Ribosomes

• Comprise ribosomal RNA (rRNA) and proteins, forming two subunits: large and small.

• Synthesize proteins according to mRNA sequences, crucial for cellular function.

• Present in all forms of life, indicating common ancestry and evolutionary significance.

• Binding Sites on Ribosomes:

  • Small Subunit: Binds mRNA for translation, enabling the decoding of genetic information.

  • Large Subunit: Binds tRNA at A (aminoacyl), P (peptidyl), and E (exit) sites during translation, facilitating protein assembly.

Endoplasmic Reticulum (ER)

Types of ER

• Rough ER:

  • Studded with membrane-bound ribosomes, giving it a rough appearance.

  • Functions:

    • Compartmentalizes the cell, enhancing efficiency in biochemical processes.

    • Synthesizes proteins destined for secretion or incorporation into membranes.

• Smooth ER:

  • Lacks ribosomes, resulting in a smooth appearance.

  • Functions:

    • Detoxification of drugs and poisons, particularly in liver cells.

    • Lipid synthesis, including phospholipids and cholesterol, vital for membrane integrity.

    • Storage of calcium ions (Ca2+), essential for muscle contraction and signaling.

Golgi Complex

• Membrane-bound structure with flattened sacs known as cisternae.

• Functions:

  • Folding and chemical modification of newly synthesized proteins, such as glycosylation and phosphorylation.

  • Packaging proteins into transport vesicles for trafficking to various parts of the cell, including lysosomes, cell membrane, or secretion outside the cell.

Mitochondria

• Characterized by a double membrane:

  • Outer membrane: Smooth and permeable to small molecules and ions.

  • Inner membrane: Highly convoluted, forming folds called cristae, which increase surface area for metabolic reactions.

• Function: ATP production through oxidative phosphorylation, an essential energy currency of the cell.

Lysosomes

• Membrane-enclosed organelles filled with hydrolytic enzymes (acid hydrolases).

• Function: Digests macromolecules and defective organelles (process known as autophagy), helping maintain cellular hygiene by recycling components and clearing waste.

Vacuoles

• Membrane-bound sacs serving varying functions based on cell type.

• In plants, a large specialized central vacuole plays a critical role in maintaining turgor pressure, storing nutrients, and sequestering waste products.

Chloroplasts

• Specialized organelles in photosynthetic plants and algae, enabling the conversion of solar energy into chemical energy.

• Composed of a double membrane and contain thylakoids arranged in stacks called granum.

• Roles: Integral to photosynthesis, converting light energy into ATP and NADPH, used in the Calvin Cycle for sugar synthesis.

Roles of Organelles

• Smooth ER: Detoxification and storage of calcium ions (Ca2+), vital for various cellular processes.

• Golgi Bodies: Modification and sorting of proteins, preparing them for secretion or delivery to organelles.

• Lysosome: Digestion of macromolecules, contributing to intracellular digestion and waste processing.

• Vacuole: Maintains turgor pressure in plant cells, essential for structural integrity and growth.

Ribosome Locations

• Bound Ribosomes: Attached to the Rough ER; synthesize proteins for secretion or for inclusion in cellular membranes.

• Free Ribosomes: Located in the cytosol; synthesize cytosolic proteins that function within the cell itself.

Mitochondria and ATP Synthesis

• Cristae: Inner membrane folds where the electron transport chain occurs, crucial for ATP generation.

• Generates a proton gradient utilized by ATP synthase for ATP production, linking cellular respiration with energy supply.

Chloroplasts and ATP Synthesis

• Thylakoids: Membranous structures where light-dependent reactions occur, generating ATP and NADPH for the Calvin Cycle.

• Central to plant metabolism and energy storage, enabling growth and reproduction in plants.

Central Vacuole in Plant Cells

• Maintains turgor pressure through the storage of water, crucial for plant structure and stability.

• Stores nutrients, enzymes, and waste products, serving as a reservoir of chemical resources for the cell.

Food Vacuoles and Lysosomes

• Food vacuoles formed during phagocytosis fuse with lysosomes to digest food materials, contributing to nutrient acquisition in single-cell organisms.

Transport Vesicles

• Formed from the Rough ER and Golgi, transport materials throughout the cell, acting as carriers for modified proteins and lipids.

Contractile Vacuoles in Osmoregulation

• Found in protists living in hypotonic environments; expel excess water to prevent lysis, maintaining osmotic balance.

Composition of Ribosomes

• Ribosomes consist of rRNA and proteins; they assemble large and small subunits necessary for protein synthesis.

Types of RNA

• mRNA: Messenger RNA, carries the codon sequence from DNA to ribosomes for translation.

• rRNA: Ribosomal RNA, a structural component of ribosomes that plays a key role in translation.

• tRNA: Transfer RNA, brings specific amino acids to the ribosome during protein synthesis, matching codons with the corresponding amino acids.

Ribosomes and Protein Synthesis

• Free ribosomes synthesize cytosolic proteins that function within the cell.

• Rough ER ribosomes synthesize proteins for secretion or membrane integration, linking to cellular functions and communication.

Relationship Between Ribosomes, Rough ER, and Golgi

• The ribosome binds to mRNA; if membrane-bound, it moves to Rough ER where synthesization occurs.

• The Rough ER packages proteins into vesicles that are sent to the Golgi for further modification before their final destination.

Intracellular Digestion

• The lysosome's role in cellular digestion stems from its hydrolytic enzymes, breaking down complex molecules and recycling cellular components for reuse.