3.3 Topic 3 - 3.3.3 Digestion and absorption

Question 1

Large biological molecules such as starch and proteins are too big to cross cell membranes. This means that …

Answer 1

… they cannot be absorbed from the gut into the blood.

Question 2

What happens to large biological molecules during digestion?

Answer 2

They are broken down into smaller molecules such as glucose and amino acids which can cross cell membranes and therefore be absorbed from the gut into the blood to be transported around the body for use by the body cells.

Question 3

During hydrolysis, bonds are broken by adding water. What happens during the hydrolysis of carbohydrates?

Answer 3

Carbohydrates are hydrolysed into disaccharides and then monosaccharides.

Question 4

During hydrolysis, bonds are broken by adding water. What happens during the hydrolysis of fats?

Answer 4

Fats are hydrolysed into fatty acids and monoglycerides.

Question 5

During hydrolysis, bonds are broken by adding water. What happens during the hydrolysis of proteins?

Answer 5

Proteins are hydrolysed into amino acids.

Question 6

What type of enzymes are used to break down biological molecules in food?

Answer 6

Digestive enzymes.

Question 7

Digestive enzymes are produced by specialised cells in the digestive systems of mammals. Where are these enzymes then released?

Answer 7

Into the gut to then mix with the food.

Question 8

What enzyme breaks down carbohydrates?

Answer 8

Amylase.

Question 9

What is amylase? + what bond is broken?

Answer 9

Amylase is a digestive enzyme that catalyses the conversion of starch [a polysaccharide] into the smaller sugar maltose [a disaccharide]. This involves the hydrolysis of the glycosidic bonds in starch.

Question 10

Where is amylase produced? [2]

Answer 10

In the salivary glands [release amylase into the mouth].
&
In the pancreas [releases amylase into the small intestine].

Question 11

What are membrane-bound disaccharides?

Answer 11

Enzymes which are attached to the cell membranes of epithelial cells lining the ileum [final part of the small intestine].

Question 12

What do membrane-bound disaccharides do?

Answer 12

They help to break down disaccharides into monosaccharides. This involves the hydrolysis of the glycosidic bonds.

Question 13

What are 3 examples of disaccharides?

Answer 13

Maltose, sucrose and lactose.

Question 14

What are 3 examples of monosaccharides?

Answer 14

Glucose, fructose and galactose.

Question 15

What ….saccharides can be transported across the cell membranes of the ileum epithelial cells via specific transporter proteins?

Answer 15

Monosaccharides.

Question 16

What enzyme breaks down lipids?

Answer 16

Lipase [+ the help of bile salts].

Question 17

What do lipase enzymes do? + what bond is broken?

Answer 17

Lipase enzymes catalyse the breakdown of lipids into monoglycerides and fatty acids. This involves the hydrolysis of the ester bonds in lipids.

Question 18

What is a monoglyceride?

Answer 18

A glycerol molecule with one fatty acid attached.

Question 19

Where are lipases produced?

Answer 19

In the pancreas [they work in the small intestine].

Question 20

Where are bile salts produced?

Answer 20

In the liver.

Question 21

What is the role of bile?

Answer 21

To emulsify lipids [they cause the lipids to form small droplets].

Question 22

True or false? Several small lipid droplets have a bigger surface area than a single large droplet for the same volume of lipid.

Answer 22

True.

Question 23

What does the formation of small lipid droplets do to the surface area?

Answer 23

Greatly increases the surface area of lipid that’s available for lipases to work on.

Question 24

What happens one the lipid has been broken down? + what is formed?

Answer 24

The monoglycerides and fatty acids stick with the bile salts to form tiny structures called micelles.

Question 25

What is an arrow diagram of the break down of a large lipid droplet?

Answer 25

Big lipid droplet + bile salts [–> emulsification] small lipid droplets [–>lipase digestion of lipid] micelles.

Question 26

What enzymes breaks down proteins?

Answer 26

Endopeptidases and exopeptidases.

Question 27

What are endopeptidases and exopeptidases called together?

Answer 27

A combination of different proteases [or peptidases].

Question 28

What do proteases [or peptidases] do and what are they? + what bond is broken?

Answer 28

They are enzymes which catalyse the conversion of proteins into amino acids by hydrolysing the peptide bonds between amino acids.

Question 29

Do endopeptidases hydrolyse peptide bonds within or outside a protein?

Answer 29

Within.

Question 30

What are 2 examples of endopeptidases?

Answer 30

Trypsin and chymotrypsin.

Question 31

Where are endopeptidases synthesised and secreted into?

Answer 31

Synthesised in the pancreas and secreted into the small intestine.

Question 32

What is the name of another endopeptidase with is released into the stomach by cells in the stomach lining?

Answer 32

Pepsin.

Question 33

In what conditions does pepsin only work in? + what are the conditions provided by?

Answer 33

Acidic conditions which are provided by hydrochloric acid in the stomach.

Question 34

What do exopeptidases do?

Answer 34

They act to hydrolyse peptide bonds at the ends of protein molecules. They remove single amino acids from proteins.

Question 35

What are dipeptidases? + what do they do?

Answer 35

They are exopeptidases that work specifically on dipeptides. They act to separate the two amino acids that make up a dipeptide by hydrolysing the peptide bond between them.

Question 36

Where are dipeptidases often located?

Answer 36

They are ofter located in the cell-surface membrane of epithelial cells in the small intestine.

Question 37

What are the products of digestion absorbed across?

Answer 37

The ileum epithelium into the bloodstream [across cell membranes].

Question 38

How is glucose absorbed? + what other molecule is also absorbed this way?

Answer 38

Glucose is absorbed by active transport with sodium ions via a co-transporter protein. Galactose is also absorbed int he same way.

Question 39

How is fructose absorbed?

Answer 39

Fructose is absorbed via facilitated diffusion through a different transporter protein.

Question 40

What helps to move monoglycerides and fatty acids towards the epithelium?

Answer 40

Micelles.

Question 41

How do micelles allow monoglycerides and fatty acids to be absorbed?

Answer 41

Because micelles constantly break up and reform they can ‘release’ monoglycerides and fatty acids, allowing them to be absorbed.

Question 42

What are monoglycerides and fatty acids, allowing them to diffuse directly across the epithelial cell membrane?

Answer 42

Lipid-soluble.

Question 43

How are amino acids absorbed?

Answer 43

Via co-transport, in a similar way to glucose and galactose. Sodium ions are actively transported out of the ileum epithelial cells into the blood. This creates a sodium ion concentration gradient. Sodium ions can then diffuse from the lumen of the ileum into the epithelial cells through sodium-dependent transporter proteins, carrying the amino acids with them.