3.1.2 Carbohydrates

Being large and insoluble, what sugars cannot diffuse out of cells?

Starch & Glucose

What is an isomer?

Different structural arrangements of the same molecular formula!

How is beta-glucose different to alpha glucose?

The OH is above the H.

What makes up Lactose?

1 Galactose + Glucose molecule

What makes up Sucrose?

1 Glucose + 1 Fructose molecule

How could you test for reducing sugars?

1) Add 2cm3 solution of the food for test. 2) Add an equal volume of Benedict's reagent. 3) Heat the mixture in a gently boiling water bath for five minutes. blue - none / green - very low / yellow - low / orange - medium / red - high

How is starch and glycogen being insoluble useful for storage?

1) Doesn't effect osmosis in cells. 2) Won't diffuse out of cells

If the result of the original test is negative (remains blue), there could still be non-reducing sugars present. What is the test for non-reducing sugars?

1) Get a sample of the test solution and add dilute HCl and carefully heat it in a water bath thats been brought to the boil. 2) Neutralise it with sodium hydrogen carbonate. Then carry out the BR test for reducing sugars. 3) If the test remains negative (blue), there aren't any sugars.

Glycogen and cellulose are both carbohydrates. Describe 2 differences between the structure of a cellulose molecule and a glycogen molecule.

1. cellulose is made up of unbranched chains; glycogen is highly branched. 2. glycogen is made up of alpha-glucose monomers, cellulose is made up of beta-glucose.

The unbranched chain of starch can be wound into...

a tight coil

Starch is a carbohydrate often stored in plant cells. Describe and explain 2 features of starch that make it a good storage molecule.

1. unbranched chains can coil up and so a large amount can be stored in a smaller volume. 2. starch is insoluble, so it doesn't cause cell's to bloat by affecting their water potential.

What is a hydrolysis reaction?

A hydrolysis reaction breaks a chemical bond between two molecules through the addition of a water molecule.

What monomers make up starch and glycogen?

Alpha glucose

Describe amylopectin

Amylopectin is branched, enzymes can get at the glycosidic bonds easier. So glucose can be released quicker!

Describe amylose

Amylose is unbranched, and its bonds angles allow it to coil up, so its nice and compact for energy storage!

How does the structure of glycogen effect its function?

Animals store excess glucose as glycogen. It's structure is similar to that of amylopectin, except it is even more branched. Lots of branches means that glucose can be released quickly for use in respiration etc. It's also very compact!

What are the two isomers of glucose?

Beta and Alpha glucose

What monomers make up cellulose?

Beta glucose

How is a glycosidic bond formed?

By a condensation reaction between two monosaccharides. This is also how disaccharides are formed!

What does the condensation of beta-glucose form?

Cellulose

Describe the basic structure and functions of glycogen.

Found in animals (stored as small granules in the liver and muscles) and bacteria. It has shorter chains but is more highly branched than starch.

Describe the basic structure and functions of starch.

Found in many parts of the plant as small granules. Lots are found in storage organs and seeds.

Name three common monosaccharides.

Glucose, Fructose and Galactose

Name three polysaccharides:

Glycogen, Cellulose and Starch

Why is glycogen being more highly branched than starch useful to animals?

It can be simultaneously acted on by enzymes to release glucose monomers. This is important to animals which have a higher metabolic rate and thus respiratory rate than plants.

Describe the basic structure and functions of cellulose.

Long, unbranched chains of beta-glucose. The adjacent beta-glucose molecules bond, forming straight chains of cellulose. The chains are further connected with hydrogen bonds to form strong micro-fibrils. Thus, cellulose can provide structural support!

How does the structure of cellulose effect its function as a strong structural material?

Many hydrogen bonds form cross links with adjacent chains. The molecules are grouped to form microfibrils which in turn are grouped to form fibres. The numerous hydrogen bonds add considerable strength to cellulose making it an important structural molecule.

Give three examples of monomers.

Monosaccharides, nucleotides and amino acids.

What is a polysaccharide?

More than two monosaccharides joined together by condensation reactions!

What are monomers?

The smaller units from which larger molecules are made!

Describe the test for starch.

The test is carried out at room temperature: 1) Place 2cm3 of the sample into a test tube with potassium iodide solution. 2) The presence of starch is indicated by a blue-black coloration.

Life as we know it, is carbon based. This is due to Carbon's ability to bond with four other atoms, thus forming a backbone for life to develop. Therefore:

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

What are monosaccharides?

They're the monomers from which larger carbohydrates are made.

What forms Starch?

Two isomers of alpha glucose, amylopectin and amylose.

Chains of starch may be what?

branched or un-branched! And are found in plants.

Hydrogen bonds add...

collective strength

Glucose is __________ transported and __________ used in respiration.

easily readily

A condensation reaction...

joins two molecules together with the formation of a chemical bond and involves the elimination of a H2O molecule.

Monosaccharides are the monomers from which...

larger carbohydrates are formed!

Cellulose molecules form...

long, straight and unbranched chains

Cellulose is a major component of...

plant cell walls! The cellulose cell wall prevents the cell from bursting as water enters it by osmosis. It does this by exerting an inward pressure that prevents any further influx of water.