CELL SIZES: 

• Size of Cells (and efficiency) 

  • Microscopic cell size → large surface-to-volume ratio

  • Plasma membrane - phospholipid bilayer w/ embedded proteins

    • some proteins form channels that shield ions and hydrophilic molecules as they pass through hydrophobic center of membrane 

    • others serve as pumps (using energy to actively transport molecules in/out of cell)

• Prokaryotic vs. Eukaryotic

  • ALL CELLS HAVE: PLASMA MEMBRANE, DNA, RIBOSOMES. AND CYTOSOL (CYTOPLASM)

  • Bacteria and Archaea → prokaryotic cells 

    • all others are eukaryotic 

  • Eukaryotic cells are distinguished from prokaryotes by having: 

    • Membrane enclosed nucleus 

    • Membrane enclosed organelles that perform specific functions

  • Prokaryotes are smaller and simpler in structure 

• Endosymbiont Theory (eukaryotes) 

  • Organelles (chloroplasts and mitochondria) were formerly small prokaryotes that began living w/ smaller cells and were incorporated into larger cells over time 

• Membrane Bound Organelles: 

  • Membrane-enclosed organelles compartmentalize a cell’s activities 

  • Organelles and other structures of eukaryotic cells can be organized into four basic functional groups: 

    • Nucleus and ribosomes carry out genetic control of cell 

    • ER, Golgi, Lysosomes, Vacuoles, Peroxisomes → manufacture, distribute, and breakdown molecules 

    • Mitochondria in all cells and chloroplasts in plant cells function in energy processing 

    • Cytoskeleton, Plasma Membrane, and Plant Cell Wall → Structural support, movement, and communication between cells 

• Viruses

  • Contain DNA, but cannot replicate it w/o hosts cell division 

  • Contain proteins, but no ribosomes, so they need host 

  • Cannot maintain homeostasis w/o host 

  • Not composed of cells - does not adhere to cell theory 

MICROSCOPES, CELL THEORY, AND ORGANIZATION:

• Scientists/Discoveries: 

  • 1665, Hooke: 

    • Crude microscope to examine bark from oak tree 

  • 1673, Leeuwenhoek: 

    • Used more refined lens to describe living cells from blood, sperm, and ponds 

  • 1838, Schleiden: 

    • All plants are made of cells 

  • 1839, Schwann: 

    • All animals are made of cells 

  • 1855, Virchow: 

    • New cells can only be produced from existing cells (observed mitosis/cell division) 

  • All of these led to the cell theory

    • All living things are composed of cells 

    • Cells are the basic unit of structure/function 

    • All cells come from existing cells 

• Microscopes: 

  • Light microscope - display living things 

    • Allows light to pass through one or more convex lenses to produced enlarged image of specimen 

  • Scanning and Transmission Electron Microscopes → reveal ultrastructure of cells 

  • Magnification → increase in an object’s image size compared with its actual size 

  • Resolution → measure of the clarity of an image 

• The Cell: 

  • Smallest unit of life 

  • SA/vol ratio decreases when size increases

  • Small cells function more efficiently than larger cells

    • Exchange materials in/out 

NUCLEUS AND RIBOSOMES: (genetic control) 

• Nucleus: 

  • Houses cell’s DNA, which directs protein synthesis via mRNA 

• Ribosomes: 

  • Ribosomal subunits are assembled in the nucleolus 

  • Composed of rRNA and proteins 

  • Synthesizes proteins according to directions from DNA via transcription 

  • Synthesized proteins are for use in cell and are exported 

  • Cells that make lots of proteins have a large number of ribosomes

ENERGY ORGANELLES: (mitochondria and chloroplasts)

• Photosynthesis - conversion of light energy from the sun to the chemical energy of sugar molecules by producers/autotrophs 

• Chloroplasts - the photosynthesizing organelles of plants and algae (thylakoids containing chlorophyll) 

• Mitochondria - organelles that carry out cellular respiration in nearly all eukaryotic cells 

• Mitochondria have two internal compartments 

  • Intermembrane space - narrow region between inner and outer membrane 

  • Mitochondrial matrix - contains mitochondrial DNA, ribosomes, and many enzymes that catalyze some of the reactions of cellular respiration

MANUFACTURING, DISTRIBUTION, AND BREAKDOWN: (ER, lysosomes, golgi, vacuoles, peroxisomes) 

• Endomembrane System 

  • Many organelles interact in the synthesis, distribution, storage, and export of molecules 

• ER - membranous network of tubes and sacs 

  • Smooth ER - synthesizes lipids and processes toxins, calcium ion storage in muscle cells 

  • Rough ER - produces membranes and ribosomes on its surface and makes membrane and secretory proteins; hydrolytic enzymes and formation of transport vesicles

• Golgi Apparatus - stacks of sacs in which products of ER are process and then sent to other organelles or to the cell surface 

  • Modification and storage of ER products 

  • Formation of lysosomes and transport vesicles 

• Lysosomes - house enzymes that break down ingested substances and damaged organelles 

  • Digestion and recycling (macromolecules + damaged organelles) 

• Vacuoles - large vesicles with a variety of functions 

  • Some protists have contractile vacuoles used for water balance 

  • Plant cells contain a large central vacuole that store molecules and wastes and facilitates growth 

• Peroxisomes - diverse metabolic compartments that do not originate from endomembrane system 

  • Break down toxic hydrogen peroxide waste 

CELL MEMBRANE STRUCTURE: 

• Fluid mosaic model - used to describe a membrane’s structure (diverse protein molecules suspended in fluid phospholipid bilayer) 

• Plasma membrane has selectively permeable 

  • Enter: oxygen, carbon dioxide, small, nonpolar molecules; some water molecules 

  • Cannot: large, polar, water-soluble molecules; water molecules 

• Protein Types: 

  • Transport Proteins - allow specific molecules or ions to enter/exit cell 

    • ie. channel or active 

  • Enzymes - grouped to carry out specific reactions 

  • Attachment Proteins 

    • attach to extracellular matrix and cytoskeleton

    • Help support membrane 

    • Coordinate external/internal changes 

  • Receptor Proteins 

    • Signal molecules to bind to receptor proteins 

    • Relay messages by activating other molecules inside the cell 

  • Junction Proteins - form intercellular junction that attach adjacent cells 

  • Glycoproteins - ID tags 

    • May be recognized by membrane proteins of other cells 

PASSIVE TRANSPORT: 

• Concentration Gradient - low → high

• Diffusion - tendency of particles to spread out evenly in an available space 

  • Diffusion across a cell does not require energy, so it is passive transport

• Osmosis - diffusion of water across a selectively permeable membrane

  • If a membrane permeable to water but not to a solute, water will cross the membrane until the solute concentration is equal on both sides (equilibrium) 

• Tonicity - ability of a surrounding solution to cause a cell to gain/lose water in order to reach equilibrium

  • Hypertonic - cells shrink (shriveled in both)

  • Hypotonic - cells swell; hypo = hippo (lysed in animal but normal in plant)

  • Isotonic - animal cells are normal, but plant cells are flaccid 

FACILITATED DIFFUSION: 

• Hydrophilic (polar) substances move across membrane with the help of specific transport proteins (facilitated diffusion) 

  • Does not require energy 

  • Relies on concentration gradient 

• The more amount of transport proteins for a particular solute in a membrane, the faster the solute’s rate of diffusion

  • Very rapid diffusion of water into and out of certain cells is made possible by a protein channel called an aquaporin 

ACTIVE TRANSPORT: 

• Active transport - a cell must expend ATP energy to move solutes against the concentration gradient 

• Cell’s use two mechanisms to move large molecules across a membrane 

  • Exocytosis - export bulky molecules (proteins/polysaccharides) 

  • Endocytosis - take in large molecules 

    • Phagocytosis - engulfment of a food particle by the cell wrapping cell membrane around it, forming a vacuole 

    • Receptor mediated - uses membrane receptors for specific solutes 

    • Pinocytosis - engulfment of small particles suspended in extracellular fluid 

  • In both, material to be transported is packaged within a vesicle that fuses with the membrane 

  • As a cell grows, its plasma membrane expands