Lecture 2.1: Energy Production from Carbohydrates (1)

Question 1

What is Anabolism?

Answer 1

The synthesis of larger molecules from simple molecules

(Monomers to Polymer)

Question 2

What is Catabolism?

Answer 2

The breakdown of complex molecules in living organisms to form simpler ones

(Polymer to Monomer)

Question 3

What are the 4 Stages of Catabolism?

Answer 3

1: Extracellular, GI Tract. Lipids, Carbs broken down into smaller parts so they can be taken into cells
2: Intracellular in cytosol and mitochondria [Glycolysis]
3: Intracellular in mitochondria [Krebs Cycle]
4: Intracellular in mitochondria [Oxidative Phosphorylation]

Question 4

Recommend Daily Intake of C,L&P

Answer 4

Carbs: 15%
Lipids: 8%
Proteins: 5%

Question 5

What are Carbohydrates?

Answer 5

General formula: (CH2O)n
Contain aldehyde or ketone group
Hydrophilic

Question 6

Monosaccharides

Answer 6

Glucose
Fructose
Galactose

Question 7

Aldose

Answer 7

Aldehyde containing sugar

Question 8

Ketose

Answer 8

Ketone containing sugar

Question 9

Isomers of Glucose

Answer 9

D and L

But only D isomer is naturally occurring

Question 10

Common Disaccharides

Answer 10

Lactose: Galactose + Glucose
Maltose: Glucose + Glucose
Sucrose: Glucose + Fructose

Question 11

α-glucose vs β-glucose

Answer 11

α-glucose: -OH group is below on Carbon 1
β-glucose: -OH group is above on Carbon 1

Question 12

Monosaccharide Shape

Answer 12

Not Planer

They assume “boat” or “chair” shapes in 3D space

Question 13

Oligosaccharides

Answer 13

Contain 3 –12 monosaccharides

Question 14

Polysaccharides

Answer 14

Contain 10 – 1000 monosaccharides

Question 15

Glycogen

Answer 15

– Human Starch, stored in liver and skeletal muscle
– α-glucose
– Contains α1,4 and α1,6 glycosidic bonds
– Highly Branched Structure [allows more rapid breakdown from all ends for
energy production]

Question 16

Starch

Answer 16

– Polymer of glucose found in plants
– Mixture of amylose (α1-4 bonds) and amylopectin and α1-4 andα1-6
glycosidic bonds
– Less branched than glycogen
– GI tract enzymes release glucose and maltose

Question 17

Cellulose

Answer 17

– Structural polymer of glucose in plants
– β1-4 linkages
– No GI enzymes to digest β1-4 Linkages
– It forms dietary fibre that is important for GI function

Question 18

Digestion of Dietary Carbohydrates: where? what enzymes?

Answer 18

Mouth: Salivary α-amylase

Pancreas: α-amylase

Small intestine: Pancreatic amylase

Disaccharidases attached to brush border membrane of epithelial cells (enterocytes): lactase, sucrase, maltase, isomaltase

Question 19

Carbohydrate Transport

Answer 19

Glucose, galactose and fructose are transported to enterocytes by facilitated or active transport

GLUT2 (glucose transporter type 2)
SGLT1 (Na+/glucose/galactose cotransporter)
GLUT5 (fructose transporter type 5)

They are transported from enterocytes to blood by GLUT2 and then transported to target tissues via various transporters

Question 20

GLUT Transporters and their corresponding organs

Answer 20

Brain: GLUT3
Heart/Fatty Tissue/Skeletal Muscle: GLUT4
Enterocytes: GLUT1
Liver/ Pancreatic β-cells/ Intestines/ Kidney: GLUT2
Jejunum/ Kidney: GLUT5

Question 21

Lactose Intolerance: Science

Answer 21

Loss of / reduced lactase activity
→ Therefore Inability to hydrolyse lactose

Results from reduced expression of the LCT gene

Onset from late childhood to early adulthood

Question 22

Lactose Intolerance: Consequences

Answer 22

Undigested lactose is passed to the large intestine

Increases osmotic pressure and draws in H2O causing osmotic diarrhoea

Fermented by colonic bacteria produces organic acids (acetic and lactic
acids) and H2, CO2 and CH4 gases causing abdominal cramps and flatulence

Question 23

Lactose intolerance: Symptoms, Clinical Tests, Management

Answer 23

No immune system involvement/ Not allergic reaction

Symptoms: abdominal pain, bloating, diarrhoea, and nausea appear in 30
to 120 minutes following consumption of lactose

Clinical Tests: Positive hydrogen breath test, Positive stool acidity test

Management: Decrease or elimination of the amount of lactose in diet, Consumption of lactase-treated foods or lactase supplements

Question 24

Anaerobic Glycolysis: Lactate Dehydrogenase (LDH) Reaction

Answer 24

Overall reaction of the 11- step anaerobic glycolysis:

Glucose + 2 Pi + 2 ADP → 2 lactate + 2 ATP + 2 H2O

Question 25

Where Does Lactate Go?

Answer 25

The lactate produced by skeletal muscle and RBCs is released into the blood

It is then metabolised by the liver, heart and kidney

2 NADH + (2 H+) + 2 pyruvate (2 NAD+) + 2 lactate

This is facilitated by LDH in both directions

Question 26

Plasma Lactate Concentrations

Answer 26

Blood concentration normally constant: <1 mM

Hyperlactaemia: 2-5 mM in blood, Below renal threshold, No change in blood pH (buffering capacity)

Lactic acidosis: Above 5 mM in blood, Above renal threshold, Blood pH lowered

Question 27

Essential fructosuria

Answer 27

Caused by fructokinase deficiency

Fructose accumulates in urine

No symptoms

Question 28

Fructose Intolerance

Answer 28

Caused by aldolase deficiency

Fructose-1-P accumulates in liver, liver damage and hypoglycaemia

Symptoms: poor feeding as baby, vomiting, nausea, abdominal pain

Treatment- elimination of sucrose and fructose from diet

Question 29

Galactokinase Deficiency‐Non‐Classical Galactosaemia

Answer 29

Very rare

↑ Galactose in blood (Galactosaemia) and urine (Galactosuria)

Galactose and Galactitol accumulation causes cataracts

Treatment ‐ dietary restriction (lactose and galactose)

Question 30

GALT Deficiency‐ Classical Galactosaemia

Answer 30

Galactosaemia and Galactosuria

Galactose-1-P and Galactitol accumulate causing cataracts

Brain and Liver damage

Treatment ‐ dietary restriction (lactose and galactose)