BIOC192 Lecture 23 - Metabolism: Digestion of Food Molecules

Question 1

what are the main macronutrients contributing to the energy production in. the body?

Answer 1

• carbohydrates
• proteins
• fats
• nucleic acids

Question 2

what are carbohydrates broken down into?

Answer 2

monosaccharides

Question 3

what are proteins broken down into?

Answer 3

amino acids

Question 4

what are nucleic acids broken down into?

Answer 4

nucleotides

Question 5

what are fats broken down into?

Answer 5

FFAs, MAG, and cholesteral

Question 6

what do salivary glands contain and what do they start?

Answer 6

saliva (neutral pH) contains mucous and amylase which starts the digestion of carbohydrates

Question 7

what 3 things does the stomach secrete?

Answer 7

1) secretes acid (0.1 M of HCI) causing denaturing
2) secretes pepsinogen –> pepsin causing protein digestion
3) secretes mucous layer for protection against the acids conditions

Question 8

what does the liver secrete?

Answer 8

secretes most digestive enzymes including amylase, lipase and several proteases

Question 9

what does the liver synthesis and what is this important for?

Answer 9

synthesis of bile salts/acids (stored in the gall bladder) that is important for fat digestion

Question 10

where is the final phase of digestion and absorption?

Answer 10

the small intestine

Question 11

what are the two main phases of digestion?

Answer 11

1) hydrolysis of bonds connecting monomer units in food macromolecules
2) absorption of products from GI tract?

Question 12

what occurs during the hydrolysis of bonds connecting monomer units in food macromolecules?

Answer 12

1) carbohydrates: glycosidic bonds - starch –> disaccharides
2) proteins: peptide bonds
3) fat: triacylglycerol ester bonds

Question 13

how many percent of energy intake does the digestion of dietary carbohydrates provide?

Answer 13

40-50%

Question 14

what are the 3 dietary carbohydrates?

Answer 14

1) starch
2) simple sugars i.e sucrose, lactose, fructose, glucose
3) fibre i.e cellulose

Question 15

what is the main component of plant starch?

Answer 15

amylopectin

Question 16

what is the relationship between the functional groups in monosaccharides and orientation?

Answer 16

the functional group in monosaccharides can be in either of 2 orientations

Question 17

what are the 6 enzymes involved in carbohydrate digestion?

Answer 17

1) salivary amylase
2) pancreatic amylase
3) maltase
4) lactase
5) sucrase
6) isomaltase

Question 18

what is amylose?

Answer 18

a linear polymer of alpha (1->4) liked glucose units

Question 19

what is amylopectin?

Answer 19

a branched polymer of alpha (1->4) and alpha (1->6) linked glucose units

Question 20

what has a similar branched structure to amylopectin?

Answer 20

glycogen

Question 21

where can glycogen be present?

Answer 21

can be present in consumer foods such as liver and muscle

Question 22

what occurs during the hydrolysis of starch?

Answer 22

• starch digestion is when the enzyme amylase hydrolyses alpha (1->4) glycosidic bonds
  the repeated internal attack yielding smaller and smaller oligosaccharides producing maltose/isomaltose disaccharides as end products

Question 23

what does the digestion of dietary protein supply?

Answer 23

supplies amino acids to make body proteins

Question 24

what is the digestion of dietary fibre a source of?

Answer 24

source of nitrogen for purines, pyrimidines and haem

Question 25

what are the 8 essential amino acids required for the human body that are acquired from the environment?

Answer 25

1) leucine
2) lysine
3) threonine
4) tryptophan
5) isoleucine
6) methionine
7)
phenylalanine
8) valine

Question 26

what form are all proteases in the human body secreted as?

Answer 26

secreted as inactive forms (zymogens or proenzymes)

Question 27

how are all proteases in the human body activated by?

Answer 27

activated by the cleavage of peptides from their structure

Question 28

how is protease specificity determined?

Answer 28

determined by adjacent amino acid side chains

Question 29

what are the 2 types of peptidases involved in protein digestion?

Answer 29

1) endopeptidase

2) exopeptidase

Question 30

what is the function of endopeptidases?

Answer 30

attack peptide bonds WITHIN the protein (peptide) polymer

Question 31

what is the function of exopeptidases?

Answer 31

attack peptide bonds at the end of the protein (peptide) polymer

Question 32

how is pepsinogen activated to pepsin?

Answer 32

pepsinogen, the inactive zymogen (proenzyme) is activated to pepsin following the exposure of pepsinogen to HCI in the stomach
-in the acidic stomach environment, part of the pepsinogen protein unfolds, which activates the pepsin protease and results in hydrolysis of part of the pepsinogen protein sequence to generate a stably activated pepsin protease