Problem 13 - Biology: The Unity and Diversity of Life

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

a) Amino acid, b) Carbohydrate, c) Polypeptide, d) Fatty acid.

Step 1: Identify the carbohydrate

Carbohydrates are composed of carbon, hydrogen, and oxygen, generally following the formula \(C_x(H_2O)_y\). In the list provided, \(\mathrm{C}_6 \mathrm{H}_{12} \mathrm{O}_6\) matches the characteristic formula of a carbohydrate. Therefore, \(\mathrm{C}_6 \mathrm{H}_{12} \mathrm{O}_6\) is glucose, a simple sugar, and represents a carbohydrate.

Step 2: Identify the fatty acid

Fatty acids typically have a long hydrocarbon chain with a carboxylic acid group. In the list given, \(\mathrm{CH}_3(\mathrm{CH}_2)_{16} \mathrm{COOH}\) has this structure, with a long chain of hydrocarbons \(\mathrm{(CH}_2)_{16}\) and a terminal carboxylic acid \(\mathrm{COOH}\). Hence, this compound is a fatty acid.

Step 3: Identify the amino acid

Amino acids have an \(\mathrm{NH}_2\) group, a central carbon (\(\mathrm{C_H_R} \)), and a \(\mathrm{COOH}\) (carboxyl group). The structure \(\mathrm{NH}_2-\mathrm{CHR}-\mathrm{COOH}\) directly matches the general structure of an amino acid, which usually consists of an amino group (\(\mathrm{NH}_2\)), a carboxylic acid group (\(\mathrm{COOH}\)), and an R-group or side chain \(\left(\mathrm{R}\right)\). Thus, this is an amino acid.

Step 4: Identify the polypeptide

Polypeptides are chains of amino acids. In the list, '(methionine)_{20}' indicates a sequence or chain of 20 methionine amino acids. Therefore, this is a polypeptide comprised of multiple methionine units linked together.

Key Concepts

Carbohydrates

Carbohydrates are essential biomolecules that provide energy to living organisms. They are made up of carbon, hydrogen, and oxygen, generally following the formula \(C_x(H_2O)_y\). One of the most common carbohydrates is glucose, which has the molecular structure \(C_6H_{12}O_6\). This formula indicates that for every carbon atom, there is one water molecule, hence the name carbohydrate. Carbohydrates can be classified into simple and complex types:

• Simple Carbohydrates: These include monosaccharides like glucose and fructose, and disaccharides like sucrose and lactose.
• Complex Carbohydrates: These are polysaccharides like starch and cellulose, which consist of long chains of sugar units.

They play various roles such as providing energy, storing energy, and serving as structural components in organisms.

Fatty Acids

Fatty acids are carboxylic acids with long hydrocarbon chains, which can either be saturated or unsaturated. They are an important component of lipids found in the body, and are critical to many biological processes. The basic structure involves:

• Hydrocarbon Chain: Long chain made up of carbon and hydrogen atoms.
• Carboxyl Group: A functional group with the structure \(- ext{COOH}\).

In the given example, \(\mathrm{CH}_3(\mathrm{CH}_2)_{16}\mathrm{COOH}\), the "\(\mathrm{CH}_3\)" symbolizes the methyl end, followed by 16 methylene units "\(\mathrm{(CH}_2)_{16}\)" ending with a carboxyl group "\(\mathrm{COOH}\)." Fatty acids are not only vital for storing energy but also act as building blocks for producing hormones and cell membranes.

Amino Acids

Amino acids are the building blocks of proteins and play a vital role in nearly all biological processes. Each amino acid has a fundamental structure comprising:

• Amino Group (\(\mathrm{NH}_2\)): This is a group consisting of a nitrogen atom attached to two hydrogen atoms.
• Carboxyl Group (\(\mathrm{COOH}\)): Known as the carboxy functional group.
• R-group or Side Chain: This varies from one amino acid to another and defines the properties and types of amino acids.

In the example \(\mathrm{NH}_2-\mathrm{CHR}-\mathrm{COOH}\), the "\(\mathrm{CHR}\)" component represents the central carbon to which the amino group, carboxyl group, and side chain \(R\) are attached. Amino acids serve multiple functions, such as building proteins and enzymes, and they participate in cell signaling and immune responses.

Polypeptides

Polypeptides are long chains of amino acids linked together by peptide bonds. When multiple amino acids join, they form a polypeptide chain which eventually folds into a specific three-dimensional shape to become a protein. Proteins are responsible for countless functions within organisms, such as catalyzing metabolic reactions and supporting cellular structures. The key component of a polypeptide includes:

• Peptide Bond: Created when the amino group of one amino acid bonds with the carboxyl group of another.
• Primary Structure: The unique sequence of amino acids in a polypeptide chain.

A practical example is \((\text{methionine})_{20}\), representing a polypeptide made of 20 methionine amino acids linked together. Polypeptides are crucial for sustaining life, playing roles in functions ranging from cellular movement to immune protection.