Cell Structure and Function

Basic Unit of Life: Cells are the fundamental building blocks of all living organisms.
Types of Cells:
- Prokaryotic: Lack a nucleus; smaller, simpler (e.g., bacteria).
- Eukaryotic: Have a nucleus; larger, more complex (e.g., plant and animal cells).
Cell Membrane:
- Semi-permeable barrier controlling movement of substances in and out.
- Composed of a phospholipid bilayer with embedded proteins.

Metabolism: All chemical reactions occurring within the cell, including energy production and biosynthesis.
Transport Mechanisms:
- Passive Transport: Movement without energy (e.g., diffusion, osmosis).
- Active Transport: Movement requiring energy (e.g., sodium-potassium pump).
Protein Synthesis:
- DNA in the nucleus is transcribed to mRNA, which is translated at ribosomes to form proteins.

Signal Transduction: Process by which cells respond to external signals through receptors.
Types of Signaling:
- Autocrine: Signals act on the same cell.
- Paracrine: Signals act on nearby cells.
- Endocrine: Hormones travel through the bloodstream to distant cells.
Cell-Cell Communication:
- Via gap junctions (direct connections) or chemical signals.

Mitosis: Process of somatic cell division resulting in two identical daughter cells.
- Phases: Prophase, Metaphase, Anaphase, Telophase.
Meiosis: Reduction division producing gametes with half the chromosome number.
- Essential for sexual reproduction; involves two rounds of division (Meiosis I and II).
Cell Cycle:
- Phases include Interphase (G1, S, G2) and Mitotic phase (M).

Nucleus: Contains genetic material (DNA); site of transcription.
Mitochondria: Powerhouse of the cell; site of ATP (energy) production via cellular respiration.
Ribosomes: Sites of protein synthesis; found free in cytoplasm or attached to the rough endoplasmic reticulum.
Endoplasmic Reticulum (ER):
- Rough ER: Studded with ribosomes; synthesizes proteins.
- Smooth ER: No ribosomes; synthesizes lipids and detoxifies.
Golgi Apparatus: Modifies, sorts, and packages proteins and lipids for secretion or use within the cell.
Lysosomes: Contain enzymes for digestion of macromolecules and waste.
Chloroplasts (in plants): Site of photosynthesis; convert light energy into chemical energy.
Cytoskeleton: Provides structural support, maintains cell shape, and facilitates movement (includes microtubules, microfilaments, and intermediate filaments).

Cells are the fundamental building blocks of all living organisms.
Prokaryotic cells are smaller and simpler, lacking a nucleus, with examples including bacteria.
Eukaryotic cells are larger and more complex, containing a nucleus; examples include plant and animal cells.
The cell membrane is a semi-permeable barrier that regulates the movement of substances, composed of a phospholipid bilayer with embedded proteins.

Metabolism encompasses all chemical reactions occurring within the cell, including energy production and biosynthesis.
Passive transport involves the movement of substances without energy expenditure, such as diffusion and osmosis.
Active transport requires energy to move substances against their concentration gradient, exemplified by the sodium-potassium pump.
Protein synthesis begins with DNA transcription to mRNA in the nucleus, followed by translation at ribosomes to produce proteins.

Signal transduction is the mechanism through which cells interpret and respond to external signals via receptors.
Autocrine signaling allows cells to affect themselves, while paracrine signaling influences nearby cells, and endocrine signaling involves hormones traveling through the bloodstream.
Cell-cell communication occurs through gap junctions for direct connections or through chemical signaling pathways.

Mitosis results in two identical daughter cells through multiple phases: Prophase, Metaphase, Anaphase, and Telophase.
Meiosis is a reduction division producing gametes with half the chromosome number necessary for sexual reproduction, involving two rounds of division: Meiosis I and II.
The cell cycle consists of Interphase (subdivided into G1, S, and G2) and the Mitotic phase (M).

The nucleus houses genetic material (DNA) and is the site for transcription of RNA.
Mitochondria are known as the powerhouse of the cell, responsible for ATP production through cellular respiration.
Ribosomes are the sites of protein synthesis, existing freely in the cytoplasm or attached to the rough endoplasmic reticulum (RER).
The rough endoplasmic reticulum synthesizes proteins, while the smooth endoplasmic reticulum synthesizes lipids and detoxifies harmful substances.
The Golgi apparatus modifies, sorts, and packages proteins and lipids for transport inside or outside the cell.
Lysosomes contain digestive enzymes that break down macromolecules and cellular waste.
Chloroplasts, found in plants, are responsible for photosynthesis, converting light energy into chemical energy.
The cytoskeleton provides structural support, maintains cell shape, and facilitates movement, consisting of microtubules, microfilaments, and intermediate filaments.