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Chapter 3 Cellular Level
Human Anatomy and Physiology (Athabasca University)
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Chapter 3: The Cellular Level of Organizaion
Cells
 Living structural and funcional units enclosed by a membrane.
Cell Division
 All cells arise from cell division; one cell divides into two idenical cells.
Cell Biology (cytology)
 Study of cellular structure and funcion.
3.1 Parts of a Cell
1. Plasma Membrane
 Flexible outer surface separaing the external and internal environments.
 Selecive barrier that regulates low of materials for normal cellular aciviies.
 Plays a role in communicaion between cells.
2. Cytoplasm
 Area between the membrane and nucleus
i. Cytosol (intracellular luid): contains water, dissolved solutes, and paricles.
ii. Organelles: characterisic shapes and funcions.
3. Nucleus
 Contains the DNA
 Chromosomes : a single molecule of DNA, contains thousands of genes .
 Genes: controls the aspect of cellular structure and funcion.
Downloaded by Yury Elena Ezhov ([email protected])
lOMoARcPSD|1516709

3.2 The Plasma Membrane
Plasma Membrane Funcions:
 Sturdy lipid (amphipathic) barrier that surrounds the cytoplasm of the cell.
 Allows passage of several lipid-soluble molecules, but prevents polar substances to come in or
out.
o Ion Channels (integral proteins) are pores or holes that lets speciic ions, such as K
+
, low
through. They are selecive .
o Carriers selecively move polar substances or ions across the membrane.
 Proteins in the layer can act as signal receptors or links the plasma membranes to
intra/extracellular proteins.
o Receptors (integral proteins) recognizes and binds to speciic molecules. Speciic
molecules that bind to the receptor is called a Ligand.
o Enzymes catalyze chemical reacions in and outside the cell.
o Linkers connect proteins of plasma membrane to other cells. S
o Idenity Markers (glycoprotein and glycolipids) enable a cell to recognize other similar
cells during issue formaion, and recognize and respond to dangerous foreign cells.
Plasma Membrane Structure:
 The Lipid Bilayer two back-to-back layers of 3 types of lipid molecules.
1. Phospholipids (75%): Phosphate (polar, hydrophilic) head, and faty acid (non-polar,
hydrophobic) tail. They orientate themselves with the head outward – cytosol and
extracellular luid – and tails point inward, hydrophobic membrane interior.
2. Cholesterol (20%): hydroxyl head (polar) forms hydrogen bonds with the phosphate
of phospholipids. Sif, steroid rings (non-polar tails) it with the faty acids of the
membrane.
3. Glycolipids (5%): carbohydrate (polar) head faces the extracellular luid (outside of
cell), while the faty acid (non-polar) tails are in the membrane layer.