Transcript Chapter 4 Prokaryotic Cell

Chapter 4
Prokaryotic cell
• Bacteria are prokaryotic organisms
• DNA is not enclosed within a membrane
• DNA is not associated with histone
proteins ( no nucleosomes)
• No membrane bound organelles.
• Cell walls – peptidoglycan
• Divide by binary fission
Curved rod
Bent rod
Loose spiral
Tight spiral
Glycocalyx
• Capsule – gelatinous substance – outside
the cell wall.
• Polysaccharides
• Contribute to the virulence
• Protect bacteria from phagocytosis
• Capsulated Streptococcus pneumoniae –
pneumonia
• Uncapsulated – destroyed by WBCs
•
•
•
•
•
•
•
•
•
Streptococcs mutans – surface of teeth
Tooth decay
Flagella
long filamentous
Movement – motile
Rotate their flagella to swim
Exhibit chemotaxis
Positive chemotaxis – towards substances
Negative chemotaxis - move away
Spirochetes
Treponema pallidum
syphilis
Fimbriae
• Gram - bacteria have hair like structures.
• Shorter thinner than flagella
• Numerous
• Attachment – virulence
• Neisseria gonorrhoeae – fimbriae –
Mucous membrane – colonize the area
• No fimbriae – cannot colonize
Pili
•
•
•
•
One or two pili
Longer than fimbriae
Used for conjugation
Join two bacterial cells together for DNA
transfer
Cell wall
• Protects internal structures and plasma
membrane
• Made up of peptidoglycan
• Glycan – sugar – repeating units of disaccharide
• N-acetylmuramic acid
• N-acetylglucosamine
• Peptido-peptide-amino acids
• Rows are sugars are cross linked by amino acid
chains.
Lipoprotein
Phospholipid
lipopolysaccharide
Lipid A
Endotoxin
Septic shock
•
•
•
•
•
•
•
•
Mycoplasma has no cell walls
Cell wall can be damaged
Antibiotic penicillin
Stops the formation of peptide cross
bridges in peptidoglycan
Lysozyme-enzyme-tears, saliva, mucus
Breaks the bond between sugar
molecules.
Gram- more resistant – outer membrane
Gram+ more sensitive – peptidoglycan is
exposed to the environment
Plasma membrane
•
•
•
•
•
•
Encloses the cytoplasm
Phospholipids and proteins
No sterols – exception is mycoplasma
Phospholipids are arranged in a bilayer
Proteins are inserted
Structure – fluid mosaic
• Plasma membrane – selectively
permeable (semipermeable)
• Damaged by alcohol, polymyxin
• Molecules constantly cross the membrane
• Nutrients get into the cell
• Waste products move out of the cell
• Active process and passive process
• Passive process – molecules move from
an area of high concentration to low
concentration. Energy is not used.
• Active process – molecules move from an
area of low concentration to high
concentration Energy is used.
• Passive process
• Simple diffusion, facilitated diffusion,
osmosis
• Simple diffusion – molecules move from
an area of high concentration to low
concentration.
• CO2 and O2 cross the membrane by
means of simple diffusion.
• Facilitated diffusion – molecules move
from an area of high concentration to low
concentration. Energy is not used.
• Transport proteins are used.
• Osmosis – movement of water molecules
from an area of high concentration of
water to an area of low concentration of
water through a selectively permeable
membrane.
• hypotonic – solute concentration lower
outside the cell. Water moves into the cell.
• Cell swells up and breaks down. Osmotic
lysis.
• Cell walls are damaged – bacteria
undergo osmotic lysis.
• Hypertonic – solute concentration is higher
outside the cell.
• water moves out of the cell. Plasma
membrane shrinks away from the cell wall.
• Plasmolysis
• Most bacteria cannot survive in a
hypertonic environment
Active process
• Active transport - molecules move from an area
low concentration to high concentration. Energy
is used. Transport proteins are involved. Ribose,
histidine
• Group translocation – molecules move from an
are low concentration to high concentration.
Energy is used. Transport proteins are involved.
While the molecule is being transported, it is
chemically altered.
• Glucose transported across the membrane,
phosphate is added.
• Cytoplasm – carbohydrates, proteins,
lipids, ribosomes, DNA, inclusions
• Nuclear area (nucleoid) – long circular,
double stranded DNA – chromosome
• Genetic information needed for the
structure and function of the cell.
• Some bacterial cells – small circular DNA
– plasmid
• Plasmids make the bacterium resistant to
antibiotics.
• Ribosomes – two subunits
• Each subunit is made up of proteins and
ribosomal RNA.
• 70S ribosomes – smaller, less dense than
80S ribosomes
• Protein synthesis
• Inclusions – organic or inorganic
• Metachromatic granules – phosphate –
used by the cell to make ATP.
• Corynebacterium diphtheriae
• Polysaccharide granules – glycogen or
starch
• Lipid inclusions – hydroxybutyric acid
• Bacillus, Mycobacterium
• Sulfur granules – Thiobacillus – uses
sulfur for energy.
• Carboxysomes – enzyme – ribulose
diphosphate carboxylase.
• Needed for photosynthesis
• Cyanobacteria – photosynthetic bacteria
• Gas vacuoles – hollow cylinders covered
by protein.
• Float at a certain depth in water - light
Endospores
• Clostridium and Bacillus
• Dormant stage of the cell
• Resistant to hostile environmental
conditions
• Heat, UV light, disinfectant, desiccation
• Nutrient depletion
• sporulation
• Endospores – dehydrated
• DNA, RNA, ribosomes, enzymes, dipicolinic
acid, calcium ions.
• Stay dormant for thousands of years.
• When conditions are favorable, spores
germinate into vegetative cells.
• Sporulation is not reproduction.
• One cell – one spore – germinates into a single
cell.
• No increase in the number of cells