Cell Biology Study Notes

Definition: Process by which cells communicate with each other and respond to signals.
Types:
- Autocrine signaling: Cell targets itself.
- Paracrine signaling: Cell targets nearby cells.
- Endocrine signaling: Hormones released into the bloodstream to target distant cells.
Mechanisms:
- Receptor-ligand interactions: Specific binding of signaling molecules (ligands) to cellular receptors.
- Signal transduction pathways: Sequence of events that lead to a cellular response, often involving multiple proteins and second messengers (e.g., cAMP, Ca²⁺).
Outcomes: Altered gene expression, changes in cell metabolism, cell growth, or apoptosis.

Prokaryotic Cells:
- Lack a nucleus and membrane-bound organelles.
- Contain a cell wall, plasma membrane, ribosomes, and genetic material in a nucleoid region.
Eukaryotic Cells:
- Have a nucleus and membrane-bound organelles (e.g., mitochondria, endoplasmic reticulum, Golgi apparatus).
- Larger and more complex than prokaryotic cells.
Common Organelles:
- Nucleus: Contains genetic material; site of transcription.
- Mitochondria: Powerhouse of the cell; ATP production via cellular respiration.
- Ribosomes: Sites of protein synthesis.
- Endoplasmic Reticulum: Rough ER (with ribosomes) for protein synthesis; Smooth ER for lipid synthesis.

Metabolism: All biochemical reactions within the cell, including catabolism (breaking down) and anabolism (building up).
Energy Production: Primarily through cellular respiration (glycolysis, Krebs cycle, oxidative phosphorylation).
Protein Synthesis: Translation of mRNA into polypeptides, essential for cell function and structure.
Cell Growth and Division: Controlled by the cell cycle (interphase, mitosis, cytokinesis).

Direct Communication: Gap junctions (in animal cells) and plasmodesmata (in plant cells) allow for the exchange of ions and small molecules.
Chemical Signals: Hormones and neurotransmitters act as signaling molecules to relay information.
Receptor Types:
- Membrane receptors: Bind to external ligands, activating intracellular signaling pathways.
- Intracellular receptors: Bind to ligands that can cross the plasma membrane and influence gene expression.

Structure: Phospholipid bilayer with embedded proteins, cholesterol, and carbohydrates.
Functions:
- Selective permeability: Regulates the entry and exit of substances.
- Cellular recognition: Glycoproteins and glycolipids facilitate cell-cell recognition and signaling.
- Transport mechanisms:
  - Passive transport: Diffusion and osmosis (no energy required).
  - Active transport: Requires energy to move substances against their concentration gradient (e.g., sodium-potassium pump).
Fluid Mosaic Model: Describes the plasma membrane as a dynamic structure with components that move laterally within the layer.

Process through which cells communicate and respond to signals.
Autocrine signaling: Cells communicate with themselves.
Paracrine signaling: Cells communicate with nearby cells.
Endocrine signaling: Hormones travel through the bloodstream to distant targets.
Receptor-ligand interactions: Involves the specific binding of signaling molecules to their receptors on cells.
Signal transduction pathways: Series of molecular events that pass signals from receptors to cellular responses, often utilizing second messengers like cAMP and Ca²⁺.
Cellular responses can include altered gene expression, metabolic changes, growth, or programmed cell death (apoptosis).

Prokaryotic Cells: Do not have a nucleus; lack membrane-bound organelles; genetic material located in the nucleoid; possess a cell wall and plasma membrane.
Eukaryotic Cells: Contain a nucleus and membrane-bound organelles such as mitochondria and Golgi apparatus; more complex and larger than prokaryotic cells.
Common Organelles:
- Nucleus: Site for genetic material storage and transcription.
- Mitochondria: Main site for ATP production via cellular respiration, often referred to as the powerhouse of the cell.
- Ribosomes: Responsible for protein synthesis (translation).
- Endoplasmic Reticulum: Rough ER synthesizes proteins due to ribosome presence; Smooth ER is involved in lipid synthesis.

Metabolism: Encompasses all biochemical reactions in cells, including breaking down (catabolism) and building up (anabolism).
Energy Production: Primarily achieved through cellular respiration mechanisms like glycolysis, Krebs cycle, and oxidative phosphorylation.
Protein Synthesis: Involves translating mRNA into polypeptides necessary for cell function and structure.
Cell Growth and Division: Governed by the cell cycle phases: interphase, mitosis, and cytokinesis.

Direct Communication: Gap junctions in animal cells and plasmodesmata in plant cells enable direct transfer of ions and small molecules.
Chemical Signals: Hormones and neurotransmitters serve as key signaling molecules to convey information between cells.
Receptor Types:
- Membrane receptors: Bind to external signaling molecules and activate intracellular signaling cascades.
- Intracellular receptors: Interact with ligands that cross the plasma membrane, affecting gene expression.

Structure: Comprises a phospholipid bilayer enriched with proteins, cholesterol, and carbohydrates.
Functions:
- Selective permeability: Controls which substances enter or exit the cell.
- Cellular recognition: Glycoproteins and glycolipids are crucial for cell-cell recognition and signaling processes.
Transport mechanisms:
- Passive transport: Includes diffusion and osmosis, requiring no energy.
- Active transport: Energy-dependent process that moves substances against their concentration gradient (e.g., sodium-potassium pump).
Fluid Mosaic Model: Illustrates the plasma membrane as a dynamic structure with components able to move laterally within the bilayer.