Membrane Transport
Passive Transport: net movement of molecules from H to L concentration without ATP; used for import and export of materials |
Facilitated Diffusion: (1) Large quantities of water pass through aquaporins (2) Charged ions, (Na+ and K+), require channel proteins to move through membrane (3) Membranes may become polarized by movement of ions across the membrane |
Active Transport: uses ATP to transport molecules and establish/maintain concentration gradients; requires membrane proteins |
Exocytosis: internal vesicles fuse with plasma membrane and secrete large macromolecules out of cell |
Endocytosis: cell takes in macromolecules and particulate matter by forming new vesicles derived from plasma membrane |
Selective Permeability
-Selective permeability is a direct consequence of membrane structure
-Small, non polar molecules can pass through (N2, O2 and CO2)
-Hydrophilic substances (large polar molecules and ions) need embedded channels and transport proteins
-Polar uncharged molecules (H20) pass though in small amounts
-Allows for the formation of concentration gradients of solutes across the membrane |
Surface Area to Volume Ratio
-Smaller cells typically have a higher SA:V for more efficient exchange of materials with environment
-As V increases, SA decreases, demand for internal resources increases
-Increasing cell size decreases SA:V
-Membrane folds can increase SA:V |
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Prokaryotic vs. Eukaryotic
Prokaryotes |
Eukaryotes |
Typically have circular chromosomes (plasmid) |
Typically have multiple linear chromosomes (can have plasmids too) |
Unicellular |
Multicellular |
No membrane bound nucleus |
Membrane bound nucleus |
Rare: microtubules, cytoskeleton; also chlorophyll scattered in cell |
Lysosomes, peroxisomes, microtubules, ER, Mitochondria, Cytoskeleton, Vesicles, Golgi, Chloroplasts |
Smaller ribosomes, have vacuoles |
Larger ribosomes, have vacuoles |
Chemically complex cell wall |
Chemically simple cell wall |
1-10um |
10-100um |
Groups of genes (operons) are transcribed in a single mRNA molecule |
Groups of genes may be influenced by the same transcription factors to coordinately regulate expression |
Cell Compartmentalization
-Membrane-bound organelles evolved from once free-living prokaryotic cells via endosymbiosis
-Prokaryotes generally lack internal membrane- bound organelles but have internal regions with specialized structures and functions.
-Eukaryotic cells maintain internal membranes that partition the cell into specialized regions
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Cell Organelles
Ribosomes |
Comprise ribosomal RNA (rRNA) and protein; Synthesize protein according to mRNA sequence; Found in all forms of life (evidence of common ancestor) |
Endoplasmic Reticulum (ER) |
Rough ER: compartmentalizes the cell; Smooth ER: detoxification and lipid synthesis |
Golgi |
Fold and chemically modify newly synthesized proteins; Packaging proteins for trafficking |
Mitochondria |
Powerhouse of cell; Double membrane provides compartments for different metabolic reactions |
Lysosomes |
Contain hydrolytic enzymes for intracellular digestion, recycling of a cell’s organic materials, apoptosis |
Vacuoles |
Storage and release of macromolecules and cellular waste products; In plants, aids in retention of water for turgor pressure |
Osmosis
Water moves (by osmosis) from areas of H H20 potential/L solute concentration to areas of L H2O potential/H solute concentration
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