lectures on Physiology Cell, and all about the Cell.

1. Physiology is the study of normal functions of various systems and
organs of the body. Physiology is the science that seeks to explain the
physical and chemical mechanisms that are responsible for the origin,
development and progression of life.
Human physiology is usually studied under following headings:
1. General Physiology
2. Blood and its Constituents
3. Nerve and Muscle Physiology
4. Cardiovascular Physiology
5. Respiratory Physiology
6. Gastrointestinal Physiology
7. Renal Physiology
8. The Endocrine System
9. Reproductive Physiology
10. Central Nervous System and Special Senses

2. General Physiology.
It is a branch of physiology concerned with the basic functional
activities of living matter.
Cell is the basic structural and functional unit of the body. Each organ
is an aggregate of many different cells.
Each type of cell is specially adapted to perform one or a few
particular functions. The entire body contains about 100 trillion cells.
All of them have certain basic characteristics that are alike.
The 2 major parts of the cell are Nucleus and Cytoplasm.
• The Nucleus is separated from the cytoplasm by a Nuclear
membrane.
• The cytoplasm is separated from the surrounding fluids by a cell
membrane, also called a Plasma membrane.
The different substances that make up a cell are collectively called
PROTOPLASM.
Protoplasm is composed mainly of 5 basic substances:
1. Water
2. Electrolytes
3. Proteins
4. Lipids
5. Carbohydrates
• Water is the principal fluid medium of the cell; it is present in
most cells in a concentration of 70 to 85 %.

3. • Important ions/electrolytes of the cell include potassium,
magnesium, sulphate, bicarbonate and smaller quantities of sodium,
chloride and calcium.
• After water, the most abundant substances in most cells are
proteins that normally constitute 10 to 20 % of the cell mass. These
proteins are divided into 2 basic types: structural proteins and
functional proteins.
• Lipids constitute only about 2 % of total cell mass. Especially
important lipids are Phospholipids, cholesterols and triglycerides.
• Carbohydrates have little structural function in the cell. They
play a major role in the nutrition of the cell. Most human cells do not
maintain large stores of carbohydrates. The amount usually averages
about 1 % of total cell mass. The amount increases about 3 % in the
muscle cells, about 6 % in the liver cells.

4. PHYSICAL STRUCTURE OF THE CELL:
Each cell is formed by
1. Cell membrane
2. Cytoplasm
3. Nucleus
1. Cell membrane:
It is a thin, pliable, elastic structure only 7.5 to 10 nm thick. It is
composed of proteins and lipids. The approximate composition is
proteins 55%, phospholipids 25%, cholesterol 13%, other lipids 4%
and carbohydrates 3%.
Lipid layer of cell membrane:
The central lipid layer is a bilayered structure. It is composed of
phospholipids, sphingolipids and cholesterol.
Phospholipid molecules are arranged in 2 layers. The outer part is
called head portion and the inner part is called tail portion. The head
portion is soluble in water and is hydrophilic. The tail portion is
insoluble in water and is hydrophobic.
Hydrophobic tail portions meet in the center. Hydrophilic head
portions of outer layer face the ECF and those of the inner layer face
the cytoplasm.
Cholesterol molecules are arranged in between the phospholipid
molecules.

5. Functions: lipid layer is semi permeable membrane and allows only
fat soluble substances like oxygen, carbon dioxide and alcohol to pass
through it.
Protein layers of the cell membrane:
These layers cover the 2 surfaces of central lipid layer. They are
classified into 2 categories:
1. Integral or trans membrane proteins that pass through entire
thickness of cell membrane.
2. Peripheral proteins which are embedded in outer and inner
surfaces of the cell membranes. Examples are: receptors, transport
proteins, enzymes, antigens and adhesion proteins.
Functions:
1. Integral proteins Provide structural integrity.
2. Channel proteins Help in diffusion of water soluble substances
like glucose and electrolytes.
3. Carrier proteins Help in transport of substances across the cell
membrane.
4. Act as pumps, by which ions are transported.
5. Receptor proteins Serve as receptor sites for hormones and
neurotransmitters.
6. Some of the protein molecules form the enzymes and control
chemical reactions within the cell membrane.
7. Some proteins act as antigens and induce antibody formation.

6. Carbohydrates of cell membrane:
They are either attached to proteins and known as Glycoproteins or
attached to lipids and known as Glycolipids.
Carbohydrate molecules form a thin and loose covering layer over the
entire surface of the cell membrane called GlycoCalyx.
FUNCTIONS OF CELL MEMBRANE:
1. Protect the cytoplasm and the orgenelles.
2. Acts as semi permeable membrane which allows only some
substances to pass through it and acts as a barrier for other substances.
3. Nutrients are absorbed into the cell through cell membrane.
4. Metabolites and other waste products from the cell are excreted
out through the cell membrane.
5. Exchange of Oxygen and Carbon dioxide take place through cell
membrane.
6. Maintenance of shape and size of the cell.

7. 2: CYTOPLASM:
It is a jelly like material formed by 80% of water.
It is Made up of 2 zones: ectoplasm and endoplasm.
ORGENELLES IN CYTOPLASM:
Orgenelles are the small organs of the cells. Some of them are bound
by limiting membrane and others do not have limiting membrane.
Orgenelles with limiting membrane are:
a) Endoplasmic reticulum
b) Golgi apparatus
c) Lysosomes
d) Peroxisome
e) Centrosomes and centrioles
f) Secretory vesicles
g) Mitochondria
h) Nucleus
i) Orgenelles without limiting membranes are
j) Ribosomes
k) Cytoskeleton
a) Endoplasmic reticulum:
It is a network of tubular and vesicular structures.
It contains a fluid medium called endoplasmic matrix.

8. The endoplasmic reticulum forms the link between nucleus and cell
membrane.
Endoplasmic reticulum is of two types: rough er and smooth er.
Rough endoplasmic reticulum: it is rough, bumpy and bead like. The
rough appearance is due to attachment of granular ribosomes to its
outer surface.
The rough endoplasmic reticulum is concerned with synthesis of
proteins and degradation of worn out materials.
Smooth endoplasmic reticulum:
It is formed by many interconnected tubules. It does not have
ribosomal attachment. It is concerned with formation of non-protein
substances such as steroids and cholesterol. This type of endoplasmic
reticulum is abundant in cells that are involved in synthesis of lipids,
phospholipids, lipo-proteins, steroid hormones, sebum etc.
Outer surface of smooth endoplasmic reticulum contains many
enzymes which are involved in many metabolic processes.
It is the major site of storage and metabolism of calcium.
It is also concerned with catabolism and detoxification of toxic
substances like some drugs and carcinogens.

9. b) GOLGI APPARATUS:
Golgi apparatus is membrane bound organelle. It is present in all the
cells except RBCs. It is named after the discoverer Camillo Golgi.
Each golgi apparatus consists of 5 to 8 flattened membranous sacs
called the cisternae.
It has 2 ends or faces. Cis face and trans face.
The cis face is positioned near endoplasmic reticulum. Reticular
vesicles from ER enter the golgi apparatus from here. The trans face
is situated near cell membrane, the processed substances make their
exit from trans face.
The golgi apparatus is concerned with processing, packaging and
labelling of materials.
Glycoproteins and lipids are modified and processed. They are packed
in the form of vesicles, secretory granules and lysosomes which are
transported to the other part of the cell or out of the cell.
c) LYSOSOMES:
Lysosomes are formed by Golgi apparatus. They have the thickest
covering membrane.
Lysosomes are of 2 types:
Primary L: which is pinched off from golgi apparatus. It is inactive in
spite of having hydrolytic enzymes.
Secondary L: which is active. It is formed by fusion of the primary
lysosome with other substance.

10. Lysosomes are called garbage system of the cell because of their
degradation activity. About 50 different hydrolytic enzymes are
present in lysosomes.
Important lysosomal enzymes are:
Proteases which hydrolyze proteins into amino acids.
Lipases which hydrolyze lipids into fatty acids and triglycerides.
Amylases which hydrolyze carbohydrates into glucose.
Lysosomes are concerned with degradation of macro molecules;
worn out orgenelles; removal of excess secretory products in the cell.
d) PEROXISOMES:
They are pinched off from endoplasmic reticulum. They contain
oxidative enzymes such as catalase, urate oxalate and D amino acid
oxidase.
Peroxisomes are concerned with breakdown of fatty acids by means
of Beta oxidation; degradation of toxic substances like hydrogen
peroxide; formation of major site of oxygen utilisation in the cells;
acceleration of gluconeogenesis from fats; in formation of myelin and
bile acids.
e) MITOCHONDRION:
It is a rod shaped or oval shaped structure with a diamemer of 0.5 to 1
micron. The outer membrane is smooth; the inner membrane is folded
in form of shelf like projections called cristae. Cristae contain many
enzymes and proteins which are involved in respiration and synthesis

11. of adenosine triphosphate (ATP). Mitochondria are concerned with
production of energy and synthesis of ATP.
f) RIBOSOMES:
Ribosomes are orgenelles without limiting membrane. They are
granular and small dot like structure with a diameter of 15n.
Ribosomes are of 2 types:
Ribosomes That are attached to ER.
Free ribosomes.
Ribosomes are called protein factories.
Messenger RNA carries genetic code for protein synthesis from
nucleus to ribosomes. The ribosomes arrange the amino acids into
proteins.
3. NUCLEUS:
Nucleus is most prominent and the largest cellular organelle. It has a
diameter of 10 to 22 micron and occupies 10% of total cell volume.
Nucleus is present in all the cells of the body except RBCs.
The cells with nucleus are called Eukaryotes and those without
nucleus are called Prokaryotes. Presence of nucleus is necessary for
cell division.

12. Nucleus is covered by a membrane called nuclear membrane and
contains many components. Major component of nucleus are
nucleoplasm, chromatin and nucleolus.
NUCLEAR MEMBRANE is double layered and porous in nature.
The pores are lined by proteins. Exchange of materials between
nucleoplasm and cytoplasm occurs through these pores.
NUCLEOPLASM is a highly viscous fluid that forms the ground
substance of nucleus. It surrounds chromatin and nucleolus. It
contains matrix, nucleotides and enzymes. The nuclear matrix form
the structural framework for organizing chromatin.
CHROMATIN is a thread like material made up of Deoxyribonucleic
acid (DNA).
Just before cell division, the chromatin condenses to form
chromosomes.
CHROMOSOME is a rod shaped nuclear structure. It is formed from
a single DNA molecule coiled around histone molecules.
Chromosomes are visible only during cell division under microscope.
All the dividing cells of the body except reproductive cells contain 23
pairs of chromosomes, known as Diploid cells. Each pair consists of
one chromosome inherited from mother and one from father. Among
23 pairs, one pair is concerned with determination of sex of the
person. These chromosomes are called sex chromosomes. Among sex
chromosomes, one is called X chromosome and another one is called
Y chromosome. The cells of females have two X chromosomes and

13. cells of males have one X chromosome and one Y chromosome.
Remaining 22 pairs are called autosomes.
The reproductive cells called gametes or sex cells contain only 23
single chromosomes. These are called Haploid cells.
NUCLEOLUS is a small, round granular structure which contains
RNA and some proteins.
FUNCTIONS OF THE NUCLEUS:
1. Control of all the cell activities.
2. Synthesis of RNA.
3. Formation of subunits of ribosomes.
4. Sending genetic instruction to cytoplasm for protein synthesis
through mRNA .
5. Control of cell division through genes.
6. Storage of hereditary information and transformation of this
information from one generation to the next.
DEOXYRIBONUCLEIC ACID (DNA)
DNA is a double stranded complex nucleic acid. It is formed by
Deoxyribose, phosphoric acid and four types of bases. Each DNA
molecule consists of two polunucleotide chains, which are twisted
around one another in the form of a double helix. The two chains are
formed by the sugar deoxyribose and phosphate. These two
substances form the backbone of DNA. Both chains of DNA are
connected with each other by some organic bases.

14. Each nucleotide is formed by:
1. Deoxyribose: sugar
2. Phosphate.
3. One of the following organic bases:
i) Purines: Addnine (A), Guanine (G)
ii) Pyrimidines: Thymine (T), Cytosin (C)
The adenine of one strand binds with thymine of opposite strand. The
cytosine of one strand binds with Guanine of the other strand.
The hereditary information encoded in the DNA is called Genome.
Each DNA molecule is divided in discrete units called Genes.
GENES: Gene is the basic hereditary unit of the cell. It contains
message or code for synthesis of specific protein from amino acids.
In the nucleotide of the DNA, three of the successive base pairs are
called a triplet or codon. Each codon codes for one amino acid. There
are 20 amino acids and there is separate code for the each amino acid.
RIBONUCLEIC ACID (RNA)
It contains a long chain of nucleotide. It is similar to DNA but it
contains ribose instead of deoxyribose.
Each nucleotide is formed by
1) Ribose : sugar
2) Phosphate.
3) One of the following organic bases:
a) Purines: Addnine (A), Guanine (G)

15. b) Pyrimidines: Uracil (U), Cytosin (C)
Types of RNA:
1) Messenger RNA (mRNA): carries genetic code for the amino
acid sequence for synthesis of protein from DNA to cytoplasm.
2) Transfer RNA (tRNA): responsible for decoding of genetic
message present in mRNA.
3) Ribosomal RNA (rRNA): responsible for assembly of protein
from amino acids in the ribosomes.
GENE EXPRESSION:
It is the process by which the information encoded in the gene is
converted into functional gene product that is used for protein
synthesis. It envolves 2 steps:
Transcription and translation.
1) Transcription: it means copying. It indicates copying of genetic
code from DNA to mRNA. The mRNA enters the cytoplasm and
activates the ribosome for protein synthesis.
2) Translation of genetic code: the mRNA moves out of the
nucleus into cytoplasm. Ribosomes get attached to it. The sequence of
codons are recognized by tRNA. According to sequence, different
amino acids are transported from cytoplasm to ribosome by tRNA.
With the help of rRNA, the protein molecules are assembled from
amino acids.