Lecture Notes 10/16-11/15

cell structure and function

development of cell theory

• 1665 Robert Hooke-Royal Society of England
• dead cork cells
• "cell" from cellulae (Latin-"small room")
• 1838 Scheiden "Botanist" stated all plants made of cells
• Schwann "Zoologist" all animals made of cells
• derived that
1. all living things are composed of cells
2. cell is the basic unit of structure/function of life
• 1858 Virchow studied cell division
1. cells come only from preexisting cells
2. life comes from lie

methods of studying cells

• microscopes
• high speed centrifuge/differential centrifugation
• cell size (small) most human cells between 5-20 μ
• determined by surface area to volume ratio
• surface increases by the square (area)
• volume increases by the cube (volume)
• small size needed for volume (where life occurs)
• be able to acquire needed materials through its suface area
• size & shape determined by cell function
• strategies to increase surface area
• folding projections long & thin etc.

major cell types

• prokaryotic cells (before nucleus)
• very small (1-10 microns)
• no membrane bounded organelles
• have cytoplasm, cell membrane, nucleoid region, cell wall
• ex: bacteria, blue-green algae (uniform color)
• eukaryotic cells (true nucleus)
• 4 major cell lines (4 kingdoms)
• Plant, Animal, Fungi, Protista
• all have nucleus and membrane bounded organelles

organelle journey

1. nucleus
• nuclear membrane (double) has huge pores but smaller than DNA
• contains chromatin (DNA + protein)
• becomes chromatin at division
• stains easily (iodine, methylene blue)
  
2. nucleolus
• forms ribosomal DNA
• site of activity in nucleus
3. ribosomes
• RNA and protein
• 2 subunits
• cytoplasmic organelles
• endomembrane system
4. endoplasmic reticulum (ER)
• system of channels and saccules continous with outer layer of nuclear membrane
• rough ER-protein/lipid synthesis, products move to Golgi apparatus
• smooth ER-no ribosomes, may produce lipids and steroid hormones, detoxify drugs in liver (alcohol etc.), muscle cells store Ca⁺⁺, forms transport vehicles
5. Golgi apparatus
• stack of apparatus
• inner face towards ER
• outer face towards cell membranes
• protein filled vesicles from ER move to Golgi to be modified (2, 3, 4 levels of structure and/or lipo or glyco proteins formed here)
6. lysosomes (loose body)
• contain hydrolytic enzymes (40+) "suicide bags"
• digest worn out or foreign molecules
• common in white blood cells
7. microbodies
• similar to lysosomes
• contain specific enzymes-catalase
• peroxisomes-hydrogen peroxide H₂O₂ produced and destroyed by catalase
• glyoxysomes-leaves that photosynthesize germinating seeds to convert lipids into sugars for metabolism
8. vacuoles
• large membrane sac
• large in plants (central vacuole)
• reduces volume of living material
• so improves surface area to volume ratio
• filles with water osmosis-turgor pressure (turgid cells)
• smaller in animals
• storage area for cells
• pigments besides chlorophylls (flowers)
• toxic substances (chemical defense)
9. chloroplasts (anabolic rxns)
• contain pigments of photosynthesis
• double membrane contains thylakoid
• have own DNA, reproduce selves by division
• make some of own proteins
• theory-captured bacteria (symbionts)
10. mitochondria (catabolic rxns)
• double membrane system
• internal membrane folded into cristae
• intermembrane space critical to electron transport and ATP production
• has own DNA (eve theory)
• captured bacteria (symbionts)
• reproduce themselves by divison
11. cytoskeleton
• network of interconnected filaments and tubules from nucleus to plasma membrane maintains cell shape and moves organelles appear and disappear during cell cycle made up of monomers of actin, myosin, tubulin
12. actin and myosin (found in muscles as well as cytoskeleton)
• actin moves organelles around and forms pseudopodia in Amoeboid movement
13. intermediate filaments
• between actin filaments and microtubules
• take part in cell to cell junctions in skin protein keratin which is tough
14. microtubules
• tubulin subunits
• small hollow cylinder about 25 nm from 0.2 to 25 microns in length
• two forms (lambda and beta) forms dimer which is a lambda and beta pair
• forms strings of dimers (doublets) that coil to form tube
  
• 13 rows of dimers
15. centrioles
• 9 triplents arranged in circle with no center
• animal cells have two at right cells
• plants have centrosomes but not centrioles
16. cilia and flagella
• differ by length but have a 9 + 2 circular arrangement
• the 2 are in the center of the 9 microtubule doublets
• eukaryotes have membranes surrounding them but prokaryotes don't

cell membrane

• unit membrane is composed of a phospholipid bilayer with proteins
1. by weight the membrane is 50% lipid and 50% protein
2. hydrophobic fatty acid face inwards
3. hydrophilic phosphate with many different groups attached faces outwards
• E for external environment
• C for cytosol or cytoplasm
4. produced by endoplasmic reticulum with inner face of similar or same composition as E face or outer face of membrane
• phospholipids freely rotate on their long axis in the membrane but seldom flip-flop between layers
• takes ATP energy to do this
• results in the membrane being asymmetrical with distinct inner and outer layers of different protein composition and function
• cholesterol molecules fit between the fatty acid tails
1. reduces permeability of membrane
2. increase stiffness of membrane
3. can flip-flop between layers
• two major methods used to study unit membrane
1. freeze fracture
• freeze a solution of cells (red blood) in liquid nitrogen
• take cube of "ice" and split it with a sharp edge
  
• by chance alone some membrane will be separated between the bilayer
• place sample in a leofelizer to "etch" (freeze dry) it to expose the edge of the membrane
• examine with a scanning electron microscope
• can readily see E face and P (or C) face with proteins embdedded within (E face has glycolipids and proteins, P face has cytoskeletal filaments
1. cell fusion with immunoglobins and florescent dyes
• from cell culture use cells from two different but related species (human and mouse)
• membranes fuse and at first proteins remain separate
• after 30-40 min membrane proteins have completely interspersed with each other
• can move at about 2 μm/sec laterally in membrane
  
• asymmetry makes/allows each side of the membrane to be functionally distinct from each other (mitochondria, chloroplasts), enzyme action one side vs. other side
• disulfide bridges, tertiary bonding, vanderwaal's forced, ionic interactions
  
• membrane proteins
• peripheral proteins (on outside and inside of membrane)
  
• integral proteins
• anchored by covalent bonds or molecular interactions
• pH change or shaking can disrupt them
• integral proteins within membrane
  
• hydrophilic on surfaces and hydrophobic within membranes
• channel proteins-form pores
• carrier proteins-phagocytosis or pinocytosis, selective
• receptor proteins-for protein hormones, vitamins, or lipoproteins that may need to gain entry
• enzymatic proteins-for photosynthesis or respiration, especially electron transport
• LAB-differential centrifugation, segregate parts
• reside: starch grains, provides energy for embryo
• digestion = hydrolysis
• H₂O₂ is an oxidizer
• peroxisomes reduce it to water and oxygen
• presence of oxidizing molecules cause aging
• vacuoles hard to see, mostly salt and water
• turgor pressure-tree roots
• chromoplasts-petals, not green/plastids
• large vacuoles broken into smaller
• different ratios of different colored chromoplasts
• insects-largest group of plant consumers
• plants develop defenses, i.e. caffeine
• anabolism-build up
• catabolism-break down
• chloroplast
• 2-outer eukaryotic, inner prokaryotic
• outer membrane-clear, thylakoid green
• endosymbion theory-mitochondria/chloroplasts-bacteria adapted symbiosis
• monochlonoantibodies
• glamuglobulims
• ave theory-chloroplasts and mitochondria have own DNA
• trace ancetry through mutations
• MTAC = microtubule organizing center
• centrioles produce microtubules
• filaments fasten cells together
• SPM = semipermeable osmosis
• Ψ_s = -iCRT
• microtubule-hollow, 9 sets of triplets
• plants lack centrioles
• centrosomes located in MTOC region
• shaft of glagellum-ring of 9 microtubule doulbets anchored to central pair
• ATP changes shape
• membrane is extension of cytoplasm
• basal body at the bottom, then doublets continue
• cytoplasmic streaming
• animal cell
• hypotonic-burst, lysis
• hypertonic-shrivels, crenation
• Singer and Nicolson-fluid-mosaic model, freeze-fracture of membrane
• asymmetrical phospholipid bilayer
• Gibbs' free energy
• endosymbiosis theory-membrane through invagination
• MMC-major histocompatibility complex
• faciliated diffusion-no ATP
• energy causes protein to change shape
• doesn't take very much
• solute is moving through diffusion until even with membrane
• sodium potassium pump-active transport mechanism
• gradient high → low
• diabetes
• type I-juvenile
• type II-obesity