The document provides a detailed overview of various cell organelles and their functions, emphasizing structures such as chromosomes, the nucleus, ribosomes, and the endoplasmic reticulum. It explains processes like protein synthesis, cellular division, and membrane structure, particularly the fluid mosaic model of the plasma membrane. Each organelle's specific role is highlighted, from energy production in mitochondria to storage in vacuoles.

1. FUNCTIONS OF CELL ORGANELLES
• Chromosomes
- Usually in the form of chromatin
- Contains genetic information
- Composed of DNA
- Thicken for cellular division
- Set number per species (i.e. 23 pairs for human)

2. NUCLEAR MEMBRANE
Surrounds nucleus
- Composed of two layers
- Numerous openings for nuclear traffic
Function.
-The external membrane is continuous with the membrane of the
endoplasmic reticulum (ER).
-The mRNA exported from the nucleus travels to the ribosomes ,
which either float freely in the cytosol or are bound to the cytosolic
side of the endoplasmic reticulum.
-Each ribosome is made up of proteins associated with a number of
structural RNA molecules called ribosomal RNA (rRNA).
-assembles the genes and enter biochemical “machinery” for protein
synthesis (translation).

3. Nucleus and nucleolus
- Spherical shape
- Visible when cell is not dividing
- Contains RNA for protein manufacture
Function.
-Contains a liquid known as karyolymph, a nucleolus, and chromatin.
-Chromatin contains deoxyribonucleic acids (DNA), the carriers of genetic
information.
-Site for the synthesis of DNA and RNA through the process of DNA replication
and Transcription.
-Site for the post transcription modification like splicing, 5’ capping and
polyadenylation

4. NUCLEAR PORE
High-molecular-weight protein complexes (125 MDa) megadaltons located
within the nuclear envelope.
Function.
They allow large molecules such as transcription factors, RNA polymerases or
cytoplasmic steroid hormone receptors to pass into the nucleus, nuclear
molecules such as mRNA and tRNA to pass out of the nucleus, and other
molecules such as ribosomal proteins to travel both ways and The reaction is
(ATP-dependent).

5. CENTRIOLES
-Paired cylindrical organelles near nucleus
-
- Composed of nine tubes, each with three tubules
-
- Involved in cellular division
-
- Lie at right angles to each other

6. Chloroplasts
A plastid usually found in plant cells
- Contain green chlorophyll where photosynthesis takes place
Vacuoles
-Membrane-bound sacs for storage, digestion, and
waste removal
- Contains water solution
- Contractile vacuoles for water removal (in
unicellular organisms)

7. Cytoskeleton
Composed of microtubules
- Supports cell and provides shape
- Aids movement of materials in and out of cells
Function:
Allows the cell to maintain and change its shape (during cell division, etc.), make selective
movements (migration, cilia), and conduct intracellular transport activities (vesicle, mitosis).
It contains actin filaments as well as microtubules and intermediate filaments (e.g.,
vimentin and desmin filaments, neurofilaments, keratin filaments) that extend from the
centrosome.

8. Endoplasmic reticulum
-Tubular network fused to nuclear membrane
- Goes through cytoplasm onto cell membrane
- Stores, separates, and serves as cell's transport system
- Smooth type: lacks ribosomes
- Rough type (pictured): ribosomes embedded in surface
Function
The ER membrane containing the synthesized membrane proteins or export proteins
forms vesicles which are transported to the Golgi apparatus.

9. • rough endoplasmic reticulum- Ribosomes can
attach to the cytosolic surface of parts of the
ER, forming a rough endoplasmic reticulum
(RER).These ribosome synthesize export
proteins as well as transmembrane proteins
for the plasma membrane, endoplasmic
reticulum, Golgi apparatus, lysosomes, etc.
• smooth endoplasmic reticulum-Contains no
ribosomes and is the production site of lipids
(e.g., for lipoproteins.) and other substance

10. Golgi apparatus
-Protein 'packaging plant' and modification
- A membrane structure found near nucleus
- Composed of numerous layers forming a sac
Function.
-Polysaccharide synthesis; protein processing (post translational
modification), e.g., glycosylation of membrane proteins.
-packaging” of proteins meant for export into secretory vesicles (secretory
granules), for example, the contents of which are exocytosis into the
extracellular space,

11. -Digestive ‘plant' for proteins, lipids, and carbohydrates
- Transports undigested material to cell membrane for removal
- Vary in shape depending on process being carried out
- Cell breaks down if lysosome explodes
Lysosome

12. Mitochondria
-Second largest organelle with unique genetic structure
- Double-layered outer membrane with inner folds called cristae
- Energy-producing chemical reactions take place on cristae
- Controls level of water and other materials in cell
- Recycles and decomposes proteins, fats, and carbohydrates, and forms urea.
Function
-site of oxidation of carbohydrates and lipids to CO2 and H2O and associated O2
expenditure.
-The Krebs cycle (citric acid cycle), respiratory chain and related ATP synthesis also
occur in mitochondria aka (powerhouse of cell)

13. Ribosomes
-Each cell contains thousands of ribosomes
- Composes 25% of cell's mass
- Stationary type: embedded in rough endoplasmic reticulum
- Mobile type: injects proteins directly into cytoplasm
-It functions as Machinery for protein synthesis

14. Cell wall
Most commonly found in plant cells
- Controls turgidity
- Extracellular structure surrounding plasma membrane
- Primary cell wall: extremely elastic
- Secondary cell wall: forms around primary cell wall after
growth is complete

15. Peroxisomes.
● Are microbodies containing enzymes (imported via a
signal sequence) that permit the oxidation of certain
organic molecules (R-H), such as amino acids and fatty
acids.
• The peroxisomes also contain catalase, which transforms
hydrogen peroxide into water and oxygen gas. It also
oxidizes toxins, such as alcohol and other substances.
catalase
2H2O2 2H2O + O2(g)

16. THE CELL MEMEBRANE
• The plasma membrane is a phospholipid bilayer in
which protein molecules are either partially or
wholly embedded
• The phospholipid bilayer has a fluid consistency,
comparable to that of light oil.
• The proteins are scattered throughout the
membrane; therefore they form a mosaic pat- tern.
• This description of the plasma membrane is called
the fluid-mosaic model of membrane structure.
• They are usually 5-8nm (50-80Å) thick.(An
angstrom is 0.1nm or one ten-billionth of a metr)

17. FUNCTION OF PLASMA MEMBRANE
• Biological membranes usually defines cellular
boundaries by dividing the cell into discrete and distinct
compartments.
• They also organize complex metabolic reactions to
ensure balance in the system.
• Acts in signal reception by response to the environment.
• Therefore ensuring communication between the cell and
the external environment.
• They protect the cell integrity by being selectively
permeable.
• Provide anchoring sites for filaments and cytoskeleton.

18. THE FLUID MOSAIC MODEL OF PLASMA MEMBRANE
• This model seems to be the most acceptable model of representing the
structural and molecular composition of the plasma membrane. It was
proposed by J.S.Singer and G.L. Nicholson in 1972.
• The fluid mosaic model shows that the plasma membrane is amphipathic.
That is, it contains both the hydrophobic (non-polar) tail and the
hydrophilic (polar) heads.
• The membrane is composed of a phospholipid bilayer in which proteins
are embedded.
• The hydrophilic heads of phospholipids are a part of the outside surface
and the inside surface of the membrane while the hydrophobic tails make
up the interior of the membrane.
• Note the plasma membrane’s carbohydrate chains are attached to the
outside surface and cytoskeleton filaments are attached to the inside
surface.
STRUCTURE OF PLASMA MEMBRANE

19. Amphipathic Nature Of The Plasma Membrane

20. Fluid Mosaic Structure Of The Plasma Membrane

21. Composition of the Plasma Membrane
• Most plasma membranes are made up of the
proteins, lipids and carbohydrates.
• The composition by percentage of these components
depends greatly on the functions of the cell on which
they are found.
Example,
• neurons have more lipids in the form of
sphingomyelin which coat the myelin sheaths for
signal transmission
while
• the retinal cells have more proteins like rhodopsin
which is the light absorbing glycoproteins.