C1

• Cell


  The smallest structural unit of living material of a multicellular organism, composed of a membrane-bounded nucleus and cytoplasm containing specialized organelles and inclusions
• Cellular shape, size, and structure


  • Vary widely and express adaptations for specific functions in specialized tissues and organs
  • Most cells share general structural characteristics despite varying degrees of functional differentiation
  • Cells are the structural and functional units of life in all tissues, organs, and organ systems
• Prokaryotes and Eukaryotes


  • Prokaryotic cells lack a nuclear envelope, histones, and membranous organelles, while eukaryotic cells have basic structural and functional features covered in this chapter
• Cellular shape


  • Influenced by factors like cell specialization, cellular contact, pressure, and inherent capacity to alter shape, can be round, stellate, spindle-shaped, elongated, columnar, squamous, cuboidal, or other shapes
• Cellular size


  • Varies among species and within the body of an organism, with most mammalian cells ranging between 10-30 microns
• Cellular structure


  • Despite shape diversity, organelles have a spatially organized position within the cell
• Cellular functions


  • Nourishment, reproduction, growth, and development are basic activities of living organisms
• Cellular components


  • Eukaryotic cells have three major components: cell membrane, cytoplasm, and nucleus
• Protoplasm


  The colloidal form of protoplasm composed mainly of different substances that make up a cell, a complex aggregation of chemicals interacting to manifest properties of living entities
• Chemical composition of the cell

  • Water 85%
  • Proteins 10%
  • Lipids 2%
  • Carbohydrates 1%
  • Electrolytes 2%
• Compartmentalization of the protoplasm

  • The cell is made up of plasma membrane, cytoplasm, and nucleus, each with specific properties and functions
• Cell membrane


  Envelops the cell, composed of proteins, lipids, and carbohydrates
• Cell functions


  • Metabolism
  • Irritability
  • Contractility
  • Secretion
  • Conductivity
  • Excretion
  • Endocytosis
  • Exocytosis
  • Growth
  • Maintenance
  • Reproduction
• Cell membrane


  • Envelops the cell and composed entirely of proteins, lipids, and carbohydrates
• Cell membrane proteins mostly are glycoproteins
• Intrinsic proteins


  Protrude all the way through the membrane and provide structural channels for diffusion of water-soluble substances, especially ions, between the ECF & the ICF. They are carrier proteins for active transport and also act as enzymes
• Extrinsic proteins


  Attached loosely to the outer and inner surface of the membrane, do not penetrate, and control intracellular functions
• Cell membrane carbohydrates occur mainly as oligosaccharide moieties in combination with proteins and lipids
• Membrane oligosaccharides have a characteristic branching structure and project from the cell’s outer surface forming a superficial, loose carbohydrate coat called the glycocalyx
• Glycocalyx functions include cellular recognition and adhesion, attachment between cells, acting as receptors for binding hormones like insulin, protection, antigenicity through immunoglobulins, and participation in immune reactions
• Functions of glycocalyx


  • Cellular recognition and adhesion
  • Attachment
  • Acting as receptors for binding hormones
  • Protection and antigenicity through immunoglobulins
• Cell membrane lipids


  • Phospholipids
  • Sphingolipids
  • Cholesterol
• Fluid Mosaic Model of Singer and Nicolson describes the cell membrane as a lipid bilayer composed primarily of phospholipid molecules arranged perpendicularly with hydrophilic and hydrophobic ends
• The lipid bilayer is fluid, allowing portions of the membrane to flow and is permeable to water-soluble substances and fat-soluble substances
• Leaflet theory states that the cell membrane has a sandwich-like structure with two protein layers laid upon a layer of lipid
• Components of the Cytoplasm

  • Cytosol
  • Hyaloplasm
• Components of cytoplasm


  • Dissolved proteins
  • Electrolytes
  • Glucose
  • Minute quantities of lipid compounds
• Hyaloplasm


  An aqueous gel bearing the organelles, composed of proteins, lipids, carbohydrates, and inorganic materials such as Ca++, Na+, and K+
• Ectoplasm (cortex)


  The zone of cytoplasm immediately beneath the cell membrane, providing a semi-solid gel-like support for the cell membrane
• Endoplasm


  A more liquefied portion of the cytoplasm between the cortex and the nuclear membrane
• Three groups of cytoplasmic structures

  • Cytoplasmic organelles
  • Cytoplasmic inclusions
  • Cytoskeleton
• Cytoplasmic organelles include mitochondria, ribosomes, endoplasmic reticulum, Golgi complex, phagosomes, lysosomes, and peroxisomes
• Mitochondria are the chief source of ATP (energy) for the cell and are known as the "powerhouse of the cell"
• Structure of mitochondria


  • Various shapes: spherical, ovoid, filamentous, comparable in size to bacteria (usually 6-12 μm in length and 0.2 μm in diameter), bounded by two unit membranes (outer and inner)
• Functions of mitochondria


  Site of Kreb’s cycle, provide energy for chemical and mechanical work, contain enzymes for oxidative phosphorylation and fatty acid oxidation, synthesize their own DNA and RNA
• The mitochondrial matrix contains water, solutes, large matrix granules, circular DNA, and mitochondrial ribosomes similar to those of bacteria
• The matrix contains numerous enzymes involved in specialized mitochondrial functions such as the Krebs cycle, yielding mainly CO2 and NADH
• Mitochondria


  • Contain enzymes for oxidative phosphorylation and fatty acid oxidation
  • Synthesize their own DNA and RNA
  • Possess genetic and protein-synthetic potential for reproducing themselves
  • Grow and reproduce by fission or budding
  • Can undergo rapid movement and shape changes
• Ribosomes


  Protein-synthesizing organelles
• Ribosomes


  • Two basic types: mitochondrial ribosomes (smaller, like prokaryotic) and cytoplasmic ribosomes of eukaryotes
  • Composed of two subunits, separate entities prior to protein synthesis