Chapter 3:
Cells: The Living Units
Lecture # 6 & 7
Objectives: 1. Define cell.
2. Discuss structure and function of cell organelles.
3. Describe the chemical composition of the plasma membrane and relate it to
membrane function.
4. Compare the structure and function of tight junctions, desmosomes, and gap
junctions.
5. Relate the plasma membrane structure to active and passive transport
mechanisms.
6. List several roles of membrane receptors.
7. Name and describe the composition of extracellular matrix.
Cell Theory:
1. The cell is the basic unit of structure and function in living things.
2. Activity of the organism depends on activity of cells.
3. Cells come from preexisting cells.
Parts of Cell: Structure and Function
Structure
Function
Holds organelles, contains dissolved nutrients
Cytosol
Mitochondria
Site of aerobic respiration for production of ATP
Ribosomes
Site of protein synthesis w/ mRNA and tRNA
Rough endoplasmic
reticulum
Smooth endoplasmic
reticulum
Golgi apparatus
Attachment site for ribosomes, transport of proteins to Golgi
Lysosomes and
peroxisomes
Cytoskeleton
Contain digestive enzymes to break up things brought into cell
Centrioles
Used by animal cells to pull chromosomes apart during
mitosis/meiosis
Cilia and flagella
Cell locomotion
Nuclear envelope
and pores
Nucleoli
Contains chromatin w/in nucleus, allows material to enter and leave
nucleus
Chromatin
Genetic information made of DNA
Detoxification of cell, lipid synthesis, storage of calcium
Packages and secretes proteins from cell
Made of microtubules, intermediate and microfilaments to support
cell
Site of ribosome assembly in nucleus
Cell Membrane: fluid mosaic model of phospholipids, cholesterol (for fluidity), proteins,
glycoproteins, and glycolipids. Also called phospholipids bilayer
I. Protein functions: found either all the way through the membrane or on only one side
A. Integral: found all the way through the membrane; act as transporters, enzymes,
receptors, for intercellular joining, cell-cell recognition, attachment to cytoskeleton and
extracellular matrix (ECM).
B. Peripheral (Glycocalyx): found on one side of membrane in gooey, carbohydraterich area at cell surface to provide highly specific biological markers for recognition.
Membrane Junctions
I. Tight junctions: proteins fuse together; ex. epithelial cells of intestines
II. Desmosomes: act like rivets to hold skin, heart, muscle, neck of uterus together
III. Gap junctions: allow chemicals to pass between adjacent cells; heart and smooth muscle
synchronize contractions
Membrane Transport (Interstitial Fluid): soup of nutrients that surrounds cells.
Selectively permeable membrane around cell. Ability to select is lost with damage to cell, as in
burns.
I. Passive Processes: no energy (ATP) is required
A. Diffusion: movement along concentration gradient (high to low). Size of molecule,
temperature, lipid solubility and presence of carrier protein all determine rate of diffusion.
Oxygen, carbon dioxide, vitamins A, D, E, alcohol, water and glucose with a carrier all enter cells
by diffusion.
B. Osmosis: diffusion of solvent from dilute solution to concentrated solution (along the
concentration gradient of water). The following terms refer to the environment outside of the
cell:
1. Isotonic: no net osmosis. Concentrations inside and outside of cell are
equal.
2. Hypertonic: net water movement out of cell. Cells will shrivel or crenate.
3. Hypotonic: net water movement into cell. Cells swell and lyse.
C. Filtration: occurs along a pressure gradient (high pressure ( low pressure). Not a
selective process, common in kidney.
II. Active Transport: requires ATP for movement against a concentration gradient, from low
to high.
A. Sodium/Potassium Pump: used to establish membrane potential. Energy (ATP)
is used against a concentration gradient to put more sodium outside of the cell and more
potassium inside (3:2 ratio)
B. Exocytosis: vacuoles and vesicles fuse with cell membrane, material is released.
C. Endocytosis: large material that is needed inside of the cell is engulfed.
1. Phagocytosis: engulf with pseudopodia
2. Receptor-mediated: engulf specific substances
Membrane Receptors: integral, peripheral ad glycoproteins can serve as binding sites for
substances.
Extracellular Matrix: materials outside of cell made of proteins and polysaccharides that can
hold the cells together, particularly found in connective tissue.