Transcript Bacterial Structure and Function

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Small, smaller, smallest
• Science uses the metric system
– Each unit differs by 1000x (103)
– Length: meter, millimeter, micrometer, nanometer
– Molecules are too small to talk about length
• Units are molecular weight: grams/mol
• i.e. how much do 6.023 x 1023 molecules weigh?
• What sizes are we talking about?
– We can see things about 0.1 mm (100 µm)
– Bacteria are generally 1 – 5 µm (0.0001 mm)
– We need special microscopes to see smaller than that.
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Something can’t be smaller than
the parts it is made of!
Sand is used to make bricks, and bricks are assembled to
make a house. A house can’t be smaller than a brick; a
brick can’t be smaller than grains of sand.
Likewise, small molecules are combined to make polymers
and polymers are used to make cells.
cic.nist.gov/lipman/sciviz/scan/jun24_ptC1a.jpg
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In the world of small, what’s big?
• Cells of eukaryotic organisms are big
– Nerve cells can be quite long
– White blood cells are about 10 µm in diameter
– An amoeba may be around 20 µm
• Prokaryotes and cell organelles are smaller
– E. coli is about 1 µm long
– A mitochondrion is about the same size
• Particles are smaller
– Viruses range from 20 to 200 nm (0.02 – 0.2 µm)
– Ribosomes, found inside cells, are about 20 nm
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In the world of small, what’s smaller?
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• Ribosomes, viruses, cell walls are made of polymers
– Ribosomes and viruses are combinations of proteins and
nucleic acids
– Cell walls are made of large molecules like
peptidoglycan and lipopolysaccharide
• Polymers are larger than the monomers they are
made of
– Proteins range from 10,000 to 500,000 MW
– Bacterial DNA is over 1 mm long! (but very skinny)
– Polysaccharides can be > 100,000 MW (grams/mol)
In the world of small, what’s smallest?
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• These are all small molecules ranging from 18 g/mol
to 1,000 g/mol
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Water, oxygen gas, nitrogen gas
Sugars (glucose, sucrose, etc.)
Amino acids
Nucleotides
Fatty acids, cholesterol, (even phospholipids aren’t big)
Organic acids found in metabolism
Vitamins
Antibiotics and most other drugs
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Life and Cells
• What is Life?
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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.
• Eubacteria and Archaebacteria
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Bacterial Appearance
• Size
– 0.2 µm – 0.1 mm
– Most 0.5 – 5.0 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.jpeg
http://www.cellsalive.co
m/howbig.htm
http://www.ionizers.org/S
izes-of-Bacteria.html
Overview of
prokaryotic cell.
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From Membrane Out:
lecture 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
• Brief review of eukaryotic cell structure.
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Structure of phospholipids
http://biyoloji_genetik.sitemynet.com/genel_biyoloji/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.ultran
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Cell Membranes
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• 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 (peripheral)
or transmembrane (integral)
– Involved primarily with transport
– Degradation and biosynthesis
– Site of ATP synthesis
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Membrane structure
http://www.slic2.wsu.edu:82/hurlbert/micro101/images/cytomemb.gif
Outside the cell membrane:
the 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, providing
structural support and influencing the
shape of the cell.
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Division of the Eubacteria:
Gram Negative and Gram Positive
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• Gram stain invented by Hans Christian Gram
• 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.
– Gram positives stain purple; Gram negatives stain pink.
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Gram Negative
Gram Positive
http://www.conceptdraw.com/s
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iveEnvelope.gif
http://www.conceptdraw.com/s
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veEnvelope.gif
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
Units added to
PG as a pair.
NAG:
N-acetyl glucosamine
NAM: N-acetyl muramic acid
(NAG + lactic acid)
Glycan chains cross-linked with amino acids
•G- and G+ vary w/
DAP vs. lysine and
at the interbridge.
•Note the presence
of unusual “D”
amino acids.
•Peptides attached
to NAM.
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Peptidoglycan is a 3D molecule
Cross links are both horizontal and vertical between
glycan chains stacked atop one another.
http://www.sp.uconn.edu/~terry/images/other/peptidoglycan.gif;
http://www.alps.com.tw/cht/img/anti-allergy_002.jpg
Teichoic acid and lipoteichoic acid
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Found in G+ cell wall
Teichoic acid and lipoteichoic acid
Structure and Function
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•Polymer of phosphate and ribitol or glycerol
R: sugar or amino acid
•Lipoteichoic acid covalently attached to
membrane lipids.
•Major contributor to negative charge of cell
exterior.
•Appears to function in Ca++ binding
http://www.bact.wisc.edu/Microtextbook/images/textbook/structure/TAcid.gif;http://www.p
alaeos.com/Kingdoms/Prokaryotes/Images/GramPosCellEnvelope.gif
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
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• Osmosis: a special case of diffusion
– Water flows from where it is more concentrated (a dilute
solution) to where it is less concentrated (a solution with
many solute molecules)
• Osmosis requires a “semi-permeable” membrane
– One which water, but not dissolved substances, can pass
through.
Cells typically have lots of dissolved
substances; the net flow of water is
into the cell (unless resisted).
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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.gif
Osmosis definitions
• 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 can flow both ways; we
are considering NET flow.
• Terms are comparative terms,
like the word “more”.
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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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Bacteria and Osmotic pressure
• Bacteria typically face hypotonic environments
– Insides of bacteria filled with proteins, salts, etc.
– Water wants to rush in, explode cell.
– Protection from hypertonic environments is different,
discussed later.
• Peptidoglycan provides support
– Limits expansion of cell membrane
– Growth of bacteria and mechanism of penicillin
• Penicillin inhibits crosslinking, weakens wall
• Resting bacteria aren’t making new wall, aren’t
vulnerable
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Cell Wall Exceptions
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• 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)