Metabolism - Lecture Twenty-Three

Question 1

Carbohydrates ➝

Answer 1

Monosaccharides

Question 2

Protein ➝

Answer 2

Amino acids

Question 3

Nucleic acids ➝

Answer 3

Nucleotides

Question 4

Fat ➝

Answer 4

Free fatty acids, monoacylglycerols and cholesterol

Question 5

Salivary glands

Answer 5

Saliva (neutral pH) contains mucous and amylase which start the digestion of carbohydrates

Question 6

Stomach

Answer 6

Storage and mixing of food with gastric juices, slowly releases chyme into intestine

Question 7

What does the stomach secrete?

Answer 7

Acid (0.1M HCl)

Pepsinogen ➝ Pepsin = Protein digestion

Question 8

Pancreas

Answer 8

Slightly alkaline pH 7 which secretes most of the digestive enzymes including amylase, lipase and several proteases

Question 9

Liver

Answer 9

Synthesis of bile salts/acids (stored in gall bladder) important for fat digestion

Question 10

Small intestine

Answer 10

Final phase of digestion and absorption

Question 11

Digestion: first phase

Answer 11

Hydrolysis of bonds connecting monomer units in food macromolecules
Carbohydrate: Glycosidic bonds - starch → disaccharides
Proteins: Peptide bonds
Fat: Triacylglycerol ester bonds

Question 12

Digestion: second phase

Answer 12

Absorption of products from gastrointestinal tract into body

Question 13

Digestion of dietary carbohydrates

Answer 13

Provides 40-50% of energy intake

Question 14

Dietary carbohydrates

Answer 14

Starch, simple sugars and fibre

Question 15

Amylopectin

Answer 15

Main component of plant starch

Question 16

Maltose

Answer 16

Present in honey

Question 17

Cellobiose and lactose

Answer 17

Are stereoisomers of one another

Question 18

Cellobiose

Answer 18

Repeating disaccharide unit in cellulose

Question 19

Lactose

Answer 19

Present in milk

Question 20

Sucrose hydrolysed to

Answer 20

glucose and fructose

Question 21

Starch from plants consists mainly of

Answer 21

Amylose

Amylopectin

Question 22

Glycogen

Answer 22

Glycogen has a similar branched structure to amylopectin and can be present in consumed foods

Question 23

Glycogen synthesis in animals

Answer 23

From glucose and stored in liver and muscles and then broken down to glucose when required by the body

Question 24

The breakdown of glycogen

Answer 24

Stored in liver and muscle cells to glucose requires a ‘de-branching enzyme’

Question 25

The enzyme amylase hydrolyses

Answer 25

Alpha (1➝4) glycosidic bonds

Question 26

Lactose intolerant

Answer 26

Lactase enzyme deficiency causes bloating, flatulence and diarrhoea due to fermentation of factor by intestinal bacteria

Question 27

Essential amino acids

Answer 27

``` Leucine Lysine Threonine Isoleucine Methionine Phenylalanine Valine ```

Question 28

Protein digestion

Answer 28

Involves hydrolyses of specific peptide bonds and is performed by several different proteases

Question 29

Protein digestion: proteases secreted

Answer 29

As inactive forms (zymogens and proenzymes)

Question 30

Protein digestion: proteases activated

Answer 30

By cleavage of peptides from their structure

Question 31

How is protease specificity determined?

Answer 31

By adjacent amino acid side chains

Question 32

Pepsin =

Answer 32

Aromatic i.e. Phe and Tyr

Question 33

Trypsin =

Answer 33

+ charged i.e. Lys and Arg

Question 34

Chymotrypsin =

Answer 34

Aromatic i.e. Phe and Tyr

Question 35

Endopeptidases

Answer 35

Attack peptide bonds within the protein polymer e.g. pepsin, trypsin and chymotrypsin

Question 36

Exopeptidases

Answer 36

Attack peptide bonds at the end of protein polymer e.g. amino peptidases and carboxypeptidase

Question 37

Pepsinogen

Answer 37

Inactive zymogen (proenzyme) is activated to pepsin following exposure of pepsinogen to HCl in the stomach

Question 38

In the stomach acidic environment, part of the pepsinogen protein unfolds

Answer 38

This activates the pepsin protease and results in hydrolysis of part of the pepsinogen protein sequence to generate stably activated pepsin proteases