Properties of Life and Biological Organization

Fundamental Properties of Life

Living organisms share several key properties that distinguish them from non-living matter. These properties are essential for the maintenance and propagation of life.

• Energy Transformation: Life requires the transformation of energy and matter to sustain biological processes.

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

• Response to Stimuli: Organisms respond to environmental stimuli and maintain homeostasis.

• Growth and Development: The ability to grow, develop, and undergo metabolic processes is fundamental.

• Reproduction: Life reproduces and passes genetic information to offspring.

• Indefinite Existence: Life can exist indefinitely without any energy input from the environment is NOT considered a property of life. Additional info: perpetual existence without energy input violates the laws of thermodynamics.

Cell Structure and Membrane Properties

Membrane Proteins and Fluid Mosaic Model

The cell membrane is composed of a lipid bilayer with embedded proteins, forming the fluid mosaic model. Membrane proteins can move laterally within the bilayer, contributing to membrane fluidity and function.

• Membrane Fluidity: Increasing the proportion of phospholipids with unsaturated hydrocarbon tails increases membrane fluidity.

• Lateral Drift: Experiments show faster lateral drift of both mouse and human proteins in hybrid cells, supporting the fluid mosaic model.

• Cholesterol: Cholesterol maintains the rigidity of the lipid bilayer and is a precursor for steroid synthesis.

• Defective Cholesterol Molecules: Can lead to familial hypercholesterolemia, affecting LDL uptake and contributing to atherosclerosis.

Transport Across Membranes

Cells regulate the movement of substances across their membranes through various mechanisms, including passive and active transport.

• Na+/K+ Pump: Maintains the voltage gradient across the cell membrane, essential for nerve impulse transmission.

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

• Osmosis: The diffusion of water across a selectively permeable membrane. In hypotonic solutions, animal cells lyse and plant cells become turgid.

Biochemical Properties of Water

Hydrogen Bonding and Water Structure

Water molecules form hydrogen bonds, which are responsible for many of water's unique properties.

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

• Density: Ice is less dense than liquid water due to hydrogen bonding.

• Cohesion: Water molecules stick together, allowing for processes like transpiration in plants.

Biological Molecules and Functional Groups

Carbohydrates and Glycosidic Linkages

Carbohydrates are composed of monosaccharides linked by glycosidic bonds.

• Monosaccharides: Simple sugars that are the building blocks of carbohydrates.

• Glycosidic Linkage: A covalent bond between monosaccharides.

Functional Groups in Biomolecules

Functional groups confer specific chemical properties to biological molecules.

• Fatty Acids: Carboxyl group is an important component.

• Protein Structure: Certain functional groups stabilize tertiary structure via strong bonds (e.g., disulfide bridges).

• Acids: Molecules that lose H+ in aqueous solution.

• Ionic Bonds: Can stabilize tertiary structure of polypeptides.

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: Local folding (e.g., alpha helices, beta sheets).

• Tertiary Structure: Overall 3D shape stabilized by interactions between R groups, including hydrogen bonds, ionic bonds, and covalent bonds.

• Quaternary Structure: Association of multiple polypeptide chains.

• Mutation Effects: Changes in DNA can alter primary structure, affecting protein conformation and function (e.g., sickle cell anemia).

Protein Denaturation and Chaperones

Proteins can lose their functional shape due to changes in pH, temperature, or other factors. Chaperone proteins assist in proper folding.

• Denaturation: Loss of protein structure and function.

• Chaperones: Help refold denatured proteins; mutations can lead to accumulation of misfolded proteins.

• Ubiquitin: Tags misfolded proteins for degradation; defects lead to accumulation of misfolded proteins.

Cellular Organelles and Functions

Endoplasmic Reticulum and Golgi Apparatus

Organelles play specialized roles in cell function and metabolism.

• Rough Endoplasmic Reticulum (ER): Involved in protein synthesis and detoxification.

• Golgi Apparatus: Processes and packages proteins and lipids.

• Lysosomes: Degrade large, complex molecules; defects can cause diseases like Tay-Sachs.

Signal Transduction and Cell Communication

Signal Pathways and Receptors

Cells communicate through signal transduction pathways involving receptors and ligands.

• Ligands: Molecules that bind to receptors to initiate a signal.

• Receptor Tyrosine Kinases: Signal transduction proteins that function by forming dimers and adding phosphate groups to proteins.

• Gated Ion Channels: Respond to neurotransmitters by allowing ions to pass through the membrane.

Tables

Comparison of Key Biological Terms

Protein Structure Levels

Key Equations

• Osmosis:

• Hydrogen Bonding: (dotted line represents hydrogen bond)

• Na+/K+ Pump: per ATP hydrolyzed

Example Applications

• Sickle Cell Anemia: A single amino acid change in hemoglobin leads to altered protein structure and function.

• Familial Hypercholesterolemia: Defective cholesterol molecules impair LDL uptake, increasing risk of atherosclerosis.

• Tay-Sachs Disease: Defective lysosomal enzymes lead to accumulation of undigested lipids.

Additional info: Some explanations and context have been expanded for clarity and completeness.