2. carbohydrates

CarbohydratesSaccharides

The basic formula is:

Cx(H

20)

yor (CH

2O)

n

All carbohydrates are Aldehydes or ketones

Aldehydes oxidise easily and make good reducing agents.

They have many –OH groups

MONOSACCHARIDESThese are simple sugars

They are used to release energy or as monomers in larger molecules.

They are sweet

They are soluble in water

e.g. glucose: C6H

12O

6

TEST FOR REDUCING SUGARS

Reducing sugars are able to

Reduce Copper II Sulfate to Copper I oxide (Blue, soluble) (red, insoluble)

Benedict’s solution is made

using Copper II sulfate

which is a blue solution

Benedict’s test

This solution tested positive for reducing sugars

This solution is negative for reducing sugars

Ring Structures

Glucose can exist as a chain or fold around to form a 6 sided ring structure

Note the carbons are numbered 1-6

Carbon 6 is outside of the ring attached to carbon 5

Note carbon 6 is above the ring Some OH and some H groups are below the ring

Carbon 1 is asymmetrical

It has 4 different groups attached

HOHO and C

In nature glucose exists in two forms

In beta glucose the OH is above the ring structure

Alpha glucose Beta glucose

ALPHA GLUCOSE BETA GLUCOSE

DisaccharidesThese are formed by condensation – removing water

These are both molecules of -∝ glucoseA bond is formed by removing OH from carbon 1 on one moleculeAnd an H on carbon 4 of the adjacent molecule

This is an ∝-1.4 glycosidic bond Water is made

Maltose is the disaccharide formed

Lactose a disaccharide formed by joining Galactose and Glucose

SucroseThis is a disaccharide that is a non-reducing

sugar

Test for Non-Reducing Sugar1. Carry out Benedict's test: negative result so no reducing sugars

2. Hydrolyse the unknown to split the sugar into monosaccharides:

Add hydrochloric acid Heat in a water bath neutralise using hydrogen carbonate

3. Repeat Benedict's test

If it goes Brick red this time there is non-reducing sugar present

POLYSACCHARIDES

e.g. starch, glycogen, cellulose

Polysaccharides are food and energy stores

They are large and insoluble so do not affect water potential or influence chemistry of cell

They can fold into compact shapes

Polysaccharides are easily converted by hydrolysis to sugars when required

STARCHStarch is a polymer of α-glucose

This is the main storage compound in plants

Has two components:

Amylose and

amylopectin

AMYLOSEStraight chain of -glucose molecules joined by 1,4 α αglycosidic bondsHelically coiled making it compact.200-1500 residues

AMYLOPECTINMakes up about 70% starchMany more residues, 2000-200-000Some residues joined with 1,4 glycosidic bonds and αhelically coiled Some branched with 1,6 glycosidic bondsα

Alpha 1,6, glycosidic bond

Alpha 1,4 glycosidic bond

GLYCOGENGlycogen is the storage polysaccharide in animal

cells (particularly in liver and muscle cells) and many fungi

Similar in structure to amylopectin but has more branching and is larger

CELLULOSE

50% of Carbon in a plant is cellulose

It is the most abundant organic molecule on earth

Cellulose is an unbranched polymer of 2000-3000 β-glucose molecules

Held by β 1,4-glycosidic bonds

Beta glucoseCannot form glycosidic bonds like thisThe OH of the first molecule is above the ring structure

If one molecule flips through 180 degrees then the OH groups align on carbon 1 and 4 and condensation can occur

Beta 1,4,glycosidic bond

The next glucose molecule will need to be the same as the first oneThis time the beta-1,4 glycosidic bond is formed below the ring structure

And so on…Cellulose is a long, straight molecule

Cellulose molecules lie next to each other and are held together by weak hydrogen bondsThere are many of these bonds which makes the overall structure strong

These molecules are bundled into microfibrils which are in turn bundled into cellulose fibresThese fibres have a high tensile strength