Biological Molecules - Protein Digestion & Absorption

Question 1

What is digestion?

Answer 1

• Hydrolysis of large insoluble molecules into smaller soluble molecules
• Polymers into monomers

Question 2

What is absorption?

Answer 2

• Small soluble molecules (monomers) crossing the epithelial cells lining the small intestine (ileum) and being absorbed into the blood stream

Question 3

What is assimilation?

Answer 3

• Monomers being built into polymers in the cells
• E.g. a polypeptide being made from the amino acid monomers in a condensation reaction

Question 4

What is diffusion?

Answer 4

• The movement of molecules from a high to low concentration down a concentration gradient

Question 5

What is facilitated diffusion?

Answer 5

• The movement of molecules from a high to low concentration down a concentration gradient
• Using either a protein ion channel or a carrier protein (uses the natural kinetic energy of the molecule so is a passive process)

Question 6

What is active transport?

Answer 6

• Movement of molecules against a concentration gradient, from low to high concentration
• Using the energy from ATP to change to shape of a carrier protein

Question 7

Describe protein digestion

Answer 7

• Endopeptidases hydrolyse the peptide bonds between the amino acids in the centre of the polypeptide, this increases the surface area as it creates more ends for exopeptidase
• Exopeptidase hydrolyse the peptide bonds between the terminal amino acids of the peptides formed by endopeptidases. This creates dipeptides and single amino acids
• Membrane bound dipeptidases hydrolyse the peptide bonds between the amino acids in these dipeptides

Question 8

Describe the processes involved in the absorption of the products of polypeptide digestion

Answer 8

• Sodium ions are transported out of the epithelial cell into the blood capillary by active transport which requires energy as ATP
• This creates a low concentration of sodium ions in the cell
• Sodium ions enter the cell by facilitated diffusion, taking an amino acid with it. This is a passive process as it goes from a high concentration in the lumen to a low concentration in the cell
• Amino acids enter the cell by co-transport, through a co-transport protein
• Amino acids enter the blood capillary from the cell by facilitated diffusion, through a carrier protein