Cells are the smallest functional units of the body. They are grouped together to form tissues, each of which has a specialised function, e.g. blood, muscle, bone. Different tissues are grouped together to form organs, e.g. heart, stomach, brain. Organs are grouped together to form systems
Cell is defined as the structural and functional unit of the living body.
General Characteristics of Cell–
👉 Needs nutrition and oxygen
👉 Produces its own energy necessary for its growth, repair and other activities
👉 Eliminates carbon dioxide and other metabolic wastes
👉 Maintains the medium, i.e. the environment for its survival
👉 Shows immediate response to the entry of invaders like bacteria or toxic substances into the body 6. Reproduces by division.
Structure of Cell-
Each cell is formed by a cell body and a membrane covering the cell body called the cell membrane.
👉 Cell membrane
Cell membrane is a protective sheath, enveloping the cell body. It is also known as plasma membrane or plasmalemma. This membrane separates the fluid outside the cell called extracellular fluid (ECF) and the fluid inside the cell called intracellular fluid (ICF). The cell membrane is a semipermeable membrane.
Composition of Cell Membrane-
Cell membrane is composed of three types of substances-
👉 Lipids (40%)
👉 Carbohydrates (5%).
Function of Cell Membrane-
👉Protective function- Cell membrane protects the cytoplasm and the organelles present in the cytoplasm
👉Selective permeability- Cell membrane acts as a semipermeable membrane, which allows only some substances to pass through it and acts as a barrier for other substances
👉 Absorptive function- Nutrients are absorbed into the cell through the cell membrane
👉 Excretory function- Metabolites and other waste products from the cell are excreted out through the cell membrane
👉 Exchange of gases- Oxygen enters the cell from the blood and carbon dioxide leaves the cell and enters the blood through the cell membrane.
👉 Maintenance of shape and size of the cell- Cell membrane is responsible for the maintenance of shape and size of the cell.
Cytoplasm of the cell is the jelly like material formed by 80% of water. It contains a clear liquid portion called cytosol and various particles of different shape and size. These particles are proteins, carbohydrates, lipids or electrolytes in nature.
Organelles in Cytoplasm-
Organelles with limiting membrane-
✍️ Endoplasmic reticulum-
Endoplasmic reticulum is a network of tubular and microsomal vesicular structures which are interconnected with one another. two types
1.Rough Endoplasmic ( Granular endoplasmic ) -
Reticulum It is the endoplasmic reticulum with rough, bumpy or bead-like appearance. Rough appearance is due to the attachment of granular ribosomes to its outer surface.
- Synthesis of proteins
- Degradation of wornout organelles
2-Smooth Endoplasmic(Agranular recticulum)-
Reticulum It is the endoplasmic reticulum with smooth appearance. It is also called agranular reticulum.
1. Synthesis of lipids and steroids
2. Role in cellular metabolism
3. Storage and metabolism of calcium
4. Catabolism and detoxification of toxic substances
✍️ Golgi apparatus-
Golgi apparatus or Golgi body or Golgi complex is a membrane-bound organelle, involved in the processing of proteins. It is present in all the cells except red blood cells. It is named after the discoverer Camillo Golgi.
Processing, packaging, labeling and delivery of proteins and lipids
Lysosomes are the membrane-bound vesicular organelles found throughout the cytoplasm. The lysosomes are formed by Golgi apparatus. The enzymes synthesized in rough endoplasmic reticulum are processed and packed in the form of small vesicles in the Golgi apparatus
1. Degradation of macromolecules
2. Degradation of wornout organelles
3. Removal of excess of secretory products
4. Secretion of perforin, granzymes, melanin and serotonin
Peroxisomes or microbodies are the membrane limited vesicles like the lysosomes. Unlike lysosomes, peroxisomes are pinched off from endoplasmic reticulum and not from the Golgi apparatus.
1. Breakdown of excess fatty acids
2. Detoxification of hydrogen peroxide and other metabolic products
3. Oxygen utilization
4. Acceleration of gluconeogenesis
5. Degradation of purine to uric acid
6. Role in the formation of myelin
7. Role in the formation of bile acids
✍️ Centrosome and centrioles-
Centrosome is the membrane-bound cellular organelle situated almost in the center of cell, close to nucleus. It consists of two cylindrical structures called centrioles which are made up of proteins. Centrioles are responsible for the movement of chromosomes during cell division.
Movement of chromosomes during cell division
✍️ Secretory vesicles-
Secretory vesicles are the organelles with limiting membrane and contain the secretory substances. These vesicles are formed in the endoplasmic reticulum and are processed and packed in Golgi apparatus
✍️ Mitochondria- mitochondria are know as the powerhouse of cell. the energy required for various chemical activities needed for life is released by mitochondria in the form of ATP is know as the energy current of the cell.
1. Production of energy
2. Synthesis of ATP
3. Initiation of apoptosis
Nucleus is the most prominent and the largest cellular organelle. It has a diameter of 10 µ to 22 µ and occupies about 10% of total volume of the cell.
STRUCTURE OF NUCLEUS -
Nuclear Membrane- Nuclear membrane is double layered and porous in nature. This allows the nucleoplasm to communicate with the cytoplasm.
Nucleoplasm-Nucleoplasm is a highly viscous fluid that forms the ground substance of the nucleus. It is similar to cytoplasm present outside the nucleus.
Chromatin- Chromatin is a thread-like material made up of large molecules of DNA. The DNA molecules are compactly packed with the help of a specialized basic protein called histone.
Chromosomes -Chromosome is the rod-shaped nuclear structure that carries a complete blueprint of all the hereditary characteristics of that species. A chromosome is formed from a single DNA molecule coiled around histone molecules. Each DNA contains many genes.
Nucleolus -Nucleolus is a small, round granular structure of the nucleus. Each nucleus contains one or more nucleoli. The nucleolus contains RNA and some proteins, which are similar to those found in ribosomes.
1. Control of all activities of the cell
2. Synthesis of RNA
3. Sending genetic instruction to cytoplasm for protein synthesis
4. Formation of subunits of ribosomes
5. Control of cell division
6. Storage of hereditary information in genes (DNA)
Organelles without limiting membrane -
Ribosomes are the organelles without limiting membrane. These organelles are granular and small dot-like structures with a diameter of 15 nm. Ribosomes are made up of 35% of proteins and 65% of ribonucleic acid (RNA)
Ribosomes are called ‘protein factories’ because of their role in the synthesis of proteins
Cytoskeleton is the cellular organelle present throughout the cytoplasm. It determines the shape of the cell and gives support to the cell.Cytoskeleton consists of three major protein components:
2. Intermediate filaments
1. Determination of shape of the cell
2. Stability of cell shape
3. Cellular movements