Robert Hooke (1635-1703) first described cells in 1665.
Modern cell theory includes four principles:
All living organisms are composed of cells.
Nothing smaller than a cell is considered to be alive.
Life evolved only once, and all living organisms have descended from the earliest cells.
Cells arise only from preexisting cells.
surface area-to-volume relationships (Fig 5.2)
The Plasma Membrane
polar ends of phospholipids (Fig. 5.4)
fatty acid chains
bilayer of phospholipids (Fig.5.5).
Proteins within the membrane
cell surface proteins. (Fig. 5.6)
Membrane defects. EX: Cystic fibrosis
Prokaryotic cells evolved 2 billion years before eukaryotic cells.
Have a rigid cell wall around their plasma membranes, and ribosomes, but no internal membrane-bounded organelles. Some have one or more flagella.
Eukaryotic cells are thought to have evolved as a result of two processes: infolding of the membrane system (Fig. 20.1) and endosymbiosis (Fig 5.18) of several types of prokaryotic cells (Fig. 20.2). A more detailed image here and here. And a movie!
The Nucleus: The Cell's Control Center (Fig 5.12)
lipid bilayer forms the nuclear envelope
The Endomembrane System - (Fig. 5.15) a tightly packed mass of membranes that divides the cell into compartments, channels the transport of materials, and provides surfaces on which enzymes act.
Endoplasmic Reticulum: The Transportation System - (Fig. 5.13)
Rough ER has ribosomes associated with it (makes proteins), smooth ER does not.
Organelles that contain their own DNA, giving evidence for their ancient past as solitary bacteria.
The Cytoskeleton: Internal Framework of the Cell
determine the shape of animal cells
provide a place for enzymes to attach so that metabolic reactions are more efficient
move chromosomes during cell division Centrioles - (Fig. 5.20)
cilia and flagella (9+2) arrangement (Fig.
Special Things About Plant Cells
Transport Across Cell Membranes
Movement across the cell membrane occurs in
1. Water leaks through membrane imperfections.
2. Particles and liquids are engulfed by the membrane folding around them.
3. Proteins in the membrane allow the passage of certain molecules.
receptor-mediated endocytosis (Fig 5.32)