Life and Cells

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.g
if
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//www.cellsalive.com/howbig.htm http//www.io
nizers.org/Sizes-of-Bacteria.html
http//smccd.net/accounts/case/biol230/ex3/bact.jp
eg
4
Overview of prokaryotic cell.
5
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.

6
Structure of phospholipids
http//biyoloji_genetik.sitemynet.com/genel_biyolo
ji/genel_biyoloji_logos/phospholipids.gif
7
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
8
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
Membrane structure
http//www.slic2.wsu.edu82/hurlbert/micro101/imag
es/cytomemb.gif
10
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.
11
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.
12
Division of the EubacteriaGram Negative and
Gram Positive

• 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?

13
Gram Negative Gram Positive
http//www.conceptdraw.com/sampletour/medical/Gram
NegativeEnvelope.gif http//www.conceptdraw.com/sa
mpletour/medical/GramPositiveEnvelope.gif
14
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
Monomers of peptidoglycan
Units added to PG as a pair.
NAGN-acetyl glucosamine
NAM N-acetyl muramic acid (NAG lactic acid)
16
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
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
18
Teichoic acid and lipoteichoic acid
Found in G cell wall
19
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
20
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
21
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

• 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)