Chronic Diseases - Biochemistry

Question 1

List 3 functions of carbohydrates

Answer 1

1. Energy source
2. Energy storae
3. Structural component

Question 2

What is the general formula of a carbohydrate?

Answer 2

(CH₂O)_n

Question 3

What is a monosachharide?

Answer 3

1 sugar unit

Question 4

What is a disaccharide?

Answer 4

2 sugar units

Question 5

What is an oligosaccharide?

Answer 5

3 to 10 sugar units

Question 6

What is a polysaccharide?

Answer 6

11to > 100 sugar units

Question 7

Fill the table of the classification of monosaccharides according to number of carbons

Answer 7

Question 8

What is the general name of the two monosaccharide functional groups shown?

Answer 8

Question 9

Draw the general structure of an aldoses and ketoses

Answer 9

Question 10

What are isomers?

Answer 10

Compounds with the same chemical formula but different structures

Question 11

Carbohydrate isomers that differ in configurationaround only one specific carbon atom are defined as what?

Answer 11

Epimers of each other

Question 12

What are enantiomers?

Answer 12

Pairs of structures that are mirror images of each other. The structures cannot be superimposed (placed/laid over each other)

Question 13

Describe the concept of D and L designations

Answer 13

• D and L designations are based on the configuration of the single asymmetric carbon atom in glyceraldehyde
• L isomers have H attached to left (below carbon back bone plane) and D isomers have OH attached to the right (above carbon back bone plane)

Question 14

99% of monosaccharides with 5 or more carbon atoms form a ring structure. How are the ring structures formed?

Answer 14

When forming a ring structure, the aldehyde or ketone function reacts with the hydroxyl group of the same monosaccharide

Question 15

Cyclization creates an anomeric carbon atom. What does this mean?

Answer 15

In a cyclic carbohyrate, an anomeric carbon is the carbon that was the carbonyl carbon in the acyclic form

Question 16

a) Describe the function of glucose
b) Which sources can we obtain glucose from?

Answer 16

a)

• Primary energy source
• Preferred energy source of brain
• Required energy source of cells with few or no mitochondria
• Essential in excercising muscle

b)

• Diet
• Degradation of glycogen
• Gluconeogenesis

Question 17

a) Describe the function of fructose
b) Which sources can we obtain fructose from?

Answer 17

a) Ehances glucose metabolism and sweeter than glucose

b)

• Fruits
• Vegetables
• Honey

Question 18

a) Describe the function of galactose
b) Which sources can we obtain galactose from?

Answer 18

a) Aids in glucose metabolsim - energy source and less sweet than glucose
b) Dairy products

Question 19

Describe the structure and role of maltose

Answer 19

• Alpha glucose + Alpha glucose
• glycosidic bond between glucose and glucose
• Major degradation of starch
• Malt sugar

Question 20

Describe the structure and role of sucrose

Answer 20

• Sucrose + fructose
• α(1→2)β-glycosidic bond between glucose and fructose
• Prevalent in sugar caneand sugar beats
• Table sugar

Question 21

Describe the structure and role of lactose

Answer 21

• Glucose + galactose
• β(1→2) glycosidic bond between glucose and galactose
• In mammalian milk
• Milk sugar

Question 22

Discuss the structure and function of cellulose

Answer 22

• Polysaccharide of beta glucose monomers
• β(1→4) glycosidic bond between glucose and glucose
• Hydrogens in between linkages which forms microfibrils which is very strong. This is found in cell wall in plants - structural support
• Humans cannot digest cellulose as we do not have the enzyme to break down the β(1→4) glycosidic bond
• Form dietary fibre

Question 23

Discuss the structure and function of starch

Answer 23

• Polysaccharide of alpha glucose mono
• Amylose - unbranched polymer, α(1→4) glycosidic linkages
• Amylopectin - branched polymer, α(1→4) and branches at α(1→6) linkages
• Prevalent in all plant seed and tubers
• Storage energy in plants

Question 24

Discuss the structure and function of glycogen

Answer 24

• Polysaccharide of alpha glucose monomers
• Branched
• Mainly α(1→4) linkages and branches at α(1→6) linkages
• Energy storage in animals and fungi

Question 25

Discuss the digestion of carbohydrates in the body

Answer 25

1. Mouth: salivary α-amylase hydrolyses α(1→4) glycosidic bonds in maltose and dextrin (mixtures of polymers of D-glucose units linked by α-(1→4) or α-(1→6) glycosidic bonds) to form glucose
2. Small intestine: pancreatic α-amylase breaks down more maltose and dextrin to form glucose
3. Upper jejunum: brush border membrane-associated oligosaccharidases and disaccharidases of intestinal mucosal cells (maltase, fructase and sucrase) breeak down oligosaccharides and disaccharides into glucose, fructose and galactose

Question 26

Describe the absorption of carbohydrates

Answer 26

Monosacharides are absorbed by intestinal mucosal cells (from lumen to enterocyte)

• Glucose, galactose: sodium-dependant glucose cotransporter 1 (SGLT-1)
• Fructose: sodium-independant monosaccharide transporter (GLUT-5)

All three monosaccharides are transported from the intestinal cells into the portal circulation by GLUT-2

Question 27

Discuss glucose metabolism including its role in glycolysis and pentose phosphate pathway

Answer 27

• Glucose is broken down to pyruvate in glycolysis → acetyl CoA → CO₂ (Krebs cycle)
• Glucose can be resynthesized from pyruvate in gluconeogenesis
• In anaerobic conditions pyruvate is reduced to lactate (anaerobic glycolysis)
• In the pentose phosphate pathway glucose produces NADPH and ribulose-5-P → ribose-5-P → precursor for DNA and RNA
• Glucose can be stored in the form of glycogen (glycogenesis)

Question 28

a) Give 2 deficiences in carbohyrate degradulation
b) Give and explain the symptoms

Answer 28

a) Lactose intolerance and isomaltose/sucrose intolerance

b)

• Undigested carbohydrate will pass in large intestine → osmotic diarrhoea
• Bacterial fermentation of carbohydrate produces large volumes of CO₂ and O₂ → abdominal cramps, diarrhoea, flatulence