TYPES OF RIBOSOMES

FREE RIBOSOMES: Free ribosomes are found in the cytoplasm of the cell. They occur as single ribosomes or as groups called polysomes or polyribosomes. Synthesize those proteins that are important for the formation of cell structure units. BOUND RIBOSOMES: Bound ribosomes are present in the membrane of RER. The ribosomes produce proteins packed in vesicles, are exported to the exterior of the cell. NON- CYTOPLASMIC RIBOSOMES: Ribosomes are also located in the mitochondria and the chloroplast of eukaryotic cell. These ribosomes are smaller in size and resemble prokaryotic ribosomes. (70S) FUNCTION: The primary function of ribosomes is the synthesis of proteins. GOLGI APPARATUS; DISCOVERY: An italian neurologist (physician) Camillo Golgi in 1898 discovered Golgi appratus. OCCURRENCE AND DISTRIBUTION: The Golgi apparatus occurrs in all cells expect the prokaryotic cells (mycoplasmas, bacteria and blue-green algae) and eukaryotic cells of certain

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RIBOSOMES

RIBOSOMES
Ribosomes are small, dense,rounded and granular particles of the ribonucleoprotein.

DISCOVERY
Ribosomes was studied by palade in 995 for the first time.

OCCURRENCE AND DISTRIBUTION:
These are small granular structures found in prokaryotes and eukaroyets. They occur either freely in the matrix of mitochondria chloroplast and cytoplasm (i.e, cytoplasmic matrix) or remain attached with the membranes of the endoplasmic reticulum nucleus.

ROLE
They carry put proteins synthesis by translating mRNA in the polypeptide chain.

CHEMICAL COMPOSITION
Ribosomes are composed of proteins and ribosomal RNA. Ribosomal RNA in eukaryotes is a four types and three types in prokaryotes. Ribosomes are formed in the nucleolus.

STRUCTURE:
These are small cytoplasmic granules ranging from 20nm-30nm in diameter. Ribosomes are consisting of two sub units of unequal size that fit closely together.
Ribosomes found in eukaryotic cell are 80S, and prokaryotic cell are 70S.

SUBUNITS
The subunits are referred as the smaller subunits and the larger subunits. The larger subunits in eukaryotes is 60S while in prokaryotes is 50S. The smaller subunits in eukaryotes is 40S and in prokaryotes 30S.

SVEDBREG UNIT:
"S" refers to Svedbreg unit that is the sedimentation rate in ultracentrifuguation.

EUKARYOTIC RIBOSOMES:
Its smaller sub unit is 30S and Larger subunit is 50S and complex is 70S.

PROKARYOTIC RIBOSOMES: Its smaller sub unit is 40S and larger sub unit is 60S and complex is 80S.

ENDOPLASMIC RETICULUM

ENDOPLASMIC RETICULUM
Endoplasmic reticulum is an extensive network of interconnected channels and vesicles called cisternae, these membranous channels extends from the nuclear membrane into the cytoplasm. The membrane enclosed space between the cisternae is called the lumen of ER.

TYPES OF ENDOPLASMIC RETICULUM
On the basis of the presence or the absence of the ribosomes there are two types of ER

SMOOTH ENDOPLASMIC RETICULUM
The surface of smooth ER is devoid of the ribosomes, and thus called the smooth ER.

FUNCTION OF SMOOTH ENDOPLASMIC RETICULUM:

AS A TRANSPORT SYSTEM
The endoplasmic reticulum acts as an intracellular circulatory or transporting system. The channels help in the transport of material in the cell.

DETOXIFICATION OF TOXIC SUBSTANCE
Smooth ER helps in the detoxification of toxic substance in liver

LIPID METABOLISM:
Smooth ER helps in lipid metabolism.

ROUGH ENDOPLASMIC RETICULUM:
The surface of the rough ER is studded with ribosomes and thus is called as rough endoplasmic reticulum. RER is in direct contact with the nuclear membrane, and RER the nuclear membrane is also studded with ribosomes.

FUNCTION OF ROUGH ENDOPLASMIC RETICULUM:

SKELETAL FRAMEWORK:
The endoplasmic reticulum provides an ultra- structural skeleton frame work to the cell and gives mechanical support to the colloidal cytoplasmic matrix.
AS A TRANSPORT SYSTEM:
The endoplasmic reticulum acts as an intracellular circulatory or transporting system.
The channels help in the transport of material in the cell.
PROTEIN SYNTHETIC MACHINERY:
Rough ER helps in the synthesis of proteins.
FORMATION OF NUCLEAR ENVELOP:
The ER membranes from the new nuclear envelope after each nuclear division.

CHROMOSOMES

CHROMOSOMES
During cell division chromatin material becomes shorter and thicker forming chromosomes, chromosomes stains dark and under compound microscope appears to be made up of arms and centromeres.
Centromeres attached the two arms called chromatids. Centromeres has a proteins called kinetochore proteins through which chromosomes is attached to the spindle fibers during cell division.

COMPOSTION OF CHROMOSOMES:
A chromosomes is composed of DNA and proteins. (one chromosomes =one DNA molecules)

DIPLOID AND HAPLOID NUMBER OF CHROMOSOMES
The full number of chromosomes in normal body cells is diploid (2n) whereas haploid (n) is the half number of chromosomes present in germ or gamete cells. For example, human sperms and eggs have 23 each and those of Drosophila have 4 each in sperms and eggs. So in this way after fertilization the number of chromosomes remains constant in the next generation

EUCHROMATIN:
Euchromatin is the well dispersed form of chromatin which takes lighter DNA-stain and is genetically active, i.e. it is involved in gene duplication, gene transcription (DNA- dependent RNA synthesis) and morphological expression of a gene through some type of protein synthesis.

HETEROCHROMATIN:
Heterochromatin is the highly condensed form of chromatin which takes dark DNA-stain and is genetically inert. Such type of chromatin exists both in the region of centromere (called constitutive heterochromatin) and in the sex chromatin (called facultative heterochromatin) and is late replicating one.

NUCLEUS

NUCLEUS

DISCOVERY
Nucleus was for the first time described by the English Robert Brown in 1831.
OCCUERENCE AND DISTRIBUTION
Nucleus is present in all eukaryotic cells. The nucleus is centrally located and roughly spherical cellular component which controls all the vital activities of the cytoplasm and carries the heredity material the DNA in it.
CELL WITH NO NUCLEUS:
Prokaryotic have no nucleus. Mammalian erythrocytes (red blood cells) lose their nuclei when they mature.
SIZE
It is typically 10 um in diameter.
IMPORTANCE
It is one of the most important organelle because it controls all the metabolic activities and his the genetic information in the form of chromosomes and DNA.

STRUCTURE OF NUCLEUS
Nucleus consist of
1) Nuclear envelop
2) Nucleolus
3) Nucleoplasm and
4) Chromosomes
NUCLEAR ENVELOP:
The nucleus is bounded by two membranes, which together called nuclear envelope.
The outer membrane of the nuclear envelope is continuous with the endoplasmic reticulum.
NUCLEAR PORES:
Over the surface of the nuclear envelope, are shallow depressions called nuclear pores. These pores helps in the transport of the proteins into the nucleus and mRNA from nucleus into the cytoplasm.
NUMBER OF NUCLEAR PORES:
Egg cells have maximum number of pores, while minimum in RBCs.
NUCLEOLUS:
It is a granular body with in the nucleus and is not bounded by a membrane. There may be one or more nucleoli in the nucleus.
REGIONS OF NUCLEOLUS:
It is composed of two regions; the peripheral granular area composed of precursor which helps in synthesis of ribosomal sub units, and the central febrile area consisting large RNA and DNA.
NUCLEOPLASM:
The space between the nuclear envelope and the nucleolus is filled by a transparent, semi- solid granular ground substance or the matrix known as the nucleoplasm
It is a colloidal mixture of organic and inorganic salts and ions.
FUNCTION OF NUCLEOPLASM:
Nucleoplasm houses nuclear content. It also serves as storage place for enzymes, raw material needed for DNA replication and synthesis of RNA.
ROLE OF NUCLEUS:
RNA SYNTHESIS:
RNA is synthesized and stored in the nucleolus.
FORMATION OF RIBOSOMES:
Proteins imported from the cytoplasm are assembled with RNA forming ribosomal sub units. These sib units then exit the nucleus through the nuclear pores to the cytoplasm, where a large and a small sub units can assembled into a ribosome.

THE ROLE OF PROTEINS, LIPIDS AND CHLORESTOL

THE ROLE OF PROTEINS, LIPIDS AND CHOLESTEROL

PROTEINS AND THEIR ROLE:
TRANSPORT:
Transmembrane proteins from water channels through which the transport of material and ions takes place.
CELL RECOGNITION:
Extrinsic proteins help in the recognition of the cell and foreign particles.

ADHESION:
Some of the proteins help in the adhesion of cell to each other.

ROLE OF LIPIDS:
AS ANTI-FREEZE:
Unsaturated Fatty acid tails helps in protecting the cell membrane from freezing.

ROLE OF CHOLESTEROL
*) Cholesterol prevents the plasma membrane from overexpansion.
ROLE OF GLYCOLIPIDS AND GLYCOPROTEINS:
*) It helps in the formation of glycocalyx, which in some bacteria facilitate attachment to the substrate. Furthermore acts as hormone receptors.
FUNCTION OF PLASMA MEMBRANE:
CELL SHAPE:
Plasma membrane gives specific shape to the cell.
PHAGOCYTOSIS:
Plasma membrane helps in phagocytosis and pinocytosis
EXCREATION:
Plasma membrane helps in the excretion of the waste materials from the cell, (urea,uric acid etc.)
CELLULAR SECRETION:
Plasma membrane helps in the secretion of useful substances (hormones, enzymes, etc.)
Plasma membrane prevents the escape of cytoplasmic organelle from the cell.