CELL PHYSIOLOGY
STRUCTURE AND FUNCTION
LECTURE-----2
DR ZAHOOR ALI SHAIKH
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CELL PHYSIOLOGY
 Cell is basic building block of the body.
 Cell has THREE major parts:
1. Cell Membrane or Plasma Membrane
2. Nucleus : It has Genetic Material
3. Cytoplasm: It has organelles, dispersed in the
GELATIN like liquid, the CYTOSOL
 Cell performs basic essential functions for its own
survival and a specialized task for Homeostasis
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CELL MEMBRANE OR PLASMA
MEMBRANE
 It covers the cell and separates the cell from
its surroundings.
 It controls the movements of molecules
between Intracellular fluid(ICF) and
Extracellular fluid(ECF).
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NUCLEUS
 Spherical or Oval in shape, located near the
center of the cell.
 It is surrounded by double layered membrane
which separates it from the rest of the cell.
 Within the Nucleus is cell Genetic Material DNA(
Deoxyribonucleic acid).
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Functions of DNA
TWO Main Function
 Two Main Function of DNA are:
1– Directs protein synthesis
2– Serving as genetic blue print during cell
replication therefore produces cell like itself
(same cell)
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OTHER FUNCTIONS OF DNA
 DNA controls the cell activity(control center).
 DNA provides instruction or CODES for
synthesis of protein in the cell (enzymes).
 HOW DNA controls cell activity ?
 DNA sends coded message via messenger
RNA to the cytoplasm RNA (Ribosome).
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OTHER FUNCTIONS OF DNA (CONT)
 Ribosomal RNA (in cytoplasm) translates this
message and makes appropriate amino acid
sequence for protein synthesis.
 Transfer RNA --- it transfers appropriate
amino acid to their proper site in the protein
under construction in ribosome's (cytoplasm).
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TYPES OF RNA
 There are THREE types of RNA:
1. Messenger RNA [mRNA] - (from DNA to
cytoplasm)
2. Ribosomal RNA [rRNA] - in cytoplasm
3. Transfer RNA [tRNA] - in cytoplasm
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CYTOPLASM
 It surrounds the Nucleus. It has membrane
enclosed structures called ORGANELLES,
which are dispersed in CYTOSOL (gel like
mass of cytoplasm).
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ORGANELLES- present in
cytoplasm
Membranous Organelle
FIVE main types are there:
1-Endoplasmic Reticulum( ER)
i. Rough ER- has RIBOSOMES (Granules)
ii. Smooth ER - has NO RIBOSOMES
2-Golgi Apparatus
3-Mitochondria
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ORGANELLES (CONT)
4-Lysosomes
5-Peroxisomes
Non-membranous Organelle [three] :
1- Ribosome
2-Vaults
3- Centrioles
 Each organelle does specific job.
 We will discuss the organelles one by one.
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1. ENDOPLASMIC RETICULUM (ER)
 ER - TWO Types :
1. Rough ER (Flattened sacs)
2. Smooth ER (Inter connected Tubules)
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ROUGH ENDOPLASMIC RETICULUM
 Why we call it Rough ER ?
 Because it has particles which give it rough or
granular appearance – these particles are
RIBOSOMES, RNA protein complexes which
synthesize protein under the direction of
Nuclear DNA.
 Some Ribosome are free and present in
cytosol.
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ROUGH ER (CONT)
 It is protein making factory.
 It synthesizes new protein in ER lumen. Some
proteins are secretary products e.g.
hormones or enzymes (all enzymes are
proteins) .
 Other protein are synthesized for new plasma
membrane or organelle membrane.
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SMOOTH ENDOPLASMIC RETICULUM
 It has no ribosome, therefore, no protein
synthesis in smooth ER.
 It serves other purpose.
- Newly synthesized protein and lipids in
rough ER pass into smooth ER.
- It gives rise to transport vesicles which
contain new protein.
- Transport vesicle move to Golgi apparatus.
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SMOOTH ER (CONT)
- Membranous wall of smooth ER has
enzymes for synthesis of lipids.
- In liver cells smooth ER has enzyme which do
Detoxification of drugs.
- In muscle cells, smooth ER is called
Sarcoplasmic Reticulum which contain
calcium and plays important role in muscle
contractions.
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2. GOLGI APPARATUS
 It directs molecular traffic.
 Newly synthesized molecules in rough ER
which just came from smooth ER enter Golgi
sack or layer.
 Golgi complex directs the product for its final
destination e.g. that becomes part of plasma
membrane or incorporated in Lysosomes.
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3. MITOCHONDRIA
 They are called ‘Power Plants’ of the cell.
 They are rod or oval shaped.
 Number of Mitochondria present in the cell
depend on cell activity.
 Number of Mitochondria vary from hundred
to thousands.
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MITOCHONDRIA (CONT)
 They take energy from the food and use for cellular
activities.
 Energy derived from food is stored in ATP.
 When ATP (Adenosine Triphosphate) is split, energy
is released.
 Energy released from ATP is used by the cell for
-synthesis of protein in ER
-membrane transport
-mechanical work e.g. contraction of heart muscle,
skeletal muscle
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MITOCHONDRIA (CONT)
 Mitochondria have their own DNA (it is
different from cell nucleus DNA).
 Mitochondrial diseases are recognized which
cause nervous system and muscle diseases.
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4. LYSOSOMES
 They work as intra-cellular Digestive System.
 Lysosomes are membrane enclosed sacks
containing powerful enzymes, capable of
removing bacteria and cellular debris.
 There are about 300 Lysosomes in a cell.
 Lysosomes appear granular-these granules
are protein aggregates of powerful digestive
enzymes.
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LYSOSOMES (CONT)
 How Lysosomes work ?
 When extra-cellular material to be attacked
by Lysosomes is brought into the cell by
process of Endocytosis (endo=within).
 Endocytosis is done by 2 ways:
1. Pinocytosis
2. Phagocytosis
 Lysosomes destroy bacteria by hydrolytic
enzymes.
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5. PEROXISOMES
 They have oxidative enzymes.
 They destroy various waste produced in the
cell and toxic compounds that have entered
the cell e.g. Ethanol.
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NON-MEMBRANOUS ORGANELLES
 1. RIBOSOMES
 Ribosomes carry out protein synthesis.
 They are present free in cytosol.
 NOTE – [ Ribosomes are attached to the
rough endoplasmic reticulum also]
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NON-MEMBRANOUS ORGANELLES
 2. VAULTS
 They are newly discovered organelle.
 Cell may contain thousands of vaults.
 Octagonal shape organelle transports
messenger RNA or Ribosomal units from the
nucleus to cytoplasmic ribosome.
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NON-MEMBRANOUS ORGANELLES
 3. Centrosome, Centrioles
 Centrosome is located in the cytoplasm, near the
nucleus.
 Two centrioles surrounded by protein lie at the
center of centrosome.
 Centrosome is cell’s microtubule.
 Microtubule are part of cytoskeleton.
 Centrioles form mitotic spindle to direct
movements of chromosomes.
 In some cells centriole form cilia, flagella.
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What You Should Know From
This Lecture
 What are cell’s three major subdivisions ?
 Control Center in the Cell – DNA
 Types of RNA
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


- mRNA
- rRNA
- tRNA
Organelles present in the Cytoplasm
- Membranous
- Non-membranous
Important Functions
Ribosomes - Protein Synthesis
Mitochondria - Power House
Lysosomes - Bacterial Digestion
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THANK YOU
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