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   

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