Problem 14 - Biology: Concepts and Applications

Question

In the following list, identify the carbohydrate, the fatty acid, the amino acid, and the polypeptide: a. \(\mathrm{NH}_{2}-\mathrm{CHR}-\mathrm{COOH}\) b. \(\mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6}\) c. (methionine) 20 \(\mathrm{d} . \mathrm{CH}_{3}\left(\mathrm{CH}_{2}\right)_{16} \mathrm{COOH}\)

Step-by-Step Solution

Answer

Carbohydrate: \( \mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6} \), Fatty Acid: \( \mathrm{CH}_{3}\left(\mathrm{CH}_{2}\right)_{16} \mathrm{COOH} \), Amino Acid: \( \mathrm{NH}_{2}-\mathrm{CHR}-\mathrm{COOH} \), Polypeptide: (methionine) 20.

Step 1: Identify the Carbohydrate

A carbohydrate is typically a compound consisting of carbon, hydrogen, and oxygen, often in the proportion of 1:2:1. From the list provided, \( \mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6} \) is structured similarly to glucose, a simple sugar that is a carbohydrate. Thus, the carbohydrate in the list is \( \mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6} \).

Step 2: Identify the Fatty Acid

Fatty acids are long chains of hydrocarbons ending with a carboxylic acid group. From the options, \( \mathrm{CH}_{3}\left(\mathrm{CH}_{2}\right)_{16} \mathrm{COOH} \) fits this description with its long chain hydrocarbon structure followed by a carboxyl group. Hence, the fatty acid is \( \mathrm{CH}_{3}\left(\mathrm{CH}_{2}\right)_{16} \mathrm{COOH} \).

Step 3: Identify the Amino Acid

An amino acid has an amino group (\(\mathrm{NH}_2\)) and a carboxyl group (\(\mathrm{COOH}\)) attached to a central carbon. The structure \( \mathrm{NH}_{2}-\mathrm{CHR}-\mathrm{COOH} \) perfectly matches that of an amino acid. Thus, the amino acid is \( \mathrm{NH}_{2}-\mathrm{CHR}-\mathrm{COOH} \).

Step 4: Identify the Polypeptide

Polypeptides are chains of amino acids. The notation (methionine) 20 implies a chain consisting of 20 methionine amino acids, which qualifies as a polypeptide. Therefore, the polypeptide is (methionine) 20.

Key Concepts

Carbohydrate

Carbohydrates are essential biomolecules made of carbon, hydrogen, and oxygen, often in a specific 1:2:1 ratio. Glucose, a well-known simple sugar, exemplifies this composition, having the formula \( \mathrm{C_{6}H_{12}O_{6}} \). These molecules are vital energy sources and structural materials for organisms.
Carbohydrates can be classified into categories:

• Monosaccharides: Simplest form of carbohydrates, including glucose and fructose.
• Disaccharides: Formed by joining two monosaccharides (e.g., sucrose).
• Polysaccharides: Long chains of monosaccharides, such as starch and cellulose, serving as energy reserves or structural elements.

This versatility in forms allows carbohydrates to play multiple roles in biological processes.

Fatty Acid

Fatty acids are long chains of hydrocarbons with a terminal carboxylic acid group. They are key components of lipids and play crucial roles in energy storage and cell membrane structure. An example is \( \mathrm{CH_{3}(CH_{2})_{16}COOH} \), which has a long hydrocarbon chain followed by a carboxyl group.
Fatty acids can be classified based on the presence of double bonds:

• Saturated Fatty Acids: No double bonds, meaning they are fully saturated with hydrogen atoms.
• Unsaturated Fatty Acids: Contain one or more double bonds, impacting the fluidity and melting point of lipids.

These molecules are not only energy-dense but also serve as signaling molecules and constituents of bio-membranes.

Amino Acid

Amino acids are foundational units of proteins, featuring an amino group (\(\mathrm{NH_{2}}\)), a carboxyl group (\(\mathrm{COOH}\)), and a variable side chain (R group) linked to a central carbon. The general structure is depicted as \( \mathrm{NH_{2}-CHR-COOH} \). This basic structure allows amino acids to join in specific sequences to create proteins.
Amino acids are:

• Essential: Must be obtained from the diet as the body cannot synthesize them (e.g., valine, leucine).
• Non-essential: Can be synthesized by the body (e.g., alanine, glutamine).

Amino acids play a pivotal role in numerous biological functions, including enzyme catalysis, signaling, and tissue repair.

Polypeptide

Polypeptides consist of multiple amino acids linked by peptide bonds, forming the primary structure of proteins. They are longer chains, with sequences that define protein functionality. The notation (methionine) 20 indicates a chain of 20 methionine amino acids, demonstrating a simple polypeptide structure.
Polypeptides can:

• Fold into specific shapes, dictating their functional properties and interactions.
• Form complex structures when more polypeptides combine, creating proteins.
• Serve as hormones, enzymes, structural components, and immune response elements.

The variety in polypeptide structures and functions highlights their fundamental role in maintaining life processes.