Biochemistry: Oligosaccharides and Lipids

Oligosaccharides

Oligosaccharides are carbohydrates that consist of a range of three to ten monosaccharides.
- The prefix "oligo" means few.
- These saccharides have various biological applications, particularly as cell markers or identifiers for organisms and functions.

They are prominent in a range of applications, especially as part of cell membrane structures.
These oligosaccharides play crucial roles in recognition processes, helping cells identify one another.

Antigens: An example of their importance is in the human immune system where oligosaccharides are part of antigens that help the bodyrecognize its own cells versus foreign substances.
They are also involved in determining blood types:
- Blood Type Classification:
- Type A: Contains specific oligosaccharides (A markers).
- Type B: Contains different oligosaccharides (B markers).
- Type AB: Contains both A and B markers.
- Type O: Lacks A and B markers entirely, which makes it a universal donor as it does not trigger an immune response in other blood types.

Blood transfusions require matching oligosaccharide markers to prevent immune system reactions that could arise from the introduction of foreign markers.
Type O blood can be given to anyone because it does not possess the A or B markers that could be recognized as foreign.

Oligosaccharides are essential to many biological systems, acting as identifiers for cells, where variations in their structures can have significant implications in medical contexts, particularly transfusions.

When discussing monosaccharides, understanding their structural aspects is essential, including their cyclic forms and linkages.

Anomeric Carbon: The carbon atom that is attached to two oxygen atoms in cyclic sugars, crucial for determining the sugar's configuration (alpha or beta).
- Alpha and Beta Forms:
- Beta linkage: When the hydroxyl group (OH) on the anomeric carbon is above the plane of the sugar (pointing up).
- Alpha linkage: When the hydroxyl group is below the plane of the sugar (pointing down).
Understanding these concepts is vital for nomenclature and functional properties in chemical bonding.

During sugar cyclization, carbons are numbered, with the first carbon referred to as carbon one. Linkages such as a 1-4 linkage are crucial for structural biology.

Lipids: A broad category of biological compounds that are hydrophobic and do not readily mix with water.

Lipids are defined by their hydrophobic nature and are soluble in organic solvents such as:
- Mineral spirits
- Hexane
- Toluene
Most lipids consist of fatty acids, which are long hydrocarbon chains ending in a carboxylic acid group.

Fatty acids gain properties based on the presence of double bonds, influencing their saturation:
- Saturated Fatty Acid: No double bonds present, typically solid at room temperature.
- Unsaturated Fatty Acid: Contains one or more double bonds, which introduces kinks in the structure, making them liquid at room temperature and commonly referred to as oils.

Essential fatty acids: Fatty acids that cannot be synthesized by the body and must be obtained through diet (e.g., Omega-3 such as linolenic acid).
- Sources include:
- Fish (especially salmon)
- Flaxseed
- Walnuts
- Canola oil
These fatty acids play structural roles in cell membranes and other physiological functions.

Delta system: Starts numbering from the carboxylic acid carbon in the chain, indicating the position of double bonds by superscript numbers.
- For example, linoleic acid could be referenced as $ ext{C}{18} ext{H}{32} ext{O}_2$ with double bonds at positions 9 and 12.
Omega system: Starts numbering from the last carbon (tail) in the chain, determining the type of fatty acid (Omega-3 or Omega-6) based on the position of the first double bond.
- For example, Omega-3 refers to a double bond at the 3rd carbon from the tail.

Triglycerides: Formed when three fatty acids are esterified to glycerol, a three-carbon alcohol.

The body uses triglycerides as a form of energy storage; they are broken down during metabolic processes to release energy when needed.
Triglycerides can also exist as fats (solid) or oils (liquid), classified based on saturation rather than phase at room temperature.

The structure of triglycerides and mechanism of formation involve:
- Hydrolysis reactions breaking ester bonds, leading to the generation of glycerol and fatty acids.
Solid fats from animals are often considered less healthy whereas liquid oils (typically unsaturated) are associated with better health outcomes.

The understanding of lipids, particularly fatty acids, and their structures, forms the basis of numerous concepts in biochemistry related to cellular functions, nutrition, and health.