Transcript Bio-261-chapter-3

Chapter 3
Microscopy and Cell structure
Biology 261
Prof. Santos
• Microscope- tool used to see objects too small
to be seen by the naked eye. Types of
microscopes used in the study of
microorganisms include;
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light microscope
phase contrast microscope
confocal microscope
interference microscope
fluorescence microscope
electron microscope
atomic force microscope.
Terms to know
• Bright field microscopy- lights rays are used to
evenly illuminate the field of view.
• Dark field microscopy- light is directed
towards the specimen at an angle. This makes
it possible for the unstained specimen to
appear more visible against a dark background.
Electron Microscope
Electron microscope- uses a beam of electrons
to create an enlarged image of the specimen.
An electron microscope can magnify a
specimen up to 250,000x closer. The
wavelength used is less than the wavelength of
light, thus the resolution is greater.
2 types
• TEM- transmission electron microscope allows
one to see fine detail structures inside the cell.
• SEM- scanning electron microscope allows
one to see the surface details of cells like the
membrane proteins.
3-Phase contrast microscope- allows you
to see unstained cells by altering the
background of the cell. This microscope
has a device that allows it to amplifies
differences in refractive index to create a
contrast.
4-fluorescence microscope
Projects ultra violet light causing fluorescent
molecules in the specimen to emit a longer
wavelength.
5- Confocal microscope
Mirrors are used to scan a laser beam
across successive regions and planes of a
specimen. A computer program constructs
a 3D image.
6- Interference microscope causes the
specimen to appear as a 3D image.
8- Atomic force microscope
This very powerful microscope produces a very detailed
image of the surface of an specimen by using a very sharp
probe (stylus) to move across the surface and “feel” the bumps
and valleys of the atoms of the surface.
Prokaryote vs Eukaryote
Structure of prokaryote cell
1-Flagella provides motility. The flagella is made
up of three basic parts, filament, hook and
basal body.
• Chemotaxis- movement towards a
chemical
• Phototaxis- movement towards light
• Aerotaxis- movement towards oxygen
• Magnetotaxis- reaction towards the
magnetic field
• Thermotaxis- movement towards a
specific temperature
2-Pili proteins that enable the bacterium to
adhere to surfaces. Fimbriae allow bacteria to
adhere to surfaces and sex pili allow DNA
transfer between bacteria.
3-The capsule a viscous and gelatinous layer that
surrounds bacteria. It enables bacteria to
adhere to certain surfaces and allows
organisms to avoid innate defense systems and
cause diseases. Ex, Streptococcus pneumoniae.
4- slime layer- gel like layer that is diffuse and
irregular. This layer is composed of
polysaccharides and enables the bacteria to
adhere to surfaces and grow as biofilm.
Ex; Streptococcus mutans grows as biofilm on
your teeth to form dental plaque.
5- The cell wall a rigid covering consisting of
peptidoglycan that gives the bacterium its
shape and protection.
• The type of cell wall distinguishes between 2
types of bacteria; gram negative and gram
positive.
• Peptidoglycan is a macromolecule found only
in bacteria.
• The basic structure of peptidoglycan is an
alternating series of 2 major subunits, Nacetylmuramic acid (NAM) and Nacetylglucosamine (NAG). These subunits are
covalently bonded to each other to form a
glycan chain.
• Attached to each NAM molecule is a string
of 4 amino acids, a tetrapeptide chain.
Cross linkages can form between adjacent
chains thus joining adjacent glycan chains.
• In gram negative bacteria these tetrapeptides
are joined directly.
• In gram positive bacteria they are usually
joined indirectly by a peptide interbridge.
• In gram positive bacteria the peptidoglycan
layer is thick.
• In gram negative bacteria the peptidoglycan
layer is thinner.
Teichoic acid
• In gram positive bacteria there are polymers of
teichoic acid present. These teichoic acid polymers
are covalently linked to the NAM molecules of the
glycan chain. Some are linked to the cytoplasmic
membrane and are called lipoteichoic acids.
• These polymers consists of ribitol-phosphates and
glycerol phosphates molecules joined together.
Sugars and D- alanine may be attached to these
polymers providing antigenic determination.
• Teichoic acid provides rigidity to the cell wall
and give the cell negative polarity due to the
fact that they stick out above the
peptidoglycan.
Gram positive
Outer membrane
• In gram negative bacteria there is an outer
membrane outside the peptidoglycan. It is a
unique lipid bilayer.
• The outer membrane is unlike any other
membrane. The outside leaflet consists of
Lipopolysaccharides instead of phospholipids.
• The outer membrane is sometimes called the LPS or
lipopolysaccharide layer.
• The outer membrane is joined to peptidogylcan by
means of lipoproteins
• Two parts are importance for medical reasons;
a- Lipid A is the portion that anchors the LPS in the
lipid bilayer. It plays a role in the immune system.
b- O specific polysaccharide is a chain of sugar
molecules opposite the Lipid A. Allows for
identification.
periplasm
• In gram negative bacteria, it is the space
between the inner and outer membrane.
ENDOPLASMIC RETICULUM (ER)
Flagellum
Nuclear
envelope
Nucleolus
Rough Smooth
ER
ER
NUCLEUS
Chromatin
Centrosome
Plasma
membrane
CYTOSKELETON:
Microfilaments
Intermediate filaments
Microtubules
Ribosomes
Microvilli
Golgi apparatus
Peroxisome
Mitochondrion
Lysosome
Eukaryotic cell
1- Plasma membrane consisting of asymmetrical
lipid bilayer.
The cell membrane consists of proteins and
lipids.
Internal protein parts
2- Cilia/flagella are protein structures that
consists of microtubules in a 9 +2
arrangement. Cilia and flagella function in
motility.
3- cytoskeleton consists of proteins such as
microtubules, actin filaments and intermediate
filaments that function in cell structure/support
and act as a molecular monorail.
4- ribosomes are involved in protein production.
5- Chloroplast- double membrane bound
organelle involved in photosynthesis
6- Endoplasmic reticulum is a system of canals
involved in the production of macromolecules
destined to be secreted to other organelles or
outside. Two types, smooth and rough.
7- Golgi Apparatus is a system of flat
membranes involved in the modification of
material made in the ER. The vesicles are
coated with special carbohydrates and
phosphate groups that signal the vesicles to
their specific location.
9- Nucleus is the control center of the cell.
Contains the genetic material and is
surrounded by a nuclear envelope.
10- Mitochondrion is the site of cellular
respiration
11- Lysosomes
12- peroxisomes are organelles use to oxidize
substances, breaking down lipids, and
detoxifying certain chemicals.