Digestion and absorption

What is digestion?

hydrolysis of large insoluble substances to smaller soluble substances

- that can be absorbed through the bloodstream

roles of enzymes in the complete breakdown of starch

• Amylase: hydrolyses starch into maltose

  • by hydrolysing the glycosidic bonds

• Maltase: hydrolyses maltose to glucose

  • by hydrolysing the glycosidic bonds

the process of starch digestion

1. glucose moves into epithelial cell with sodium via carrier protein

2. sodium removed from epithelial cell by AT and moves into the blood, maintaining a low concentration of sodium

3. glucose moves into blood by facilitated diffusion

In a person with a blocked pancreatic duct, starch digestion is affected.

Explain how

blocked pancreatic ducts means that less amylase can enter the small intestine

• so less starch is digested

Healthy people have amylase in their blood. Explain why this doesn’t cause any harmful effects,

amylase is specific to starch

also theres no starch in human blood

Explain how the epithelial cels that line the small intestine are adapted for the absorption of glucose.

1. microvilli which provide large SA

2. many mitochondria which produce ATP

3. carrier proteins for active transport

4. carrier proteins for facilitated diffusion

5. co-transport fo sodium (ions) and glucose

6. membrane-bound enzymes that digest disaccharides, producing glucose

structure of proteins

• proteins are polymer of amino acids joined by peptide bonds, formed by condensation reaction

• primary structure: order of AA

• secondary structure: folding of polypeptide chain due to hydrogen bond

  • forms alpha helix and beta pleated sheets

• tertiary: unique 3D shape formed by the folding of polypeptide chain

  • due to hydrogen bonding, ionic bonding and disulfide bridges

• quaternary structure: 2 or more polypeptide chain

Explain why releasing protein-digesting enzymes into the blood can be harmful the body

these enzymes could digest hormones/antibodies in the blood

Co-transport of sodium and glucose

1. Sodium ions actively transported from ileum to blood

- maintains concentration gradient for sodium

2. glucose enters by facilitated diffusion with sodium ions

Explain why the combined action of endopeptidases and exopeptidases are more efficient that exopeptidases on their own

1. Endopeptidases hydrolyse internal peptide bonds and exopeptidases hydrolyse amino acids at the ends

2. so increase in SA

Role of enzymes in digestion of proteins

1. Hydrolysis of peptide bonds

2. Exopeptidases act at the end of the polypeptide chain

• hydrolyse amino acids at the ends of the chain

3. Endopeptidases act in the middle of polypeptide chain and hydrolyse internal peptide bonds

4. Dipeptidases acts b/w 2 amino acids

Trypsin is a protease.

Suggest the advantage of producing trypsin in an inactive form inside cells in the pacreas

doesnt digest proteins inside the cells

• so pancreatic cells are not destroyed

What are lipids digested by?

Lipase and the action of bile salts

Where is lipase produced and how does lipase digest lipids?

Pancreas and small intestine

Hydrolyses the ester bond in triglycerides to form the monoglycerides and fatty acids

Where are bile salts produced and what do they do?

liver

Emulsify lipids to form tiny droplets called micelles

What are micelles?

water soluble vesicles formed of fatty acids, glycerol and bile salts

describe the action of membrane-bound dipeptidases and explain their importance

• hydrolyses peptides to release amino acids

• amino acids can cross cell membranes, whereas dipeptides cannot cross cell membrane

Explain the advantages of lipid droplet and micelle formation

1. Droplets increase surface areas for lipase / enzyme action

   • So faster hydrolysis/digestion of lipids

2. Micelles carry fatty acids and glycerol through membrane to epithelial cell

Golgi apparatus in lipid transport

1. Modifies lipids

2. Combines triglycerides with proteins

3. Packages them for exocytosis

Digestion and absorption of lipid molecules

1. Micelles contain bile salts and fatty acids

- this makes fatty acids more soluble in water

2. Micelles carry fatty acids to lining of epithelium

3. Fatty acids absorbed by diffusion

When in cell:

1. Triglycerides reform

2. Vesicles move to cell membrane