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Typical Cell
  • -a.k.a composite cell
  • -varies in size, structure, & function
Cell Structure
  • 3 main structures
    - Plasma Membrane (made of lipoproteins)
    - Cytoplasm = contains cytosol with organelles
    -Nucleus
  • Each cell contains variety of membranes
    - plasma membrane
    - membranous organelles = canals and sacs
    - nonmembranous = made of microfilaments
Fluid Mosaic Model
  • Theory explaning how cell membranes are constructed
  1. molecules of cell membrane are arranged in sheet
  2. mosaic of molecules is fluid; molecules are able to float around slowly
  3. illustrates molecules of cell membrane form continuous sheet
Cell Membranes
  • Chemical attractions hold them together
  • Groupings of molecules form rafts that float around membrane
    - rafts may pinch inward, bringing material into cell/organelle
Primary Structure of Cell Membrane
  • double layer of phospholipid molecules
  • heads are hydrophilic
  • tails are hydrophobic
  • molecules arranged in bilayer in water
  • cholesterol scattered among phospholipids - lets membrane funtion in body temp.
  • most of membrane is hydrophobic - water cannot pass easily
Membrane Proteins
  • cell controls what goes in/out of membrane due to membrane proteins in phospholipid bilayer
  • some membrane contains carbohydrates (glycoproteins) - act as I.D. markers
  • Signal Transduction - allows a msg to be carried across membrane
Cytoplasm
  • gel-like substance of cells containing organelles suspended in watery fluid called cytosol
Rough Endoplasmic Reticulum
  • contain ribosomes on surface
  • synthesizes proteins, which move toward golgi and eventually out the cell
  • function in protein synthesis and intracellular transportation
Smooth Endoplasmic Reticulum
  • No Ribosomes
  • Sythesizes lipids & carbohydrates & creates membranes for use throughout cell
  • removes and stores Ca
Ribosomes
  • some attached to R.E.R.
  • others are free in cytoplasm
  • made of two subunits (large & small) - contain ribosomicRNA
  • those on RER make proteins for plasma membrane
  • free ones are for domestic use
Golgi Apparatus
  • a.k.a. golgi complex
  • consists of cisternae stacked on one another
  • located near nucleus
  • processes protein molecules from RER
  • Processed proteins leave final cisternae thru vesicle; contents then secreted outside cell
Lysosomes
  • Made of microscopic sacs "pinched off" from Golgi
  • Digestive system of cell (act as garbage collector)
  • Enzymes digest proteins of defective cell parts
Proteasomes
  • Hollow, protein cylinders found throughout cytoplasm
  • break down abmormal/misfolded and unwanted proteins
  • break down proteins one at a time by tagging with ubiquitin molecules and unfolding it as it enters proteasome.. then breaking apart peptide bonds
  • proteins -> amino acides ->recycle
Peroxisomes
  • small membranous sacs containing enzymes that detoxifies harmful substances
  • Often seen in kidney and livers
Mitochondria
  • made of microscopic sacs
  • wall composed of inner and outter membranes separated by fluid
  • enzyme molecules attached to both membranes
  • "power plant" of cells. ¬†provide about 95% of energy supply
  • has it's own DNA molecule - allows it to replicate copies of itself and make own enzymes
Nucleus
  • spherical body in center of cell
  • enclosed with envelope with many pores (2 membranes)
  • Contains DNA (heredity molecule)
    - nondividing cells = chromatin: threads or granules
    - dividing cells = chromosomes:  early stages of cell division (coiled up)
  • functions of nucleus = functions of molecules
  • determines both function and structure of cells and heredity
Cytoskeleton
  • cell's internal supporting framework made up of rigid, rodlike pieces
  • provide support and allow movement
Cell Fibers
  • Detailed arranged fivers of varying lengths that form a 3D shaped lattice
  • Fivers support ER, Mitochondria, 7 "free" ribosomes
  • 3 main fibers
Microfilaments
  • smallest cell fibers
  • cell's muscles
  • thin, twisted strand of protein molecule
  • lie parallel to long axis of cell
  • able to slide past one another, causing shortening of cell
Intermediate Filaments
  • twisted protein strands
  • thicker than microfilaments
  • form supporting framework in many cells
Microtibules
  • tiny, hollow tubes
  • thickest of cell fibers
  • made of protein subunits arranged in spiral fashion
  • funtion is to move things around in cell
Centrosome
  • near nucleus that coordinates building and breaking of microtubules in cell
  • a.k.a. microtubule-organizing center (MTOC)
  • Plays important role during cell division
  • location is identified by centrioles
Centrioles
  • tiny cylinders
  • sit @ right angles to each other
  • occurs when centrioles separate in preparation for cell division
  • Pericentriolar material - cloud like material surrounds it
  • involved in formation of microtubular cell extensions
Cell Extensions
  • cytoskeleton forms projections that extend plasma membrane outward to form tiny, fingerlike processes
  • 3 types
Microvilli
  • found in epithelial cells (surface) that lines intestines and areas where absorption is important
  • help increase surface area of manyfold
Cilia
  • have cylinders made of microtubules at the core
  • short and more numerous than flagella
Flagella
  • have cylinders made of microtubules at the core
  • found only in human sperm cells
  • help sperm swim
Cells are held together by fibrous nets or direct connections

  • 3 types of direct connections
Desmosome
  • fibers on outer surface interlock with each other; anchored internally by intermediate filaments of cytoskeleton
  • Spot desmosomes, connect adjacent membranes
  • belt desmosomes encircle cell like collar
Gap Junctions
  • membrane channels of adjacent plasma membranes adhere to each other
  • 2 effects
  1. form gaps/tunnels that join cytoplasm of 2 cells
  2. fuse two plasma membranes into single structure
Tight Junctions
  • Occur in cells joined by collars of tightly fused material
  • molecules cannot go thru the cracks of tight junctions
  • occur in lining of intestines and etc where it is important to control what gets thru sheet of cells
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