Transcript Cell Wall

Lecture 4
Prokaryote Cell
Structure & Function
Cell Diagram: Mariana Ruiz, pub domain
Size of Living Things
1 m = 100 cm = 1,000mm = 1,000,000 µm = 1,000,000,000nm
1mm = 1000 µm = 1000000nm
1 µm = 1000nm
Diagrams: http://www.cellsalive.com/howbig.htm
The Cellular Level of Organization
Living things are constructed of cells.
Living things may be unicellular or multicellular.
Cell structure is diverse but all cells share common characteristics.
Cells are small so they can exchange materials with their surroundings.
Surface area relative to the volume decreases as size of cell increases.
- limits the size of cells
___________________ states:
1. All organisms are composed of one or more cells.
2. Cells are the basic unit of structure and function in organisms.
3. All cells come only from other cells.
Two basic types of cells
_____________________
_____________________
Diagrams:
Prokaryotic & Eukaryotic Cell, Mariana Ruiz
Prokaryotes
Binary Fission
Tell me about Prokaryotes…
Diagrams:
Prokaryotic Mariana Ruiz
Binary Fission, JW Schmidt
Prokaryote Genetics
___________
Region of cytoplasm where chromosomal DNA is located.
Usually a singular, circular chromosome
____________
Small extra piece of chromosome/genetic material.
5 - 100 genes
Not critical to everyday functions.
Can provide genetic information to promote:
- Antibiotic resistance
- Virulence factors
(molecules produced by pathogen that specifically influence host's function to
allow the pathogen to thrive)
- Promote conjugation
(transfer of genetic material between bacteria through cell-to-cell contact)
STRUCTURE OF MICOBIAL CELLS
Prokaryotes
______________
Also known as proto-plasm.
Gel-like matrix of water, enzymes,
nutrients, wastes, and gases and contains
cell structures.
Location of growth, metabolism, and
replication.
______________
Bacteria’s way of storing nutrients
Staining of some granules aids in
identification
STRUCTURE OF MICOBIAL CELLS
Prokaryotes
_______________
Found within cytoplasm or attached to plasma membrane.
What are they made of?
What do they do?
Composed of a small (30S) subunit and a large (50S) subunit.
Cell may contain thousands of ribosomes.
Eukaryotic Cells
_________________
Cellular "scaffolding" or "skeleton" within the cytoplasm.
Major advance in prokaryotic cell biology in the last decade
has been discovery of the prokaryotic cytoskeleton.
Previously thought to be a feature only of eukaryotic cells.
Diagrams/Photos:
Fluorescent Cell: NIH, Pub Domain
Prokaryotes - Plasma Membrane
Separates the cell from its environment.
Phospholipid molecules oriented so that hydrophilic (__________) heads directed
outward and hydrophobic (__________) tails directed inward.
Proteins embedded in two layers of lipids (lipid bilayer).
___________________ to allow substances to pass into and out of the cell.
Diagrams:
Prokaryotic Cell, Mariana Ruiz
Membrane: NIST
Prokaryotes – Plasma Membrane as a Barrier
Primary function of plasma membrane → regulate
movement of molecules entering or leaving cell.
Movement of molecules across plasma membrane requires
energy.
PASSIVE TRANSPORT
Movement of molecules is passive if no energy sources of
the cell are expended.
_____________ = when molecules move from a higher to
a lower concentration.
What type of things might affect the rate of diffusion?
Diffusion Animation: biologycorner.com
Prokaryotes – Plasma Membrane as a Barrier
PASSIVE TRANSPORT (Continued)
_____________ Diffusion
Proteins assist in diffusion of molecules across plasma membrane.
Movement only occurs in the presence of a concentration gradient.
Some molecules move across the membrane more quickly if diffusion is facilitated
by a carrier molecule.
Diagram:
Facilitated diffusion, Mariana Ruiz
Prokaryotes – Plasma Membrane as a Barrier
Osmosis
Diffusion of ________ across the plasma membrane.
Environment surrounding cells may contain amounts of
dissolved substances (solutes) that are…
equal to
less than
greater than
…those found within the cell.
Tonicity
__________: no net movement of water between
cell and environment
__________: a higher concentration of solute.
__________: a lower concentration of solute.
Water will always move toward a hypertonic
environment!!
Diagrams:
Osmosis - www.scienceaid.co.uk/biology/plants/osmosis.html
Blood Cells: Mariana Ruiz
Prokaryotes – Plasma Membrane as a Barrier
_______________ TRANSPORT
How most molecules move across the plasma membrane.
Analogous to a pump moving water uphill.
Types of active transport are classified by type of energy used to drive molecules across
membranes.
ATP Driven Active Transport
Energy from adenosine triphosphate (ATP) drives substances across the plasma membrane
with the aid of carrier molecules.
Diagram:
Source unknown
Prokaryotes – Cell Wall
Peptidoglycan is a huge polymer of interlocking chains of
identical peptidoglycan monomers.
Backbone of peptidoglycan molecule composed of two
derivatives of glucose:
N-acetylglucosamine (NAG)
N-acetlymuramic acid (NAM)
NAG / NAM strands are connected by interpeptide bridges.
Peptidoglycan
- Rigid mechanical support
- Freely permeable to solutes
Image:
Peptindoglycan Structure: NicolasGrandjean
Prokaryotes - Cell Wall
From the peptidoglycan inwards all bacteria are very similar. Going
further out, the bacterial world divides into two major classes (plus a
couple of odd types). These are:
Gram-positive
Gram-negative
Images: PHIL Public Health Image Library
Prokaryotes - Cell Wall: Gram-Negative & Gram-Positive
Image:
Prokaryotic Cell, Mariana Ruiz
Gram +-, Julian Onions
Why are these differences
in cell wall structure so
important?
Images: Sources unknown
Prokaryotes - Glycocalyx
Some bacteria have an
additional layer
outside of the cell wall
called the glycocalyx.
This additional layer can
come in one of two
forms:
1. Slime Layer
2. Capsule
STRUCTURE OF MICOBIAL CELLS
Prokaryotes - Glycocalyx
Some bacteria have an additional layer outside of the cell wall
called the glycocalyx.
This additional layer can come in one of two forms:
1. ______________________
glycoproteins loosely associated with the cell wall.
Slime layers cause bacteria to adhere to solid surfaces and help
prevent the cell from drying out.
Streptococcus
The slime layer of Gram+ Streptococcus mutans allows it to
accumulate on tooth enamel (yuck mouth and one of the causes of
cavities).
Other bacteria in the mouth become trapped in the slime and form
a biofilm & eventually a buildup of plaque.
Staphylococcus
The slime layer of Gram+ Staphylococcus allows it to thrive in the
salty, hypertonic environment of the skin.
Glycocalyces are not specific to Gram+ or Gram- bacteria,
sometimes only some members of a certain species (strains) have a
glycocalyx, whereas others don’t.
STRUCTURE OF MICOBIAL CELLS
Prokaryotes - Glycocalyx
2. ___________________
polysaccharides firmly attached to
the cell wall.
Capsules adhere to solid surfaces and to
nutrients in the environment.
Adhesive power of capsules is a major
factor in the initiation of some bacterial
diseases. Capsule also protect bacteria
from being phagocitized by cells of the
hosts immune system.
STRUCTURE OF PROKAROTIC CELLS
Prokaryotes - Glycocalyx
Bacterial Capsule and Meningococcal Infection
Meningococcal infection is caused by meningococcal
bacteria (Neisseria meningitidis).
Causes:
1.
meningococcal meningitis (infection of the
meninges/spinal cord)
2.
meningococcal septicaemia (blood poisoning).
Of the two forms, meningococcal septicaemia is the
most dangerous.
Meningococcal bacteria are the most common cause
of bacterial meningitis.
Meningococcal bacteria grow
in pairs called diplococci often
surrounded by a capsule coat.
Over a million of these would
fit on the head of a pin.
Approximately 5% of people who suffer from
meningococcal meningitis will die.
http://www.meningitisuk.org/about-meningitis/bacterial-meningitis.htm
STRUCTURE OF PROKAROTIC CELLS
Prokaryotes - Endospores
Dormant, tough, non-reproductive
structure produced by small
number of bacteria.
Primary function of endospores:
_________________________
_________________________
Resistant to radiation,
desiccation, lysozyme,
temperature, starvation, and
chemical disinfectants.
A stained preparation of Bacillus
subtilis showing endospores as green
and the vegetative cell as red
Endospores commonly found in soil
and water, where they may
survive for long periods of
time.
Image:
Stain: Jerry Keplinger, James H. Quillen College of Medicine
Procedure: Source link no longer works
STRUCTURE OF PROKAROTIC CELLS
_____________________
The most significant cause of pseudomembranous colitis
Severe infection of the colon, often happening after normal gut flora is eradicated by
use of antibiotics. The C. difficile bacteria naturally resides in the body, but
becomes overgrown.
C. difficile overgrowth is harmful because the bacterium releases toxins that cause:
* Bloating and constipation
* Diarrhea with abdominal pain
* Severe diarrhea with mucus and blood present in feces
* Body aches and severe abdominal pain caused from ulcerated intestines
•
Treatment includes specific anticlostridial antibiotics, e.g. metronidazole or
vancomycin.
•
News story link: http://www.thesun.co.uk/sol/homepage/news/article860499.ece
STRUCTURE OF PROKAROTIC CELLS
Prokaryotes – Surface Appendages
Some prokaryotes have distinct appendages that allow them
to move about or adhere to solid surfaces.
Consist of delicate stands of proteins.
___________
Long, thin extensions that allow some bacteria to move about
freely in aqueous environments.
____________ (endoflagella)
Wind around bacteria, causing movement in waves.
____________
Most Gram- bacteria have these short, fine appendages
surrounding the cell. Gram+ bacteria don’t have.
No role in motility. Help bacteria adhere to solid
surfaces. Major factor in virulence.
____________
Tubes that are longer than fimbriae, usually shorter than
flagella. Use for movement, like grappling hooks, and also
use conjugation pili (singular = pilus) to transfer plasmids.
Images:
Flagella: Mike Jones Wiki
Axial Filament: Indiana USchool of Med
EColi: Pub Library of Science
Neisseria gonorrhoeae
Gonorrhoeae one of the most communicable disease in the US.
125 cases per 100,000. Teens 15-19 yo 634 cases per 100,000. Young adults
20-25 460 per 100,000.