Carbohydrate digestion Flashcards
What are the principal dietary constituents (x6)
Carbohydrate Fat Protein Vitamins Minerals Water
How does the body take in water
Orally
Through the skin
What are the monosaccharides
Glucose, Galactose, Fructose
How many Carbons are in in the monosaccharides
Glucose and Galactose = 6
Fructose = 5
What type of sugar is glucose
A reducing sugar (it gets oxidised)
What type of sugar is fructose
A oxidising sugar (it gets reduced)
Are monosaccharides soluble in water
Yes
Where are monosaccharides absorbed
The Small Intestine
What are the Disaccharides
lactose, Sucrose, Maltose
What monosaccharides make up lactose
Glucose and Galactose
What monosaccharides make up sucrose
Fructose and glucose
What monosaccharides make up maltose
glucose and glucose
What links the monomers of a disaccharide
Glycosidic bonds
What is a glycosidic bond?
Covalent bond between hydroxyl and anomeric carbon 1 of glucose
Where is maltose found
It is the breakdown product of starch
Where is lactose found
Main sugar in milk
What is common of maltose and lactose
They both have the anomeric carbon available for oxidation and so are REDUCING SUGARS
Where is sucrose found
Table sugar
What portion of diet is sucrose
25%
Is sucrose a reducing sugar?
No
It does not have an anomeric carbon free so there is no oxidation site
What are the 3 polysaccharides
Starch
Cellulose
Glycogen
What does starch consist of
Many glucose monomers linked together
What are the two types of starch structures
Amylose
Amylopectin
What are features of amylose
the glucose are in a straight line with a1-4 bonding
Can have 1000s of glucose residues
What portion of diet is amylose
20-25%
What are the features of amylopectin
It is branched (every 24-30 residues is attached a1-6)
What portion of our diet is amylopetin
75-80%
Where is cellulose found
Plant cell walls
What links the monomers in Cellulose
B-1,4 glycosidic bonds
How is cellulose digested
By bacteria in the gut
Where is glycogen found
Animals (animal storage of glucose)
What are the features of glycogen
A1-4 linkage with branches every 6-12 residues
Where is glycogen found in the body
90% liver and muscle
How do the proportions of muscle in the liver and muscle vary
There is more glycogen in muscle by volume
There is more glycogen in liver by concentration
What can pack for glucose: glycogen or starch
Glycogen
Why store glucose in polymers
prevents cells lysing
What enzyme initially starts to break down polymers and where
Amylase breaks down the A1-4 bonds
In the saliva
What isomer of glucose will glucose transporters recognise
D-glucose
Does amylase operate in the stomach?
No - its too acidic
What transporter carries glucose and galactose across the enterocytes
The SGLUT-1 transports
Sodium dependant hexose transporter
How does the sodium exit with cell
Via the sodium/potassium pump
What transporter carries glucose and galactose out of the enterocytes
Glut-2
This is facilitated transport and not active
How does fructose enter the enterocyte
Through Glut-5 receptor
How does fructose leave the enterocyte
Through Glut-2
