2.1 & 2.2 Notes

Gene Function: Genes are fundamental in directing the production of proteins, which are critical for various cellular processes and life itself.
Cellular Machinery Analogy: The cell's internal machinery acts like a factory, with specialized parts designed to produce specific substances based on the genetic instructions (genes).

Function: Ribosomes are responsible for synthesizing proteins.
Structure: They are the smallest cellular components involved in protein synthesis and are not membrane-bound organelles.
Types:
- Eukaryotic Ribosomes: Referred to as $80S$ .
- Prokaryotic Ribosomes: Referred to as $70S$ .
- The primary difference between $70S$ and $80S$ ribosomes is solely their size.

Origin: The system originates from the nuclear membrane, which can pinch off to form other membrane-bound organelles, analogous to soap bubbles fusing or growing.
Composition: The entire system is interconnected and called the endomembrane system, composed of several components, all with similar membrane structures.
Endoplasmic Reticulum (ER): A system of interconnected tunnels.
- Smooth ER: Primarily deals with the synthesis and metabolism of fats and lipids, not proteins.
- Rough ER: Involved in protein synthesis and modification, covered with ribosomes.
Golgi Apparatus (Golgi Body/Complex):
- Structure: Composed of flattened sacs (cisternae) that receive, modify, and package proteins and lipids.
- Cis-face: The receiving end where vesicles from the ER fuse, releasing their contents.
- Processing: Contents are passed through a series of tubes within the Golgi, undergoing modifications (e.g., converting a precursor protein into functional keratin, mucin, insulin, or other hormones).
- Trans-face: The "shipping" side of the Golgi apparatus, from which modified proteins and lipids are packaged into new vesicles for transport to their final destinations within or outside the cell.
- Secretory Vesicles: Vesicles bud off from the trans-face, carrying their contents to the plasma membrane for exocytosis (secretion outside the cell) or to other organelles.

Lysosomes:
- Function: Contain digestive enzymes that break down waste materials and cellular debris, foreign invaders like bacteria, and worn-out organelles.
- Formation: Formed by budding from the Golgi apparatus.
- Analogy: Act as the cell's recycling and waste disposal units.
Peroxisomes:
- Function: Contain enzymes that perform various metabolic functions, including breaking down fatty acids and detoxifying harmful substances (e.g., alcohol in liver cells).
- By-product: Produce hydrogen peroxide ( $H<em>2O</em>2$ ) as a by-product, which is then converted into water and oxygen by other enzymes within the peroxisome.

Function: Membrane-bound sacs involved in storage and waste removal.
- Central Vacuole (Plants):
- Large, single vacuole, can occupy $30\%$ to $80\%$ of cell volume.
- Stores water, nutrients, waste products, and pigments.
- Maintains turgor pressure against the cell wall, providing structural support.
- Small Vacuoles (Animals and Fungi):
- More numerous and smaller.
- Involved in temporary storage or transport.
- Phagocytic vacuoles formed during endocytosis.

Function: Contains the cell's genetic material (DNA) and controls cell growth, metabolism, and reproduction by regulating gene expression.
Structure:
- Nuclear Envelope: A double membrane that surrounds the nucleus, perforated by nuclear pores.
- Nuclear Pores: Regulate the passage of macromolecules (proteins, RNA) between the nucleus and the cytoplasm.
- Nucleolus: A dense structure within the nucleus where ribosomal RNA (rRNA) is synthesized and assembled with proteins to form ribosomal subunits.
- Chromatin: The complex of DNA and proteins (histones) that forms chromosomes within the nucleus. The DNA contains the genes.
- Euchromatin: Loosely packed chromatin, active in gene transcription.
- Heterochromatin: Tightly packed chromatin, largely inactive.

Function: The "powerhouses" of the cell, responsible for generating most of the cell's supply of adenosine triphosphate (ATP), used as a source of chemical energy. This process is called cellular respiration.
Structure:
- Outer Membrane: Smooth and permeable to small molecules.
- Inner Membrane: Highly folded into structures called cristae, increasing the surface area for ATP synthesis. Contains electron transport chain components.
- Matrix: The innermost compartment, containing enzymes for the Krebs cycle, mitochondrial DNA, and ribosomes.
Significance: Essential for fueling all cellular processes, including protein synthesis, transport, and other metabolic activities.