Cell Structure

Cell : the structural and functional building unit of all living organisms .
Types of cells:
Prokaryotic cells
Eukaryotic cells
• No nucleus
• Has nucleus
• Unicellular
• Multicellular and unicellular
• No membrane bounded
• Has membrane bounded organelles
• Primitive
• Advanced
• Circular DNA
• Linear DNA
• Reproduction by Binary
• Reproduction by mitosis and miosis
• Include:
• Include:
1_ Bacteria
1_ Animals
4_protista ( animal like Protista
(protozoa) _ plant like Protista(algae) _
fungi like Protista)
Bacteria cell
Animal cell
Plant cell
Cell organelles
Organelle: specific structure in cytoplasm that performs certain function.
Classification of cell organelles:
Non membrane bounded
• Ribosome (in prokaryotes &
• Chromosome (in prokaryotes &
• Centrosome (in animal cell only)
• Cytoskeleton (in eukaryotes
• Nucleolus (only in eukaryotes)
Membrane bounded
• In eukaryotes only
A) _ single membrane bounded
• Endoplasmic Reticulum
• Golgi Apparatus
• Lysosomes
• Vacules & Vesciles
B_Double membrane bounded
• Nucleus (in eukaryotes)
• Mitochondria (in eukaryotes)
• Plastid (in plant & algae)
_ Non membrane bounded organelle.
_ Present in all cells.
_ The site of protein synthesis.
_ They are formed of 2 subunits, one large & one small.
_Made of ribosomal RNA (r RNA) & protein (histones).
_ They are the smallest organelles in the cell, and seen only by Electron
Microscope (E.M).
_They are either attached to rough endoplasmic reticulum or scattered in
_ Small ribosomes scattered in mitochondria & chloroplast.
• Centrosomes and Centrioles:
- Present in animal cell only.
- Lie outside the nucleus and organize the spindle fibers required for cell
Two centrioles, at right angles to each other make up one centrosome.
Centrioles and spindle fibers have the same structure, they consist of 27
microtubules (9 triplet of microtubules arranged in a circle).
• Cytoskeleton:
- In eukaryotic cells.
- It is a complex network of protein filaments that extent through
cytoplasm and gives the cell its shape, and enable it to move.
It includes 3 types:
1-Microtubules: - thick hollow tubes.
-formed of protein (tubulin).
-make up cilia, flagella, centrioles, and spindle fibers.
2-Microfilaments: -made of protein (actin).
-form cleavage furrow during cell division in animal
-help Amoeba to move by sending out pseudopods.
-make skeletal muscles contract by sliding along
Myosin filaments.
3-Intermediate filaments.
Cilia & Flagella:
- Both have same internal structure.
- Both are made of microtubules.
- They differ in length; cilia are short, flagella are long.
- Both consist of 20 microtubules (9 peripheral pairs of microtubules
organized around central pair of microtubules).
(9*2)+2 = 20
(9*3) = 27
• Nucleus:
- Present only in eukaryotes.
- Control all cell activities.
- Surrounded by double membrane (nuclear membrane).
- It contains: a) Nucleolus: produce RNA & Ribosomes.
b) Chromatin network (DNA wrapped by histones).
- Prominent region inside the nucleus of a cell that is not divided.
- One or two nucleoli are visible in a non-divided cell.
- Formed tangles of chromatin & ribosomes.
- Its function is ribosomes formation.
• Endoplasmic Reticulum:
- It is a system of membrane channels that traverse the cytoplasm.
- Present in all eukaryotic cells.
- It is single membrane bounded organelles.
- There are two types:
a) Rough Endoplasmic Reticulum: - It saddened with ribosomes.
- It is the site of protein synthesis.
- transport protein through cytoplasm.
b) Smooth Endoplasmic Reticulum: - Not covered with ribosomes.
- synthesize steroid hormones and other
– connect rough ER to Golgi apparatus.
- detoxifies the cell.
Golgi Apparatus:
- Present in eukaryotic only.
- Single membrane bounded organelle.
- It modifies, stores, & pack substances produced in R.E.R.
(Shipping department of the cell).
- Produce lysosome, exocytic veiscles, & exocytic vacuoles.
• Lysosome:
- Present in eukaryotic cells.
- Single membrane bounded organelle.
- It is a sac of hydrolytic (digestive) enzymes.
- A site of intracellular digestion (digest foreign bodies like viruses and
bacteria, expired organelles & lipids).
- Apoptosis (programmed cell death): lysosome rupture inside
precancerous cell, releasing digestive enzymes within the cell that will
• Vacules & viscles:
- They are single membrane bounded structures.
- Present in eukaryotic cells.
- Vacules are large & viscles are small.
- Important for storing of water, nutrients, metabolic wastes.
- Vacules are the largest organelle in plant cell.
- Contractile vacuoles in fresh water protesta (like amoeba & paramecium)
pump excess water out of the cell.
Vesicles are found in many places in cells, including axon of a neuron,
where they release neurotransmitter into a synapse.
The normal pass way for protein molecule that will be secreted out of the
cell: 1) R.E.R 2)viscle 3)golgi apparatus 4) exocutic viscle
5) plasma membrane
Present in eukaryotic cells (cell has many mitochondria).
Double membrane organelles.
The site of cellular respiration & energy production.
They contain their own DNA & self-replicate.
• Chloroplast:
- Present in plant & algae.
- Double membrane organelle.
- It is green because it contains chlorophyll.
- The site of photosynthesis.
- It has its own DNA & self-replicate (like mitochondria).
Cell or Plasma Membrane:
- Selective permeable membrane that controls what enter and leave the
- Fluid musaic: plasma membrane formed of many particles move around
to control particles movement through membrane.
- Consist of: 1) phospholipid bilayer (phosphate head hydrophilic & lipid
tail is hydrophobic).
2) protein
3) carbohydrates
4) cholesterol
• Cell Wall:
Found in:
1) Bacteria, cell wall is formed of (peptidoglycan).
2) Fungi, cell wall is formed of (chitin).
3) Plants & algae, cell wall is formed of (cellulose).
_ There are small channels across cell walls communicating cytoplasm
between adjacent (plant) cells called (plasmodesmata).
Techniques to study cell
A) Microscopes
Magnification = magnification of ocular lens * magnification of objective
_Transmission electron microscope (TEM) is useful in studying interior
of cells.
_Scanning electron microscope (SEM) is useful in studying surfaces of
B) Ultracentrifuge