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 cell’s 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

Organelles

• 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

Mitochondria

• 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

Centrioles

• Pairs of microtubular structures
• Play a role in cell division

NUCLEUS

• IT CONTROLS ALL CELL ACTIVITIES

Definition

• 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.