CARBOHYDRATE METABOLISM Flashcards
what is the first enzyme that acts to break down sugars?
salivary amylase
what is the enzyme used near the pancreas?
pancreatic amylase
what is used to breakdown glucose?
maltose
what does lactase and sucrase do?
- lactase breaks down lactose to galactose and glucose
- sucrase breaks down sucrose to glucose and fructose
how is glucose transported in our bloodstream?
using Na+ glucose cotransporter
- glucose in the extracellular plasma membrane will enter the transporter thing in plasma membrane containing Na+ and then both Na+ and the glucose molecule be released and enter the intracellular of the plasma membrane
how is glucose transported in cells?
glucose from outside the cell will be transported in the cell with the help of glucose transporter lodged in the plasma membrane
what are the four processes of carbohydrate metabolism?
glycogenolysis, glycolysis, glyconeogenesis and glycogenesis
where do we store our glycogen?
liver glycogen : maintains blood glucose
muscle glycogen : supplies energy during muscle contraction
what is the principle of biological banking?
- we withdraw glucose from glycogen when we need energy as glucose can provide ATP\
- when there is too much glucose, glucose will be converted to glycogen to store the glucose for later use
how do you form glycogen?
glucose to glucose-6-phosphate to glycogen and vice versa
- glucose-6-phosphate can undergo glycolysis, pentose phosphate pathway and synthesis of glycogen
what is the difference between having high in energy and low in energy?
- low in energy means low in sugar hence there will be a need to breakdown glycogen to get more free glucose units
- high in energy means high in sugar hence there will be a need to store excess glucose in the form of glycogen
how is glycogen degradation done?
GLYCOGEN PHOSPHORYLASE cleaves off glucose units from glycogen polymer with the help of phosphate to generate glucose-1-phosphate
- However, glycogen phosphorylase CANNOT cleave glucose near the 3-4 units from branch point
what to do if there’s 3-4 units from branch point?
DEBRANCHING ENZYME :
removes branches of the 3-4 units by moving chain of glucose from branch point to end
- if you don’t have this debranching enzyme, you have glycogen debranching enzyme deficiency/glycogen storage disease
how is G-1-P converted to G-6-P?
with the help of phsophoglucomutase
what happens if there is too little/much glucose present in our body?
too little glucose : not enough energy for brain or other tissues
too much glucose : diabetes which can cause many symptoms such as blindness, nerve damage and multiple organ failure
how do we control glycogen degradation when there is not enough glucose?
by controlling glycogen phosphorylase enzyme with the help of PHOSPHORYLASE KINASE
- Glycogen phosphorylase b (less active) ; glycogen is not broken down
- glycogen phosphorylase a (more active) ; glycogen is broken down into glucose units for energy usage
- phosphorylase kinase helps to convert glycogen phosphorylase b to a by adding a phosphate group
how does phosphorylase kinase works?
- muscle contraction requires pulses of calcium ions which directly control phosphorylase kinase
- inactive phosphorylase kinase + Ca++ will activate phosphoryl kinase which in turn will phosphorylate and activate glycogen phosphorylase
what happens when there is too much glucose?
phosphoprotein phosphatase-1 will convert more active glycogen phosphorylase a to less active glycogen phosphorylase b
how is phosphoprotein phosphatase-1 activated?
- when you eat too much sugar, pancreas releases insulin which cause it to increase which will activate PP1 (excess energy level)
how do you convert glucose to glycogen when there is a need to store away glucose in the form of glycogen?
GLYCOGEN SYNTHASE :
- stitching together glucose molecules in the form of uridine diphosphate-phosphate (UDP) using the enzyme glycogen synthase
how is UDP derived?
1 ) G-1-P converts to UDP-glucose with the help of UTP to form UDP-glucose (G-1-P uridyl transferase)
2 ) UDP-glucose is converted to UDP by glycogen synthase
what happens when the glucose chain in glycogen is getting to long?
uses glycogen branching enzyme to move part of the chain to another branch point
how is glycogen synthase regulated?
PHOSPHORYLASE KINASE :
- Glycogen Synthase b (less active) ; does not make glycogen
- Glycogen synthase a (more active) : make glycogen
- inactivates glycogen synthase a by adding a phosphate group
PP-1 :
- activates glycogen synthase b by removing a phosphate group converting it to form glycogen synthase a
what happens when you eat a meal?
1 ) INSULIN binds insulin receptor on cell surface which simulate cells to uptake glucose and bound insulin receptor activates insulin-stimulated protein kinase
2 ) protein kinase phosphorylates and activates PP-1
3 ) PP-1 dephosphorylates and INACTIVATES glycogen phosphorylase and dephosphorylates and ACTIVATES glycogen synthase
what happens when glucose in blood decrease?
1 ) GLUCAGON bind to glucagon receptor on cell surface which leads to increase cyclic AMP
2 ) cAMP with increased Ca++ activates phosphorylase kinase which phosphorylates and ACTIVATES glycogen phosphorylase and phosphorylates and INACTIVATES glycogen synthase
