CARBOHYDRATE METABOLISM 3

Question 1

• Breakdown of food molecules by hydrolysis into simpler chemical units that can be used by cells in their metabolic processes

Answer 1

Digestion

Question 2

• Begins in the mouth

Answer 2

Carbohydrate digestion:

Question 3

o – Converts lactose glucose and galactose

Answer 3

Lactase

Question 3

catalyzes the hydrolysis of alpha-glycosidic linkages of starch and glycogen to produce smaller polysaccharides and disaccharide – maltose

Answer 3

Enzyme salivary “Alpha-amylase”

Question 3

o – converts maltose to glucose

Answer 3

Maltase

Question 4

o – Converts sucrose to glucose and fructose

Answer 4

Sucrase

Question 5

o Phosphorylation of glucose - phosphate group from ATP is transferred to the hydroxyl group on carbon 6 of glucose
o Reactions catalyzed by Hexokinase
o Endothermic reaction
o Energy needed is derived from ATP hydrolysis

Answer 5

• Step 1: Formation of glucose-6-phosphate

Question 5

o The six-carbon stage of glycolysis is an energy-consuming stage
o Phosphate derivatives glucose and fructose are formed via a ATP coupling
reactions.

Answer 5

Steps 1-3: Six carbon stage

Question 6

o Glucose 6 phosphate is isomerized to Fructose -6-Phosphate.
o Enzyme: Phosphoglucoisomerase

Answer 6

• Step 2: Formation of Fructose-6-phosphate

Question 6

o Further phosphorylation of Fructose-6-bisphosphate
o Endothermic reaction
o Energy derived from ATP hydrolysis
o Enzyme: phsphofructokinase

Answer 6

• Step 3: Formation of Fructose 1,6-bisphosphate

Question 7

o C6 species is split into two C3 species
o Two C3 species formed are dihydroxyacetone phosphate and glyceraldehyde
3-phosphate
o Enzyme : Aldolase

Answer 7

• Step 4: Formation of Triose Phosphates

Question 8

• Reaction intermediates are derivatives of glycerol and acetone
• A reaction intermediates are phosphorylated derivatives of dihydroxyacetone, glyceraldehyde, glycerate, or pyruvate

Answer 8

Three-Carbon Stage of Glycolysis (Steps 4-10)

Question 8

o Dihydroxyacetone phosphate is isomerized to glycerldehyde 3-phosphate
o Enzyme: Triosephosphate isomerase

Answer 8

• Step 5: Isomerization of Triose Phosphates

Question 8

o Diphosphate from step 6 is converted back to monophosphate species
o It is an ATP producing step
− C1 high energy phosphate group of 1,3-bisphosphoglycerate is transferred
to an ADP molecule to form an ATP
o Enzyme: phosphoglycerokinase
o Two ATP molecules are produced for each original glucose molecule

Answer 8

• Step 7: Formation of 3-Phosphoglycerate

Question 9

o Isomerization of 3-phosphoglycerate to 2-phosphoglycerate
− Phosphate group moved from C-3 to C-2
o Enzyme: Phosphoglyceromutase

Answer 9

• Step 8: Formation of 2-phosphoglycerate

Question 10

o This is an alcohol dehydration reaction – results in another high energy
phosphate group containing compound
o Enzyme: Enolase

Answer 10

• Step 9: Formation of Phosphoenolpyruvate

Question 11

Practice Exercise
* Indicate at what step in the glycolysis pathway each of the following events occur:

o Second formation of ATP occurs –
o Second “energy-rich” compound is produced –
o Second time ATP is converted to ADP –
o A hydration reaction occurs –

Answer 11

o Step 10
o Step 9
o Step 3
o Step 9

Question 11

o High energy phosphate is transferred from phosphoenolpyruvate to ADP
molecule to produce ATP and pyruvate
o Enzyme: Pyruvate kinase
o Two ATP molecules are produced for each original glucose molecule
o Note: Steps 1,3 and 10 are control points for glycolysis

Answer 11

• Step 10: Formation of Pyruvate

Question 12

• ]: A branched polymer form of glucose is the storage form of
  carbohydrates in humans and animals (animal starch):

Answer 12

Glycogen

Question 13

\o Starting material is glucose 6-phosphate – from first step of glycolysis
o Enzyme phosphoglucomutase catalyzes conversion of glucose 6-phosphate to
glucose 1-phosphate

Answer 13

• Step 1: Formation of glucose 1-phosphate

Question 13

o High energy compound UTP (uridine triphosphate) activates glucose 1-
phosphate to uridine diphosphate glucose (UDP-glucose)

Answer 13

• Step 2: Formation of UDP Glucose

Question 14

o The glucose unit of UDP-glucose is attached to the end of a glycogen chain
and UDP is produced
o UDP reacts with ATP to form UTP and ADP

Answer 14

• Step 3: Glucose transfer to a Glycogen Chain

Question 15

o Phosphoglucomutase isomerizes glucose 1-phosphate is to glucose 6-
phosphate (reverse of the first step of glycogenesis)

Answer 15

• Step 2: Glucose 1-phosphate Isomerization

Question 15

o Glycogen phosphorylase catalyzes the removal of an end glucose residue from
a glycogen molecule as glucose 1-phosphate.

Answer 15

• Step 1: Phosphorylation of a glucose residue

Question 16

* stores in muscle and liver tissue are depleted within 12-18 hours from fasting or in even less time from heavy work or strenuous physical activity

Answer 16

Glycogen

Question 17

* helps to maintain normal blood-glucose levels in times of inadequate dietary carbohydrate intake

Answer 17

Gluconeogenesis

Question 18

* : 10 step process in which glucose is converted to pyruvate

Answer 18

Glycolysis

Question 18

* : 11-step process in which pyruvate is converted to glucose

Answer 18

Gluconeogenesis

Question 18

* : 2-Step process in which glycogen is synthesized from glucose 6- phosphate

Answer 18

Glycogenesis

Question 19

* : Glycogenolysis is the process in which glycogen is converted to glucose 6-phosphate

Answer 19

Glycogenolysis

Question 20

* Names ending with “lysis” -

Answer 20

Breakdown

Question 21

* Names ending with “genesis” -

Answer 21

Synthesis

Question 22

Practice Exercise * Identify each of the following as a characteristic of one or more of the following processes: glycolysis, glycogenesis, glycogenolysis, and gluconeogenesis. o Glycogen is the final product. - o Glucose is the initial reactant. - o Glucose 1-phosphate is produced in the first step. - o ADP is converted to ATP in this process. -

Answer 22

o Glycogenesis o Glycolysis o Glycogenesis o Glycolysis

Question 22

The ________________ A metabolic pathway in which glucose is used to produce NADPH, ribose 5- phosphate (a pentose phosphate) and numerous other sugar phosphates

Answer 22

pentose phosphate pathway:

Question 23

− Involves three steps through which glucose 6-phosphate is converted to ribulose 5-phosphate and CO2

Answer 23

o Oxidative stage

Question 24

− In the first step of the nonoxidative stage of the pentose phosphate pathway, ribulose 5-phosphate (ketose) is isomerized to ribose 5- phosphate (aldose)

Answer 24

o Nonoxidative stage

Question 25

* The second major method for controlling carbohydrate metabolism, besides enzyme inhibition by metabolism is

Answer 25

hormonal control

Question 26

* Three major hormones control carbohydrate metabolism:

Answer 26

o Insulin o Glucagon o Epinephrine

Question 27

* 29 amino acid peptide hormones * Produced in the pancreas by alpha cells * Released when blood glucose levels are low * Principal function is to increase blood-glucose concentration by speeding up the conversion of glycogen to glucose (glycogenolysis) in the liver

Answer 27

Glucagon

Question 28

* Also called adrenaline * Released by the adrenal glands in response to anger, fear, or excitement * Function is similar to glucagon, i.e., stimulates glycogenolysis * Primary target of epinephrine is muscle cells * Promotes energy generation for quick action * It also functions in lipid metabolism

Answer 28

Epinephrine