digestion + enzymes

Question 1

what are the two ways in which the digestie system breaks down food?

Answer 1

1) physical digestion
- the break down of large food peices into smaller ones
- to increase surface area for chemical digestion

2) chemical digestion
- enzymes catalyse hydrolysis reactions
- that breaks bonds in large insolubale molecules to form smaller soluable ones

Question 2

what are the key components involved in digestion?

hint: list them + briefly explain what they do

Answer 2

1) salivary glands
- secrete saliva containing amylase

2) oesophagus
- transports food to the stomach

3) stomach
- stores + digests food
- produces acids to destroy pathogens

4) liver
- produces bile salts
- to aid lipid digestion

5) pancreas
- secretes proteases, lipases, amylases

6) small intestine
- contains ileum = long muscular tube

7) large intestine
- absorbs water + stores waste

8) rectum
- stores faeces before removal via anus

Question 3

list the three main digestive enzymes + what they do/what they digest

Answer 3

1) carbohydrases
- hydrolyse carbohydrates
- into monosaccharides

2) lipases
- hydrolyse lipids (fats and oils)
- into glycerol + fatty acids

3) proteases
- hydrolyse proteins
- into amino acids

Question 3

describe the process of starch digestion

hint: 4 points to be made

Answer 3

1) salivary amylase break down starch into maltose
2) stomach acid denatures salivary amylase
3) pancreatic amylase continues starch digestion (in small intestine)
4) eptheliual cells produce maltase to break maltose into alpha glucose

Question 4

describe the process of lipid digestion

Answer 4

1) bile salts emulsify lipids into micelles
- this increases surface area of lipids

2) pancreatic lipase breaks down micelles into fatty acids and monoglycerides

Question 5

where are lipids digested?

Answer 5

small intestine

Question 6

how does lipase actually work?

Answer 6

breaks ester bond between monoglycerides and fatty acids

Question 7

what are the bonds found between carbohydrates, lipids, and proteins?

Answer 7

carbohydrates= glycosidic
lipids= ester
proteins= peptide

Question 8

what are the three types of protease?

Answer 8

1) endopeptidases:
- hydrolyse internal peptide bonds
- to form shorter polypeptides
- increasing number of ends for protease to work on

2) exopeptidases
- hydrolyse peptide bonds at ends of polypeptide
- removes terminal amino acids or dipeptides

3) dipeptidases
- break down any remaining dipeptides into amino acids

Question 9

describe how glucose/amino acids are transported into the bloodstream in the small intestine

hint: this question is asking you to explain co transport!!!

Answer 9

• sodium ions actively transported out of epithelial cells
• creates concentration gradient
• sodium ions diffuse from lumen –> epithelial cells via co transporter proteins (down conc gradient)
• co transporter protiens carries glucose/amino acids into cell with sodium
• conc of glucose/amino acids increases
• glucose/amino acids move by facilitated diffusion from epithelium cells into blood

Question 10

describe how triglycerides + other lipids are absorbed into the bloodstream

might be asked as a 6 marker!!!

Answer 10

1) micelles broken down to release fatty acids + monoglycerides
2) because they are non polar, they diffuse across phospholipid bilayer into epithelial cells
3) triglycerides reformed in endoplasmic reticulum
4) triglycerides packed into chylomicrons
5) chylomicrons released by exocytosis into lacteals
6)chylomicrons transported via lymph vessels into bloodstream

Question 11

describe how a protein would be digested?

this may also be asked in the form of an example of a protein e.g. ‘describe how an antibody would be digested’

Answer 11

• peptide bonds are hydrolysed
• endopeptidass break internal peptide bonds
• exopeptidases break terminal peptide bonds
• dipeptidases break dipeptides into amino acids