1
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
2
The Essential Cell
Separates inside from environ.
Genetic
blueprint
Needed for
protein synthesis
http://web.jjay.cuny.edu/~acarpi/NSC/images/cell.gif
3
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
4
Rods (bacilli)
cocci
spirochetes
http://www.scientificpsychic.com/health/hygiene.html
Spirillum
http://www.daviddarling.info
/images/spirillum.jpg
Filamentous
www.theguardians.com/Mic
robiology/begg1_bg.jpg
Square
www.boingboing.net/bacteria.jpg
Overview of
prokaryotic cell.
5
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.
6
Structure of phospholipids
http://biyoloji_genetik.sitemynet.com/genel_biyoloji/genel_biyoloji_logos/phospholipids.gif
7
8
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
et/BiologyPages/L/LipidBilayer.gif
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
9
10
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.
11
12
Gram stain
Gram stain
invented by Hans
Christian Gram
Divides Eubacteria
into two main
groups based on
stain.
Correlates with
two types of cell
wall architecture.
Division of the Eubacteria:
Gram Negative and Gram Positive
13
• Stain is valuable in identification.
– Gram positives stain purple; Gram negatives stain pink.
• Architecture:
– Gram positives have a thick peptidoglycan layer in the
cell wall;
– Gram negatives have a thin peptidoglycan layer and an
outer membrane.
• BUT When we say Gram positive…
– Cells stain purple? Or have a particular structure?
14
Gram Negative
Gram Positive
http://www.conceptdraw.com/s
ampletour/medical/GramNegat
iveEnvelope.gif
http://www.conceptdraw.com/s
ampletour/medical/GramPositi
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”.
15
16
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.
17
18
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
19
Found in G+ cell wall
Teichoic acid and lipoteichoic acid
Structure and Function
20
•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
21
Effect of osmotic pressure on cells
• Hypotonic:
water rushes in;
PG prevents cell
rupture.
• Hypertonic:
water leaves
cell, membrane
pulls away from
cell wall.
plasmolysis
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
Lysozyme found in secretions cuts peptidoglycan
Antibiotic penicillin prevents cross linking
Cells in isotonic medium are not harmed
22
Cell Wall Exceptions
23
• 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)