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 peptidyl 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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