Small, smaller, smallest

1
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.

2
Something cant 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 cant be
smaller than a brick a brick cant 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
www.littleitalymd.com/images/BrickLayer.gif
www.kevscartoons.com/images/illustration/chil...
3
In the world of small, whats 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

4
In the world of small, whats smaller?

• 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 gt 100,000 MW (grams/mol)

5
In the world of small, whats smallest?

• These are all small molecules ranging from 18
  g/mol to 1,000 g/mol
• Water, oxygen gas, nitrogen gas
• Sugars (glucose, sucrose, etc.)
• Amino acids
• Nucleotides
• Fatty acids, cholesterol, (even phospholipids
  arent big)
• Organic acids found in metabolism
• Vitamins
• Antibiotics and most other drugs

6
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.
• Eubacteria and Archaebacteria

7
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//www.cellsalive.com/howbig.htm http//www.io
nizers.org/Sizes-of-Bacteria.html
http//smccd.net/accounts/case/biol230/ex3/bact.jp
eg
8
Overview of prokaryotic cell.
9
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
• Brief review of eukaryotic cell structure.

10
Structure of phospholipids
http//biyoloji_genetik.sitemynet.com/genel_biyolo
ji/genel_biyoloji_logos/phospholipids.gif
11
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
12
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
  (peripheral) or transmembrane (integral)
• Involved primarily with transport
• Degradation and biosynthesis
• Site of ATP synthesis

13
Membrane structure
http//www.slic2.wsu.edu82/hurlbert/micro101/imag
es/cytomemb.gif
14
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, providing
structural support and influencing the shape of
the cell.
15
Division of the EubacteriaGram Negative and
Gram Positive

• 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.

16
Gram Negative Gram Positive
http//www.conceptdraw.com/sampletour/medical/Gram
NegativeEnvelope.gif http//www.conceptdraw.com/sa
mpletour/medical/GramPositiveEnvelope.gif
17
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.

18
Monomers of peptidoglycan
Units added to PG as a pair.
NAGN-acetyl glucosamine
NAM N-acetyl muramic acid (NAG lactic acid)
19
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.

20
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/peptid
oglycan.gif http//www.alps.com.tw/cht/img/anti-a
llergy_002.jpg
21
Teichoic acid and lipoteichoic acid
Found in G cell wall
22
Teichoic acid and lipoteichoic acidStructure and
Function

• 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/text
book/structure/TAcid.gifhttp//www.palaeos.com/Ki
ngdoms/Prokaryotes/Images/GramPosCellEnvelope.gif
23
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.

24
Osmosis

• 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).
25
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
26
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.

27
Effect of osmotic pressure on cells

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

28
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 arent making new wall, arent
  vulnerable

29
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)