Characteristics of Eukaryotic Cellular Structures

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Eukaryotic Cells

Extracellular structures

  1. A cell wall surrounding the plasma membrane gives strength and rigidity to the cell and is composed primarily of cellulose in plants (peptidnglycans in bacterial “envelopes”);
  2. Animal cells are not supported by cell walls;
  3. Slime capsules composed of polysaccharides or glycoproteins coat the cell walls of some bacterial and algal cells.

Plasma membrane

  1. Lipid bilayer through which extracellular substances (e.g.. nutrients, water) enter the cell and waste substances or secretions exit the cell;
  2. Passage of substances may require expenditure of energy (active transport) or may be passive (diffusion).

Nucleus: Master control of cellular functions via its genetic material (DNA)

  1. Nuclear membrane: Double membrane controlling the movement of materials between the nucleus and Cytoplasm contains pores that communicate with the ER
  2. Chromatin: Nudcoprotcin component of chromosomes (seen clearly only during nuclear division when the chromatin is highly condensed); only the DNA component is hereditary material.
  3. Nudeolus: Site(s) on chromatin where ribosomal RNA (rRNA) is synthesized; disappears
    from light microscope during cellular replication.
  4. Nucleoplasm: Nonchromatin components of the nucleus containing materials for building DNA and messenger RNA (mRNA molecules serve as intermediates between nucleus and cytoplasm).

Cytoplasm

  1. Contains multiple structural and enzymatic systems (e.g.. glycolysis and protein synthesis) that provide energy to the cell;
  2. Executes the genetic instructions from the nucleus.

Ribosome

Site of protein synthesis;consists of three molecular weight classes of ribosomal RNA molecules and about 50 different proteins

Endoplasmic Reticulum

Internal membrane system (designated ER); rough endoplasmic reticulum (RER) is studded with ribosomes and modifies polypeptide chains into mature proteins (e.g., by glycosylation): smooth endoplasmic reticulum (SER) is free of ribosomes and is the site of lipid synthesis.

Mitochondria

Production of adenosinc triphosphatc (ATP) through the Krebs cycle and electron transport chain; beta oxidation of long-chain fatty acids; ATP is the main source of energy to power biochemical reactions

 

Golgi body (apparatus)

Sometimes called dictyosome in plants; membranes where sugars, phosphate, sulfate. or fatty acids arc added to certain proteins; as membranes bud from the Golgi system they are marked for shipment in transport vesicles to arrive at specific sites (e.g., plasma membrane, lysosome)

Lysosome

Sac of digestive enzymes in all eukaryotic cells that aid in intracellular digestion of bacteria and other foreign bodies; may cause cell destruction if ruptured

Vacuole

Membrane-bound storage deposit for water and metabolic products (e.g.. amino adds, sugars); plant cells often have a large central vacuole that (when filled with fluid to create turgor pressure) makes the cell turgid

Centrioles

Form poles of the spindle apparatus during cell divisions; capable of being replicated after each cell division: rarely present in plants

Cytoskeleton

Contributes to shape, division, and motility of the cell and the ability to move and arrange its components; consists of microtubules of the protein tubulin (as in the spindle fibers responsible for chromosomal movements during nuclear division or in flagella and cilia), microfilaments of actin and myosin (as occurs in muscle cells), and intermediate filaments (each with a distinct protein such
as keratin)

Cytosol

The fluid portion of the cytoplasm exclusive of the formed elements listed above; also called hyaloplasm; contains water, minerals, ions, sugars, amino acids, and other nutrients for building macromolecular biopolymers (nucleic acids, proteins, Lipids. and large carbohydrates such as starch and cellulose).