It is the basic living structural and functional unit of body.
Cell can be studied under two major parts- cell membrane & cell organelles.
All living cells are made up of a substance called protoplasm, which is slightly opaque, colorless & soft jelly like consisting of water and large no. of substances in solution or suspension form.
Protoplasm within the cell and outside the nucleus is called cytoplasm.
Cell Membrane/ Plasma Membrane/ Cytoplasmic Membrane
Outermost layer of a cell is cytoplasmic membrane.
It is bio-molecular layer of phospholipid molecules, coated with protein layer on each surface.
It is trilaminar, lipid bilayer.
It has small pores and acts as a selective sieve through which certain substances are allowed to enter into the cell (endocytosis) and some substances are transported outside the cell (exocytosis)
It has active transport processes all across the cell membrane.
Lipids mainly are phospholipids but cholesterol and glycolipids are also present.
Carbohydrates are also present in the cell membrane.
Principally cell membrane is made up of lipids and proteins.
All membrane lipids are Amphipathic.
It is divided into the hydrophilic polar head and the hydrophobic hydrocarbon tails.
The glycolipids are sugar containing lipids.
Cholesterol is more abundant towards the outside of the plasma membrane.
It is studied under 2 main forms
a) Integral proteins/ Transmembrane proteins
i. Channel protein
They are responsible for the transfer of small water-soluble substance.
ii. Carrier protein
They helps to transfer materials across the bilayer through active transport mechanism.
These bind with different neurotransmitters or other chemical substances leading to changes in intracellular reactions.
These are also proteins and they actively transfer the ions across the bilayer against the concentration gradient.
b) .Peripheral Protein
They are also called as Extrinsic protein.
They do not penetrate the lipid membrane completely, but remain attached to the integral proteins.
FUNCTIONS OF CELL MEMBRANE
They act as receptors for hormones and enzymes.
It has small pores and active transport processes that help in transferring of substances across the cell membrane.
- Endoplasmic Reticulum (ER)
a. Smooth endoplasmic reticulum or Agranular ER
b. Rough Endoplasmic reticulum or granular ER
4. Golgi apparatus or Golgi bodies
Membrane bound central mass within the cell that contains chromosomes .
Protoplasm inside the nucleus called nucleoplasm.
The eukaryotic nucleus is bound by double membrane, called nuclear membrane .
And this nuclear membrane is externally continuous with Endoplasmic Reticulum’s membrane.
Nuclear membrane contain pores that allow movement of substances in and out of nucleus.
FUNCTIONS OF NUCLEUS
Nucleus contain nucleoli (Singular is nucleolus)
Nucleolus is cluster of DNA
Nucleus contain 46 Chromosomes which contain genes, responsible for the maintenance of the cellular structure as well as for the control of the cellular activities.
Nuclear membrane has pores which allow transfer of water and water soluble materials (ions) and sometimes proteins in and out of nucleus.
Continuous membrane system that forms forms flattened sacs within cytoplasm are called endoplasmic reticulum.
The total surface area of ER in some cells, liver cells for instance, can be as much as 30-40 times the cell membrane area.
Single membranous organelle.
It is of 2 types:- a). Smooth endoplasmic reticulum or Agranular ER
b). Rough Endoplasmic reticulum or Granular ER.
a.) Smooth endoplasmic reticulum or Agranular ER
The amount of smooth endoplasmic reticulum varies from cell to cell.
Function of Smooth Endoplasmic reticulum :-
Synthesis of fatty acids and phospholipids .
Certain enzymes present in smooth ER, modify and detoxify many toxic chemicals and carcinogens.
b.) Rough Endoplasmic reticulum or Granular ER
Endoplasmic reticulum carries granules and those granules are called Ribosomes.
RER is called “rough” because its appearance is granular and rough.
Function of Rough Endoplasmic reticulum
Because of presence of ribosome, rough ER is responsible for synthesis of certain proteins.
Also responsible for production of antibodies.
Ribosomes are small granules which are made up of ribosomal RNA (rRNA) and many ribosomal proteins.
They are made up of 2 subunits, the smaller one and the larger one ,both containing RNA of smaller and larger size respectively.
Can be 70S ( found in prokaryotes and in mitochondria) or 80S (found in eukaryotes.).
Ribosomes are of 2 types;- One attached to endoplasmic reticulum & others free in cytosol, called cytoplasmic or free ribosomes.
FUNCTIONS OF RIBOSOMES:-
1.Synthesis of protein.
2.Free ribosomes produces proteins to be utilized by the cell itself.
Golgi apparatus or Golgi Bodies
Tightly packed system of smooth-surfaced vesicles near the nucleus called Golgi apparatus.
It is made up of continuous series of flattened membranous sacs.
The stack of Golgi sacs has 2 defined regions- Cis & Trans.
The proteins from endoplasmic reticulum come to Golgi apparatus through transfer vesicles, and fuse with the sacs of cis region.
These raw proteins are then carried to trans region.
FUNCTIONS OF GOLGI BODIES:-
1.They stores proteins and are also responsible for modifying them.
2.Through secretary vesicles these proteins are secreted outside the cell when needed.
It is called powerhouse of the cell.
Has its own DNA, RNA, proteins and ribosomes and are thus semiautonomous organelles.
Number of mitochondria vary from cell to cell.
It can be less than hundreds to more than several thousand, depending on the energy requirements of the cell.
The mitochondria is composed of two lipo-protein membranes.
a.)The outer one is intact and covers the whole structures
b).Inner one is folded internally to form shelves.
FUNCTIONS OF MITOCHONDRIA:-
Many oxidative enzymes are present in mitochondria.
These enzymes cause oxidation of nutrients, CO2 & water.
Releases energy which is utilized in the formation of ATP (Adenosine Triphosphate) : Oxidative phosphorylation.
Hence, mitochondria are called as powerhouse of cell.
Intracellular vesicle surrounded by a lipoprotein unit membrane.
Filled with a large number of small granules which are aggregates of digestive enzymes(approx. 40 types of hydrolytic enzymes)
Also called suicidal bags.
FUNCTIONS OF LYSOSOMES:-
These digestive enzymes can digest proteins, nucleic acid, mucopolysaccharides , glycogen etc.
Paired cylindrical organelles composed mainly of tubulin protein.
Centrosome comprises of two centrioles surrounded by pericentriolar material.
Situated near the nucleus
FUNCTION OF CENTRIOLES :-
Important role in cell division.
Many cells contain fine tubular structures called microtubules which are arranged in bundles.
FUNCTIONS OF MICROTUBULES:-
Provides rigid physical structures for certain parts of cells like cilia.
They are also responsible for movements in cytoplasm.
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Attribution of images :-
Image of nucleus – By Mariana Ruiz LadyofHats
Image of Golgi bodies – By Kelvinsong – Own work, CC BY 3.0,