There are three class of macromolecules that we will consider, proteins, complex carbohydrates and lipids. Their formation is through reactions known as condensation reactions. During such reactions covalent bonds are formed between smaller molecules and a small molecule, mainly water, is expelled.
Digestion of large molecules such as starch, lipids and proteins involves enzyme catalysed hydrolysis reactions. Hydrolysis involves the breaking of bonds by the insertion of a water molecule. Consider the animation below, it shows the digestion of a dipeptide by a protease enzyme.

Proteins are long polymer chains of amino acids joined end to end. Protein digestion starts in the stomach where strong hydrochloric acid and proteases start the breaking down of large proteins into smaller chains of amino acids. This process continues in the small intestine where all the protein chains are separated into individual amino acids.

Stomach acid starts the chemical breakdown of proteins by denaturing them and causing them to uncoil, thus making it easy for enzymes to cleave proteins into smaller pieces and finally into amino acids.

Cells lining the wall of the stomach produce an enzyme called pepsin. Pepsin is a protease enzyme, that is released as an inactive form called pepsinogen and is activated into pepsin only in the presence of a strong acid. Pepsin starts the process of breaking peptide bonds and splits long protein chains into smaller chains (polypeptides). Proteases, released from the pancreas into the small intestine, cleave the polypeptides even further and eventually free individual amino acids to be absorbed into the blood stream. Cells lining the small intestine release more proteases that complete the breakdown of protein into amino acids.

What bond is broken by a protease?
What type of bond holds amino acids together in a protein.
What is involved in hydrolysis?
What is the general name for an enzyme that breaks covalent bonds in a protein chain to release amino acids?
The chemical breakdown of proteins starts in the
What is the role of stomach acid in the digestion of protein?
The group of atoms shown on the right represent an:
Another name for a protein chain is a  

The digestion of lipids is also a hydrolysis reaction which is facilitated (catalysed) by enzymes known as lipases. Lipases catalyse the hydrolysis of fats into two fatty acids and a monoglyceride. Lipases a produced in the pancreas and secreted via the pancreatic duct into the duodenum. Bile is also active in the digestion of fats albeit in a physical reaction only. Bile is produced in the liver and stored in the gall bladder where it is concentrated. Bile acts as a surfactant to physically break down fats in the digestive tract. It acts as an emulsifier, much like soap, to physically break up fat into smaller particles with a greater surface area.


The animation below shows the hydrolysis of a triglyceride.

Digestion of fats takes place in the
Bile acts
Lipases breakdown ________ into ___________ .
The hydrolysis of triglycerides yields
A triglyceride is made up of

A hand written note was found on a desk.

The item labelled "a" on the diagram is most likely to be

The item labelled "b" on the diagram is most likely to be

The items labelled "c" and "d" on the diagram is most likely to be

The item labelled "e" on the diagram is most likely to be

Carbohydrates, such starch, cellulose and glycogen are polymers of smaller molecules, known as monosacharides, mainly glucose. The formation
of these polymers of glucose involves a condensation reaction between two hydroxy groups (OH) one from each glucose molecule to produce water and a glycosidic link. A glycosidic link involves an oxygen atom joined to two carbon atoms. So every time a glucose molecule is covalently linked to the chain a water molecule is given off. See the diagram below.

Digestion of these long carbohydrates, polysaccharides, involves hydrolysis of the covalent bonds holding the small molecules together. In essence it is the reverse of the synthesis reaction shown above. Digestion of these polysaccharides starts in the mouth with salivary amylase. Amylase hydrolysis the bonds in starch to produce maltose molecules. Maltose is a disaccharide formed by two glucose molecules.

Digestion of carbohydrates is temporarily suspended in the stomach but continues in the small intestine with enzymes secreted from the pancreas such as pancreatic amylase and other enzymes attached to the membrane of cells lining the small intestine such as maltase as well as sucrase and lactase.

Maltase breaks maltose into two glucose molecules which are then absorbed into the blood stream and taken to the liver.

Digestion of carbohydrates takes place in the
Carbohydrates are not digested in the
Starch and cellulose are examples of a
A carbohydrate is made up of 30 molecules of glucose. How many molecules of water were expelled in the making of this carbohydrate?
A carbohydrate made of 30 molecules of glucose will have
Water is formed during condensation reaction in the formation of


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