Fibers, starch and sugar are essential ingredients in our food and are important in our diet. These food ingredients are an important source of carbohydrates, or "carbs", that are converted to glucose, which provides energy to our body. Carbohydrates are biomolecules composed of carbon, hydrogen, and oxygen atoms, which are the main nutrients essential to our body. Carbohydrates are also known in biochemistry as "saccharides" which means "sugars."

Carbohydrates are classified into monosaccharides, disaccharides, oligosaccharides, and polysaccharides based on their structure. Carbohydrates perform multiple functions in living organisms. Plant cells are made of cellulose and the exoskeleton of insects is made of chitin. Therefore, carbohydrates are essential for the structural and functional role of the organism. We get a lot of carbohydrates from our diet, including grains, bread, potatoes, sugar, lactose from milk, honey, fruits, and glucose and fructose from vegetables.

Metabolism is the process in which your body converts the food that you eat into the form of energy by breaking down the large molecules into smaller ones.

Some MCQs

Which among the Following Enzymes does not Participate in Galactose Metabolism?

a) Glucokinase

b) Galactokinase

c) Galactose-1-Phosphate Uridyl transferase

d) UDP-Galactose 4- epimerase

Answer: Glucokinase

Which of the Following Enzymes is Considered as Defective in Galactosemia- a Fatal Genetic Disorder in Infants?

a) Glucokinase

b) Galactokinase

c) Galactose-1-Phosphate Uridyl transferase

d) UDP-Galactose 4- epimerase

Answer: Galactose-1-Phosphate Uridyl Transferase

Erythrocytes Undergo Glycolysis for Production of ATP. The Deficiency of Which Enzyme Leads to Hemolytic Anemia-

a) Glucokinase

b)Phosphofructokinase

c) Phosphoglucomutase

d) Pyruvate Kinase

Answer: Pyruvate Kinase

In the Liver, the Accumulation of which among the Following Metabolites Attenuates the Inhibitory of ATP on Phosphofructokinase?

a) Glucose-6-Phosphate

b) Citrate

c) Fructose-1,6-Bisphosphate

d) Fructose-2,6-Bisphosphate

Answer: Fructose-2,6-Bisphosphate

The Most Active Site of Protein Synthesis is the-

a) Nucleus

b) Ribosome

c) Mitochondrion

d) Cell sap

Answer: Nucleus

How many Total Molecules of ATP are Synthesized from ADP via Glycolysis of a Single Molecule of Glucose?

a) 36

b) 38

c) 2

d) 4

Answer: 36

Mutation in which of the Following Enzymes Leads to a Glycogen Storage Disease Known as Tarui’s Disease?

a) Glucokinase

b)Phosphofructokinase

c) Phosphoglucomutase

d) Pyruvate Kinase

Answer: Phosphofructokinase

Cancer Cells have High Energy Demands for Replication and Division. Increased Flux of glucose into Glycolysis Replenishes the Energy Demand. Which of the Following Enzymes Plays an Important Role in Tumor Metabolism?

a) Glucokinase

b)Phosphofructokinase

c) Phosphoglucomutase

d) Pyruvate Kinase M2

Answer: Pyruvate Kinase M2

The Rate of Absorption of Sugars by the Small Intestine is Highest for -

a). Pentoses

b). Disaccharides

c). Polysaccharides

d). Hexoses

Answer: Hexose

Which of the Following is not a Polymer of Glucose?

a) Glycogen

b) Cellulose

c) Amylase

d) Insulin

Answer: Insulin

An Essential for the Conversion of Glucose to Glycogen in Liver is -

A. UTP

B. GTP

C. Pyruvate kinase

D. Guanosine

Answer: UTP

Which of the Following Glucose Transporters (GLUT) are Important in Insulin-Dependent Glucose Uptake?

a) GLUT1

b) GLUT2

c) GLUT3

d) GLUT4

Answer: GLUT4

Which of the Following Metabolites Negatively Regulates Pyruvate Kinase?

a) Fructose-1,6-Bisphosphate

b) Citrate

c) Acetyl CoA

d) Alanine

Answer: Alanine

Which of the Following Glycolytic Enzymes is Inhibited by Accumulation of Long Chain Fatty Acid in the Liver?

a) Hexokinase

b) Glucokinase

c) Phosphofructokinase

d) Pyruvate kinase

Answer: Glucokinase

Glycogen Synthesis is Increased by -

a) Cortisone

b) Insulin

c) GH

d) Epinephrine

Answer: Insulin

Gluconeogenesis Occurs in the Liver and Which Organ -

a) Kidney

b) Muscle

c) Heart

d) Fat

Answer: Heart

Adrenaline acts on which Enzyme in Glycogenolysis?

a) Glucokinase

b) Hexokinase

c) Phosphorylase

d) Glucose diphosphate

Answer: Phosphorylase

Which among the Following Statements about Phosphofructokinase-2 (PFK-2) is False ?

a) PFK-2 is bifunctional enzyme having kinase domain, phosphatase domain and regulatory domain

b) Activated protein kinase A phosphorylates PFK-2 and activates phosphatase domain

c) PFK-2 catalyzes the conversion of fructose-6-phosphate to fructose 2-6 bisphosphate

d) PFK-2 phosphatase activity is activated by insulin signaling pathway

Answer: Activated Protein Kinase A Phosphorylates PFK-2 and Activates Phosphatase Domain

Which among the Following Hormones decreases Blood Glucose and Increases Uptake of Glucose in Various Tissues like Skeletal Muscle, Adipose Tissues?

a) Glucagon

b) Epinephrine

c) Cortisol

d) Insulin

Answer: Insulin

The First Product of Glycogenolysis is -

a)Glucose-6-phosphate

b)Glucose 1,6 diphosphate

c)Glucose-1-phosphate

d)Fructose-1-phosphate

Answer: Glucose-1-Phosphate

Enzymes Concerned with the Citric Acid Cycle are Found in the -

a) Nucleus

b) Ribosomes

c) Mitochondria

d) Nonparticulate cytoplasm

Answer: Mitochondria

Which among the Following Statements is True?

a) Glycolysis occurs only in mammalian cells

b) Glycolysis occurs in mitochondria

c) Glycolysis occurs in presence and absence of oxygen

d) Glycolysis occurs when ATP concentration is high

Answer: Glycolysis occurs in Presence and Absence of Oxygen

What high Energy Phosphate Compound is Formed in the Citric Acid Cycle through Substrate level Phosphorylation?

a) ATP

b) TTP

c) ITP

d) GTP

Answer: GTP

The Conversion of Glucose-6-Phosphate to Fructose-6-Phosphate is an Example of which of the Following Reactions?

a) Phosphate transfer

b) Isomerization

c) Dehydration

d) Aldol cleavage

Answer: Isomerisation

The Net Gain of ATP during Conversion of Glucose to Pyruvate is -

a) 1 ATP

b) 2 ATP

c) 1 ATP +1 GTP

d) 4 ATP

Answer: 2 ATP

During the Conversion of Glucose to Pyruvate, Two NADH Molecules are Generated. Which of the Following Steps Generates NADH?

a) Conversion of fructose-6-phosphate to fructose-1-6-bisphosphate

b) Conversion of glyceraldehydes-3-phosphate to 1-3-bisphosphoglycerate

c)Conversion of 3-phosphoglycerate to 2-phosphoglycerate

d) Conversion of phosphoenolpyruvate to pyruvate

Answer: Conversion of glyceraldehydes-3-phosphate to 1-3-bisphosphoglycerate

Which One of the Following is a Monosaccharide?

a) Maltose

b) Sucrose

c) Fructose

d) Starch

Answer: Fructose

Which among the Following Steps is Inhibited during Arsenate Poisoning?

a) Glyceraldehyde-3-phosphate dehydrogenase

b) 3-phosphoglycerate mutase

c) Enolase

d) Pyruvate kinase

Answer: Glyceraldehyde-3-phosphate dehydrogenase

The End Product of Glycolysis under Anaerobic Conditions is -

a) Lactic acid

b) Pyruvic acid

c) Acetoacetic acid

d) Oxaloacetic acid

Answer: Lactic acid

Gluconeogenesis is the Production of Glucose from Non-Carbohydrate Molecules. Which of the Following is not Substrate for Gluconeogenesis?

a) Lactate

b) Alanine

c) Glycerol

d) Acetyl CoA

Answer: Acetyl CoA

Carbohydrates Metabolism

Carbohydrate metabolism is nothing but a number of biochemical processes involved in the formation, breakdown and conversion of carbohydrates in the body. The most important carbohydrate is glucose. Glucose is a monosaccharide that is metabolized by almost all known organisms.

Dietary glucose is abundant in starch. Amylase is an enzyme that breaks down starch and helps metabolism. Glucose comes from many sources, including lactose (from milk), fructose (from fruits), and sucrose (from sugar). The active membrane transport system supports the uptake of fructose, glucose, and fructose, known as monosaccharide species. The monosaccharide component is formed by the division of disaccharides by a special intestinal glucosidase. Types of glucose, such as maltose, are hydrolyzed by isomaltase, reducing their ability to produce the desired results. Lactose intolerance is caused by a deficiency of lactase, an enzyme required to break down lactose in lactose and other dairy products.

The small intestine contains intestinal mucosal cells that transport monosaccharides to the circulation, where they reach the liver. Here, galactose and fructose are converted to glucose. The liver's main task is to regulate glucose levels in the blood, in other words, to act as glucose in the blood. The excess glucose molecules produced are mainly stored as glycogen in liver and muscle cells. It is also stored in adipocytes in the form of metabolized fat. When food intake is restricted, only glycogen, instead of fat, is used to maintain adequate levels of glucose in the bloodstream. Fat can be used for oxidative regeneration of Adenosine Triphosphate (ATP) and reducing power (NADH).

Since every digestible form of carbohydrates is in the end converted to glucose, it is important to understand how glucose can provide energy in the form of adenosine triphosphate (ATP) to various different cells and tissues. Glucose is usually metabolized in three stages of carbohydrate metabolism.

Glycolysis
Krebs Cycle
Electron transport chain/ Oxidative Phosphorylation

Importance of Carbohydrates in our Diet

Carbohydrates provide energy to our body and are an excellent source of vitamins, minerals and nutrients. They provide instantaneous energy in the form of glucose, which is the main source of energy for our body and can also be stored. These carbohydrates should be included in our daily diet in the form of bread, potatoes, fiber, fruits, vegetables and whole grains. People these days are so sensitive to nutrition that they avoid foods that contain carbohydrates, which is not good for our health. You need to have a balanced diet. You should try to eat fiber-rich foods such as fruits and vegetables. Complex carbohydrates are the ultimate source of energy and are low in calories. Therefore, we need to get "correct carbohydrates" in our diet for our good health.

Weight Loss Associated with Carbohydrates

Eating a low carb diet can help you lose weight better than eating a low fat diet. In a 2004 study published in Nutrition & Metabolism, researchers fed obese subjects a low-carbohydrate or low-fat diet which included included meat, oil, fish and vegetables, and low-fat diets included whole grains, fruits, vegetables, low-fat dairy products and meat. Researchers found that subjects on a low-carb diet had a significant weight and fat loss compared to a low-fat diet. Eating a low-carb diet helps reduce appetite by preventing blood sugar fluctuations. Also, the high protein content of a low carb diet may require more energy to digest and burn calories in the process.