lecture 9 - Macronutrients & MetabolismCarbohydrates

Question 1

metabolism refers to

Answer 1

the sum of the chemical reactions that occur within the body.
divided into catabolism and anabolism.

Question 2

Catabolism

Answer 2

• break down molecules and typically release energy.

Question 3

Anabolism

Answer 3

• synthesize molecules and typically require energy to occur.

Question 4

The metabolism of carbohydrates via

Answer 4

the pathways of glycolysis, the citric acid cycle, anaerobic respiration, and aerobic respiration.

Question 5

Slide 46

Question 6

General mechanisms of digestion & absorption

Answer 6

Summary:
Different mechanisms for digestion andabsorption. Not only for carbohydrates. There are 5:​
No digestion needed – drinking sports drink, coke, eating sugar​
Luminal hydrolysis of polymers to monomers – protein, but also when you have carbohydrates​
Brush-border hydrolysis of oligomer to monomer​
Intracellular hydrolysis​
Luminal hydrolysis followed by intracellular resynthesis

Question 7

Digestive process for dietary carbohydrates

Answer 7

2-Step Digestion Process
1. Intraluminal hydrolysis
Starch -> oligosaccharides -> salivary and pancreatic amylase

2. membrane digestion (brush border microvilli)
   Oligosaccharides -> monosaccharides -> brush border disaccharidases (alpha dextrinase, lactase, maltase, sucrase)

Question 8

Intraluminal hydrolysis

Answer 8

Begins with the action of Salivary Amylase & finishes with pancreatic amylase
Salivary and pancreatic amylases – secreted in an active form
Salivary amylasein the mouth initiates starch digestion
Salivary amylase is inactivated by gastric acid, partially protected by complexing with oligosaccharides.
Pancreaticα-amylasecompletes starch digestion in the lumen of the small intestine

Question 9

Membrane digestion

Answer 9

Involves Hydrolysis of Oligosaccharides to Monosaccharides by Brush Border Disaccharidases

Small intestine - three brush border oligosaccharidases:
lactase, glucoamylase (most often called maltase), and sucrase-isomaltase.
Lactasehas only 1 substrate; it breaks lactose into glucose and galactose.
Maltasecan degrade the α-1,4 linkages in straight-chain oligosaccharides up to 9 monomers in length. Cannot split either sucrose or lactose.
Thesucrasemoiety of sucrase-isomaltase is required to split sucrose into glucose and fructose.
Theisomaltasemoiety of sucrase-isomaltase is critical; it is the only enzyme that can split the branching α-1,6 linkages of α-limit dextrins

Question 10

A
Salivary & pancreatic α-amylase are endoenzymes.
digest the linear internal α-1,4 linkages between glucose residues, but they cannot break terminal α-1,4 linkages (i.e., between the last two sugars in the chain).
cannot split the α-1,6 linkages at the branch points of amylopectin or the adjacent α-1,4 linkages.
As a result, the products of α-amylase action are linear glucose oligomers, maltotriose (a linear glucose trimer), maltose (a linear glucose dimer), and α-limit dextrins (which contain an α-1,6 branching linkage).

B
The brush border oligosaccharidases are intrinsic membrane proteins with their catalytic domains facing the lumen.
The sucrase-isomaltase is actually two enzymes, and, therefore, four oligosaccharidases split the oligosaccharides produced by α-amylase into monosaccharides.