CARBOHYDRATE METABOLISM

Question 1

1st stage of processing food products
Biochemical process by which food molecules, through hydrolysis, are broken down into simpler chemical units that can be used by cells for their metabolic needs

Answer 1

Digestion

Question 2

enzyme that hydrolyses some a-glycosidic linkage of starch and glycogen to produce smaller polysaccharide and disaccharide

Answer 2

Salivary a-amylase

Question 3

A if only the first statement is correct
B if only the second statement is correct
C if both of the statements are correct
D if neither of the statements is correct

1. Only small amounts of carbohydrates are digested in the mouth, because food is swallowed quickly to the stomach
2. In the stomach, digestion has no effect against the gastric juice; carbohydrate digestion enzyme is not present

Answer 3

C

Question 4

A if only the first statement is correct
B if only the second statement is correct
C if both of the statements are correct
D if neither of the statements is correct

1. Small intestine is not the primary site for carbohydrate digestion
2. Final step of digestion happens in the outer membrane of intestinal mucosal cell

Answer 4

B

Pancreatic alpha amylase digestive enzyme is also found in the mouth
Could hydrolyzed the polysaccharides to disaccharides (maltose, sucrose, lactose)
Has different enzymes that could breakdown the disaccharides:
Maltase: produce 2 monomer units of glucose
Sucrase: glucose and fructose units
Lactase: glucose and galactose

Question 5

A if only the first statement is correct
B if only the second statement is correct
C if both of the statements are correct
D if neither of the statements is correct

1. Monosaccharide units are absorbed in the bloodstream via capillaries in the intestinal lining (villi)
2. Galactose and fructose are converted in the heart to be glucose

Answer 5

A

Question 6

Metabolic pathway by which glucose (a C6 molecule) is converted into two molecules of pyruvate (a C3 molecule)
Can happen in active skeletal muscle
Chemical energy in the form of ATP is produced, and NADH-reduced coenzymes are produced
Oxidation process; no molecular oxygen is utilized (anaerobic pathway)
Oxidizing agent: NAD

Answer 6

Glycolysis

Products: pyruvate and NADH
Glucose to pyruvate
10 step process; every step is known to be enzyme catalyzed
Has 2 stages in its overall process based on the number of carbon of the molecule involved in the process

Question 7

____ pathways: metabolic pathways in which molecular oxygen is not a participant
____ pathways: pathways that require molecular oxygen

Answer 7

Anaerobic

Aerobic

Question 8

6 Carbon Stage of Glycolysis:
Formation of Glucose 6-Phosphate.
Glycolysis begins with the phosphorylation of glucose to yield glucose 6-phosphate.
Enzyme: Hexokinase; Reacts with glucose to produce glucose 6-phosphate
Needs magnesium ion for its activity

Answer 8

1. Phosphorylation

1 phosphate from ATP will be attached to the C-6 of glucose: H in the hydroxyl group will be replaced
Energy needed is derived from ATP hydrolysis; endothermic reaction is involved
Product: glucose 6-phosphate

Question 9

6 Carbon Stage of Glycolysis:
Formation of Fructose 6-Phosphate
Glucose 6-phosphate is isomerized into fructose 6-phosphate though the enzyme
Net result: C1 is not part of the ring structure; C-6 is still in the structure
Enzyme: phosphoglucose isomerase

Answer 9

2. Isomerization

Functional group found in the structure is different
Glucose: aldehyde; Fructose: ketone
Product: fructose 6-phosphate

Question 10

6 Carbon Stage of Glycolysis:
Formation of Fructose 1,6-Bisphosphate.
Like Step 1, is a phosphorylation reaction and therefore requires the expenditure of energy (ATP)
Enzyme: phosphofructokinase; Requires magnesium ion for its activity
Additional phosphate group is bonded to the phosphate derivative of fructose

Answer 10

3. Phosphorylation

Additional phosphate group from the ATP is bonded in the C-1 of fructose
Product: Fructose 1,6-Bisphosphate
Fructose 1,6-Bisphosphate can enter only in glycolysis, while other products of step 1 and 2 can enter another metabolic pathway
Bisphosphate: when 2 Phosphate group are bonded in different C atom; they are not connected to each other; found on 2 different C atom

Question 11

3 Carbon Stage of Glycolysis:
Formation of Two Triose Phosphates.
Reacting C6 species is split into two C3 (triose) species.
Enzyme: aldolase
6-C molecule (Fructose 1,6-Bisphosphate) is cleaved forming 2 different types of triose species

Answer 11

4. Cleavage

Fructose 1,6-bisphosphate, the molecule being split, is unsymmetrical, the two trioses produced are not identical.
One product is dihydroxyacetone phosphate (acetone; ketone)
The other is glyceraldehyde 3-phosphate (glycerol; aldehyde)

Question 12

3 Carbon Stage of Glycolysis:
Formation of Glyceraldehyde 3-Phosphate
Changing the location of the functional group
Enzyme: triosephosphate isomerase

Answer 12

5. Isomerization

Dihydroxyacetone phosphate is isomerized using the enzyme forming another glyceraldehyde 3-phosphate
Double bond in C-2 will be broken down to form glyceraldehyde 3-phosphate

Question 13

3 Carbon Stage of Glycolysis:
Formation of 1,3 Bisphosphoglycerate.
Oxidizing agent: NAD (also reduced, forming NADH)
Enzyme: glyceraldehyde 3-phosphate dehydrogenase (oxidation)
H of glyceraldehyde will be replaced by the free phosphate group forming 1,3-bisphosphoglycerate

Answer 13

6. Oxidation and Phosphorylation

Product: 2 1,3-bisphosphoglycerate, 2 NADH, and 2 H
Phosphate group is added to C-1 of glyceraldehyde 3-phosphate to produce 1,3-bisphosphoglycerate
The newly added phosphate group in 1,3-bisphosphoglycerate is a high-energy phosphate group.
A high-energy phosphate group is produced when a phosphate group is attached to a carbon atom that is also participating in a double bond: carbon–carbon or carbon–oxygen

Question 14

3 Carbon Stage of Glycolysis:
Formation of 3-Phosphoglycerate.
Energy (ATP) generating; utilizes 2 ADP to produce 2 ATP molecules are produced aside from the product
Products: 2 ATP and 2 3-Phosphoglycerate
Enzyme: phosphoglycerokinase
Diphosphate species (1,3-bisphosphoglycerate) is converted into ATP (3-Phosphoglycerate)

Answer 14

7. Phosphorylation of ADP

Diphosphate species just formed are converted back to a monophosphate species.
ATP production in this step involves substrate-level phosphorylation.
Substrate-level phosphorylation is the biochemical process by which a high energy phosphate group from an intermediate compound (substrate) is directly transferred to ADP to produce ATP.

Question 15

3 Carbon Stage of Glycolysis:
Formation of 2-Phosphoglycerate.
Enzyme: phosphoglyceromutase
Mutase: it transfers the position of one functional group to another functional group within a molecule

Answer 15

8. Isomerization

It moves phosphate from C-3 to C-2 forming the 2-Phosphoglycerate
Phosphate group of 3-phosphoglycerate is moved from carbon 3 to carbon 2.

Question 16

3 Carbon Stage of Glycolysis:
Formation of Phosphoenolpyruvate (Alcohol dehydration)
Enzyme: enolase; Requires magnesium ion for its activity
Product: phosphoenolpyruvate, 2 water molecule (H2O)
C-2 and C-3 are dehydrated to form double bond

Answer 16

9. Dehydration

Phosphoenolpyruvate: there is a carbon double bond in the structure; energy-rich compound
Result is another compound containing a high-energy phosphate group
The phosphate group is attached to a carbon atom that is involved in a carbon–carbon double bond

Question 17

3 Carbon Stage of Glycolysis:
Formation of Pyruvate.
2nd step that produces ATP; similar to step 7
Products: 2 ATP and 2 pyruvate molecules after glycolysis (acetone; ketose; C2 is double bonded to O2)

Answer 17

10. Phosphorylation of ADP

Enzyme: pyruvate kinase; requires magnesium and potassium ions for its activity
Phosphoenolpyruvate transfers its high-energy phosphate group to an ADP molecule to produce ATP and pyruvate

Question 18

FILL IN THE BLANKS:
Step 1: Glucose —> glucose 6-phosphate
__ (ATP consumed)

Step 3: Fructose 6-phosphate —> fructose 1,6-bisphosphate
__ (ATP consumed)

Step 7: 2 (1,3-Bisphosphoglycerate —> 3-phosphoglycerate)
__ (ATP produced)

Step 10: 2 (Phosphoenolpyruvate —> pyruvate)
__ (ATP produced)
Product after Glycolysis:

Net: __ (ATP)

Answer 18

-1
-1
2
2
2

Question 19

Entry of Galactose and Fructose into Glycolysis:
Galactose and fructose are not directly absorbed in the bloodstream, they are converted in the liver to glucose
_____: undergoes isomerization and phosphorylation to produce glucose 1-phosphate and enter step 2 of glycolysis where it is isomerized to glucose 6-phosphate and proceed to other steps
_____: phosphorylated forming fructose 1-phosphate and enter step 4 where it cleaved into 2 triose specie

Answer 19

Glucose

Fructose

Question 20

Fates of Pyruvate:
Aerobic Conditions in humans, animals, and microorganisms
Produces:_____
Anaerobic Conditions in humans, animals, and microorganisms
Produces: _____
Anaerobic Conditions in some microorganisms
Produces: _____

Answer 20

Acetyl CoA
Lactate Fermentation
Ethanol Fermentation

Question 21

Under aerobic (oxygen-rich) conditions, pyruvate is oxidized to acetyl CoA.
Pyruvate formed in the cytosol through glycolysis crosses the two mitochondrial membranes and enters the mitochondrial matrix, where the oxidation takes place.
COO of pyruvate is removed and replaced by CoA; removed COO will become CO2
Involves oxidation and decarboxylation (because CO2 is produced)

Answer 21

Oxidation to Acetyl CoA

Enzyme: pyruvate dehydrogenase complex (oxidation)
Product: Acetyl CoA
Most acetyl CoA molecules produced from pyruvate enter the citric acid cycle (TCA); changes NAD into reduced form
All NADH can enter ETC directly or indirectly and is regenerated
Most Pyruvate are converted into acetyl CoA
The overall reaction process involves four separate steps and requires NAD, CoA-SH, FAD, and two other coenzymes (lipoic acid and thiamine pyrophosphate, the latter derived from the B vitamin thiamine)

Question 22

anaerobic
biochemical process by which NADH is oxidized to NAD without the need for oxygen.
Activated during strenuous exercise or working muscles: increase build up in lactate
Enzyme: Lactate dehydrogenase
Lactate fermentation is the enzymatic anaerobic reduction of pyruvate to lactate
The sole purpose of this process is the conversion of NADH to NAD

Answer 22

Lactate Fermentation

The lactate formed is converted back to pyruvate when aerobic conditions are again established in a cell.
Conversion of pyruvate to lactate requires NADH and H ion
RBCs can also form lactate; because there is no mitochondria
Lactate can be from RBCs and muscles
When the reaction for conversion of pyruvate to lactate is added to the net glycolysis reaction

Question 23

Enzymatic anaerobic conversion of pyruvate to ethanol and carbon dioxide
Enzyme: Pyruvate decarboxylase
NAD and NADH doesn’t appear in the equation but are both generated and consumed during the process

Answer 23

Ethanol Fermentation

Question 24

TRUE OR FALSE:

The first step in conversion of pyruvate to ethanol is a decarboxylation reaction to produce acetaldehyde.

Answer 24

TRUE

COO is removed and H is replaced in the pyruvate
Products: acetaldehyde and CO2
Enzyme: pyruvate decarboxylase
Involves yeast
CO2 bubbles causes the rise of bread and other product and also fermentation

Question 25

Acetaldehyde reduction to produce ethanol Redox reaction Enzyme: alcohol dehydrogenase (oxidation) An overall reaction for the production of ethanol from glucose is obtained by combining the reaction for the conversion of pyruvate with the net reaction for glycolysis

Answer 25

Ethanol Fermentation

Question 26

NADH produced during Step 6 of Glycolysis cannot directly participate in the electron transport chain because mitochondria are impermeable to NADH and NAD+ Glycerol 3-phosphate-dihydroxyacetone phosphate transport system shuttles electrons from NADH, but not NADH itself, across the membrane

Answer 26

Regeneration of NAD+ from NADH Dihydroxyacetone phosphate and glycerol phosphate freely cross the mitochondrial membrane The interconversion shuttles the electrons from NADH to FADH2 30 ATP molecules are produced by the muscle and nerve cells 26 ATP: oxidative phosphorylation of ETC 2 ATP: oxidation of glucose to pyruvate 2 ATP: conversion of GTP to ATP

Question 27

Glycogenesis Metabolic pathway by which glycogen is synthesized from glucose 6-phosphate Glycogen (animal starch): storage form of carbohydrate in humans and animals, found in muscle and liver tissue Muscle: source of glucose in glycolysis Liver: source of glucose to maintain normal blood glucose levels

Answer 27

Glycogen Synthesis and Degradation:

Question 28

3 Steps of Glycogenesis: The starting material for this step is not glucose itself but rather glucose 6-phosphate Glucose 6-phosphate formed during the first step of glycolysis Glucose —> Glucose 6-phosphate (with Hexokinase) Glucose 6-phosphate —> Glucose 1-phosphate

Answer 28

1. Formation of Glucose 1-phosphate Enzyme: phosphoglucomutase; isomerize glucose 6-phosphate to glucose 1-phosphate (C6 —> C1) Glucose 6-phosphate enters glycogenesis when the body needs to store glucose Reaction: isomerization Product: glucose 1-phosphate

Question 29

3 Steps of Glycogenesis: Glucose 1-phosphate from Step 1 must be activated before it can be added to a growing glycogen chain. Enzyme: UDP-glucose pyrophosphorylase The activator is the high energy compound UTP (uridine triphosphate)

Answer 29

2. Formation of UDP-glucose UMP is bonded in the phosphate of glucose 1-Phosphate Product: 2 phosphate groups, uridine diphosphate glucose

Question 30

3 Steps of Glycogenesis: The glucose unit of UDP-glucose is then attached to the end of a glycogen chain Enzyme: glycogen synthase

Answer 30

3. Glucose Transfer to a Glycogen Chain UDP formed can be converted to UTP: UDP + ATP —> UTP + ADP UTP formed can again be used in step 2 of glycogenesis

Question 31

Metabolic pathway by which glucose 6-phosphate is produced from glycogen Glycogen —> glucose 6-phosphate (Breakdown of glycogen ) Not simply reversed of glycogenesis; doesn’t require high energy compound (UTP or UDP) In muscle and brain cells an immediate need for energy is the stimulus that initiates glycogenolysis. Glucose 6-phosphate that is produced directly enters the glycolysis pathway at Step 1 and its multi step conversion to pyruvate begins.

Answer 31

Glycogen Synthesis and Degradation: Glycogenolysis Low level of glucose is the stimulus that initiates glycogenolysis in liver cells Glucose 6-phosphate produced must be converted to free glucose before it can enter the bloodstream, as glucose 6-phosphate cannot cross cell membranes This change is affected by the enzyme glucose 6-phosphatase, an enzyme found in liver cells but not in muscle cells or brain cells. Converts glucose 6-phosphate to glucose; needs water Removes phosphate in the molecule

Question 32

2 Steps of Glycogenolysis: Enzyme: glycogen phosphorylase; catalyzes the cleavage of bond by phosphate group Phosphate group is needed to react with glycogen; in the glycogen 1 glucose unit is removed and is phosphorylated to form glucose 1-phosphate

Answer 32

1. Phosphorylation of a Glucose Residue

Question 33

2 Steps of Glycogenolysis: Reverse of step 1 of glycogenesis Enzyme: phosphoglucomutase Product: glucose 6-phosphate

Answer 33

Glucose 1-phosphate Isomerization

Question 34

Metabolic pathway by which glucose is synthesized from noncarbohydrate materials; energy consuming Noncarbohydrate starting materials for gluconeogenesis: lactate from muscles, glycerol from triacylglycerol hydrolysis, amino acid from protein hydrolysis or muscle protein during starvation

Answer 34

Glycogen Synthesis and Degradation: Gluconeogenesis helps to maintain normal blood-glucose levels in times of inadequate dietary carbohydrate intake Not exact opposite of glycolysis (10 steps) 11 steps; which in step 1 is where pyruvate is converted to Oxaloacetate Enzyme: pyruvate carboxylase (pyruvate converted to Oxaloacetate) COO is added in pyruvate (COO is added in the C-4 of pyruvate) COO is from CO2

Question 35

Oxaloacetate is converted to phosphoenolpyruvate if it proceeds to gluconeogenesis Enzyme: phosphoenolpyruvate carboxykinase (requires GTP) Phosphate group of GTP and COO of Oxaloacetate is removed and yields CO2 and GDP Kinase: high-energy compound is required during the process Phosphorylation reaction is involved; in the C-2 of phosphoenolpyruvate phosphate group is bonded Phosphoenolpyruvate: there is phosphate group and pyruvate as the sugar and enol

Answer 35

Glycogen Synthesis and Degradation: Gluconeogenesis

Question 36

Step 9 of gluconeogenesis enzyme: fructose 1,6- bisphosphatase Converting fructose 1,6-bisphosphate to fructose fructose 6- phosphate; doesn’t require ATP along with step 11

Answer 36

Glycogen Synthesis and Degradation: Gluconeogenesis

Question 37

Step 11 of gluconeogenesis enzyme: glucose 6-phosphatase Coverts glucose 6-phosphate to glucose; no ATP is required Step 1 and 3 needs ATP Pyruvate to glucose requires expenditure of 4ATP and 2GTP

Answer 37

Glycogen Synthesis and Degradation: Gluconeogenesis

Question 38

Cyclic biochemical process in which glucose is converted to lactate in muscle tissue Lactate is reconverted to glucose in the liver Lactate is formed from glucose under anaerobic conditions in muscle cells When transferred to liver that is when it is converted into glucose and transferred back to the muscle

Answer 38

Cori Cycle Glucose is returned to the muscle tissue Enzyme: lactate dehydrogenase (LDH) Uses NAD as substrate and oxidizing agent and is reduced to NADH and Lactate is converted into pyruvate Formed pyruvate can be converted via gluconeogenesis then is transported into the bloodstream into the muscle

Question 39

Metabolic pathway by which glucose is used to produce NADPH, ribose 5-phosphate, and numerous other sugar phosphates. Nicotinamide Adenine Dinucleotide Phosphate (NADPH): needed in lipid synthesis; phosphorylated version of NADH

Answer 39

Pentose Phosphate Pathway Similar to NADH difference is that is has phosphate group Involved in reactions in lipids and nucleic acid reactions Ribose 5-phosphate: pentose derivative that it needed in nucleic acid Pentose ribose is a component of ATP, GTP, UTP, CoA, NAD, FAD, and RNA

Question 40

2 stages within the Pentose Phosphate Pathway: Involves three steps through which glucose 6-phosphate is converted to ribulose 5-phosphate (undergoes non oxidative stage) and CO2. Step 1 enzyme: glucose 6-phosphate dehydrogenase; Utilizes NADP; redox Glucose 6-phosphate to 6-phospho glucono-1,5-lactone

Answer 40

Oxidative stage Step 2 enzyme: gluconolactonase 6-phospho glucono-1,5-lactone to 6-phosphogluconate Step 3 enzyme: 6-phosphogluconate dehydrogenase; Utilizes NADP; redox 6-phosphogluconate to Ribulose 5-phosphate Product: Ribulose 5-phosphate; Undergoes non oxidative stage

Question 41

2 stages within the Pentose Phosphate Pathway: First step involves isomerization of ribulose 5-phosphate (a ketose) to ribose 5-phosphate (an aldose) specially when used for nucleic acid synthesis Then further conversion of ribose 5-phosphate to numerous other sugar phosphates.

Answer 41

Non Oxidative stage Ultimately, glyceraldehyde 3-phosphate and fructose 6-phosphate (both glycolysis intermediates) are formed. Product: ribulose 5-phosphate Contains provision for the conversion of ribose 5-phosphate

Question 42

Key enzyme in the non-oxidative branch of the pentose phosphate pathway that transfers a two-carbon aldehyde unit from ketose-donor to aldose-acceptor sugars.

Answer 42

Transketolase Reactants: xylulose 5-phosphate + ribose 5-phosphate —> glyceraldehyde 3-phosphate + sedoheptulose 7-phosphate

Question 43

Key enzyme in the non-oxidative branch of the pentose phosphate pathway that transfers a three-carbon aldehyde unit from ketose-donor to aldose-acceptor sugars.

Answer 43

Transaldolase Reactants: sedoheptulose 7-phosphate + glyceraldehyde 3-phosphate —> erythrose 4-phosphate + fructose 6- phosphate

Question 44

insulin, glucagon, epinephrine (major hormones for regulation of carbohydrate metabolism) Second major method for regulating carbohydrate metabolism is hormonal control

Answer 44

Hormonal Control of Carbohydrate Metabolism

Question 45

51 amino acid protein Hormone produced by the beta cells of the pancreas. promotes the uptake and utilization of glucose by cells. Thus its function is to lower blood glucose levels It is also involved in lipid metabolism

Answer 45

Insulin Only hormone in the body that could lower blood glucose level Triggered when there is a high blood glucose level Increase in the rates of glycogen and fatty acid synthesis Mechanism: it will bind in the protein receptors in the outer surface of the cells, which facilitates the entrance of glucose in the cells

Question 46

29 amino acid Polypeptide hormone produced in the pancreas by alpha cells. It is released when blood-glucose levels are low

Answer 46

Glucagon Its principal function is to increase blood-glucose concentrations by speeding up the conversion of glycogen to glucose (glycogenolysis) and gluconeogenesis in the liver Polypeptide, not protein for it is has less than 40 amino acid Effect is opposite of the insulin

Question 47

Adrenaline; from adrenal glands Similar to glucagon: increase blood glucose levels Binding to the receptor site outside cell membrane

Answer 47

Epinephrine Stimulation of glycogenolysis, the release of glucose from glycogen Its primary target is muscle cells, where energy is needed for quick action It also functions in lipid metabolism