3.3 starch digestion

what is starch made out of

many α-glucose monomers

what are enzymes involved in starch digestion

-amylase

-maltase

describe amylase. where produced?

site of action?

reaction

-produced in salivary glands & pancreas

-in mouth & small intestine

-reaction: Breaks starch into maltose by hydrolysing glycosidic bonds

explain maltose. where produced?

site of action?

reaction

-produced in epithelial cells of the small intestine. This is a membrane-bound disaccharidase (found embedded in the membranes of the epithelial cells lining the villi)

-acts in small intestine

-Reaction: Breaks maltose into two glucose molecules by hydrolysing glycosidic bonds

where does starch absorption happen (3 steps)

1. in the mouth

2. in the small intestine

3. in the epithelial lining of small intestine

explain the whole process of starch absorption (3 steps)

1. In the Mouth

• Salivary amylase begins starch digestion → Produces maltose.

• pH maintained by saliva (contains mineral salts) to keep amylase active.

• Amylase is denatured by stomach acid, stopping starch digestion in the stomach.

2. In the Small Intestine

• Pancreatic amylase continues starch breakdown → Produces maltose.

• Alkaline conditions maintained by bile released into the small intestine.

3. At the Epithelial Lining of the Small Intestine

• Maltase hydrolyses maltose → Produces glucose.

• Glucose absorbed by co-transport with sodium ions.

explain what happens in the mouth during starch digestion

• Salivary amylase begins starch digestion → Produces maltose.

• pH maintained by saliva (contains mineral salts) to keep amylase active.

• Amylase is denatured by stomach acid, stopping starch digestion in the stomach.

what happens in the small intestine during starch digestion

• Pancreatic amylase continues starch breakdown → Produces maltose.

• Alkaline conditions maintained by bile released into the small intestine.

what happens at the epithelial lining of the small Intestine during starch digestion

• Maltase hydrolyses maltose → Produces glucose.

• Glucose absorbed by co-transport with sodium ions.

role of salivary glands in starch digestion

secrete amylase which hydrolyses starch > maltose

role of pancreas in starch digestion

produces pancreatic juice containing:

-protease

-lipase

-amylase

why do we hydrolyse carbohydrates into monosaccharides

they are small & soluble so can be carried through the cell-surface membranes of cells lining the intestines & enter the blood

why does saliva contain mineral salts

to keep pH neutral

how is maltose made during starch digestion

amylase hydrolyses alternate glycosidic bonds along the starch molecule

what happens to the maltose in the stomach

HCL causes salivary amylase to denature, preventing any further hydrolysis of starch

what happens to maltose in the small intestine

-it is mixed with pancreatic juice

-it contains amylase and alkaline salts which neutralise the HCL

what happens to maltose in the ileum

smooth muscles in the small intestine force maltose down the ileum

what does maltase enzyme bind to

membranes of the ileum epithelial cells

what happens to maltose in the lining of small intestines

-epithelial cells lining the small intestines have maltase, sucrase and lactase in the cell-surface membranes

-maltose > glucose

-glucose is released into the epithelial cells

what are membrane bond disaccharides

enzymes attached to the cell membrane of epithelial cells lining the ileum (final part of the small intestines)

how can be monosaccharides be transported through the epithelial cells

via specific transporter proteins