Introduction to Cell Biology

• Scientific study of life is Biology
• Biology studies living organisms' structures, functions, growth, origins, evolution, and distribution.
• Cells are the basic unit of life
• Genes are the basic unit of heredity
• Evolution is the engine that propels the creation and extinction of species
• Living organisms share characteristics like organization, metabolism, homeostasis, growth, reproduction, response to stimuli, and adaptation through evolution.

Cell Biology

• The study of cells is cell biology
• Cell biology focuses on the structure, function, and behavior of cells Studying cells at the microscopic and molecular level is cell biology
• Cell signaling pathways, cell cycle, and how cells interact with their environment are key to cell biology
• Genetics, molecular biology, and biochemistry are related to cell biology

Cell Structure

• Cells are the basic structural and functional units of life
• Prokaryotic and eukaryotic cells are the 2 main types of cells
• Prokaryotic cells lack a nucleus & membrane-bound organelles
• Eukaryotic cells have a nucleus and other membrane-bound organelles like mitochondria, endoplasmic reticulum, and the Golgi apparatus

Prokaryotic Cells

• Prokaryotic cells are generally smaller and simpler than eukaryotic cells
• Bacteria and Archaea are prokaryotic cells
• DNA genetic material in prokaryotic cells located in the cytoplasm in a region called the nucleoid
• Cell walls provide structure and protection for prokaryotic cells
• Capsules are sticky outer layers on many prokaryotic cells to adhere to surfaces or evade immune responses
• Flagella for movement or pili for attachment are features of some prokaryotic cells

Eukaryotic Cells

• Eukaryotic cells are more complex and organized than prokaryotic cells
• Protists, fungi, plants, and animals contain Eukaryotic cells
• A nucleus containing the cell's DNA is the defining feature of eukaryotic cells
• Eukaryotic cells contain a variety of membrane-bound organelles performing specific functions:
  • Mitochondria for energy production
  • Endoplasmic reticulum for protein and lipid synthesis
  • Golgi apparatus for processing and packaging proteins
  • Lysosomes for waste disposal
  • Chloroplasts (in plant cells) for photosynthesis
• A cytoskeleton provides structural support and facilitates cell movement in Eukaryotic cells

Cell Membrane

• The cell membrane (plasma membrane) is a selectively permeable barrier around all cells
• It is made of a lipid bilayer with embedded proteins
• The lipid bilayer is composed of phospholipids
  • With hydrophilic (water-attracting) head
  • Hydrophobic (water-repelling) tails
• Proteins in the cell membrane
  • Act as channels/carriers to transport molecules
  • Serve as receptors for signaling molecules
  • Function as enzymes
  • Provide structural support
• The cell membrane regulates the movement of substances in/out of the cell
• Cell membrane plays a role in cell signaling and cell-to-cell communication

Nucleus

• The nucleus is the control center of the eukaryotic cell
• The cell's DNA is in the nucleus and organized into chromosomes
• A nuclear envelope surrounds the nucleus with a double membrane
• The nuclear envelope has pores that regulate molecule movement between the nucleus and the cytoplasm
• The nucleolus within the nucleus is the site of ribosome synthesis

Mitochondria

• Mitochondria are the powerhouses of the cell
• They produce ATP (adenosine triphosphate) through cellular respiration.
• Mitochondria have a double membrane, with the inner membrane folded into cristae
• Cristae increase surface area for ATP production
• Mitochondria have their own DNA and ribosomes suggesting they evolved from endosymbiotic bacteria

Endoplasmic Reticulum (ER)

• Endoplasmic reticulum (ER) is a network of membranes throughout the cytoplasm of eukaryotic cells
• Rough ER and smooth ER are the 2 types
• Rough ER is covered with ribosomes and is involved in protein synthesis and modification
• Smooth ER lacks ribosomes and is involved in lipid synthesis, detoxification, and calcium storage

Golgi Apparatus

• The Golgi apparatus processes and packages proteins and lipids.
• It consists of cisternae, which are flattened, membrane-bound sacs
• Proteins and lipids from the ER are transported to the Golgi apparatus in vesicles
• Within the Golgi apparatus, they are modified, sorted, and packaged into new vesicles for delivery to other parts of the cell or for secretion

Lysosomes

• Lysosomes contain digestive enzymes
• They break down waste materials and cellular debris
• Lysosomes fuse with vesicles containing the materials to be digested
• Enzymes within the lysosome break down the materials into smaller molecules to be reused by the cell

Cell Signaling

• Cell signaling is communication between cells
• Cells communicate through
  • Direct contact
  • Releasing signaling molecules that travel to other cells
• Signaling molecules bind to receptors on the surface of target cells, triggering intracellular events
• These events can lead to changes in gene expression, cell metabolism, or cell behavior
• Cell signaling coordinates activities of cells in multicellular organisms

Cell Cycle

• The cell cycle is the series of events in a cell leading to division and duplication
• Interphase and mitosis are the 2 main phases
• Interphase is the period the cell cycle grows & prepares for division
• Mitosis is the process of nuclear division, separating chromosomes into 2 identical sets
• Cytokinesis, division of the cytoplasm, follows mitosis
• The cell cycle is tightly regulated to divide properly
• Disruptions in the cell cycle can lead to uncontrolled cell growth and cancer

Cell Communication

• Cells communicate in a number of ways:
  • Direct contact: gap junctions
  • Local signaling: growth factors or neurotransmitters
  • Long-distance signaling: hormones
• Reception, transduction, and response, all involve cell communication

Cell Metabolism

• Cell metabolism encompasses all chemical processes within a cell
• These processes:
  • Catabolism: complex molecules broken down into simpler ones, releasing energy
  • Anabolism: complex molecules synthesized from simpler ones, requiring energy
• Enzymes regulate metabolic reactions
• ATP is the main energy currency of the cell