Cell : The Unit of Life

Mitochondria, Plastids, Ribosomes,Cytoskeleton


  • Mitocondria is also called as powerhouse of the cell as they produce 95% of ATP.
  • It is considered as semi - autonomous organelle because it has separate protein syntheeizing machinery (ribosomes & proteins) independent of nuclear control.
  • It was first observed in striated muscles of insects as granules by kolliker (1880), he called them as "sarcosomes".
  • Each mitocondria is a double membrane-bound structure. The inner compartment is called as matrix. The inner membrane forms a number of infoldings called the cristae (singular crista) towards the matrix. (Crista increases the surface area).
  • Oxysomes have ATPase enzyme molecules. so it is responsible for ATP synthesis. These are the functional unit of mitocondria. These elementary particles are also called F0 − F1 particles.
  • Intermediate products of cell respiration are used in the formation of steroids, cytochromes, chlorophyll etc.
  • Mitocondria contain electron transport system. The second step of cellular respiration (energy formation) takes place in mitocondria
  • Plastids are semi-autonomous organelle having DNA, RNA, ribosomes and double membrane envelope. These are largest cell organelles in plant cell.
  • Haeckel (1865) discovered plastid, but the term first used by schimper (1883).
  • Plastids of three types namely Leucoplasts, chromoplasts, and chloroplast.
  • Leucoplasts are colourless plastids.
    Eg:- Amyloplast - synthesize & store starch grain
    Elaioplast (lipidoplast, oleoplast) - store lipids & oils.
    Aleuroplast (proteinoplast) - store proteins.
  • Chromoplast are coloured plastids other than green. They are in red, orange, yellow etc colours are due to the presence of carotenoid they are present in petals & fruits.
  • Chloroplast are double membrane bound organelle and green coloured plastids due to the presence of chlorophyll.
  • They have various shape.
    Cup shaped → Eg :- Chlamydomonas sp.
    Stellate shaped → Eg :- Zygonema.
    Collar (or) gridle → ulothrix.
    Spiral (or) ribbon → Spirogyra
    Reticulate / net → oedogonium
    Discoid → Voucheria
    Spherical → Chlorella
    Biconvex/ovoid → Angiosperm.
  • Chlorophyll a, b, c, d are types of the pigment.
    Chlorophyll a : C55 H72 O5 N4 Mg (with methyl group).
    Chlorophyll b : C55 H70 O6 N4 Mg (with aldehyde group)
    Chlorophyll c : C35 H32 O5 N4 Mg
    Chlorophyll d : C54 H70 O6 N4 Mg
  • Ribosomes are smallest known organelle without membrane. They are known as organelle within organelle. (because it is also present in ER).
  • Types of ribosomes are are 70s and 80s. 70s is present in prokaryotes, mitocondria and plastids of eukaryotes. 80s ribosomes are found in cytoplasm of eukaryotes.
  • Levine and good enough (1874) observed 77s ribosomes in fungal mitocondria, 60s libosome in animal mitocondria and 55s in mammalian mitocondria.
  • Ribosomes are also called as protein factories of the cell enzyme peptidys transferase occurs in large subunit of ribosome which helps in protein synthesis.
  • Cytoskeleton are framework of fibrous elements became necessary to support the extensive system of membranes. They are of three types namely microtubules, microfilament and intermediate filament.
  • Microfilaments are present in the microvilli, misele fibre (called myofilament) etc. But these are absent in prokaryotes. They are mainly formed of actin (contractile protein).
  • Microfilaments forms a part of cytoskeleton and change the cell shape, motility and division during development.
  • Microtubules are electron microscopic structure found only in the eukaryotic cellular structure like cilia, filagella, centriole basal body, astral fibres, spindle fibres. They are formed of tubulin protein.
  • Microtubules of asters and spindle fibres of the mitotic apparatus helps in movement of chromosomes towards the opposite poles in cell division
  • Intermediate filaments are supportive elements in the cytoplasm of the eukaryotic cells but they are absent in RBC (mammeals) IFs are larger then the microfilaments. (~ 10nm thick)
  • If provide support to myofibrils which is essential for their contraction.

View this video for the topics Mitochondria, Plastids & Ribosomes from 18:18 to 53:23

View this video for the topic Cytoskeleton from 0:13 to 6:45

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