Essential Concepts in Biochemistry: Fractionation and Carbohydrates
Subcellular Fractionation: Isolating Cell Components
Subcellular fractionation is the process used to separate and isolate intracellular molecules and organelles from cells.
Stages of Subcellular Fractionation
- Extraction
- Homogenization
- Differential Centrifugation
Extraction (Tissue Sampling)
This stage involves obtaining a tissue sample from a living organism, as tissues contain the cells required for analysis.
Homogenization
The tissue is blended or dissolved in a benign medium (under appropriate conditions) to disrupt the cell membranes and release the cell contents.
Differential Centrifugation
A procedure used to separate cellular components based on size and density, resulting in distinct fractions.
Key Fractions Separated by Centrifugation
- Nuclear Fraction: Contains DNA.
- Mitochondrial Fraction: Contains enzymes.
- Microsomal Fraction: Contains smooth and rough endoplasmic reticulum, and lysosomes.
Experimental Approaches in Biochemistry
Key procedures used in biochemical analysis include:
- Isolation: Techniques like salt fractionation.
- Molecular Structure Determination: Techniques like mass spectrometry.
- Functional Analysis: Analyzing the molecule's role in the body.
Major Advances in Biochemistry
- Determining the structures of many biomolecules.
- Isolation and establishment of the function of key cellular organelles.
Reverse Transcription Defined
Reverse transcription is the inverse process by which genetic information from RNA can be transcribed into DNA.
Glucose: Structure and Biological Role
Glucose is a fundamental monosaccharide that can be used to form other carbohydrates in the body. It constitutes an important fuel source in mammals and is a universal combustible tissue source for the fetus.
Glucose Synthesis in Plants (Photosynthesis)
In plants, glucose is synthesized through photosynthesis from CO2 and water and is subsequently stored as starch or cellulose.
Monosaccharides: Simple Carbohydrates
Monosaccharides are the simplest carbohydrates and are incapable of being hydrolyzed. Their general formula is (CnH2nOn). They are subdivided based on the number of carbons:
- Trioses (3 carbons)
- Tetroses (4 carbons)
- Pentoses (5 carbons)
- Hexoses (6 carbons)
- Heptoses (7 carbons)
Disaccharides
Disaccharides are carbohydrates that, when hydrolyzed, yield two molecules of monosaccharides.
Polysaccharides
Polysaccharides are carbohydrates that, upon hydrolysis, produce more than ten monosaccharide molecules. They may be linear or branched.
Starch Composition and Hydrolysis
Starch is a homopolymer called a glucan, consisting of alpha-glucoside chains. When hydrolyzed, starch produces glucose. Starch is composed of two main components:
- Amylose (approximately 20%)
- Amylopectin (approximately 80%)
Key Biochemical Reactions
Hydrolysis
The breaking of a chemical bond through the incorporation of water.
Dehydration Synthesis (Condensation)
A reaction that forms chemical bonds (e.g., glycosidic bonds) by releasing or losing a molecule of water.
Molisch's Test (Carbohydrate Detection)
This test uses alpha-naphthol and sulfuric acid. It reacts with carbohydrates to form a characteristic violet ring.
Fehling's Test (Reducing Sugars)
This test recognizes reducing sugars. A positive reaction is characterized by the formation of a brick-red precipitate.