This document provides an overview of cell organelles and their functions. It describes the endoplasmic reticulum, including rough ER which synthesizes proteins, and smooth ER which synthesizes lipids and regulates calcium. It also details the Golgi apparatus, mitochondria, lysosomes, peroxisomes, ribosomes, cytoskeleton, and nucleus. The key functions of each organelle are summarized such as protein synthesis, energy production, waste disposal, structural support, and genetic material storage.

2. Introduction
 What is a wall?
 Wall is made up of what?
 What are the functions of wall?
 Structural unit
 Functional unit
 Similarly our body is also made up of 100 trillion
structural and functional units
Cell

3. Components of cell
Cell basics . . . Plasma membrane
Nucleus
Organelles
Cytosol
Cytoplasm

4. Cell organelles
 Organelles are specialized structures that have
characteristic shapes and perform specific functions
in cellular growth, maintenance and reproduction.
 Endomembrane system:
 Endoplasmic reticulum (rough and smooth)
 Golgi Complex
 Mitochondria
 Ribosome
 Lysosomes
 Peroxisomes
 Centrosomes and centriole

5. Endoplasmic reticulum
 System of flattened membrane-bound vesicles and
tubules
 Continuous with the outer membrane of the nuclear
envelop, Golgi complex
 Types:
 Rough ER
 Smooth ER

6. Rough endoplasmic reticulum
 Rough due to membrane bound ribosomes.
 13 million ribosomes per liver cell.
 Protein synthesizing cells
 Plasma cells, Nerve cells, Acinar cells of Pancreas
 Liver cells
 Functions :
 Synthesis of proteins to:
 Be secreted outside the cell,
 Be membrane bound,
 Remain in the ER or Golgi complex.

7. Smooth endoplasmic reticulum
 Devoid of ribosomes
 Functions:
 Synthesis of steroid hormones.
 Leydig cells and cells of adrenal cortex
 Regulates Ca2+ ion release into cytosol
 Important for muscle contraction and other regulatory
mechanisms.
 Skeletal , smooth and cardiac muscles (sarcoplasmic
reticulum)
 Degradation and detoxification in concert with
Lysosomes and Peroxisomes.

8. Ribosomes
 Ribosomes are tiny spheres consisting
of ribosomal RNA and several
ribosomal proteins
 Containing 85% of cell’s RNA
 Ribosomal Subunits
 Large + small subunits made in the
nucleolus and assembled in the
cytoplasm
 They occur free (singly or in clusters)
or together with endoplasmic
reticulum.

9.  Free ribosomes are loose in cytosol
 Synthesize proteins found inside the cell (Hb)
 Membrane-bound ribosomes
 Attached to endoplasmic reticulum or nuclear
membrane
 Synthesize proteins needed for plasma membrane or for
export
 10 to 20 together form a polyribosome
 Inside mitochondria, ribosomes synthesize
mitochondrial proteins

10. Golgi apparatus
 Collection of membranous vesicles and sacs
 Near nucleus towards the site of secretion.
 Well developed in exocrine glands
 Has several layers called cisternae, arranged like a stack of
pancakes.
 Vesicles bud from rough ER and merge into first layer of
Golgi complex.
 Cis face towards ER, Trans face towards cell membrane.
 Functions:
 Synthesis of carbohydrate and complex proteins
 Packaging of proteins coming from ER
 Synthesis of Lysosomal enzymes
 Glycosylation of proteins.
 Forms secretory vesicles

11. Golgi apparatus

12. Mitochondria
 Oval /globular structures
 Approximately 0.5-1 µm in diameter; may be very long in
some cells (5-1 2µm)
 Membranes - inner membrane and outer membrane
 Inner membrane has large surface area and folds inward
forming cristae; contains membrane proteins responsible for
internal respiration (ETC)and ATP synthesis
 Lollipop-shaped globular structures
 Outer membrane –enzymes of biological oxidation
 Intermembrane space is similar to cytoplasm in
concentration of small molecules
 Matrix - contains enzymes responsible for many steps of
metabolism(Krebs cycle), DNA, ribosomes, etc.

14. Functions of mitochondria
 Mitochondria are the site of ATP production in the
cell by the catabolism of nutrient molecules.
 Mitochondria self-replicate using their own DNA.
 increases with need for ATP
 circular DNA with 37 genes
 Mitochondrial DNA (genes) are usually inherited only
from the mother.

15. Lysosomes
 Membrane-enclosed vesicles that contain powerful digestive
enzymes (several hundred)
 Contain acid hydrolytic digestive enzymes (40) made in the rough ER
(Internal pH reaches 5.0).
 Vary in shape and size from cell to cell, from 25nm to 1µm
 Vesicles is formed by budding from Golgi complex.
 Types:
 Primary Lysosomes
 Secondary Lysosomes
 Residual bodies
 Functions:
 Digest foreign substances
 Autophagy (autophagosome forms)
 Recycles own organelles autolysis
 Lysosomal damage after death(suicidal bag)
 Applied
 Tay-sachs disease

16. Peroxisomes
 Vesicles that contain crystalline core of oxidative
enzymes.
 Predominantly present in hepatocytes and tubular
epithelial cells
 0.1 to 1.0 µm in diameter.
 Contain 50 or more enzymes with varied functions:
 Oxidation of fatty acids,
 Cholesterol synthesis in liver,
 Not synthesized from Golgi apparatus
 made from other Peroxisomes.

17. Centrosomes
 Centrosomes are dense
areas of cytoplasm
containing the Centrioles.
 Centrioles are paired
cylinders arranged at right
angles to one another
 Close to nucleus
 Movement of chromosomes
during cell division.

18. Cytoplasmic inclusions
 Temporary components
1. Lipid droplets-adipose tissue, liver and adrenal cortex
2. Glycogen- liver and skeletal muscles.
3. Melanin pigment-epidermis, retina and basal ganglia
4. Lipofuscin
 Yellow brown pigments
 Cardiac muscle and brain cells of elderly people.

19. Cytoskeleton
 Complex network of fibers that provides
 Structural support
 Intracellular transport
 Contractility and motility
 Spatial organization
 Components:
1. Intermediate filaments – form nuclear lamina, gives
cell mechanical strength.
2. Microtubules – long, rigid, made of tubulin.
3. Microfilaments – long, flexible, made of actin.

21. Microtubules
 13 protofilaments, form hollow
tube
 Protofilaments composed of
alternating alpha and beta
tubulin monomers
 24 nm wide, easy to make/break.
 Polarity in tubulin dimers gives
filaments direction.
 Molecular motors:
 Kinesin moves towards plus end.
 Dynein moves to minus end.
 Functions:
 Cell division (mitotic spindle)
 Motility (cilia and flagella)
 Transport
Tubulin
dimers

22. Intermediate filaments
 10 nm wide, often radiate in spiral pattern.
 Heterogeneous – encoded by at least 50 genes.
 Connect the nuclear membrane to the cell membrane
 Highly resistant to stretching.
 Functions:
 Mechanically integrate the cell organelles within cytoplasm
 Provide mechanical stability
 Keratin – epithelium
 Desmin - muscle cells
 Neurofilaments – neurons
 Blistering of skin.

23. Microfilaments
 Long solid filamentous structures
 Made of double strand of actin chains, 8nm diameter.
 Unorganized network in cell cortex
 Microvilli
 Cell shape changes
 Interact with myosin during muscle contraction

24. Molecular motors
 Helps in movement of proteins, organelles inside the
cell
 Types :
I. Microtubule based molecular motors
 Conventional Kinesin-double head (towards positive end)
 Dyneins :
 Cytoplasmic –(towards negative end)
 Axonemal – oscillate (flagella and cilia)
II. Actin based molecular motors
 Myosin ( I &II)

25. Nucleus
 The nucleus is usually the most prominent
feature of a cell(10µm).
 Most body cells have a single nucleus; some
(red blood cells) have none, whereas others
(skeletal muscle fibers) have several.
 The parts of the nucleus include the nuclear
envelope which is perforated by channels
called nuclear pores, nucleoli and genetic
material (DNA).
 Nuclear membrane:
 Inner membrane is nuclear lamina.
 Outer membrane extends to endoplasmic
reticulum.
 Perinuclear cistern 40-60nm wide
 Contains all genetic material as chromatin,
segregated from the rest of the cell by the
nuclear envelope.
 Nucleolus is site of ribosomal RNA synthesis.
 Structure maintained by nuclear matrix(gel
like).

26. Nuclear Pores
 1000Å
 Serves as a water-filled channel.
 Ring of 8 multi-domain protein subunits.
 Allows passive diffusion of small molecules and
ions.
 Proteins, RNAs, other larger molecules are
actively transported.
 Opens in response to Ca2+ ions.

27. functions of nucleus
 46 human DNA molecules or chromosomes
 – genes found on chromosomes
 – Gene--is directions for a specific protein
 Non-dividing cells contain nuclear chromatin
 loosely packed DNA
 Dividing cells contain chromosomes
 tightly packed DNA

28. Chromosomes
 Each chromosome is a long molecule
of DNA that is coiled together with
several proteins.
 Human somatic cells have 46
chromosomes arranged in 23 pairs.
 Human DNA is 3 billion bp, ≈30,000
genes, 200,000x longer than average
cell width.
 Wound around protein complexes
called histones.
 Compaction depends on cell cycle
stage.
 The various levels of DNA packing are
represented by nucleosomes,
chromatin fibers, loops, chromatids
and chromosomes.