Cells and How They Work
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What is a cell?
Cell theory - all organisms are composed of one or more cells which are the smallest unit of having the poperties of life; all cells come from pre-existing cells (grow, reproduce)
How are cells linked?
- Plasma membrane - separates each cell from the environment, but also allows the flow of molecules across the membran (controls in/out)
- DNA - carries the hereditary instructions
- Cytoplams - contains a semifluid matrix (cytosol) and organelles; located between the plasma membrane and the region of DNA
Kind of Cells
- Prokaryotic - do not hae a separation fo the DNA from the remainder of the cell parts (bacteria) - no nucleus
- Eukaryotic - have a definite nucleus and membrane-bound organelles (animals, plants, fungus)
Lipid bilayer: phospholipid molecules are surrounded by water, their hydrophobic fatty acid tails cluster resulting in hydrophilic heads at the outer faces of two-layer sheet with the hydrophobic tails shielded inside.
Parts of a Eukaryotic Cell
- Organelles means "little organ" and are tiny compartments and sacs in their cytoplasm (own membrane function inside cell)
- With Membranes:
- Nucleus: protecting, controlling access to DNA
- Endoplasmic: routing, modifying new polypeptide chains; synthesizing lipids; other tasks
- Golgi body: modifying new polypeptide chains; sorting, shipping proteins and lipids
- Vsicles: transporting storing, or digesting substances in a cell; other functions
- Mitochondrion: making ATP by sugar breakdown
- Chloroplast: making sugars in plants, some protists
- Lysosome: intracellular digestion
- Peroxisome: inactivating toxins
- Vacuole: storage
- Without Membranes:
- Robosomes: assembling polypeptide chains
- Centriole: anchor for cytoskeleton
- Mix of lipids and proteins
- Bilayers of phospholipids (two fatty acids)interspersed with glycolipds and cholesterol
- Structural foundation of cell membrane
Components of the Nucleus
- Encloses DNA, the building code for cellular proteins
- Nuclear envelope: Double membrane (two lipid bilayers) with pores sperating the interior of the nucleus from the cytoplasm
- Nucleolus: a cluster of the RNA and proteins used to assemble ribosome subunits (ribosomes makes protein)
- Nucleoplasm: fluid interior portion of the nucleus
- Chromatin: All the DNA molecules and their attached proteins
- Chromosomes: The individual DNA molecules and their attached proteins
The Endomembrane System
- Endoplasmic reticulum (ER) is a protein and lipd assembly line
- Collection of inter connected tubes and flattened sacs, continuous with the nuclear membrane
- Rough ER: stacked, flattened sacs with many ribosomes attached
- Smooth ER: has no ribosomes; it is the area from which vesicles carrying proteins and lipids are budded
- Golgi bodies: finish, pack, and ship - where porteins and lipids undergo final processing, sorting and packag-ing
- Vesicles: move substances into/through cells - lysosomes (carry powerful enzmes) peroxisomes (membrane bound sacs of enzymes)
- Specialized compartments in the cell that produce energy
- disorders can cause reduced energy for cell use (Luft's syndrome - not enough ATP)
- Makes ATP: formed in inner compartment of the mitchondrion which have their own DNA and some ribosomes.
- Takes Oxygen to release
- Cytoskeleton is interconnected system of bundled fibers, slender threads, and lattices extending from the nucleus to the plama membrane in the cytosol
- Microtubles: largest element
- Microfilaments: reinforce some part of a cell, anchors some proteins in place
- Intermediate filaments: add strength like steel rods
- Flagella: quite long, whiplike, found on animal sperm cells
- Cilia: shorter, more numberous, and may function as sweeps to clear (respiratory tract of dust or materials
- Centrioles (built here)
Diffusion and Osmosis
- Lipid-soluble (hydrophobic/nonpolar) cross easy through the lipid bilayer
- Large molecules (hydrophilio/polar) must be moved by membrane transport proteins
- a solute moves down a concentrations gradient
- Concentration gradient is established when there is a difference in the number of moecules or ions of a given substance between two adjacent regions
- Move from high concentration to low concentration
- passive transport - requires energy
- Passive diffusion of water across a differentially permeable membrane in response to solute concetnration gradients (water diffuses passively - moves)affected by the relative concentrations of slutes in the fluids inside and outside the cell (tonicity)
- Isotonic - same concentration
- Hypotonic - less concentration
- Hypertonic - hugh concentration
- If the concentration of solute (salt) is equal on both sides, the water will move back in forth but it won't have any result on the overall amount of water on either side.
- "ISO" means the same
- The word "HYPO" means less, in this case there are less solute (salt) molecules outside the cell, since salt sucks, water will move into the cell.
- The cell will gain water and grow larger. In plant cells, the central vacuoles will fill and the plant becomes stiff and rigid, the cell wall keeps the plant from bursting
- In animal cells, the cell may be in danger of bursting, organelles called CONTRACTILE VACUOLES will pump water out of the cell to prevent this
- The word "HYPER" means more, in this case there are more solute (salt) molecules outside the cell, which causes the water to be sucked in that direction.
- In plant cells, the central vacuole loses water and the cells shrink, causing wilting.
- In animal cells, the cells also shrink.
- In both cases, the cell may die.
- This is why it is dangerous to drink sea water - its a myth that drinking sea water will cause you to go insane, but people marooned at sea will speed up dehydration (and death) by drinking sea water.
- This is also why "salting fields" was a common tactic during war, it would kill the crops in the field, thus causing food shortages.
Crossing Cell Membranes
- Facilitated diffusion: solutes pass through channel proteins in accordance with the concdentration gradient - no input of energy
- Active transport: solutes move against their concentration gradients with the assistance of transport prteins that change their shape with the energy supplied by ATP
- Vesicles transport large solutes
Vesicles for Transport
- Exocytosis: moves substances from the cytoplasm to the plasma membrane during secretion, moving materials out of the cell
- Endocytosis: encloses particles in small portions of plasma membrane to form vesicles that then move into the cytoplasm
- Phagocytosi: process that brings organic material into the cell
- refers to all of the chemical reactions that occur in cells
- ATP links the whole of these reactions together
- ATP is composed of adenine, ribose, and three phosphate groups
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