Fundamental Properties of Life

Characteristics of Living Organisms

Living organisms share several fundamental properties that distinguish them from non-living matter. Understanding these properties is essential for studying biology.

• Reproduction and Genetic Transmission: The ability to reproduce and pass on genetic information to offspring is a key property of life.

• Response to Stimuli and Homeostasis: Organisms can respond to environmental stimuli and maintain internal stability (homeostasis).

• Metabolic Processes: Living things grow, develop, and undergo metabolic processes to sustain life.

• Energy Utilization: Life cannot exist indefinitely without energy input from the environment.

• Structural Organization: Life requires cells with lipid bilayers, which form the basis of cellular membranes.

• Transmission of Genetic Information: Life’s processes involve the transmission of genetic information from one generation to the next.

Cell Structure and Function

Specialized Cells in the Retina

The retina contains different types of cells, including rod and cone cells, which have specialized functions in vision.

• Rod Cells: More numerous than cone cells; contain rhodopsin and are sensitive to low light but cannot distinguish colors.

• Cone Cells: Less numerous; contain photopsins and are responsible for color vision and visual acuity.

• Functional Importance: Rod cells are most functionally important when reading fine print in bright sunlight.

Water and Hydrogen Bonding

Water molecules form hydrogen bonds, which influence their physical properties.

• Ice vs. Water: Water molecules in ice form more hydrogen bonds, making ice less dense than liquid water.

• Hydration Shell: A hydration shell is a layer of water molecules surrounding a dissolved substance (solute).

Biochemistry of Water and Buffers

Carbonic Acid/Bicarbonate Buffer System

The carbonic acid/bicarbonate system is the main buffer in human blood, maintaining pH around 7.4.

• Buffer Action: If blood pH increases (becomes more basic), the equilibrium shifts to the left to produce more carbonic acid.

• If blood pH decreases (becomes more acidic), the equilibrium shifts to the right to produce more bicarbonate.

Properties of Water

Hydrogen bonding in water leads to several important properties.

• Cohesion: Water molecules stick together due to hydrogen bonds.

• Adhesion: Water molecules stick to other surfaces.

• Hydration Shell: Water forms a shell around hydrophilic molecules.

• Polarity: Water is a polar covalent molecule.

• Transport: Water can move against gravity in plants due to cohesion and adhesion.

Macromolecules and Functional Groups

Carbohydrates and Glycosidic Linkages

Carbohydrates are composed of monosaccharides linked by glycosidic bonds.

• Glycosidic Linkage: A covalent bond between two monosaccharides.

• Functional Groups: Hydroxyl, carbonyl, and other groups are commonly found in carbohydrates.

Fatty Acids and Proteins

Fatty acids and proteins contain specific functional groups that determine their properties.

• Fatty Acids: Carboxyl group is an important component.

• Protein Structure: Disulfide bonds (formed by sulfhydryl groups) help stabilize tertiary structure.

• Tertiary Structure: Stabilized by ionic bonds, hydrogen bonds, and disulfide bridges.

Cholesterol and Membrane Structure

Cholesterol is a lipid with a carbon skeleton and is a precursor for steroid synthesis.

• Structure: Contains four fused carbon rings.

• Function: Maintains fluidity of the lipid bilayer and is a precursor for hormones like testosterone.

Cell Membrane and Transport

Membrane Proteins and Fluid Mosaic Model

Membrane proteins can move laterally within the lipid bilayer, supporting the fluid mosaic model.

• Lateral Drift: Proteins and lipids can move within the membrane, contributing to its fluidity.

• Experiment: Mixing mouse and human cell membranes shows lateral drift of proteins.

Transport Across Membranes

Cells regulate the movement of substances across membranes using various transport mechanisms.

• Na+/K+ Pump: Maintains electrochemical gradients by actively transporting sodium and potassium ions.

• Aquaporins: Channel proteins that facilitate water transport without energy input.

• Osmosis: Diffusion of water across a selectively permeable membrane.

Cytoskeleton and Cell Structure

Cytoskeletal Elements

The cytoskeleton provides structural support and facilitates movement within cells.

• Microfilaments: Composed of actin; involved in cell shape and movement.

• Intermediate Filaments: Provide mechanical strength.

• Microtubules: Involved in cell division and intracellular transport.

Actin Polymerization

Drugs like cytochalasin D inhibit actin polymerization, affecting cell movement and structure.

• Effects: Inhibition of white blood cell movement, maintenance of cell shape, and flagella movement.

Cellular Organelles and Functions

Endoplasmic Reticulum and Golgi Apparatus

Organelles play specialized roles in cell function and metabolism.

• Rough Endoplasmic Reticulum: Involved in protein synthesis.

• Smooth Endoplasmic Reticulum: Involved in lipid synthesis and detoxification.

• Golgi Apparatus: Modifies, sorts, and packages proteins and lipids.

Lysosomes

Lysosomes contain digestive enzymes and are involved in breaking down cellular waste.

• Tay-Sachs Disease: Caused by defective lysosomal enzymes, leading to accumulation of lipids.

Protein Structure and Function

Levels of Protein Structure

Proteins have four levels of structure: primary, secondary, tertiary, and quaternary.

• Primary Structure: Sequence of amino acids.

• Secondary Structure: Alpha helices and beta sheets formed by hydrogen bonding.

• Tertiary Structure: Three-dimensional folding stabilized by interactions between R groups.

• Quaternary Structure: Association of multiple polypeptide chains.

Protein Denaturation and Chaperones

Proteins can lose their functional shape due to changes in pH, salt concentration, or temperature.

• Chaperone Proteins: Assist in proper folding of other proteins.

• Ubiquitin: Tags misfolded proteins for degradation.

Cell Signaling and Communication

Signal Transduction Pathways

Cells communicate using signal transduction pathways involving receptors and second messengers.

• G Protein-Coupled Receptors: Transmit signals via G proteins.

• Receptor Tyrosine Kinases: Activate signaling cascades by phosphorylation.

• Ligand-Gated Ion Channels: Open in response to neurotransmitter binding.

Experimental Data Interpretation

Proteasome Inhibitor Activity

Experimental data can be used to compare the effectiveness of drugs in inhibiting proteasome activity.

• Graph Interpretation: The graph compares the inhibitory activity of Carfilzomib and D93. D93 has better inhibitory activity than Carfilzomib at higher concentrations.

Summary Table: Key Terms and Definitions

Additional info: Some explanations and examples have been expanded for clarity and completeness, based on standard General Biology curriculum.