Life and Cells

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Life and Cells

• What is Life?
• Can grow, i.e. increase in size.
• Can reproduce.
• Responsive to environment.
• Metabolism can acquire and utilize energy.
• Schwann and Schleiden cells basic unit of life
• Prokaryotes and eukaryotes from microscopy.
• Our focus prokaryotic cells.

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Bacterial Appearance

• Size
• 0.2 µm 0.1 mm
• Most 0.5 2.0 µm

• Shape
• Coccus (cocci) rod (bacillus, bacilli) spiral
  shapes (spirochetes spirillum, spirilla)
  filamentous various odd shapes.
• Arrangement
• Clusters, tetrads, sarcina, pairs, chains

http//smccd.net/accounts/case/biol230/ex3/bact.jp
eg
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Overview of prokaryotic cell.
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From Membrane Outlecture order

• Examination of layers of bacterial cell
• Starting at cell membrane, working to outside
• A look at how cells move
• Examination of inside of bacterial cell
• A look at how things get into cells
• Review eukaryotic cell structure on your own.

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Structure of phospholipids
http//biyoloji_genetik.sitemynet.com/genel_biyolo
ji/genel_biyoloji_logos/phospholipids.gif
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How phospholipids work
Polar head groups associate with water but
hydrophobic tails associate with each other to
avoid water. When placed in water,
phospholipids associate spontaneously side by
side and tail to tail to form membranes.
http//users.rcn.com/jkimball.ma.ultranet/BiologyP
ages/L/LipidBilayer.gif
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Membrane structure
http//www.slic2.wsu.edu82/hurlbert/micro101/imag
es/cytomemb.gif
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Cell Membranes

• 50/50 lipids and proteins
• Fluid mosaic model
• Effective barrier to large and hydrophilic
  molecules
• O2, CO2, H2O, lipid substances can pass through
• Salts, sugars, amino acids, polymers, cannot.
• Proteins can be on inner, outer surfaces or
  transmembrane
• Involved primarily with transport
• Degradation and biosynthesis
• Site of ATP synthesis

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Outside the cell membranethe Cell Wall
Animal cells do not have a cell wall outside the
cell membrane. Plant cells and fungal cells
do. So do most prokaryotic cells, provided
structural support and determining the shape of
the cell.
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Division of the EubacteriaGram Negative and
Gram Positive

• Gram stain invented by Hans Christian Gram
• Gram positive cells stain purple Gram negatives,
  pink.
• When we say Gram positive
• Cells stain purple? Or have a particular
  structure?
• Architecture
• Gram positives have a thick peptidoglycan layer
  in the cell wall
• Gram negatives have a thin peptidoglycan layer
  and an outer membrane.
• Stain is valuable in identification.

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Gram Negative Gram Positive
http//www.conceptdraw.com/sampletour/medical/Gram
NegativeEnvelope.gif http//www.conceptdraw.com/sa
mpletour/medical/GramPositiveEnvelope.gif
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Function and Structure of peptidoglycan

• Provides shape and structural support to cell
• Resists damage due to osmotic pressure
• Provides some degree of resistance to diffusion
  of molecules
• Single bag-like, seamless molecule
• Composed of polysaccharide chains cross linked
  with short chains of amino acids peptido and
  glycan.

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Monomers of Peptidoglycan NAG and NAM
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Peptidoglycan structure
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2nd Law of Thermodynamics

• All things tend toward entropy (randomness).
• Molecules move (diffuse) from an area of high
  concentration to areas of low concentration.
• Eventually, molecules become randomly distributed
  unless acted on by something else.

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Osmosis
Yellow spots cannot move through membrane in
middle. Water moves into compartment where spots
are most concentrated, trying to dilute them,
make concentration on both sides of the membrane
the same.
In this example, gravity limits how much water
can flow. In a bacterium, the peptidoglycan
provides the limit.
http//www.visionengineer.com/env/normal_osmosis.g
if
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Osmosis-2

• Osmosis special case of the diffusion of water.
• Movement of water across a semi permeable
  membrane.
• If the environment is
• Isotonic No NET flow.
• Hypertonic Water flows OUT of cell.
• Hypotonic Water flows IN.
• (water flows from where it is in high
  concentration to where it is in low
  concentration.)

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Bacteria and Osmotic pressure

• Bacteria typically face hypotonic environments
• Insides of bacteria filled with proteins, salts,
  etc.
• Water wants to rush in, explode cell.
• Peptidoglycan provides support
• Limits expansion of cell membrane
• Growth of bacteria and mechanism of penicillin
• Bacteria need different protection from
  hypertonic situations
• Water leaves the cell cell membrane shrinks
• Lack of water causes precipitation of molecules,
  death

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Effect of osmotic pressure on cells

• Hypotonic water rushes in PG prevents cell
  rupture.
• Hypertonic
• water leaves cell, membrane pulls away from cell
  wall.

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PG synthesis
Penicillin interferes w/ enzymes attaching new
pieces, but old PG is cut anyway Kablam.
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Teichoic Acids

• Polymers found in Gram cell walls
• Either ribitol or glycerol phosphate
• Associated with PG
• Lipoteichoic acid attached to membrane
• Bind to cations? Help regulate autolysins?
• No one knows!

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Cell Wall Exceptions

• Mycobacterium and relatives
• Wall contains lots of waxy mycolic acids
• Attached covalently to PG
• Mycoplasma no cell wall
• Parasites of animals, little osmotic stress
• Archaea, the 3rd domain
• Pseudomurein and other chemically different wall
  materials (murein another name for PG)