CARBOHYDRATE METABOLISM

Question 1

what is the first enzyme that acts to break down sugars?

Answer 1

salivary amylase

Question 2

what is the enzyme used near the pancreas?

Answer 2

pancreatic amylase

Question 3

what is used to breakdown glucose?

Answer 3

maltose

Question 4

what does lactase and sucrase do?

Answer 4

• lactase breaks down lactose to galactose and glucose

- sucrase breaks down sucrose to glucose and fructose

Question 5

how is glucose transported in our bloodstream?

Answer 5

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

Question 6

how is glucose transported in cells?

Answer 6

glucose from outside the cell will be transported in the cell with the help of glucose transporter lodged in the plasma membrane

Question 7

what are the four processes of carbohydrate metabolism?

Answer 7

glycogenolysis, glycolysis, glyconeogenesis and glycogenesis

Question 8

where do we store our glycogen?

Answer 8

liver glycogen : maintains blood glucose

muscle glycogen : supplies energy during muscle contraction

Question 9

what is the principle of biological banking?

Answer 9

• 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

Question 10

how do you form glycogen?

Answer 10

glucose to glucose-6-phosphate to glycogen and vice versa

- glucose-6-phosphate can undergo glycolysis, pentose phosphate pathway and synthesis of glycogen

Question 11

what is the difference between having high in energy and low in energy?

Answer 11

• 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

Question 12

how is glycogen degradation done?

Answer 12

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

Question 13

what to do if there’s 3-4 units from branch point?

Answer 13

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

Question 14

how is G-1-P converted to G-6-P?

Answer 14

with the help of phsophoglucomutase

Question 15

what happens if there is too little/much glucose present in our body?

Answer 15

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

Question 16

how do we control glycogen degradation when there is not enough glucose?

Answer 16

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

Question 17

how does phosphorylase kinase works?

Answer 17

• 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

Question 18

what happens when there is too much glucose?

Answer 18

phosphoprotein phosphatase-1 will convert more active glycogen phosphorylase a to less active glycogen phosphorylase b

Question 19

how is phosphoprotein phosphatase-1 activated?

Answer 19

• when you eat too much sugar, pancreas releases insulin which cause it to increase which will activate PP1 (excess energy level)

Question 20

how do you convert glucose to glycogen when there is a need to store away glucose in the form of glycogen?

Answer 20

GLYCOGEN SYNTHASE :
- stitching together glucose molecules in the form of uridine diphosphate-phosphate (UDP) using the enzyme glycogen synthase

Question 21

how is UDP derived?

Answer 21

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

Question 22

what happens when the glucose chain in glycogen is getting to long?

Answer 22

uses glycogen branching enzyme to move part of the chain to another branch point

Question 23

how is glycogen synthase regulated?

Answer 23

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

Question 24

what happens when you eat a meal?

Answer 24

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

Question 25

what happens when glucose in blood decrease?

Answer 25

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