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Monday, 15 January 2018

Cell Structure and Function

Cell Structure and Function

Types Of cells

  1. Prokaryotes include bacteria & lack a nucleus or membrane-bound structures called organelles.
  2. Eukaryotes include most other cells & have a nucleus and membrane-bound organelles (plants, & animals) .

General Cell structure:

  • 3 principal parts:
  1. Plasma (cell) membrane.
  2. Cytoplasm & organelles.
  3. Nucleus.

Plasma membrane:

  • Surrounds, holds cell together & gives its form.10 nanometer thick.
  • Separates cells internal structures from extracellular environment 
  • Is selectively permeable, & controls passage of materials into & out of cell.
  • Participates in intracellular communication.
  • Plasma (Cell) Membrane Composed of:
  1. Double layer of phospholipids (hydrophobic/ hydrophilic parts).
  2. Proteins span, or partially span the membrane.
  3. Negatively charged carbohydrates attach to the outer surface.
  • General composition of cell membrane
  • Proteins ……………………. 55%
  • Lipids ……………………….. 41%
  • Phospholipids 25%
  • Cholesterol ……. 12% 
  • Glycolipids ……..  4%
  • Carbohydrates ……………  3%

Cytoplasm :

  •  The aqueous content of a cell (fluid, jellylike substance), that lies between cell membrane & nucleus in which organelles are suspended.
  •  Serves as matrix substance in which chemical reactions occur.
  • components of cytoplasm:
  1. Interconnected filaments & fibers
  2. Fluid = cytosol
  3. Organelles
  4.  storage substances
  5. Cytoskeleton
  6. Filaments & fibers
  7. Made of 3 fiber types
  8. Microfilaments
  9. Microtubules
  10. Intermediate filaments

  •  functions:

  1.  mechanical support
  2.  anchor organelles
  3.  help move substances


  • Subcellular structures within the cytoplasm that perform specific functions.
  • Endoplasmic Reticulum : Helps move substances within cells network of interconnected membranes .

Two types :

  1. Rough endoplasmic reticulum
  2. Smooth endoplasmic reticulum
  • Rough Endoplasmic Reticulum
  • Ribosomes attached to surface
  • Manufacture protiens
  • Not all ribosomes attached to rough ER
  • May modify proteins from ribosomes .

  • Smooth Endoplasmic Reticulum
  • No attached ribosomes
  • Has enzymes that help build molecules
  • Carbohydrates

Lipids : It is composed of two subunits: smaller (lighter) & larger (darker) subunits. The space between the two subunits accommodates a molecule of transfer RNA, needed to bring amino acids to the growing polypeptide chain.
Golgi Apparatus : Involved in synthesis of cell membrane . Packaging & shipping station of cell
Lysosomes : Contain digestive enzymes
  • Functions
  1. Aid in cell renewal
  2. Break down old cell parts
  3. Digests invaders
  • The structure of a mitochondria. The outer mitochondrial membrane & the infoldings of the inner membrane. The fluid in the center is the matrix.
  • Break down fuel molecules (cellular respiration),Glucose,Fatty acids
  • Release energy,ATP
  • Pairs of microtubular structures
  • Play a role in cell division




  • It is rounded or elongated organelle present in all mammalian cells except the red blood cell.
  • It plays an important role in heredity, cell division and controlling all cellular functions.

General characteristics

  1. Number: usually one, two may present in some liver cells and many nuclei are present in the skeletal muscle cells.
  2. Size: is variable.
  3. Shape: is variable; rounded, oval, flattened,…
  4. Position: may be central, eccentric or peripheral in position.

Structure of the nucleus :

  1. Nuclear membrane.
  2. Nuclear sap and matrix.
  3. Nucleolus.

The nuclear membrane:
  • Surround the nucleus and disappear during cell division.
  • Nuclear pores: they are the openings in the nuclear membrane.

The nuclear sap and matrix
  • It is a colloidal clear solution, which is formed of:
  • Nucleoproteins, enzymes, and some minerals.
  • According to the amount of the sap nuclei are:
  • Open face type.
  • Condensed (closed) type. 
 Functions: a medium for the ribonucleic acids interaction.

The nucleolus
  • It is a basophilic mass formed of RNA & DNA.
  • It disappear during cell division.
  • Nucleolus size depend on the cell activities.

Functions of nucleolus:
  1. Controls the cell functions.
  2. Store the genetic informations.
  3. Regulates the cell division.
  4. Forms the Ribosomal RNA.

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