A Tour of the Cell and Cell Signaling

Cell structure dictates function 

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Light microscope- visible light passes through and specimen and then through glass lenses, which manignity the image

• Magazines to aout 1,000

• Organelles (membrane-enclosed compartments) are too small to be resolved by an LM times the size of the actual specimen

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Scanning Electron microscopes- focus a beam of electrons on the surface of a specimen, providing images that look 3D

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Transmission electron microscope- focus a beam of electrons through the specimen

• Used to study the internal structure of cells

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Prokaryotic vs Eukaryotic cells

• Prokaryotic 

  • no nucleus or membrane-bound organelles
  • DNA in an unbound region called the nucleoid 
  • Organisms of the domains Bacteria and Archaea

• Eukaryotic

  • DNA is a nucleus that is bounded by a membranous nuclear envelope, membrane-bound organelles
  • Cytoplasm 
  • Large and more effective 
  • Protists, fungi, animals, and plants 

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All cells have:

1. Plasma membrane- selective barrier that allows sufficient passage of oxygen, nutrients, and waste to service every volume of the cell

   1. Double layer of phospholipids 

2. Semifluid substance called cytoplasm

3. Chromosomes (carry genes)

4. Ribosomes (make proteins)

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Larger surface area to ratio volume = more effective cell

• Small cells are more efficient at moving materials in and out 

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Nucleus- contains most of the cell’s genes

• Wrapped in a phospholipid bilayer

• Most conspicuous organelle 

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Nuclear envelope- encloses the nucleus, separating it from the cytoplasm

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Nucleolus- located in the nucleus and is the part of ribosomal RNA (rNA) synthesis

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Chromatin- unwound DNA, during interphase, being used to direct protein synthesis

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Chromosome- tightly packed DNA, during mitosis, not being used to direct protein synthesis

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Ribosomes- particles made of ribosomal RNA and protein

• Free ribosomes- make proteins to be used within the cell in the cytosol

• Bound ribosomes- make proteins for export and insertion into the membrane in the endoplasmic reticulum

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Endomembrane System

• Nuclear envelope

• Endoplasmic reticulum 

• Golgi apparatus

• Lysosomes 

• Vacuoles

• Plasma membrane 

  • Continuous or connected via vesicles 

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Endoplasmic Reticulum- next to the nucleus 

• Smooth ER- synthesizes lipids, stores calcium, detox 

• Rough ER- has bound ribosomes that make proteins for export, distributes transport vesicle (proteins surrounded by membranes), membrane factory for the cell

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Golgi apparatus modifies products of the ER

• Flattened membranous sacs called cisternae

• Manufactures certain macromolecules 

• Transports and packages into vesicles

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Lysosome- membranous sac of hydrolytic enzymes that can digest macromolecules

• Can hydrolyze proteins, fats, polysaccharides, and nucleic acids 

• Can use enzymes to recycle organelles and macromolecules

• Phagocytosis- forms a food vacuole, which fuses with a lysosome to digest molecules

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Vacuoles

• Food vacuoles formed by phagocytosis 

• Contractile vacuoles- found in freshwater protists, pump excess water out of cells

• Large central vacuole- found in mature plant cells, holds organic compounds and water

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The endomembrane system is a complex and dynamic plate rin the cell’s compartmental organization

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Mitochondria- sites of cellular respiration, a metabolic process that generates ATP

• Cristae increases the surface area for ATP synthesis 

Chloroplasts- found in plants and algae, are the sites of photosynthesis

• Thylakoids and stroma 

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Mitochondria and Chloroplasts:

• Not part of the endomembrane system

• Double proteins

• Have proteins made by the ribosomes

• Contain their own DNA

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Cytoskeleton- microfilaments all throughout the cell

• Organizes structure and activities, anchoring organelles

• Motor proteins to produce motility 

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Centrosome- microtubule-organizing center

• Centrioles- spindle fibers during animal cell division

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Extracellular components

• Cell walls of plants
• Extracellular matrix of animal cells- support, adhesion, movement, regulation 
• Intercellular junctions 
  • neighboring cells interact and communicate through direct physical contact
  • Plasmodesmata- opening between plant cells
  • Gap junctions- opening between animal cells
  • Tight junctions- prevent leakage from water-tight barrier
  • Desmosomes- anchoring junctions