Cellular Building Blocks: Nucleic Acids & Proteins

• Nucleic acids, carbohydrates, lipids, and proteins serve as the fundamental building blocks for cellular structures, interactions, and signaling.

Nucleic Acids

• DNA serves as the primary information storage molecule, providing the genetic blueprint for organisms, forms the chromatin structure in the cell nucleus, determines inherited characteristics, and enables genetic information transmission between generations.
• RNA functions as a dynamic information translator, mRNA carries genetic instructions for protein synthesis, tRNA facilitates amino acid transport during protein creation, rRNA is structural component of ribosomes, and miRNA regulates gene expression.

ATP/GTP

• ATP/GTP are energy and signaling molecules.
• ATP is the primary cellular energy currency, triggers cellular transport mechanisms, enables muscle contraction, maintains membrane potential, and facilitates molecular assembly processes.

Proteins

• Proteins undertake structural, cellular interaction, and signaling roles within cells.

Structural Roles of Proteins

• Fibrous proteins like collagen, the primary structural protein in connective tissues, and keratin, provide mechanical support in cells and tissues and structural integrity in hair and nails.
• Membrane proteins such as cell adhesion molecules, receptor proteins, channel and transport proteins, facilitate structural maintenance of cell membranes.

Cellular Interaction Roles of Proteins

• Enzymes catalyze biochemical reactions.
• Hormones are chemical messengers.
• Antibodies facilitate immune system recognition.
• Transport proteins move molecules across membranes.

Signaling Molecules of Proteins

• Receptor proteins detect external signals and trigger intracellular responses, examples include insulin receptors and growth factor receptors.
• G-protein coupled receptors are included.
• Kinase signaling proteins are included.

Carbohydrates

• Carbohydrates act as energy and recognition specialists.

Structural Roles of Carbohydrates

• Cellulose provides structure in plant cell walls.
• Glycoproteins are components of the cell membrane.
• Proteoglycans contribute to extracellular matrix structure.

Cellular Interaction Roles of Carbohydrates

• Glycosylation modifies proteins.
• Carbohydrates facilitate cell surface recognition and immune system interactions.

Signaling Molecules of Carbohydrates

• Glycans facilitate cell-cell communication.
• Glucose functions in energy signaling.
• Glycogen provides energy storage and release mechanisms.

Lipids

• Lipids serve diverse roles, notably as membrane components and signaling molecules.

Structural Roles of Lipids

• Phospholipids act as primary cell membrane components and create cellular compartments.
• Cholesterol regulates membrane fluidity.

Cellular Interaction Roles of Lipids

• Lipid rafts organize membrane proteins.
• Lipids act as cell signaling platforms and maintain membrane potential.

Signaling Molecules of Lipids

• Steroid hormones incude testosterone, estrogen, and cortisol.
• Prostaglandins mediate inflammatory responses.
• Lipids are central to signaling through lipid-based second messengers.

Integrated Molecular Interactions

• Biomolecules create interconnected systems.
• DNA → RNA → Protein represents the central dogma of molecular biology.
• Proteins modified by carbohydrates.
• Lipids facilitate protein interactions.
• Energy molecules (ATP) power transformations.

Practical Example: Muscle Contraction

• DNA provides genetic instructions.
• RNA transcribes protein synthesis.
• Proteins form muscle structure.
• ATP provides energy.
• Calcium ions (signaling) trigger contraction.
• Carbohydrates provide immediate energy.
• Lipids maintain membrane integrity.

Dehydration Synthesis

• Polymers form through dehydration reactions, with monomers recovered via hydrolysis.
• Dehydration synthesis, also known as condensation reaction, involves the removal of a water molecule between two molecules, resulting in the creation of a new covalent bond and the combination of smaller molecules into larger polymers.
• Molecular mechanism is the removal of a water, one molecule loses a hydrogen (H⁺) and another hydroxyl group (OH⁻), net result is releasing a H₂O molecule.

Polymer Formation

• In nucleic acids, nucleotides join to form DNA/RNA through phosphodiester bonds.
• In proteins, amino acids form polypeptide chains via amino bonds.
• In carbohydrates, monosaccharides combine to form polysaccharides via glycosidic bonds.
• Lipids see fatty acids connect to glycerol, creating triglycerides.

Hydrolysis

• Hydrolysis involves the addition of a water molecule to break polymer bonds, splitting polymers into smaller monomer units and is the opposite of dehydration synthesis.
• Water insertion means a water molecule breaks an existing covalent bond, hydrogen (H⁺) attaches to one fragment while a hydroxyl group (OH⁻) attaches to another.

Polymer Breakdown

• Protein hydrolysis breaks peptide bonds, polypeptides become individual amino acids, crucial in digestion.
• Carbohydrate hydrolysis breaks glycosidic bonds, polysaccharides are broken down to simple sugars, occurs in the digestive system.
• Nucleic acid hydrolysis breaks phosphodiester bonds, DNA/RNA becomes Nucleotides, happens in genetic processes.

Energy Considerations

• Dehydration synthesis is endergonic, requires energy input, anabolic (building) reaction, ATP often provides energy.
• Hydrolysis is exergonic, releases energy, catabolic (breaking down) reaction, generates useable cellular energy.

Biological Significance

• Cellular metabolism enables complex molecule creation and allows energy storage and transfer.
• Digestive processes break down food molecules, convert complex nutrients to usable forms.
• Genetic Maintenance occurs through DNA/RNA synthesis and breakdown, protein turnover, and cellular repair mechanisms.

Key Enzymes Involved

• Dehydration utilizes peptidyl transferases, glycosyltransferases, and polymerases.
• Hydrolysis uses proteases, amylases, and nucleases.