Carbohydrates and Their Importance

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Questions and Answers

What is the origin of the term 'carbohydrate'?

From the combination of carbon and water (correct)

From the observation of sugar consumption

From the study of plant cell structure

From the discovery of starches in food

What is the primary source of energy in the human body?

Carbohydrates (correct)

Fats

Proteins

Vitamins

What is the function of carbohydrates in animal and plant cells?

To provide structural support (correct)

To provide energy

To regulate hormones

To aid in digestion

What is the definition of a monosaccharide?

A simple sugar that cannot be further broken down Signup and view all the answers

What is the result of acid hydrolysis of polysaccharides?

Monosaccharides Signup and view all the answers

How are oligosaccharides characterized?

Containing 2-10 sugar units Signup and view all the answers

What is the classification of carbohydrates based on the number of sugar units?

Monosaccharides, oligosaccharides, and polysaccharides Signup and view all the answers

What is the characteristic of hexoses?

Containing 6 carbon atoms Signup and view all the answers

What is the approximate energy yield from the oxidation of one gram of carbohydrate?

4 kcal Signup and view all the answers

What happens to excess glucose when liver and muscle glycogen reserves are filled?

It is converted to TAG and deposited in adipose tissue Signup and view all the answers

What is the primary source of glucose for the body after meals?

Carbohydrates in diet Signup and view all the answers

What is the main pathway of glucose utilization in tissues?

Glycolysis and Krebs' cycle Signup and view all the answers

What is the threshold above which glucose is excreted in urine?

180 mg/dL Signup and view all the answers

What is the source of glucose for muscles during exercise?

Muscle glycogen Signup and view all the answers

What is the primary function of carbohydrates in the body?

To maintain blood glucose levels Signup and view all the answers

What type of carbohydrate is found in plant cell walls and is mostly indigestible?

Fiber Signup and view all the answers

What is the process of transforming small molecules into bigger molecules constituting the body structures and machinery?

Anabolic pathways Signup and view all the answers

What is the breakdown of large molecules into smaller molecules or reducing equivalents to produce energy?

Catabolic pathways Signup and view all the answers

What is the final product of carbohydrate digestion in the GIT?

Monosaccharides Signup and view all the answers

Which of the following is an example of an amphibolic pathway?

Glycolysis Signup and view all the answers

What is the classification of fiber based on?

Solubility in water Signup and view all the answers

Which of the following is NOT a type of carbohydrate?

Proteins Signup and view all the answers

Where does the Krebs cycle occur?

In the mitochondria Signup and view all the answers

What is the net ATP production from the complete oxidation of one glucose molecule?

38 ATP Signup and view all the answers

Where does the digestion of carbohydrates start?

In the mouth Signup and view all the answers

What is the purpose of glycogenesis?

Synthesis of glycogen from glucose Signup and view all the answers

What is the primary function of salivary amylase in the mouth?

To break down starch into dextrin and maltose Signup and view all the answers

What is the reason for the temporary halt in carbohydrate digestion in the stomach?

The high acidity inactivates the salivary amylase Signup and view all the answers

What is the main function of the hexose monophosphate pathway (HMP) or pentose phosphate pathway (PPP)?

To produce NADPH Signup and view all the answers

During a brief fast, where does glucose come from?

From the liver through glycogenolysis Signup and view all the answers

What is the final product of starch digestion in the small intestine?

Glucose Signup and view all the answers

What is the role of the liver, pancreas, and other endocrine glands in regulating carbohydrate metabolism?

To control blood glucose concentrations Signup and view all the answers

How are monosaccharides absorbed into the bloodstream?

Active transport against concentration gradient Signup and view all the answers

What is the fate of absorbed fructose and galactose in the liver?

They are converted to glucose Signup and view all the answers

What is the role of pancreatic amylase in the small intestine?

To break down starch into maltose and isomaltose Signup and view all the answers

What is the primary site of carbohydrate absorption?

Small intestine Signup and view all the answers

Study Notes

Carbohydrates

Carbohydrates include sugars, starches, and fibers found in foods such as bread, pasta, and rice.
The term "carbohydrate" comes from the observation that when sugars are heated, they produce carbon and water (hydrate of carbon).

Importance of Carbohydrates

Primary source of energy for the body.
Important structural components in animal and plant cells.
Key components of nucleic acids, free nucleotides, and coenzymes.
Major antigens are carbohydrates in nature, e.g., blood group substance.
Play a biological role as part of hormones and their receptors and enzymes.

Classification of Carbohydrates

Monosaccharides (simple sugars): contain one sugar unit, cannot be further hydrolyzed, and represent the end products of carbohydrate digestion in the human body.
Oligosaccharides: contain 2-10 monosaccharide units per molecule and give monosaccharides on acid hydrolysis.
Polysaccharides: contain more than 10 monosaccharide units per molecule and give monosaccharides on acid hydrolysis.

Monosaccharides

Classified according to the number of carbon atoms into five important groups.
Hexoses: monosaccharides containing 6 carbon atoms, help maintain blood glucose, and are an important source of "quick energy" during exercise.

Fiber

Mostly indigestible carbohydrate.
Component of plant cell walls.
Classified according to solubility in water.
Abundant in whole grains, legumes, fruits, and vegetables.

Carbohydrate Metabolism

Includes digestion, absorption, utilization, and excretion of carbohydrates.
Digestion involves the breakdown of carbohydrates into simpler molecules.
Absorption involves the uptake of digested carbohydrates into the bloodstream.
Utilization involves the conversion of absorbed carbohydrates into energy or storage forms.
Excretion involves the removal of excess glucose from the body.

Digestion and Absorption of Carbohydrates

Digestion starts in the mouth with salivary amylase, which breaks down starch into dextrin and maltose.
In the stomach, digestion halts temporarily due to the high acidity, which inactivates salivary amylase.
In the small intestine, pancreatic amylase completes the digestion of carbohydrates into monosaccharides.
Monosaccharides are absorbed into the bloodstream through active transport against a concentration gradient.

Fate of Absorbed Monosaccharides

In the liver, fructose and galactose are converted to glucose.
Glucose is utilized by the body through oxidation to produce energy, conversion to other substances, storage as glycogen or fat, or excretion in urine.

Sources of Glucose to the Human Body

Carbohydrates in the diet are the primary source of glucose for the body.
Glycogen stored in the liver and muscles can be degraded to yield glucose during fasting or exercise.
Glucose can also be synthesized from non-carbohydrate sources through gluconeogenesis.

ATP Production

Complete oxidation of one glucose molecule results in a net production of 38 ATP molecules.
Aerobic glycolysis produces 8 ATP, oxidative decarboxylation produces 6 ATP, and the Krebs cycle produces 24 ATP.

Krebs Cycle

Final common pathway for the oxidation of carbohydrates, fatty acids, and amino acids.
Occurs in the mitochondria and is aerobic.

Glycogenesis and Glycogenolysis

Glycogenesis: synthesis of glycogen from glucose in the liver and muscles.
Glycogenolysis: degradation of glycogen into glucose in the liver and muscles.

Hexose Monophosphate Pathway (HMP) or Pentose Phosphate Pathway (PPP)

Important source of NADPH for reductive syntheses.
Source of metabolically active ribose for nucleic acid synthesis.

Regulation of Carbohydrate Metabolism

The liver, pancreas, and other endocrine glands are involved in controlling blood glucose concentrations.
During fasting, glucose is supplied to the extracellular fluid from the liver through glycogenolysis and gluconeogenesis.

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Description

Learn about carbohydrates, their sources, and their importance in the body. Discover how they provide energy and serve as structural components in cells.