Carbohydrate digestion, absorption, storage and utilisation. Flashcards
Why do complex carbohydrates need to be hydrolysed?
They can only be absorbed in the monosaccharide form.
What is the name of the bonds that determine the structure of a carbohydrate?
Glycosidic bonds.
CHO can have either a branched or linear structure. What key difference determines this?
alpha-1,4 bonds create a linear structure.
alpha-1,6 bonds create a branched structure.
What is the name of the enzyme that can breakdown a-1,4 bonds?
Salivary amylase - some CHO digestion occurs in the mouth whilst the majority of CHO digestion happens in the small intestine.
If branched carbs cannot be broken down by salivary amylase, how is it digested?
By de-branching enzymes such as a-dextrinase.
How is glucose and galactose absorbed into epithelial cells?
Down a concentration gradient, facilitated by sodium via SGLT1.
Having a sodium concentration gradient between the small intestine and epithelial cells is crucial for glucose and galactose absorption. How is this maintained?
Sodium is removed from the epithelial cells via the Na+-K+ pump, consuming ATP. The sodium then diffuses back into the intestinal lumen.
How is fructose absorbed?
Diffuses down a concentration gradient via GLUT5.
How do monosaccharides leave the epithelial cells and enter the blood?
Via GLUT2.
WHat happens to monosaccharides after they enter the blood?
They are transported to the liver, where they are converted to glucose metabolites/derivatives.
What happens to glucose in the bloodstream?
It can enter tissues through facilitated transport - regulated by insulin.
Why is high levels of fructose intake bad?
Fructose uptake is not regulated by insulin, meaning elevated levels of fructose intake for extended periods can lead to insulin resistance.
What effects does insulin have on glucose uptake?
Insulin increases glucose uptake. Also, it activates hexokinase which maintains the concentration gradient for glucose within muscle tissue by converting it to glucose-6-phosphate.
How is glucose stored within the body?
In the form of glycogen. Glycogenesis is stimulated by insulin whilst glycogenolysis is stimulated by glucagon and epinephrine.
How does insulin play a role in glycogenesis?
Insulin increases the levels and activation of glucokinase which plays a key role in the synthesis of glycogen.
