3.3 - Digestion and absorption

Define digestion.

The hydrolysis of large, insoluble
molecules into smaller molecules that
can be absorbed across cell
membranes.

Which enzymes are involved in
carbohydrate digestion? Where are they
found

● Amylase in mouth
● Maltase, sucrase, lactase in
membrane of small intestine

What are the substrates and products of
the carbohydrate digestive enzymes?

● Amylase → starch into smaller polysaccharides
● Maltase → maltose into 2 x glucose
● Sucrase → sucrose into glucose and fructose
● Lactase → lactose into glucose and galactose

Where are lipids digested?

The small intestine.

What needs to happen before lipids can
be digested

They must be emulsified by bile salts
produced by the liver. This breaks down
large fat molecules into smaller, soluble
molecules called micelles, increasing
surface area.

How are lipids digested?

Lipase hydrolyses the ester bond
between the monoglycerides and fatty
acids.

Which enzymes are involved in protein
digestion? What are their roles?

● Endopeptidases= break between specific
amino acids in the middle of a polypeptide.
● Exopeptidases= break between specific amino
acids at the end of a polypeptide.
● Dipeptidases= break dipeptides into amino
acids.

How are certain molecules absorbed into
the ileum despite a negative
concentration gradient?

Through co-transport.

Which molecules require co-transport?

Amino acids and monosaccharides

Explain how sodium ions are involved in
co-transport.

Sodium ions (Na + ) are actively transported
out of the cell into the lumen, creating a
diffusion gradient. Nutrients are then taken
up into the cells along with Na + ions

Why do fatty acids and monoglycerides
not require co-transport?

The molecules are nonpolar, meaning
they can easily diffuse across the
membrane of the epithelial cells.