2.1 Enzymes & Digestion

2 TYPES:

-PHYSICAL BREAKDOWN

-CHEMICAL BREAKDOWN

PHYSICAL BREAKDOWN:

If food is large its broken down into smaller pieces, by chewing with TEETH. This provides LARGE SURFACE AREA for CHEMICAL DIGESTION. Food is churned up by muscles in STOMACH WALL, this physically breaks it up. 

CHEMICAL BREAKDOWN:

Breaks down large insoluble molecules into smaller soluble ones, carried out by ENZYMES. All digestive enzymes function by HYDROLYSIS. Hydrolysis is SPLITTING UP OF MOLECULES BY ADDING WATER TO CHEMICAL BONDS THAT HOLD THEM TOGETHER. These enzymes are called HYDROLASES. Enzymes are specific. More than 1 enzyme is needed to break down a large molecule. One enzyme usually splits a large molecule into sections, then they are HYDROLYSED into smaller molecules by 2+ enzymes. 

There are different types of digestive enzymes: 

CARBOHYDRASES: Break down CARBOHYDRATES into MONOSACCHARIDES.

LIPASES: Break down LIPIDS (FATS & OILS) into GLYCEROL and FATTY ACIDS.

PROTEASES: Break down PROTIENS into AMINO ACIDS.

-Once the large molecules have been HYDROLYSED into MONOSACCARIDES, GLYCEROL, FATTY ACIDS and AMINO ACIDS, they are absorbed from small intestine into blood. 

-They are carried to different parts of the body, and built up into large molecules. Although not necessarily of the same type they came from.

-These molecules are put into BODY TISSUES and/or used in PROCESSES WITHIN BODY. This is called ASSIMILATION.

The making of large molecules:

Organic molecules incl. carbohydrates are made up of a chain of INDIVIDUAL MOLECULES.

These INDIVIDUAL MOLECULES make up these chains calledMONOMERS. Carbon atoms of these chains join to form longer chains calledPOLYMERS. 

Polymers are based on small number of chemical elements; CARBON, HYDROGEN, OXYGEN and NITROGEN.

In carbohydrates the basic monomer unit is a SUGAR, known as aSACCHARIDE. A single monomer is called MONOSACCHARIDE. 

A pair of MONOSACCHARIDEs is called DISACCHARIDE.

Many MONOSACCHARIDES are called POLYSACCHARIDE.

Monosaccharides are SWEET TASTING soluble substances that have a general formula: (CH2O)n where n=3-7 

Best known monosaccharide is GLUCOSE. This molecule is a HEXOSE (6-carbon) sugar. Forumula: C6 H12 O6

All monosaccharides & some disaccharides are REDUCING SUGARS. Reduction is the CHEMICAL REACTION involving the GAIN of ELECTRONS. A reducing sugar is therefore a sugar that can DONATE ELECTRONS to ANOTHER CHEMICAL. In this case BENEDICT'S REAGENT. The test for reducing sugars is known as the BENEDICT'S TEST. 

Benedicts reagent is an alkaline solution of copper(II) sulphate. When a reducing sugar is heated with the benedicts reagent it forms an INSOLUBLE RED PRECIPITATE of copper(I) oxide. 

-Add 2cm3 of food sample in a test tube. If not already in liquid form, make it liquid form.  

-Add an equal volume of Benedict's Reagent.  

-Heat the mixture in a gently boiling bath for 5 minutes.

GLUCOSE + GLUCOSE -> SUCROSE  

 GLUCOSE + FRUCTOSE -> SUCROSE

GLUCOSE + GALACTOSE -> LACTOSE

When the monosaccharides join, a molecule of WATER is removed and the reaction is called CONDENSATION REACTION. The bond that is formed is a GLYCOSIDIC BOND.

When water is added to a disaccharide under suitable conditions its breaks the GLYCOSIDIC BOND releasing the monosaccharides. this is called HYDROLYSIS.