Cells and Organelles

• Lysosome is a membrane-bound vesicle containing digestive enzymes, responsible for breaking down cell waste and toxins
• Mitochondrion is an organelle where aerobic cellular respiration occurs, producing ATP to power cellular processes; it has its own DNA and ribosomes
• Chloroplast is a double membrane-bound organelle where photosynthesis takes place, containing its own DNA and ribosomes
• Vacuoles are membrane-bound sacs used for water and solute storage, playing a role in maintaining plant cell structure
• Plasma membrane is a selectively permeable barrier between the intracellular and extracellular environment, made of a phospholipid bilayer studded with molecules
• Cell wall is a sturdy border outside the plasma membrane providing strength and structure to plant, bacterial, and fungal cells
• Vesicle is a small membrane-bound sac that transports substances into or out of a cell, or stores substances within a cell
• Cytoskeleton is a large network of protein filaments critical for maintaining cell shape and transporting materials around the cell
• Chromosome is a structure composed of DNA wrapped around histone proteins, carrying the genetic information (genes) of a cell
• Cells are made up of many different structures known as organelles, which have different structures that help them perform specific functions
• Every cell is surrounded by a plasma membrane that controls what can and cannot enter the cell
• Inside each cell is a fluid substance known as cytosol, containing dissolved salts, nutrients, and molecules necessary for cell function
• All organelles except the nucleus and the cytosol in which they float make up the cytoplasm
• Important organelles and their functions:

  • Nucleus: protects and confines genetic information (DNA), contains the nucleolus for ribosome production
  • Rough ER: synthesizes and modifies proteins, close to the nucleus, coated with ribosomes
  • Smooth ER: responsible for lipid production in a cell, not coated with ribosomes
  • Ribosomes: assemble building blocks to make proteins, can float freely in the cytoplasm or be attached to the RER
  • Golgi Body: site of protein sorting, packing, and modification for use in the cell or export
• Organisms can be categorized as prokaryotes or eukaryotes based on their cellular structures
• Both prokaryotic and eukaryotic cells contain a plasma membrane, cytosol, ribosomes, and DNA
• Eukaryotic cells are both multicellular and unicellular, containing linear DNA packed in a nucleus and tend to be larger than prokaryotes
• Prokaryotic cells are unicellular, lack membrane-bound organelles (except vesicles), lack a nucleus, have a single circular loop of DNA, and may contain smaller circular units of DNA called plasmids
• Cell replication differs between prokaryotes and eukaryotes:

  • Eukaryotic somatic cells usually duplicate through mitosis
  • Eukaryotic germ cells split into four individual gametes through meiosis
  • Prokaryotic cells replicate via binary fission
• Four types of eukaryotes:

  • Animals: multicellular, heterotrophic organisms with no cell walls, having specialized tissues like nervous tissue and muscle tissue
  • Plants: multicellular, autotrophic organisms with cellulose cell walls, capable of photosynthesis
  • Fungi: multicellular or unicellular heterotrophs with chitin cell walls, involved in decomposition and nutrient cycling
  • Protists: diverse groups of mostly unicellular organisms with various modes of nutrition, locomotion, and reproduction
• To be classified as living, something must possess eight qualities:

  • Movement
  • Respiration
  • Sensitivity
  • Growth
  • Reproduction
  • Excretion
  • Nutrition
  • DNA
• The acronym MRS GREND is used to remember the eight criteria for living things: Movement, Respiration, Sensitivity, Growth, Reproduction, Excretion, Nutrition, and DNA
• Cell Theory:

  • All living things are made up of cells
  • The cell is the basic unit of structure and organization in organisms
  • All cells come from pre-existing cells