Cell Structure Quiz

Cell Structure

• The cell membrane is composed of proteins, lipids, and carbohydrates
• Lipids: Act as a barrier
• Proteins: Control substance passage and act as enzymes
• Cytoplasm: The clear liquid portion inside the cell that contains dissolved particles and organelles
• Cytosol: Cytoplasm plus dissolved particles and organelles
• Organelles: Structures within the cell that perform specialized functions
• Endoplasmic Reticulum (ER): Network of tubules and flat vesicles (ER is filled with endoplasmic matrix)
• Cell Cytoskeleton: Fibrillar proteins organized into filaments or tubules
• Actin Filaments: Found in the outer zone (ectoplasm), providing elastic support for the cell membrane
• Microtubules: Strong tubular structures composed of polymerized tubulin molecules
• Nucleus: Control center of the cell, containing DNA
• Nuclear Membrane (Nuclear Envelope): Two separate bilayer membranes, outer one continuous with ER
• Nuclear Pores: Openings in the nuclear membrane
• Nucleolus: Accumulation of RNA and proteins, no membrane, enlarges during protein synthesis

Cell Membrane (Plasma Membrane)

• Thin, elastic structure, 7.5 to 10 nanometers thick
• Basic structure is a lipid bilayer
• Composed of:
  • Proteins (55%)
  • Phospholipids (25%)
  • Cholesterol (13%)
  • Other lipids (4%)
  • Carbohydrates (3%)
• Lipid Bilayer: Composed of phospholipid molecules with a hydrophilic phosphate end and a hydrophobic fatty acid portion
• Membrane Proteins:
  • Integral Proteins: Channel, carrier protein, enzyme, receptor
  • Peripheral Proteins: Enzymes
• Membrane Carbohydrates (Glycocalyx): Protrude to the outside of the cell, forming a loose carbohydrate coat
• Glycocalyx Functions:
  • Negative electrical charge, repels other negatively charged objects
  • Attachment between cells
  • Hormone receptor
  • Immune reactions

Transport of Substances Through Cell Membranes

• Diffusion: Movement of molecules from high to low concentration
• Simple Diffusion:
  • Kinetic movement of molecules through a channel protein or lipid bilayer
  • Occurs through the lipid bilayer (for lipid-soluble substances) or through channels (protein pores)
  • Examples: Oxygen, nitrogen, carbon dioxide, alcohol
• Facilitated Diffusion: Movement of molecules across the membrane with the assistance of carrier proteins

Membrane Potential and Action Potential

• Excitable Membranes: Nerve and muscle cells that can rapidly change membrane permeability to Na+ and K+ by opening gated ion channels
• Action Potentials: Rapid changes in membrane potential that travel along nerve fibers
• Resting Stage: Polarization of the membrane with a negative potential (-90 millivolts)
• Depolarization Stage: Increased membrane permeability to Na+ ions, influx of Na+ neutralizes the negative potential, rising to a positive potential
• Repolarization Stage: Closure of Na+ channels and opening of K+ channels, rapid diffusion of K+ to the exterior re-establishes the negative resting membrane potential

Genetic Control of Protein Synthesis and Reproduction

• Genes: Nucleic acids (DNA) that control the formation of RNA
• RNA: Carries genetic information from DNA to ribosomes for protein synthesis
• DNA: Contains genetic information, double-stranded, contains thymine, self-replicating
• RNA: Synthesized by transcription, single-stranded, contains uracil

The Relationships of Chargaff

• The amount of adenine (A) equals the amount of thymine (T)
• The amount of guanine (G) equals the amount of cytosine (C)