Mitochondria and Plastids — Revision Notes

⚡ 30-Second Revision

Mitochondria — Powerhouse, aerobic respiration, ATP synthesis. Double membrane, inner membrane folded into cristae. Matrix contains Krebs cycle enzymes, circular DNA, 70S ribosomes. Replicates by binary fission.
Plastids — Plant/algae organelles. Double membrane, circular DNA, 70S ribosomes. Originate from proplastids.

- Chloroplasts: Photosynthesis. Thylakoids (light reactions), stacked into grana. Stroma (Calvin cycle). - Chromoplasts: Color (carotenoids), e.g., fruits/flowers. - Leucoplasts: Colorless, storage. Amyloplasts (starch), Elaioplasts (oils), Aleuroplasts (proteins).

Semi-autonomous — Own DNA & ribosomes, but nuclear control.
Endosymbiotic Theory — Origin of both from engulfed prokaryotes.

2-Minute Revision

Mitochondria and plastids are crucial double-membraned organelles in eukaryotic cells, both sharing a semi-autonomous nature due to their own circular DNA and 70S ribosomes, supporting the endosymbiotic theory.

Mitochondria are the 'powerhouses,' generating ATP through aerobic respiration. Their inner membrane forms cristae, maximizing surface area for the electron transport chain and ATP synthase in the matrix.

Plastids are diverse, primarily in plants. Chloroplasts perform photosynthesis, converting light energy into glucose using chlorophyll in their thylakoid membranes (light reactions) and the stroma (Calvin cycle).

Chromoplasts provide color, while leucoplasts (like amyloplasts) store substances such as starch. Understanding their distinct structures and the specific locations of their metabolic pathways (e.g., Krebs cycle in mitochondrial matrix, light reactions on thylakoids) is key for NEET.

5-Minute Revision

Let's consolidate the core concepts of mitochondria and plastids, vital for NEET. Both are double-membraned organelles, believed to have evolved via the endosymbiotic theory, evidenced by their possession of circular DNA and 70S ribosomes, similar to prokaryotes. This also makes them semi-autonomous, capable of self-replication and synthesizing some proteins, yet largely controlled by the nuclear genome.

Mitochondria: These are the cellular 'powerhouses,' responsible for aerobic respiration. Structurally, they have a smooth outer membrane and a highly folded inner membrane, forming cristae. These cristae dramatically increase the surface area for the electron transport chain (ETC) and ATP synthase, crucial for oxidative phosphorylation.

The inner compartment, the matrix, houses enzymes for the Krebs cycle and fatty acid oxidation. Thus, glucose breakdown leads to ATP generation.

Plastids: Found in plants and algae, these are a diverse group originating from proplastids, capable of interconversion.

1
Chloroplasts — The most important, carrying out photosynthesis. They have an outer and inner membrane, enclosing the stroma. Within the stroma are flattened sacs called thylakoids, which stack to form grana. The light-dependent reactions occur on the thylakoid membranes (chlorophyll captures light, ATP and NADPH are produced), while the light-independent reactions (Calvin cycle) occur in the stroma (CO$_2$ fixation to glucose).
2
Chromoplasts — Contain non-photosynthetic pigments (carotenoids), giving color to fruits and flowers.
3
Leucoplasts — Colorless storage plastids. Amyloplasts store starch (e.g., potato), Elaioplasts store oils, and Aleuroplasts store proteins.

Key Differences: Mitochondria respire (break down glucose, produce ATP), while chloroplasts photosynthesize (synthesize glucose, consume light). Their internal structures (cristae vs. thylakoids/grana) are adapted for their specific energy conversions.

Remember the specific locations of metabolic pathways: Krebs cycle in mitochondrial matrix, ETC on inner mitochondrial membrane; light reactions on thylakoid membranes, Calvin cycle in chloroplast stroma.

This detailed understanding is crucial for NEET.

Prelims Revision Notes

Mitochondria & Plastids: NEET Quick Recall

I. Mitochondria (Powerhouse of the Cell)

Structure — Double-membraned.

* Outer Membrane: Smooth, permeable (porins). * Inner Membrane: Highly folded into cristae (increases surface area). * Intermembrane Space: Between outer and inner membranes. * Matrix: Inner fluid-filled space. Contains: * Circular, double-stranded DNA (mtDNA). * 70S ribosomes. * Enzymes for Krebs cycle, fatty acid oxidation.

Function — Aerobic respiration, ATP synthesis (oxidative phosphorylation).

* Krebs Cycle: Occurs in matrix. * Electron Transport Chain (ETC) & ATP Synthase: Located on inner mitochondrial membrane (cristae).

Replication — By binary fission.

II. Plastids (Plant/Algae Organelles)

Origin — All develop from proplastids.
Structure — Double-membraned. Possess circular, double-stranded DNA (cpDNA) and 70S ribosomes.
Types & Functions

1. Chloroplasts: Green, site of photosynthesis. * Outer & Inner Membrane: Envelope. * Stroma: Fluid-filled space. Contains: * Circular DNA, 70S ribosomes. * Enzymes for Calvin cycle (light-independent reactions).

* Thylakoids: Flattened sacs, contain chlorophyll. Site of light-dependent reactions. * Grana (singular: Granum): Stacks of thylakoids. * Stromal Lamellae: Connect grana. 2. Chromoplasts: Colored (red, orange, yellow) due to carotenoids.

Found in fruits, flowers. Attract pollinators/dispersers. 3. Leucoplasts: Colorless, storage plastids. * Amyloplasts: Store starch (e.g., potato). * Elaioplasts: Store oils/fats. * Aleuroplasts (Proteinoplasts): Store proteins.

Interconversion — Plastids can interconvert (e.g., chloroplasts to chromoplasts during ripening).

III. Semi-Autonomous Nature & Endosymbiotic Theory

Both mitochondria and plastids are semi-autonomous because they have their own DNA and ribosomes, can synthesize some proteins, and replicate independently. However, they are dependent on nuclear genes for many proteins.
Endosymbiotic Theory Evidence — Double membrane, circular DNA, 70S ribosomes, binary fission, genetic similarity to bacteria.

Vyyuha Quick Recall

My Cell Powers Store Light:

Mitochondria: Powerhouse (ATP)
Chloroplasts: Sunlight (Photosynthesis)
Leucoplasts: Storage (Starch, Oil, Protein)