2.3 - Carbohydrates

Question 1

What is a Carbohydrate?

Answer 1

An organic molecule composed of H, C and O atoms which provide structure, energy storage and healthy diet

Can be mono, di or poly - saccharides

Question 2

What is condensation and hydrolysis

Answer 2

Condensation involves the loss of an -OH from one molecule and an -H from another molecule, which together form H2O.
Therefore, condensation involves the combination of subunits and yields water.

Hydrolysis in the addition of water

Question 3

Monosaccharide

Answer 3

A single sugar unit - they can be linked together to make larger molecules

Glucose, Ribose, Fructose

Question 4

Disaccharide

Answer 4

A disaccharide consists of two monosaccharides joined by a covalent bond

Ex. maltose is made by linking two glucose molecules together
Ex. Sucrose is made by linking a glucose and a fructose

Linked by a condensation reaction (creation of water)

Question 5

Polysaccharides

Answer 5

Polysaccharides consist of many
monosaccharide units linked together

Ex. starch, glycogen, and cellulose
All are composed of glucose molecules linked in different ways, due to differences in the type of glucose used
to make them and in the type of linkage between glucose molecules.

Linking together monosaccharides to form disaccharides and polysaccharides is an anabolic process and energy is required.
ATP supplies energy to the monosaccharides and this energy is then used when the condensation reaction occurs.

Question 6

Glucose

Answer 6

Glucose has 5 -OH groups in which any can be used for condensation but only three of them are used to link to make polysaccharides.
Glucose can have the -OH group on carbon atom pointing either up or down
Alpha Glucose - -OH group points downward
Beta Glucose - -OH group points upward

Question 7

Starch

Answer 7

Starch is made by linking alpha - glucose molecules together
Starch is made by plant cells
Molecules of both types of starch are hydrophilic but they are too large to be soluble in water. They are therefore useful in cells where large amounts of glucose need to be stored, but a concentrated glucose solution would cause too much water to enter a cell by osmosis.
energy store (glucose molecules can be added or removed)
Two forms starch amylose (unbranched) and amylopectin (branched)

Question 8

Cellulose

Answer 8

Cellulose is made by linking together beta - glucose molecules
To bring these OH groups together and allow a condensation reaction to occur, each beta - glucose added to the chain has to be positioned at 180° to the previous one
unbranched chains of beta - glucose which allow the to form bundles with hydrogen bonds linking the cellulose molecules.
linked molecules form bundles called cellulose microfibrils
very high tensile strength (prevents plant cells from bursting due to osmosis) are used as the basis of plant cell walls.

Question 9

Glycogen

Answer 9

similar to amylopectin, but more branching
Glycogen has the same function as starch in plants: it acts as a store of energy in the form of glucose, in cells where large stores of dissolved glucose would cause osmotic problems.
made by animals and some fungi
stored in the liver and some muscles in humans
glucose molecules are easily added or removed
functions to store energy in the form of glucose
Starch and glycogen molecules do not have a fixed size and the number of glucose molecules that they contain can be increased or decreased.