23

Question 1

What are the main macronutrients contributing to energy production in the body

Answer 1

Carbohydrate, protein and fat

Question 2

Why are (to a lesser extent) nucueic acidds important?

Answer 2

• protein and nucleic acid components supply body with nitrogen which is important for the biosynthesis of various nitrogen compounds that we need for cellular function

Question 3

Why are larger compounds broken down

Answer 3

To be absorbed by the body

Question 4

Main food components and what they’re broken into

Answer 4

Question 5

After macronutrients are consumes in the diet, where do they pass through?

Answer 5

The GI tract

Question 6

These smalle dmolecules are used to

Answer 6

Make ATP

Question 7

Saliva at what ph contains what to start what?

Answer 7

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

Question 8

Function of stomach - what does it do and what dies it produce

Answer 8

Storage and mixing of food with gastric juices, producing the ‘chyme’ that is slowly released into intestine

Question 9

Things that are secreted into the stomach (by the stomach?)

Answer 9

„secretes acid (0.1 M HCl) =
denaturing

„secretes pepsinogen -> pepsin secrete
= protein digestion (protease)

„secretes mucous layer (protective)

Question 10

PH of pancreas

Answer 10

„ slightly alkaline – around pH 7

Question 11

Function of pancrease

Answer 11

„secretes most of the digestive enzymes including amylase, lipase and several proteases

Question 12

Function of liver

Answer 12

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

Question 13

Function of small intestine

Answer 13

„final phase of digestion and absorption

Question 14

Two main phases of digestion

Answer 14

1. Hydrolysis of bonds connecting monomer units in
   food macromolecules

Carbohydrate: Glycosidic bonds – starch -> disaccharides
Proteins: Peptide bonds
Fat: Triacylglycerol ester bonds
(This breakdown depends on how fast it can be absorbed into the body)

2. Absorption of hydrolysis products from gastrointestinal
   tract into body

Question 15

Digestions of dietary carbohydrates - what percent of energy does it provide - what are some examples

Answer 15

Provides 40-50% of energy intake

Starch (ie. α-amylose, amylopectin)
Simple sugars ie. sucrose, lactose, fructose, glucose (diglucose)
Fibre – such as cellulose (undigestible by most mammals) (don’t have the enzyme to hydrolyse that polymer bond)

Question 16

Main component of plant starch

Answer 16

Amylopectin

Question 17

Amylopectin is the main component of…

Answer 17

…plant starch

Question 18

Amylopectin is a polymer up to ____ _____ Union s

Answer 18

1 million glucose units

Question 19

Structure of amylopectin

Answer 19

• each bond needs a specific enzyme to be hydrolysed

Question 20

Maltose is present in…

Answer 20

…honey

Question 21

Structure of maltose - what kid of polymer..

Answer 21

Disaccharide

Question 22

C ellobiose and lactose are ________ of one another

Answer 22

stereoisomers

Question 23

stereoisomers - how Cellobiose and lactose are stereoisomers of one another - what does this mean?

Answer 23

Cellobiose is a repeating disaccharide unit in cellulose
- Mammals do not have an enzyme that can hydrolyse the b(1->4) glycosidic bonds in cellulose

Lactose is present in milk
- Some people do not have the lactase enzyme and are unable to hydrolyse lactose

Question 24

How do stereoisomers arise

Answer 24

The functional groups in monosaccharides can be in either of two orientations

There is a convention of numbering the carbon atoms

(- any functional groups - like hydroxyl groups can either be pointing out of the carbon or out the other side of the plane of the ring - this influences overall structure (although it has the same chemical make up as another stereoisomer group)

Question 25

What is sucrose made of

Answer 25

Fructose and glucose

Question 26

Sucrose is hydrolysed to form

Answer 26

Glucose and fructose

Question 27

Consumption of ‘high fructose corn syrup’ is increasing - why

Answer 27

Enzyme hydrolysis of ‘corn starch’ to glucose and isomerization to fructose - easier then other ways of sweetenening?

Question 28

Answer 28

Question 29

Starch from plants consists mainly of:

Answer 29

- Amylose (a linear polymer of a(1->4) linked glucose units) - Amylopectin (a branched polymer of a(1->4) and a(1->6) linked glucose units)

Question 30

H ydrolysis of glycogen

Answer 30

Glycogen has a similar branched structure to amylopectin Glycogen can be present in consumed foods such as liver and muscle Glycogen is synthesized in animals from glucose and stored in liver and muscle, and then broken down to glucose when required by the body The breakdown of glycogen stored in liver and muscle cells to glucose requires a ‘debranching enzyme’ (will be discussed further in Prof. Julian Eaton-Rye’s lectures)

Question 31

Glycogen has a similar branched structure to

Answer 31

Amylopectin

Question 32

Glycogen can be present in consumed food such as…

Answer 32

… liver and muscle

Question 33

Glycogen is ____ in animals from _____ and stored in ___ and _____, and then broken down to glucose when required by the body

Answer 33

synthesized glucose liver muscle

Question 34

The breakdown of glycogen stored in liver and muscle cells to glucose requires a_______

Answer 34

‘debranching enzyme’

Question 35

Hydrolysis of starch - digestion of starch

Answer 35

(Sequential hydrolysis process) The enzyme amylase hydrolyses a(1->4) glycosidic bonds Repeated internal attack yielding smaller and smaller oligosaccharides producing maltose/isomaltose disaccharides as end products

Question 36

Final digestion at ‘Brush Border’ after amylase digestion, what happens - what enzymes do what cells secrete ? What happens after?

Answer 36

Intestinal epithelial cells secrete … Maltase/isomaltase Maltose/isomaltose ——-> 2 glucose Sucrase Sucrose ———> fructose + glucose Lactase Lactose ———> galactose + glucose The monosaccharides are now absorbed into the body

Question 37

Isomaltose and maltose

Answer 37

- different isomers = different enzymes

Question 38

Overview of dietary carbohydrate processing in the gastrointestinal tract

Answer 38

Question 39

Lactose interlace - how it occurs - what is causes - how to fix it

Answer 39

L actase enzyme deficiency (genetic basis) Causes bloating, flatulence and diarrhoea due to fermentation of lactose by intestinal bacteria Need to avoid lactose in diet

Question 40

Digestion of dietary protein - what this supplies to the body

Answer 40

Supplies amino acids to make body proteins Supplies essential amino acids Source of nitrogen for purines, pyrimidines, haem Carbon skeletons can be used as fuel (N converted to urea and excreted in urine)

Question 41

Essential amino acids

Answer 41

Leucine Isoleucine Lysine Methionine Threonine Phenylalanine Tryptophan Valine (Non-essential are the amino acids we have evolved to have enzymes to break down/synthsystie/ interconvert ) Could be obtained form plant or animal sources

Question 42

Kwashiorkor - what is it caused by, what does it result in - what is low in the blood and what does that affect

Answer 42

‘Kwashiorkor’ is the result of a deficiency of dietary protein which causes an osmotic imbalance in the gastrointestinal system, causing the abdomen to swell (oedema) due to retention of water In addition, the level of albumin in the blood is low affecting colloidal osmotic (oncotic) pressure, and also transport of molecules, eg hormones and drugs

Question 43

How are proteases activated ?

Answer 43

by cleavage of peptides from their structure

Question 44

All proteases secreted as

Answer 44

All proteases secreted as inactive forms (zymogens or proenzymes) - this minimises unwanted hydrolysis of body structure

Question 45

Protein digestion

Answer 45

Involves hydrolysis of specific peptide bonds Performed by several different proteases All proteases secreted as inactive forms (zymogens or proenzymes) All proteases activated by cleavage of peptides from their structure

Question 46

Protease specificity is determined by

Answer 46

adjacent amino acid side chains in protein substrate

Question 47

Examples of amino acid side chains that determine a specific protease specificity

Answer 47

Pepsin = aromatic - ie Phe, Tyr Trypsin = positively charged - ie Lys, Arg Chymotrypsin = aromatic - ie Phe, Tyr Whether bond is hydrolysed or not depends on the amino acid side chain

Question 48

Two stages of protein digestion

Answer 48

Endopeptidases attack peptide bonds within the protein (peptide) polymer - Examples: pepsin, trypsin, chymotrypsin Exopeptidases attack peptide bonds at the end of protein (peptide) polymer - Two types: - Aminopeptidase - Carboxypeptidase

Question 49

Endopeptidases vs Exopeptidase in protein digestion

Answer 49

Endopeptidases attack peptide bonds within the protein (peptide) polymer Exopeptidases attack peptide bonds at the end of protein (peptide) polymer

Question 50

How is Pepsinogen activated to pepsin

Answer 50

Pepsinogen, the inactive zymogen (proenzyme) is activated to pepsin following exposure of pepsinogen to HCl in the stomach In the stomach acidic 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 stably activated pepsin protease - activated pepsin can also directly activate inactive pepsin (causes it to refold and become active)

Question 51

Protein digestion – sequential hydrolysis by proteases DIAGRAMS

Answer 51

Question 52

Enterokinase flow on effects on proteases from pancreas - how appropriate proteases are activated at an appropriate time to carry out their function

Answer 52

Membrane bound in the intestine lumen - able to hydrolyse part of the trypsinogen protein molecule activating it to active trypsin protease - active trypsin can active chymotrypsinogen to chymotrypsin - trypsin can also hydrolyse part of procarboxypeptidase to activate it