Biomolecules - Carbohydrates

Carbohydrates are organic compounds composed of carbon, hydrogen, and oxygen atoms.
They are classified into three main types: monosaccharides, disaccharides, and polysaccharides.
Monosaccharides are simple sugars with a single sugar unit, such as glucose and fructose.
Disaccharides are formed by the condensation reaction between two monosaccharides, like sucrose and lactose.
Polysaccharides consist of many monosaccharide units and are complex carbohydrates, examples include starch and cellulose.

Structure of Monosaccharides

Monosaccharides have a general formula of (CH2O)n, where n ranges from 3 to 7.
They can exist in linear or cyclic forms.
Glucose, for example, is a six-carbon sugar that can form a cyclic structure.
In a cyclic structure, one of the carbon atoms forms a bond with oxygen, creating a hemiacetal or hemiketal group.

Isomers of Monosaccharides

Isomers are molecules with the same molecular formula but different structural arrangements.
In monosaccharides, isomers can occur due to different arrangements of hydroxyl groups around the carbon atoms.
Aldose isomers have an aldehyde functional group, while ketose isomers have a ketone functional group.
For example, glucose and fructose are isomers, both having the same molecular formula, C6H12O6, but different structural arrangements.

Reducing and Non-reducing Sugars

Reducing sugars are monosaccharides or disaccharides that can reduce other compounds, particularly oxidizing agents.
They have a free anomeric carbon that can undergo oxidation.
Glucose is a reducing sugar, as it can reduce Benedict’s or Fehling’s solution.
Non-reducing sugars, such as sucrose, do not have a free anomeric carbon and cannot undergo oxidation.

Disaccharides

Disaccharides are formed by the condensation reaction between two monosaccharides.
The reaction involves the loss of a water molecule, forming a glycosidic bond.
Common disaccharides include sucrose, lactose, and maltose.
Sucrose is formed by the condensation of glucose and fructose.
Lactose is composed of glucose and galactose.
Maltose results from the condensation of two glucose molecules.

Hydrolysis of Disaccharides

Disaccharides can be hydrolyzed by adding water, breaking the glycosidic bond.
Hydrolysis of sucrose gives glucose and fructose.
Lactose hydrolysis produces glucose and galactose.
Maltose is hydrolyzed into two glucose molecules.

Polysaccharides

Polysaccharides are complex carbohydrates made up of many monosaccharide units.
They can be homopolysaccharides, composed of a single type of monosaccharide, or heteropolysaccharides, composed of different monosaccharides.
Starch, cellulose, and glycogen are examples of polysaccharides.

Structure and Function of Starch

Starch is a storage polysaccharide in plants.
It is composed of two types of glucose polymers: amylose and amylopectin.
Amylose is a linear polymer, while amylopectin is branched.
Starch is used by plants to store energy and can be hydrolyzed by enzymes like amylase.

Structure and Function of Cellulose

Cellulose is the most abundant organic compound on Earth and an important structural polysaccharide in plants.
It is composed of glucose units linked by β-1,4-glycosidic bonds.
Cellulose forms long, linear chains that are interconnected through hydrogen bonding, providing strength and rigidity to plant cell walls.
Humans cannot digest cellulose due to the lack of enzymes to break β-1,4-glycosidic bonds.

Structure and Function of Glycogen

Glycogen is the storage polysaccharide in animals, particularly in the liver and muscles.
It is highly branched, similar to amylopectin.
Glycogen serves as an energy reserve and can be rapidly hydrolyzed into glucose when needed.
The branching allows for efficient storage and quick release of glucose molecules.

Biomolecules - Carbohydrates

Structure and Function of Glycosaminoglycans

Glycosaminoglycans (GAGs) are long unbranched polysaccharides.
They are composed of repeating disaccharide units, with one of the sugars being an amino sugar.
GAGs are important components of extracellular matrices and provide structural support.
Examples of GAGs include hyaluronic acid, chondroitin sulfate, and heparan sulfate.
Hyaluronic acid is found in the synovial fluid, vitreous humor, and connective tissue of animals.

Introduction to Lipids

Lipids are a diverse group of biomolecules that are largely nonpolar and hydrophobic.
They include fats, oils, waxes, phospholipids, and steroids.
Lipids serve various functions, including energy storage, insulation, and forming cell membranes.
Fats and oils are composed of glycerol and fatty acids.
Fatty acids can be saturated or unsaturated, depending on the presence of double bonds.

Types of Lipids

Triglycerides, also known as triacylglycerols, are the most common type of lipid.
They consist of a glycerol backbone and three fatty acid chains.
Saturated fatty acids have single bonds between all carbon atoms and exist as solids at room temperature.
Unsaturated fatty acids have one or more double bonds and exist as liquids at room temperature.
Phospholipids are the major components of cell membranes and have a polar phosphate head and nonpolar fatty acid tails.

Steroids

Steroids are a class of lipids characterized by a four-ring structure.
They are involved in various physiological processes, including hormone regulation and membrane fluidity.
Cholesterol is a well-known steroid that is essential for cell membrane integrity.
Other steroids include cortisol, testosterone, and estrogen, which have specific functions in the body.

Nucleic Acids - DNA and RNA

Nucleic acids are large biomolecules composed of nucleotide monomers.
They store and transmit genetic information in cells.
DNA (deoxyribonucleic acid) is a double-stranded helical structure that carries genetic instructions.
RNA (ribonucleic acid) is single-stranded and involved in protein synthesis.
Both DNA and RNA are composed of nucleotides, which consist of a sugar, phosphate group, and nitrogenous base.

Structure of DNA

DNA has a double-helical structure, with two antiparallel strands held together by hydrogen bonding between nitrogenous bases.
The sugar-phosphate backbone forms the outer part of the helix.
Adenine (A) pairs with thymine (T), forming two hydrogen bonds.
Guanine (G) pairs with cytosine (C), forming three hydrogen bonds.
The base pairing allows for accurate DNA replication and transcription.

Structure of RNA

RNA is single-stranded and has a similar structure to one strand of DNA.
However, RNA contains ribose sugar instead of deoxyribose sugar and uracil (U) instead of thymine (T).
RNA can fold upon itself and form complex structures due to internal base pairing.
Different types of RNA molecules, such as mRNA, tRNA, and rRNA, have specific functions in protein synthesis.

Enzymes - Catalysts in Biochemical Reactions

Enzymes are biological catalysts that speed up biochemical reactions in cells.
They lower the activation energy required for the reaction to occur.
Enzymes follow the lock-and-key model, where the enzyme’s active site binds to the substrate.
The enzyme-substrate complex undergoes a reaction, producing the product.
Enzymes are highly specific and can be regulated by factors such as pH, temperature, and inhibitors.

Enzyme Regulation - Allosteric Regulation

Allosteric regulation is a process where the regulation of enzyme activity occurs at a site other than the active site.
It involves the binding of an effector molecule to the allosteric site.
The effector can be an activator or inhibitor, regulating the enzyme’s function.
Allosteric regulation allows for dynamic control of enzyme activity in response to cellular needs.
An example of allosteric regulation is the feedback inhibition of enzymes in metabolic pathways.

======"

Biomolecules - Carbohydrates

Metabolism of Carbohydrates

Carbohydrates play a crucial role in energy metabolism.
Glucose is the primary source of energy for cells.
During cellular respiration, glucose is oxidized to produce ATP.
Glycolysis is the first step of glucose metabolism, where glucose is converted into pyruvate.
In aerobic conditions, pyruvate undergoes further oxidation in the citric acid cycle and electron transport chain.

Glycolysis

Glycolysis is a metabolic pathway that occurs in the cytoplasm of cells.
It converts glucose into two molecules of pyruvate.
It is an anaerobic process and does not require oxygen.
Glycolysis produces a small amount of ATP and NADH.
The overall reaction can be summarized as: glucose + 2 NAD+ + 2 ADP + 2 Pi → 2 pyruvate + 2 NADH + 2 ATP + 2 H2O

Citric Acid Cycle

The citric acid cycle, also known as the Krebs cycle, takes place in the mitochondria.
It completes the breakdown of glucose by oxidizing pyruvate.
Pyruvate is transformed into acetyl-CoA and enters the citric acid cycle.
The cycle generates energy-rich molecules, such as NADH and FADH2, as well as GTP.
The overall reaction can be summarized as: Acetyl-CoA + 3 NAD+ + FAD + ADP + Pi → 2 CO2 + 3 NADH + FADH2 + GTP + CoA

Electron Transport Chain

The electron transport chain is the final step of glucose metabolism.
It occurs in the inner mitochondrial membrane.
NADH and FADH2 produced in glycolysis and the citric acid cycle donate electrons to the chain.
Electrons are transferred through a series of protein complexes, generating a proton gradient.
The proton gradient powers ATP synthesis through ATP synthase.

Fermentation

In the absence of oxygen, cells can undergo fermentation to regenerate NAD+.
Fermentation occurs in the cytoplasm and allows for continued ATP production.
Two common types of fermentation are lactic acid fermentation and alcoholic fermentation.
Lactic acid fermentation converts pyruvate into lactic acid.
Alcoholic fermentation converts pyruvate into ethanol and carbon dioxide.

Importance of Carbohydrates

Carbohydrates serve as a vital energy source for all living organisms.
They are crucial in the functioning of the nervous system and brain.
Carbohydrates play a role in the proper functioning of the immune system.
They are also involved in cell signaling and adhesion processes.
Carbohydrates serve as structural components in plants, forming cellulose and other polysaccharides.

Carbohydrate Derivatives

Carbohydrates can undergo various chemical modifications to produce carbohydrate derivatives.
These derivatives can have different functional groups or added substituents.
Examples of carbohydrate derivatives include amino sugars, sugar alcohols, and glycosides.
Amino sugars have an amino group (-NH2) substituent attached to the sugar.
Sugar alcohols have a hydroxyl (-OH) group replaced with an alcohol group (-CH2OH).

Clinical Significance of Carbohydrates

Abnormalities in carbohydrate metabolism can have clinical implications.
Diabetes mellitus is a disorder characterized by high blood glucose levels.
Type 1 diabetes is caused by the inability to produce insulin, while type 2 diabetes is due to insulin resistance.
Glycogen storage diseases result from deficiencies in enzymes involved in glycogen metabolism.
Disorders in carbohydrate metabolism can lead to symptoms such as hypoglycemia, fatigue, and organ damage.

Summary

Carbohydrates are vital biomolecules composed of carbon, hydrogen, and oxygen.
They are classified into monosaccharides, disaccharides, and polysaccharides.
Monosaccharides are the simplest sugars, while polysaccharides are complex carbohydrates.
Carbohydrates play a critical role in energy metabolism, cellular signaling, and structural support.
Metabolism of carbohydrates involves glycolysis, the citric acid cycle, and the electron transport chain.

Conclusion

Understanding the chemistry and metabolism of carbohydrates is crucial for a comprehensive understanding of biochemistry.
Carbohydrates are not only a source of energy but also play various roles in cellular processes.
Further research and study of carbohydrates are necessary for advancements in medicine and biochemistry.