Detailed Overview of Biological Molecules

Carbohydrates:

Structure:

• Monosaccharides: The simplest form of carbohydrates, such as glucose (C₆H₁₂O₆), which is a hexose sugar with a ring structure. Each carbon atom is attached to a hydrogen atom and a hydroxyl group (–OH), except one carbon which is double-bonded to an oxygen atom, forming a carbonyl group (C=O).

• Disaccharides: Formed when two monosaccharides undergo a condensation reaction, where a water molecule is released. For example, sucrose is formed from glucose and fructose.

• Polysaccharides: Long chains of monosaccharides linked by glycosidic bonds. Examples include starch (energy storage in plants) and cellulose (structural component of plant cell walls).

Function:

• Energy Source: Glucose is a primary energy source for cellular respiration, which generates ATP.

• Energy Storage: Starch (in plants) and glycogen (in animals) are polysaccharides used to store energy.

• Structural Role: Cellulose provides structural support in plant cell walls, and chitin is a component of fungal cell walls and exoskeletons in insects.

Lipids:

Structure:

• Fatty Acids: Long hydrocarbon chains with a carboxyl group (–COOH) at one end. Fatty acids can be saturated (no double bonds, straight chains) or unsaturated (one or more double bonds, bent chains).

• Triglycerides: Formed by three fatty acids linked to a glycerol molecule. They are the main form of stored energy in animals.

• Phospholipids: Similar to triglycerides, but one fatty acid is replaced by a phosphate group, making the molecule amphipathic (having both hydrophobic and hydrophilic regions). Phospholipids are key components of cell membranes.

• Steroids: Composed of four fused carbon rings with various functional groups attached. Cholesterol is a common steroid that maintains membrane fluidity and serves as a precursor for other steroids, like hormones.

Function:

• Energy Storage: Triglycerides store energy in fat cells (adipocytes) and are metabolized to release energy when needed.

• Membrane Structure: Phospholipids form the bilayer of cell membranes, with hydrophilic heads facing outward and hydrophobic tails facing inward.

• Signaling Molecules: Steroid hormones like estrogen and testosterone regulate various physiological processes.

Proteins:

Structure:

• Amino Acids: The building blocks of proteins, each consisting of a central carbon atom (the α-carbon) bonded to an amino group (–NH₂), a carboxyl group (–COOH), a hydrogen atom, and a variable R group (side chain) that determines the properties of the amino acid.

• Peptide Bonds: Amino acids are linked by peptide bonds formed during a dehydration synthesis reaction, where a water molecule is released.

• Levels of Structure:

  • Primary Structure: The sequence of amino acids in a polypeptide chain.

  • Secondary Structure: The folding of the polypeptide into α-helices or β-pleated sheets, stabilized by hydrogen bonds.

  • Tertiary Structure: The overall three-dimensional shape of the protein, determined by interactions between R groups, including hydrogen bonds, ionic bonds, disulfide bridges, and hydrophobic interactions.

  • Quaternary Structure: The arrangement of multiple polypeptide chains in a protein, such as in hemoglobin.

Function:

• Enzymatic Catalysis: Enzymes accelerate biochemical reactions by lowering activation energy (e.g., amylase breaks down starch).

• Transport: Hemoglobin transports oxygen in the blood, and membrane proteins facilitate the movement of substances across cell membranes.

• Structural Support: Collagen provides tensile strength in connective tissues, and keratin is a key structural protein in hair and nails.

• Signaling: Hormones like insulin regulate physiological processes, and receptor proteins transmit signals into cells.

Nucleic Acids:

Structure:

• Nucleotides: The monomers of nucleic acids, each consisting of a phosphate group, a five-carbon sugar (ribose in RNA, deoxyribose in DNA), and a nitrogenous base (adenine, guanine, cytosine, thymine in DNA, or uracil in RNA).

• DNA (Deoxyribonucleic Acid): A double-stranded helix with antiparallel strands, where adenine pairs with thymine, and guanine pairs with cytosine through hydrogen bonds.

• RNA (Ribonucleic Acid): Typically single-stranded, with uracil replacing thymine. RNA plays various roles in gene expression, such as messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA).

Function:

• Genetic Information Storage: DNA stores genetic instructions for the development and functioning of living organisms.

• Gene Expression: RNA is involved in the transcription and translation of genetic information into proteins.

• Energy Currency: ATP (adenosine triphosphate) is a nucleotide that acts as the primary energy carrier in cells.

Activity:

• Molecule Models: Use an online molecular modeling tool like PhET Interactive Simulations or MolView to visualize the structures of glucose, a triglyceride, an amino acid, and a nucleotide. If you prefer, you can draw these molecules on paper, labeling each functional group and describing its properties.

• Comparison Chart: Create a detailed comparison chart that outlines the structure, function, and examples of carbohydrates, lipids, proteins, and nucleic acids. Include specific examples such as glucose, phospholipids, hemoglobin, and DNA, and explain their roles in cellular processes.

Advanced Application:

• Case Study: Investigate a genetic disorder related to a defect in a biological molecule. For example, explore how mutations in the gene coding for the hemoglobin protein lead to sickle cell anemia. Write a report detailing the molecular basis of the disease, how the mutation alters the hemoglobin structure, and the physiological consequences of these changes.