Present in the protoplasm these organelles play am eminent role

  • NUCLEUS
  • It is a rounded, oval structure found in the middle of the cell
  • It is the controlling body of the cell and works as the head of the cell
  • It is differentiated into four parts-nuclear membranes, nucleoplasm, nucleolus and chromatin
  • NUCLEAR MEMBRANE
  • It is the double-layered membrane surrounding the nucleus of a eukaryotic cell, separating the nucleoplasm from the cytoplasm
  • It has minute pores knows the nuclear pores through which exchange of substance between the nucleus and cytoplasm takes place
  • NUCLEOPLASM
  • It is a clear gel-like ground matrix containing ions, proteins, nucleotides and ribosomes.
  • Chromatin threads and nucleolus are also embedded in it
  • NUCLEOLUS
  • It is a small ball-like structure   in the nucleus and is composed of a large amount of RNA, protein and some amount of DNA
  • Usually present as one, but sometimes more than one nucleolus is present
  • It is formed of four parts namely granular part (pars granulosa), amorphous matrix (consisting of homogeneous proteinaceous ground substance) and nucleolar chromatin(rRNA) and genes of nucleolar organising regions

CHROMATIN

  • Chromatin is made up of nucleic acid and a basic protein called histones
  • Chromatin is composed of nucleosomes which contain eight histone molecules around which DNA is wrapped
  • During cell division, chromatin condenses into chromosomes
  • Some portion of chromatin takes darker stain during interphase called heterochromatin
  • While other lightly stained parts are called euchromatin

MITOCHRONDRIA

  • Another name of the mitochondria is called the powerhouse of the cell because it provides energy for associated chemical reactions within the body
  • It is bounded by two membranes E.G the outer (smooth) and the inner (growth unto folds called cisternae) membranes
  • It also contains circular DNA along with RNA
  • The enzyme of the kerb’s cycle is present in the matrix of the/e mitochondria
  • Out of four phases of cellular respiration, all except glycolysis takes place in the mitochondria
  • The result of cellular respiration i.e., ATP molecules are accumulated within the mitochondria

ENNDOPLASMIC RETICULUM

  • These are membrane-bound channels seen in the network of delicate strands and vesicles in the cytoplasm. These are of two types
  • Rough endoplasmic reticulum [RER]: which is rough due to the presence of ribosomes on the surface
  • They aid in protein synthesis [RER]
  • Smooth endoplasmic reticulum [SER]: which is smooth as ribosomes are absent on the surface
  • It helps in lipid and steroid synthesis

GOLGI COMPLEX

  • The Golgi apparatus is the processing, packaging and secreting organelle of the cell
  • It is also known as the traffic police of the cell
  • It is a system of membranes, made up of flattened sac-like structures called cisternae
  • In plants, it is known as dictyosomes

LYSOSOMES:

  • These are single membrane-bound structure, supposed to contain hydrologic enzymes in them
  • During the presence of hydrolytic enzymes, these are also called the suicidal bags of the cells
  • These are the site of protein digestion
  • They are also the site of food digestion in the cell and of bacterial digestion in phagocytes
  • Lysosomal enzymes function at acidic medium
  • Hurler’s disease is the result of the accumulation of glycosaminoglycan due to the absence of alpha L-iduronates enzyme in the lysosome

RIBOSOMES:

  • These are small non-membranous RNA-protein complexes that are necessary for the protein synthesis hence called the protein factory of the cell
  • These are present in both prokaryotes as well as in eukaryotes
  • In low concentration of mg2+ ion, these are separated into two sub-units

CENTROSOME

  • Generally, it is found in animal cells.
  • During the cell division, it is divided into two parts of centrioles which move towards two opposite poles
  • They form mitotic spindle during cell division and is an important constituent of flagella and cilia

VACUOLES

  • These are surrounded by a single unit membrane called tonoplast and are filled with a liquid substance
  • A single large vacuole is present in plants, while in animals it is absent or is very small in size
  • It is known as a storage house of the vell in which minerals such as sugars, organic acids, O2 and CO2 are present
  • They maintain the turgidity of the plants.
  • Anthocyanin, a type of pigment is found in it

PLASTIDS

  • It is present only in plant cells
  • Plastids develop from colourless precursors called proplastids
  • Depending upon their colour, plastids are of the following types

CHLOROPLAST:

  • They are greenish plastids that possess photosynthetic pigments such as chlorophyll-alpha and b xanthophyll and carotenoids
  • The chloroplast is bounded by two-unit membranes
  • Chloroplast contains thylakoids, arranged in stacks called grana and a liquid called stroma
  • Stromal lamellae interconnect thylakoids of different grana
  • Chlorophyll pigment, responsible for photosynthesis is present on the grana surface

LEUCOPLAST

  • These are colourless plastids that are found in underground roots and stems
  • These store food and are of three types amyloplast, elaioplast, aleuroplast or proteoplast

CHROMOPLAST:

  • They are coloured plastids that are found in coloured parts of flowers, leaves, petals, fruits etc
  • These are found in the form of lycopene in tomato, carotene in carrot
A basic cell structure

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