Cell Organelles — Revision Notes

⚡ 30-Second Revision

Nucleus: — Control center, contains DNA, nuclear envelope (double membrane), nuclear pores, nucleolus (rRNA synthesis).
Mitochondria: — 'Powerhouse', aerobic respiration, ATP synthesis, double membrane, cristae, matrix, semi-autonomous.
Chloroplasts: — Photosynthesis, double membrane, thylakoids, grana, stroma, semi-autonomous (plants/algae).
Endoplasmic Reticulum (ER): — Network of cisternae/tubules.

- RER: Ribosomes, protein synthesis/secretion. - SER: Lipid synthesis, detoxification, $Ca^{2+}$ storage.

Golgi Apparatus: — Modifies, sorts, packages proteins/lipids from ER.
Lysosomes: — 'Suicidal bags', hydrolytic enzymes (acidic pH), intracellular digestion.
Vacuoles: — Storage, turgor pressure (large central in plants).
Ribosomes: — Protein synthesis, non-membranous, 80S (eukaryotes), 70S (prokaryotes, mitochondria, chloroplasts).
Cytoskeleton: — Microtubules, microfilaments, intermediate filaments; cell shape, movement, transport.
Centrosome/Centrioles: — Non-membranous, '9+0' arrangement, spindle formation (animal cells).
Peroxisomes: — Detoxification, $H_2O_2$ metabolism (catalase).

2-Minute Revision

Cell organelles are specialized compartments within eukaryotic cells, each with distinct functions. The nucleus, enclosed by a double membrane, houses DNA and controls cell activities, with the nucleolus synthesizing ribosomes.

Mitochondria are the double-membraned 'powerhouses' generating ATP via aerobic respiration, characterized by inner folds called cristae. Chloroplasts, also double-membraned, perform photosynthesis in plants, containing thylakoids stacked into grana.

Both mitochondria and chloroplasts are semi-autonomous, possessing their own DNA and ribosomes. The Endoplasmic Reticulum (ER) is a network: Rough ER (RER) synthesizes proteins for secretion, while Smooth ER (SER) synthesizes lipids and detoxifies.

The Golgi apparatus modifies, sorts, and packages ER products. Lysosomes contain acidic hydrolytic enzymes for waste breakdown. Vacuoles store substances and maintain turgor, especially the large central vacuole in plants.

Ribosomes are non-membranous protein factories. The cytoskeleton provides structural support and aids movement. Centrosomes with centrioles (non-membranous) organize microtubules for cell division in animal cells.

Peroxisomes handle oxidative reactions and detoxification.

5-Minute Revision

A comprehensive understanding of cell organelles is crucial for NEET. Start by categorizing them: membrane-bound (single vs. double) and non-membranous. Double-membraned organelles include the nucleus (genetic control, rRNA synthesis in nucleolus), mitochondria (ATP production via aerobic respiration, inner cristae for surface area), and chloroplasts (photosynthesis in plants, thylakoids/grana).

Both mitochondria and chloroplasts are semi-autonomous, possessing their own 70S ribosomes and circular DNA, supporting the endosymbiotic theory. Single-membraned organelles are part of the endomembrane system: the Endoplasmic Reticulum (ER), a network of cisternae, has two types: Rough ER (RER), studded with 80S ribosomes, synthesizes and processes proteins destined for secretion or membranes; Smooth ER (SER), lacking ribosomes, synthesizes lipids, detoxifies drugs, and stores calcium.

Products from the ER move to the Golgi apparatus, which further modifies, sorts, and packages them into vesicles. Lysosomes, containing acid hydrolases, are the cell's recycling centers, breaking down waste and cellular debris.

Vacuoles are storage sacs, notably the large central vacuole in plant cells for turgor maintenance. Other single-membraned organelles include peroxisomes, which detoxify substances using enzymes like catalase.

Non-membranous organelles include ribosomes (protein synthesis, 80S in cytoplasm/RER, 70S in mitochondria/chloroplasts/prokaryotes), the cytoskeleton (microtubules, microfilaments, intermediate filaments for shape, movement, transport), and centrosomes with centrioles (in animal cells, for spindle formation during cell division, showing a '9+0' microtubule arrangement).

Remember the '9+2' arrangement for cilia and flagella. Focus on distinguishing features, such as the presence of a cell wall, chloroplasts, and a large central vacuole in plant cells versus centrioles in animal cells.

Practice tracing pathways (e.g., protein secretion) and comparing functions (e.g., RER vs. SER, mitochondria vs. chloroplasts) to solidify your knowledge.

Prelims Revision Notes

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Nucleus: — Double membrane (nuclear envelope with pores). Contains chromatin (DNA + proteins) and nucleolus. Nucleolus: site of rRNA synthesis and ribosome assembly. Controls cell activities.
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Mitochondria: — Double membrane. Outer membrane smooth, inner membrane folded into cristae (increases surface area). Matrix contains enzymes for Krebs cycle, mitochondrial DNA, 70S ribosomes. Site of aerobic respiration and ATP synthesis. Semi-autonomous.
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Chloroplasts: — Double membrane (in plants/algae). Inner membrane encloses stroma. Stroma contains thylakoids (flattened sacs) stacked into grana. Contains chlorophyll. Site of photosynthesis. Chloroplast DNA, 70S ribosomes. Semi-autonomous.
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Endoplasmic Reticulum (ER): — Network of cisternae, tubules, vesicles. Continuous with outer nuclear membrane.

* Rough ER (RER): Ribosomes on surface. Protein synthesis (secretory, membrane proteins), folding, glycosylation. * Smooth ER (SER): No ribosomes. Lipid synthesis (steroids, phospholipids), detoxification, $Ca^{2+}$ storage.

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Golgi Apparatus: — Stack of flattened sacs (cisternae) – cis, medial, trans faces. Modifies, sorts, packages proteins/lipids from ER into vesicles.
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Lysosomes: — Single membrane. Contain acid hydrolases (active at acidic pH). Intracellular digestion, autophagy, waste breakdown.
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Vacuoles: — Single membrane. Storage (water, nutrients, waste). Large central vacuole in plants maintains turgor pressure.
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Ribosomes: — Non-membranous. Composed of rRNA and proteins. Site of protein synthesis. Eukaryotic (cytoplasmic/RER) are 80S (60S+40S). Prokaryotic, mitochondrial, chloroplast are 70S (50S+30S).
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Cytoskeleton: — Network of protein filaments.

* Microtubules: Tubulin protein. Cell shape, intracellular transport, cilia/flagella (9+2), spindle fibers. * Microfilaments (Actin): Actin protein. Muscle contraction, cell motility, cytokinesis. * Intermediate Filaments: Diverse proteins. Mechanical strength, anchor organelles.

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Centrosome/Centrioles: — Non-membranous (animal cells, lower plants). Centrosome = 2 perpendicular centrioles. Centrioles: '9+0' microtubule triplets. Form basal bodies of cilia/flagella, organize spindle fibers.
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Peroxisomes: — Single membrane. Contain oxidases and catalase. Detoxification, fatty acid breakdown, $H_2O_2$ metabolism.

Key Differences: Plant cells have cell wall, chloroplasts, large central vacuole. Animal cells have centrioles.

Vyyuha Quick Recall

To remember the functions of the Endomembrane System: 'E.R. G.L.V. P.M.'

E.R. — (Endoplasmic Reticulum): Exports Raw proteins/lipids.
G. — (Golgi): Grooms and Graduates (modifies, sorts, packages).
L. — (Lysosomes): Lyses (breaks down) waste.
V. — (Vacuoles): Volume control and Vault (storage).
P.M. — (Plasma Membrane): Protects and Manages entry/exit.