Cellular Organization: Structure, Function, and Interactions
The Cell: The Basic Unit of Life
The cell is the minimum reproductive unit and the hereditary basis of information that defines a species. It has the capacity for self-replication.
Plasma Membrane: Defining the Cell
The plasma membrane defines the cell and its interaction with the external environment. It facilitates cellular compartmentalization and interaction with the extracellular environment and other cells. The nuclear membrane differentiates “eukaryotic” from “prokaryotic” cells.
Organelles: Functional Units Within the Cell
Organelles are present in all eukaryotic cells. Their number and extent depend on cellular functions.
Mitochondria
Associated with high energy demand.
Endoplasmic Reticulum
Associated with high protein synthesis.
Golgi Apparatus
Associated with high lipid synthesis and excretion of cellular products.
Cytoskeleton
Essential for cell movement and structure.
Biological Levels of Organization
Cells can be unicellular or multicellular. In multicellular organisms, tissues are composed of differentiated cells with specific functions, organized into organs.
Differentiation and Organization
Multiple cell types arise from the same gene pool (~30,000 genes in humans) through different gene expression patterns. Mutations can lead to evolution or cancer.
Cellular Levels of Organization
Organization occurs at the molecular level with water, salts, and organic molecules (carbohydrates, lipids, proteins, nucleic acids). Structural and functional organization leads to organelles, where cellular processes have chemical bases.
Understanding the properties of biological molecules is crucial for understanding their functions.
Water: The Solvent of Life
Water is an essential organic solvent that determines the structure of molecules. It is a polar molecule with a dipole moment.
Molecular Organization
Organization progresses from atoms to molecules to macromolecules (linked together). Biological molecules primarily consist of C, H, O, and N.
Chemical Bonds
Ionic Bonds
Formed between ions with opposite charges (+ and -).
Hydrogen Bonds
Formed between an H atom participating in a polar covalent bond and another atom involved in a polar covalent bond.
Hydrophobic Interactions
Occur when water molecules exclude hydrophobic molecules.
Covalent Bonds
Involve shared electron pairs. If shared equally, the bond is nonpolar; if unevenly shared, the bond is polar.
ATP: The Energy Currency of the Cell
ATP (Adenosine Triphosphate) contains high-energy links and an electrochemical gradient. It is a nucleotide consisting of a nitrogenous base (adenine) attached to carbon 1 of a pentose sugar (ribose), which has three phosphate groups linked to its carbon 5. It is incorporated into nucleic acids. ATP is produced during photosynthesis and cellular respiration and consumed by enzymes in catalyzing many chemical processes. Its formula is C10H16N5O13P3.
Formation of Molecules
Molecules form linear structures through monomer linking/polymerization. These reactions require energy.
Noncovalent Bonds
Noncovalent bonds are important for higher-level molecular structures and macromolecules. They are weak/transient unions with low rupture energy (1-5 kcal/mol). Kinetic energy at 20°C is 0.6 kcal/mol.
Ionic Bonds in Solution
Established between charged atoms (ions) where electrons are transferred between atoms of different electronegativities. Common ions in solution include Na+, K+, Ca2+, Mg2+, Cl–.
Van der Waals Interactions
Established through transient dipoles between polar or neutral molecules, dependent on the distance between atoms. Van der Waals energy is approximately 1 kcal/mol.
Hydrogen Bonds (Detailed)
Electronegativity is the power to attract electrons. Hydrogen bonds involve a union to H with a partial positive charge. Energy: 1-2 kCal/mol, stabilizing higher-level molecular structures.
Covalent Bonds (Detailed)
Established between atoms with unpaired orbitals. The number of bonds is related to bond energy.
Links and Unpaired Electrons
The form of the bond is characteristic of molecules, influencing polarity based on the electronegativity of atoms.
Biological Molecules and Water
Biological molecules bind or break by adding or removing H2O.