Introduction to Cell & Molecular Biology (BIOL121) - Dr. S.G. Saupe (; Biology Department, College of St. Benedict/St. John's University, Collegeville, MN 56321

Cells Lecture Guide

I.  Cell theory � major biological paradigm (Schleiden, botanist, 1838; Schwann, zoologist, 1839)

  • organisms comprised of one or more cells
  • cell basic unit of organization
  • cells derived from other cells (Virchow, 1858)

II.  Exceptions?

  • fungi � filamentous, no cross walls; slime molds � �blob-like� & multinucleate; virus

III.  Cell size

  • range from 100 nm (mycoplasmas) BIG (bird eggs)
  • typically small (5-40 μm)
  • difference between big/small organisms is number of cells, not cell size
  • how many cells in the average human?
  • Why aren�t cell larger?  Or, what sets an upper limit on size? 
    1. maintain control
    2. maintain large surface/volume ratio � sa � amounts of skin or outside; vol = amt guts; s/v = proportion of sa to volume; as an object gets larger its s/v ratio decreases; e.g., cats & buildings, parachutes, Goldilocks, ice
    3. important to maximize diffusion
  • Why aren�t cells smaller? Or, what sets a lower limit on size?  Must be big enough to house necessary cellular machinery (ribosomes, DNA, etc)

IV.  Cells show unity & diversity

  • diversity � size, structure
  • unity � share man common features
  • strong evidence for evolution, evolved from common ancestral cell
  • cell theory � if cells derived from other cells, must ultimately be one original cell
  • some deductive logic � IF cells from other cells, THEN cells must contain hereditary information that is passed from parent cell to daughter cell (some consider this a fourth axiom of the cell theory)

V.  Cells show compartmentalization � organelles

  • separates activities from other parts of cells
  • allows incompatible reactions to occur (i.e., hydrophilic/hydrophobic)
  • more efficient
  • helps diffusion
  • Factory Model

VI.  Cell membrane � gate keeper

  • boundary, regulates entry/exit, cell communication & recognition
  • cytoplasm
  • cytosol

VII. Nucleus � the �brains�

  • double membrane = TWO phospholipids bilayers
  • pores, nucleoplasm
  • chromatin = DNA; euchromatin, heterochromatin
  • nucleolus

VIII.  Mitochondrion � cell powerhouse

  • double membrane
  • own DNA, RNA, ribosomes, divide by fission
  • matrix/cristae � provides hydrophobic and hydrophilic regions for two different types of reactions
  • produces ATP via cellular respiration

IX.  Plastids

  • double membrane
  • also have own DNA, RNA, ribosomes, divide by fission
  • thylakoids
  • grana, stroma
  • types:  chloroplast � site of photosynthesis; amyloplasts � store starch; chromoplast � store pigments other than chlorophyll
  • interconvert from one to the other

X.  Ribosomes � sites of protein manufacture

  • site of protein synthesis
  • 2 subunits, one large, other small
  • made in nucleus (nucleolus), subunits exported to cytoplasm
  • zip codes help tag and determine which way materials transported
  • 2 subunits don�t assemble until begin making protein
  • ribosomes may be associated with ER or not

XI.  Endoplasmic Reticulum

  • membrane sacs & tubes
  • continous & interconnect with nuclear membrane & plasma membrane
  • rough � associated with ribosomes; smooth � no ribosomes
  • functions:  support, transport (highway system), membrane synthesis, synthesis of lipids, carbohydrates

XII.  Golgi Body

  • pita-like stack of membranes
  • polarity � cis/trans
  • shipping & processing center

XIII.  Lysosomes

  • membrane sacs
  • contain hydrolytic enzymes � digest materials in cells, recycling centers
  • acidic pH (ca. 5)
  • vesicles containing smaller cell or food particle or macromolecules fuses with lysosome; damaged organelles surrounded by membrane and fuse with lysosome

XIV.  Peroxisomes & glyoxisomes

  • types of microbodies � single membrane, contain catalase
  • hydrogen peroxide generated during metabolism
  • peroxisomes - common in leaf cells; remove photosynthetic waste products
  • glyoxisomes � common in seeds; metabolize fats in seeds

XV.  Endomembrane System

  • Vacuoles & vesiciles � membrane sacs, plants with large central vacuole

XVI. Cytoskeleton System

  • roles:  (a) structural support; (b) movement; (c) maintain cell shape; (d) anchorage for cell components; (e) cytoplasmic streaming
  • Components of cytoskeleton assembled/disassembled readily
  • Three major components: microtubules, microfilaments, intermediate filaments
    1. Microtubules � α and β tubulin; hollow, assembled at one end, disassembled at other; involved in chromosomal movements, structural support, resist compression
    2. Microfilaments � actin, twisted chain, cytoplasmic streaming; resist pulling
    3. Intermediate filaments � keratin, braided chains, resist pulling

XVII.  Cell Movements

  • via motor molecules; involve various proteins � dynein (microtubules), kinesin (moves vesicles along microtubules)
  • powered by ATP
  • allow microtubules to slide past one another & walk organelles along microtubules

XVIII.  Centrosome/Centriole

  • centrosome � region near nucleus where microtubules originate
  • centrioles � 9+3 arrangement; 2 bundles at right angles to one anther

XIX.  Cilia/Flagella

  • cilia � short, many, oarlike movement
  • flagella � long, few, undulate, whiplike movement
  • features:  9+2 arrangement, held by protein
  • anchored by basal body (9+3)
  • dynein arms

XX.  Cell walls (plants, fungi, bacteria)

  • like a box that surrounds a water balloon
  • wall essentially non-living
  • initially formed during cell division, subsequent additions by exocytosis, as wall gets thicker cell space gets smaller
  • like a steel-belted radial tire; rubber matrix with steel belts (cellulose in plants)
  • cellulose; fungi � chitin; bacteria � peptidoglycan
  • many functions � protect, prevent cell from bursting in hypotonic environment

XXI.  Prokaryotic cells

  • simple structure � cell membrane, cytoplasm, ribosomes, few other organelles
  • no nucleus, DNA in nucleoid region
  • DNA large circular loop (a few linear chromosomes aka eukarotes)

XXII  Cell surface � ECM

  • animal cells
  • extracellular matrix
  • cells essentially sugar-coated (& protein-coated)
  • made of assorted CHO�s & proteins (collagen)
  • integral proteins in membrane bind to collagen via fibronectin
  • helps cells adhere & cell recognition
  • metastatic cancer � failure of cells to remain attached

XXIII � Multicellularity & Cell/Cell Connections  (not on exam, F07)

  • multicellularity involved multiple times
  • cells link together
  • plants cells joined by middle lamella (�glue�)
  • animal cells connected via:
    1. ECM
    2. tight junctions � fuse membranes, prevent leakage
    3. desmosomes � like rivets, for strength; cadherin proteins

XXIV.  Cell/Cell Communication (not on exam, F07)

  • plants � plasmodesmata � cytoplasmic channels through wall
  • animals � gap junctions

XXV.  Getting Materials into/out of cells

  • exocytosis/endocytosis
  • diffusion/osmosis across membrane
  • phagocytosis
  • pinocytosis 

XXVI.  Comparison of Eukaryotic vs. Prokaryotic cells � complete table

XXVII. Comparison of Plant & Animal cells � complete table   

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Last updated: July 14, 2009     � Copyright by SG Saupe