Biology Chapter: Cell Structure and Function

Course Objectives

• Understand the structure of cells
• Correlate cell structures with basic functions

Cell Theory

• The cell is the smallest unit of life
• All organisms are composed of one or more cells
• New cells arise from previously existing cells

Types of Cells

• Prokaryotic:
  • No nucleus
  • No organelles
  • Small (100nm-5µm)
• Eukaryotic:
  • True nucleus
  • Membrane-bound organelles
  • Larger (10-100µm)

Eukaryotic Cells and Organelles

• Nucleus:
  • Double membrane (lipid bilayer)
  • Pores permit large molecule passage
  • Contains DNA (chromatin)
  • Nucleolus manufactures ribosomes
  • Controls cell division and activities
  • Contains fluid matrix (nucleoplasm)
• Ribosomes:
  • Non-membranous structures
  • rRNA-protein complexes
  • Site of protein synthesis (assembled in nucleoli)
  • Attached or free (polyribosomes or polysomes)
• Endoplasmic Reticulum (ER):
  • Extension of nuclear envelope
  • Continuous and folded
  • Rough ER:
    • Ribosomes attached
    • Protein synthesis and folding
  • Smooth ER:
    • No ribosomes
    • Lipid synthesis, carbohydrate breakdown, and detoxification
• Golgi Complex/Body:
  • Folded membrane with enzymes
  • Modifies and packages proteins and lipids
  • Deliver finished products to plasma membrane or lysosomes
• Mitochondria:
  • Eukaryotic organelles
  • Carry out respiration (ATP production)
  • Two membranes
  • Internal folds (cristae) increase surface area -Contains mtDNA and ribosomes.
  • Site of krebs cycle (in matrix)
• Lysosomes:
  • Membranous organelles
  • Acidic medium (pH 5)
  • Contains digestive enzymes (acid hydrolases)
  • Breakdown of macromolecules and old organelles
• Peroxisomes:
  • Small, membrane-bound sacs
  • Contain powerful enzymes (catalase, uric acid oxidase)
  • Break down hydrogen peroxide, alcohol, and toxins
• Cytoplasm:
  • Semifluid matrix
  • Includes organelles and cytosol
  • Provides structure, shape and movement of cell components.
• Cytoskeleton:
  • Structural support and shape of cell
  • Cell movement
  • Composed of microtubules, microfilaments, and intermediate filaments
• Plasma Membrane: Selectively controls substance movement into and out of cell; maintains cytoplasmic volume
• Cell Wall: Provides structure and support in plant cells
• Chloroplasts: Capture light energy (photosynthesis) In plant cells.

Organelle Functions in Protein Processing

• Nucleus
• ER
• Ribosomes
• Golgi complex

Functions of the ER

• Divides cytoplasm into compartments
• Provides large surface area for chemical reactions
• Produces proteins/enzymes (rough ER)
• Produces lipids (smooth ER)
• Collects and stores synthesized products
• Function in glycosylation
• Transmits cell impulses between parts

Functions of the Golgi Complex

• Modifies proteins/lipids, preparing them for use
• Sorts/packages proteins into transport vesicles
• Transports and secretes products

Defects of Peroxisomes

• X-linked adrenoleukodystrophy:
  • Deterioration in myelin sheath of neurons due to improper fatty acid metabolism
• Zellweger syndrome: - Impaired transport of peroxisomal enzymes into peroxisomes