Q1 Uptake of the products of

digestion (small intestine)

Absorption

Q2 Breaking down large

molecules into smaller ones

Digestion

Q3 2 types of digestion

Chemical

Mechanical

Q4Where does ingestion

occur

Mouth

Q5Using the products of

digestion in cells?

assimilation

Biological Molecules

AS Biology

Biological Molecules

80% of the mass of living organisms is water.

13% is composed of organic (carbon-based) MACROMOLECULES, of which there are 4 groups CARBOHYDRATES PROTEINS LIPIDS (FATS) NUCLEIC ACID

Carbon

• Carbon-containing molecules=organic molecules

• Carbohydrates, proteins and lipids all contain carbon

• Carbon atoms can form 4 chemical bonds with other carbons or different atoms

Polymers & monomersWhat are polymers?

What are monomers?

Long chained molecules consisting of repeating units

The repeating unit that join together to form polymers

Macromolecules

Carbon chains can be straight

Carbon chains can be branched

CARBOHYDRATES

• This type of molecule contains only the elements:

»C

»H

»O

CARBOHYDRATES

Divided into 3 main types;1.Monosaccharides

Single sugars

Monosaccharides – single sugars

Examples

Alpha Glucose6 carbons

Fructose6 carbons

Galactose6 carbons

Glucose – C6H12O6

• Glucose is the best known monosaccharide, having the general formula C6H12O6.

Alpha Glucose

CARBOHYDRATES

Divided into 3 main types;1.Monosaccharides = single sugars

2.Disaccharides

sugars containing 2 monosaccharide residues

Disaccharides– 2 monosaccharide residues joined

together Examples

sucrose

Alpha Glucose

Making Chains• Disaccharides are

formed when two monosaccharides join together.

• The reaction involves the formation of a water molecule, & so is called a condensation reaction.

• The type of bond formed is called a glycosidic bond.

The bonds between the individual monomers in disaccharides and polysaccharides can be broken by hydrolysis, which is the reversal of condensation reactions.

A hydrolysis reaction does not occur by putting a carbohydrate in water – an enzyme is required. In the case of starch, this enzyme is amylase.

Breaking Chains

Disaccharides (to learn)

• There are 3 common disaccharides:

– Maltose: glucose + glucose– Sucrose: glucose + fructose– Lactose: glucose + galactose

Draw how the disaccharides: maltose and lactose are formed

• For each identify the water molecule that is produced

• Draw out the complete disaccharide & identify the glycosidic bond

galactose

CARBOHYDRATES

Divided into 3 main types;1.Monosaccharides = single sugars

2.Disaccharides = sugars containing 2 monosaccharide residues

3.Polysaccharides =

very large molecules that contain many monosaccharide residues

Making Longer Chains

• Polysaccharides are long chains of many monosaccharides joined together by glycosidic bonds.

• There are three important polysaccharides:

• Starch• Glycogen• Cellulose

Polysaccharides – many monosaccharide residues joined

together Examples

Carbohydrates

Sugars

Monosaccharides

(monomers)

Disaccharides

(dimers)

Polysaccharides

(polymers)

Glucose

Fructose

Galactose

Maltose

Sucrose

Lactose

Starch

Glycogen

Cellulose

Carbohydrate digestion

Polysaccharide

disaccharide

monosaccharide

insoluble

soluble

Carbohydrate digestion example Starch

Polysaccharide

DisaccharideMaltose

monosaccharide

Starch

Alpha glucose

Salivary amylase & pancreatic amylase

Maltase in intestinal epithelium (cells lining small intestine)

• Starch is the plant storage polysaccharide. It is insoluble and forms starch granules inside many plant cells. It’s insolubility means it does not affect the water potential of cells.

• It is not a pure substance, but a mixture of two structures (both alpha glucose polymers though)

• Amylose

• Amylopectin

Starch

Amylopectin can be broken down more easily because it has “more ends”

Glycogen is similar in structure to amylopectin. It is made by animals as their storage polysaccharide, being found mainly in muscle and the liver. Its branched structure means it can be mobilised (broken down to glucose) very quickly.

Glycogen

Cellulose is only found in plants where it is the main constituent of cell walls.

Cellulose is made from beta glucose arranged in long parallel chains. The chains are held together in a bundle by hydrogen bonds, forming microfibrils which are very strong.

The beta glycosidic bond cannot be broken down by amylase, but requires a specific cellulase enzyme. Only bacteria contain this enzyme, so herbivores like cows & termites have bacteria in their guts. Humans cannot digest cellulose – it is what we call fibre or roughage.

Cellulose

ProteinsProteins are the most complex and diverse group of bioligical compounds. They have an astonishing range of different functions:

structure e.g. collagen (bone, cartilage, tendon), keratin (hair), actin (muscle)

Enzymes e.g. amylase, catalase, pepsin (>10000)

Transport e.g. haemoglobin (oxygen), transferrin (iron)

Pumps e.g. sodium-potassium pumps in cell membranes

Hormones e.g. insulin, glucagon, adrenalin

Antibodies

Blood clotting

And many more

ProteinsProteins are made of amino acids which have a central carbon atom with three different chemical groups attached:

Carboxylic acid group

Amino group

R-group

Alpha carbon

Amino acids are so called because they have both amino groups (-NH2) and acidic groups (-COOH).

Amino acids are made of the five elements C H O N S

There are 20 different R-groups and so 20 different amino acids. This means that there are many, many different proteins with differing numbers and combinations of amino acids

Proteins- making and breaking

Joining amino acids involves, again, a condensation reaction. The bond formed is called a peptide bond

Two amino acids form a dipeptide, many amino acids form a polypeptide. In a polypeptide, one end is still the amino group and the other end the acidic group.

The same type of reaction, hydrolysis, is again involved in breaking down (or hydrolysing) proteins. This can be achieved in the presence of protease enzyme or by boiling with dilute acid.

Protein structure

Polypeptides are just a string of amino acids, but they fold up to form the complex structures of working proteins. To help understand protein structure it is broken down into four levels – but be aware that these are not real sequential stages in protein formation

PRIMARY STRUCTURE

SECONDARY STRUCTURE

TERTIARY STRUCTURE

QUARTERNARY STRUCTURE

Protein: primary structure

This is just the sequence of amino acids in the polypeptide chain, so is not really a structure at all

Gly – Pro – His – Leu – Tyr – Ser – Trp – Asp - Lys

This can also be shown using the three letter abbreviations for each amino acid:

Protein: secondary structure

This is the folding that then occurs, being held together by hydrogen bonds between the amino and carboxyl groups.

The two main types of secondary structure are the alpha helix and the beta pleat.

In the alpha helix the polypeptide chain is wound round to form a helix that is held together by many hydrogen bonds. In the beta pleat, the polypeptide chain zig-zags back and forward, once again held together by hydrogen bonds

Protein: tertiary structure

This is the three dimensional structure formed by the folding up of the whole chain, with every proteins properties and functions being related to this. E.g. the unique shape of an enzymes active site is due to its tertiary structure. Three kinds of bond hold this structure together:

Hydrogen bonds,which are relatively weak

Ionic bonds between the R-groups, which are quite strong

Sulphur bridges between the sulphur containing amino acids, which are strong

Protein: quarternary structure

This structure is found only in those proteins that contain more than one polypeptide chain, and simply means how the different chains are arranged together e.g. haemoglobin

Globular or Fibrous?

The final 3-D shape of a protein can be described as globular or fibrous

GLOBULAR: most proteins, soluble, have biochemical roles e.g. enzymes, receptors, hormones

FIBROUS: look like “ropes”, are insoluble and have structural functions e.g. Collagen, keratin

Biochemical test for proteins, carbohydrates (sugars, starch),

and lipids

Lipids

You can test for the presence of lipids by using the EMULSION TEST.1.Add alcohol to the sample of

food.Shake to dissolve any lipid.

2. Two layers of liquid will form. Pour the top layer of & add water.

3. A cloudy white EMULSION shows the presence of a lipid

Starch

The presence of starch can be teated using the iodine test.

Starch + iodine blue-black colour

With other polysaccharides, iodine remains yellow-brown

SugarsSugars can be identified with blue Benedict’s solution. However there are two types of sugar:

Reducing Sugars – these carry out reduction reactions and include all monosaccharides and most disaccharides.

When heated with Benedict’s, the colour changes from blue to green to orange/red

Non-reducng sugars (mainly sucrose in fact) do not react with Benedict’s unless first hydrolysed by heating with acid first. As Before adding Benedict’s, you must neutralise the acid with an alkali

ProteinsProteins can be identified with blue Biuret Reagent (copper sulphate and sodium hydroxide).

Blue Biuret reagent turns lilac in the presence of protein