Chapter 4
Cell Structure
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Molecules make up cells
- 30% of cell mass = macromolecules (carbs, lipids, proteins, nucleic acids)
- 70% of cell mass = Water >> important for cell structure
Discovery of cells
Father of Microbiology
- Anton van Leeuwenhoek
- Made a microscope to see microscopic organisms
- Saw cells in corks, named after monks’ chambers
Why Are Cells so Small?
Surface Area: Volume ratio
Surface Area: amt of area exposed on surface (membrane)
V: amt of space inside
As organisms get larger the SA:V gets smaller
SA must be greater than V to adequately pass materials thru cell membrane
Cell Theory
Early 1800s
Matthias Schleiden (botanist) and Theodor Schwann (zoologist) hypothesized cells have a life of their own
- All living things are made of cells
- Cells = basic unit of life
- Cells arise from pre-existing cells (not spontaneous generation as previously thought)
- Hereditary info is passed from cell (DNA)
- All cells have the basic chemical composition (carbs, proteins, lipids, etc.)
- Energy flow occurs within cells (metabolism)
3 Main Parts of a Cell
Cell Membrane
- Separates inside of cell from outside environment (lipid bilayer)
- Proteins in membrane dictates what can pass through
- Inside the membrane is cytosol
- Cytosol: mix of water, sugars, ions, protons. Organelles suspended in cytosol
Nucleus
- DNA is in there
- Defining characteristic of eukaryotes
Cytoplasm
- Cytosol, organelles, all other cellular components collectively called the cytoplasm
- This is where DNA is suspended in prokaryotes
Prokaryotes don’t have a nucleus, Eukaryotes have a nucleus
Bacteria and Archaea
Prokaryotes
- Unicellular, form colonies
- Lack a nucleus
- Archaea is more closely related to eukaryotes than to bacteria
Structural Differences
Prokaryotes are less elaborate inside than eukaryotes
Components of Nucleus
DNA
Chromatin
- Tightly packed DNA w/ specific proteins bound together
Nucleoplasm
- Fluid inside nucleus
- Chromatin suspended here
Nucleolus
- Dense region of protein and nucleic acids
- Ribosomes made here
Nuclear Envelope
- Membrane that surrounds nucleus; made of lipid bilayer
Endomembrane system
- Function: modifies, transports, and packages proteins and lipids in the cell
- Made of different organelles
- Vesicles: sacs formed by budding. Cell taxi
- Endoplasmic reticulum (ER): made from nuclear envelope. Ribosomes give it a rough appearance. Protein synthesis
- Golgi Body: has enzymes to put “finishing touches” on proteins and lipids made on ER.
- May attach sugars, oligosaccharides, or phosphate groups. Finished product: membrane proteins/lipids, proteins for secretion, or enzymes
Steps of the Endomembrane system
- Protein made on rough ER
- Wrap in vesicle
- Drifts to golgi
- Attaches to one side of golgi
- Moves through the golgi, adding finishing touches
- Exits other side of golgi
- Drifts to cell membrane
- Exocytosis: moving something inside the cell the the outside
Mitochondria
Breaks the sugar bonds (glucose) to make ATP
Mitochondria History
- Resemble bacteria (endosymbiotic theory)
- Have own DNA (DNA is circular like bacterial DNA)
- Divide independently of cell
- Has own ribosomes
Chloroplasts
Chloroplasts are a specific type of plastid that perform photosynthesis
Plastids: organelles in plants and algae that help w/ photosynthesis, storage, and pigmentation
Cytoskeleton
- System of interconnected protein filaments
- Reinforce, organize, and move cell structures
- Some permanent, some form when needed
Parts of cytoskeleton
- Microtubules
- Hollow cylinders
- Function: movement and shape
- Assemble and disassemble as needed
- Ex. mitosis
- Microfilaments
- Forms a mesh of microfilaments
- Function: supports plasma membrane and movement
- Intermediate filaments
- Stable framework
- Function: structure and strength
- Made of various proteins
- Ex. keratin
Cell Movement
Motor Proteins
Move materials throughout the cell, activated by ATP
Cilia
Short, hairlike structures. Projects from cell membrane
Pseudopods
“False feet” temporary stretched lobe, move and grab prey
Cell Interactions
Cell Junctions
Structure that connects cell to other cells and the environment
- Cells send and receive signals
- Some junctions form tissues
Tight Junctions
- Found in animals
- Make up tissues
- Fasten cell membranes of adjacent cells together
- Keep bodily fluid contained
Adhering Junctions
- In animals
- Make up cardiac muscles and skin
Gap Junctions
- In animals
- Closable channels between cells
- Open to let water, ions, and molecules from cell’s cytoplasm to another
- Let substances flow quickly between cells
Plasmodesmata
- In plants
- Open channels connecting cytoplasm of two cells
- Let substances flow quickly between cells
- Similar to gap junctions in animal cells
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