Cell Theory and Types of Cells

Cell Theory

• Living things are made of cells
• Cells are the basic unit of life
• All cells come from other cells

Types of Cells

• Unicellular: Composed of one cell
• Multicellular: Composed of many cells that organize into tissues, organs, and organ systems

Two Types of Cells

• Prokaryotic:
  • No nucleus
  • No membrane-bound organelles
  • Binary fission for division
  • Unicellular organisms (bacteria)
  • Cell walls, made of peptidoglycan
• Eukaryotic:
  • Nucleus
  • Membrane-bound organelles
  • Mitosis for division
  • Uni- or multicellular (animals, plants, fungi, protists)
  • Cell walls (some): made of chitin or cellulose

Components of ALL Cells

• Genetic material (DNA or RNA)
• Cytoplasm
• Cell membrane
• Ribosomes

Organelles

• Specialized structures within eukaryotic cells
• Work together for cell function, primarily protein production

Cell (Plasma) Membrane

• Structure:
  • Surrounds all cells
  • Made of two layers (phospholipid bilayer)
• Job:
  • Controls what enters and exits the cell
  • Maintains stable internal environment (homeostasis)

Cytoskeleton

• Structure: Threadlike fibers made of proteins
• Job:
  • Gives the cell shape
  • Moves organelles
  • Provides structural support (in animal cells)

Cytoplasm

• Structure: Jelly-like substance, mainly water
• Job:
  • Holds everything in place
  • Provides a solution for chemical reactions

Nucleus

• Structure: Contains genetic material (DNA), chromatin (spread-out DNA), chromosomes (condensed DNA) surrounded by a nuclear envelope/membrane with pores.
• Job: Protects DNA and controls cell activities.

Nucleolus

• Structure: Inside the nucleus
• Job: Makes rRNA, a component of ribosomes

Ribosomes

• Structure: Made of proteins and rRNA, located on Rough ER and floating in cytoplasm
• Job: Makes proteins in a process called translation (export proteins or proteins used within the cell)

Rough ER (Endoplasmic Reticulum)

• Structure: Has ribosomes on its surface, hugs the nucleus
• Job: Makes proteins, packages them for secretion

Smooth ER (Endoplasmic Reticulum)

• Structure: No ribosomes, attached to Rough ER
• Job: Makes lipids (membrane) and stores Ca+2

Golgi Apparatus

• Structure: Folded membrane
• Job: Gets vesicles of protein from the ER, processes, sorts, and ships proteins

Lysosomes

• Structure: Contains enzymes (animal cells only)
• Job: Breaks down dead stuff (food, bacteria, old parts of the cell), and does programmed cell death (apoptosis)

Vacuoles

• Structure: Small and numerous in animal cells, one large central one in plant cells
• Job: Storage (water, nutrients, waste)

Centrioles

• Structure: Made of microtubules, 2 centrioles together = centrosome (animal cells only)
• Job: Appear during cell division, help the cell divide by pulling chromosomes apart

Cilia and Flagella

• Structure: Cilia are short and numerous, like tiny oars; flagella are longer and fewer (1-3).
• Job: Cilia move fluid across the cell's surface; flagella move the entire cell through extracellular fluid

Mitochondria

• Structure: Inner membrane and matrix (fluid part)
• Job: Where cellular respiration happens (C6H12O6 + 6O2 → 6CO2 + 6H2O + energy (ATP)), breaks down food to release usable energy.

Chloroplasts

• Structure: Grana (stacks) and stroma (fluid) (plant cells only)
• Job: Where photosynthesis happens (6CO2 + 6H2O → C6H12O6 + 6O2), converts light energy from the sun into chemical energy in the form of sugar

Cell Wall

• Structure: Made of cellulose (plants), chitin (fungi), or peptidoglycan (bacteria) (plant, bacteria, and fungi cells only)
• Job: Protects and maintains cell shape

Central Vacuole

• Structure: One large central structure (plant cells only)
• Job: Storage center