical/coiled so is compact

• Polymer of glucose, so glucose is easily released for respiration

• Polymer of glucose, so easily hydrolysed

• Highly branched, so more ends, for faster hydrolysis

• Insoluble, so does not affect water potential

What is cellulose made up of?

Chains of beta glucose molecules

What bonds link the monomers in cellulose?

Only 1,4 glycosidic bonds

What do the type of bonds in cellulose mean for it’s structure?

It is a straight molecule

How does cellulose look?

How are alternate monomers in cellulose arranged?

They are flipped by 180 degrees

What is formed when cellulose molecules are grouped together?

Microfibrils

How are microfibrils arranged?

They run parallel to one another

Why do alternate monomers in cellulose flip?

To allow the hydroxyl groups of C1 & C4 to become adjacent and form a glycosidic bond

What is the purpose of hydrogen bonds in cellulose?

To form cross-linkages between adjacent chains

What helps to strengthen cellulose?

The many hydrogen bonds

What are microfibrils grouped together to form?

Fibres

How does cellulose look with hydrogen bonds included?

What is the relationship of cellulose’s structure to it’s function?

It has long, straight/unbranched chains of beta-glucose;

Joined by hydrogen bonding;

To form microfibrils; SO

Provides rigidity/strength.