Lecture 5 Flashcards
What are the macronutrients?
Protein, lipid, carbohydrates
What is the predominant type of carbohydrate in our diet?
monosaccharides, predominantly D-glucose
What is the mammalian store of glucose?
Glycogen in the liver and muscle
What is the store of glucose in plants?
Starch
What is the cellular structural component in plants?
Cellulose
What does pop have a high percentage of?
High fructose corn syrup.
Why does fructose contribute to obesity?
It is not metabolised in the same way glucose is.
What is the sweetest type of sugar?
Fructose
What is the average carbohydrate intake daily?
300g.
What are the different types of carbohydrate in our diet?
Polysaccharides (45-60%), disaccharides (30-40%) like sucrose or lactose. Monosaccharides (5-10%)
What is the main type of polysaccharide?
Vegetable starch which is amylose and amylopectin.
What is amylose?
A straight chain polymer of glucose with alpha-1,4 bonds
What is amylopectin?
branched chain glucose polymer with alpha-1,4 bonds and alpha-1,6 bonds between branches every 20-30 glucose monomer.
What is animal starch in meat?
Glycogen.
What are the two stages of carbohydrate digestion?
Intraluminal hydrolysis and membrane digestion
Describe intraluminal digestion of starch
Broken down into oligosaccharides (3-10 glucose) by salivary and pancreatic amylase
Describe membrane digestion
Oligosaccharides are broken down by brush border enzymes such as maltase, sucrase and isomaltase.
What are the three monosaccharides that can be absorbed?
D-glucose, D-fructose, D-galactose
Why is fibre indigestible?
We do not have an enzyme capable of breaking the beta-1,4 linkage within cellulose and hemicellulose.
At what points can amylase break down amylose and what are the products?
Any bond except the end bonds. This produces maltose and maltotriose. (2 or 3 glucose monomers).
What are the products of amylase digestion of amylopectin?
Maltose, maltotriose and alpha-limit dextrins.
What are the three enzymes present at the membrane?
Lactase, maltase and sucroisomaltase
What does lactase do?
Breaks down lactose into glucose and galactose.
What does maltase do?
Breaks down maltose and maltotriose into 2 or 3 glucose
What is maltase also called?
glucoamylase
What is sucroisomaltase?
It is a dimer of both sucrase and isomaltase.
What does sucrase do?
Breaks down sucrose into glucose and fructose
What does isomaltase do?
Breaks down all the products of amylase amylopectin digestion.
What are glucose and galactose absorbed by?
SGLT1
What is fructose absorbed by?
GLUT5
What is the basolateral transporter for all of the monomers?
GLUT2
