Carbohydrates Flashcards
(29 cards)
What are the major carbohydrates in the diet
Glucose Oligosaccharides containing (alpha 1-6) linked galactose Lactose Sucrose Maltose Fructose Starch Glycogen Cellulose Hemicellulose
What are carbohydrates digested to produce
Glucose, galactose and fructose
Can carbohydrates be digested in the stomach
No
Where does the final digestion take place and what enzymes are used
Jejunum
Using mucosal cell-surface enzymes
How are carbohydrates digested in the mouth
By salivary amylase hydrolyses which break α1-4 bonds of starch
How are carbohydrates digested in the duodenum
By pancreatic amylase which hydrolyses which break α1-4 bonds of starch
What type of muscosal cell surface enzymes are there
Isomaltase - hydrolyses α1-6 bonds
Glucoamylase - removes glucose sequentially from non-reducing ends
Sucrose - hydrolyses sucrose
Lactase - hydrolyses lactose.
Where can muscosal cell-surface enzymes be found
In the jejunum
What does a high Vmax mean
It is an efficient enzyme
What does a low Km mean
The enzyme has a high affinity for the substrate
What do glucokinase and hexokinase do
The phosphorylate glucose to glucose-6-phosphate
Where are glucokinase and hexokinase found
Glucokinase in the liver
Hexokinase in other tissues
Does glucokinase have a high or low Vmax and how does this affect its function.
High Vmax
Its an efficient enzyme so glucose will be phosphorylated quickly
Does hexokinase have a high or low Km and how does this affect its function
Low Km
It has a high affinity for the substrate but as it has a low Vmax so at low glucose concentration it cannot grab glucose effectively.
(Low Vmax means tissues are easily satisfied and will not constantly grab glucose)
What is the first step of glycogen synthesis
Glycogenin covalently binds to glucose from UDP-glucose to produce chains of about 8 glucose residues
What is the second step of glycogen synthesis
Glycogen synthase extends the glucose chains
What is the third step of glycogen synthesis
The chains are then broken down using a glycogen branching enzyme and re-attached using α1-6 bonds to give branch points
What is the first step of glycogen degradation
Glucose monomers are removed one at a time from the non-reducing ends to form glucose-1-phosphate using glycogen phosphorylase
What enzyme is used in the first step of glycogen degradation
Glycogen phosphorylase
What is the second step of glycogen degradation
The glucose near the branch is removed using a 2 step process by de-branching enzyme.
What type of activity does the de-branching enzyme have
Transferase activity
It removes a set of 3 glucose residues and attaches them to the nearest non-reducing end using α1-4 bonds
What is the third step of glycogen degradation
Glucosidase removes the final glucose by breaking a α1-6 bond to release free glucose
What is the fourth step of glycogen degradation
An unbranched chain is produced which can be further degraded or built up as needed
What is the function of glycogen in the liver
It is converted from G-1-P to G-6-P then using glucose phosphatase converted to glucose which can be transferred into the blood
