Transcript outer membrane - allaboutmicro

Collage of Basic Science and Hummanities
Submitted to : Dr. Anurag Yadav
Asst. Prof. of Microbiology
Submitted by : Lalpara Ajay Kumar A.
6th sem. Microbiology
Reg.No
:12-00053-2012
Roll No.
: 15
Seminar Topic: Anatomy and Physiology of
prokaryotic cell
Anatomy And Physiology of
Prokaryotic Cell
Bacterial Shapes,
Arrangements, and Sizes
• Vary in shape, size, and arrangement but
typically described by one of three basic
shapes:
– Coccus – spherical
– Bacillus – rod
• Coccobacillus – very short and plump
• Vibrio – gently curved
– Spirillum – helical, comma, twisted rod,
• Spirochete – spring-like
3
Bacterial Shape and Arrangement
Bacterial Arrangements
• Arrangement of cells is dependent on pattern of
division and how cells remain attached after division:
– Cocci:
•
•
•
•
•
•
Singles
Diplococci – in pairs
Tetrads – groups of four
Irregular clusters
Chains
Cubical packets (sarcina)
– Bacilli:
• Diplobacilli
• Chains
• Palisades
5
Arrangement of bacilli
Prokaryotic Cell Structure
Cytoplasmic Membrane
• Surrounds cytoplasm and defines
boundaries of cell
• Acts as barrier, but also functions as an
effective and highly discriminating conduit
between cell and surroundings
• Made up of phospholipid bilayer
Movement of Molecules through
Cytoplasmic Membrane
•
1.
2.
3.
4.
Several ways for molecules to move
through membrane
Simple Diffusion
Osmosis
Facilitated Diffusion
Active Transport
Simple Diffusion
• Does not require expenditure of energy
• Process by which some molecules move
freely into and out of the cell
• Small molecules such as carbon dioxide and
oxygen
Transport Proteins
• Transport proteins (or transporters)
responsible for:
• Facilitated Diffusion
• Active Transport
Cell Wall
• Composed of peptidoglycan
• Comprised of alternating NAG and NAM
molecules
• Attached to each NAM is four amino acid
peptide: tetrapeptide
Categories of Bacteria
• Two Major Categories:
• Difference due to difference in chemical
structures of their cell walls
– Gram positive: stains purple
– Gram negative: stains red
Gram-Positive Cell Wall
• Thick, homogeneous sheath of peptidoglycan
– 20-80 nm thick
– Includes teichoic acid and lipoteichoic acid:
function in cell wall maintenance and enlargement
during cell division; move cations across the cell
envelope; stimulate a specific immune response
– Some cells have a periplasmic space, between the
cell membrane and cell wall
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Gram-Negative Cell Wall
• Composed of an outer membrane and a thin
peptidoglycan layer
• Outer membrane is similar to cell membrane bilayer
structure
– Outermost layer contains lipopolysaccharides and
lipoproteins (LPS)
• Lipid portion (endotoxin) may become toxic when released
during infections
• May function as receptors and blocking immune response
• Contain porin proteins in upper layer – regulate molecules
entering and leaving cell
– Bottom layer is a thin sheet of peptidoglycan
• Periplasmic space above and below peptidoglycan
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Outer Membrane
• Unlike any other membrane in nature
• A lipid bilayer with the outside layer made
of lipopolysaccharides instead of
phospholipids
• Also called LPS
• Contains Porins
Periplasm
- Region between cytoplasmic membrane and
the outer membrane
- Gel-like fluid
• Filled with secreted proteins and enzymes
External Structures
• Flagella
• Axial Filaments
• Fimbrae and Pili
Filamentous Protein Appendages
• Anchored in membrane and protrude from
surface
• Flagella: long structure responsible for
motility
• Fimbrae and Pili: shorter, responsible for
attachment
Fimbriae
• Fine, proteinaceous,
hairlike bristles
emerging from the
cell surface
• Function in adhesion
to other cells and
surfaces
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Pili
• Rigid tubular structure made of pilin protein
• Found only in gram-negative cells
• Function to join bacterial cells for partial DNA
transfer called conjugation
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Four types of bacteria with flagella
• Montrichious- one flagella
• Amphitrichous- flagella at both ends
• Lophitrichous- many flagella at the end of
the cell
• Peritrichous- flagella all over entire cell
Axial Filament
• Present in Spirochetes
• Attach at end of cell, spiral around,
underneath an outer sheath
• Move like a corkscrew
Internal Structures of Prokaryotic
Cells
Cytoplasm
• Substance of cell inside the cytoplasmic
membrane
• About 80% water
• Thick, aqueous, semitransparent, elastic
Chromosome
• Found within a central location known as
nucleoid
• Single, circular, double stranded
• Consists of all DNA required by cell
• Plasmids
–
–
–
–
–
Small circular, double-stranded DNA
Free or integrated into the chromosome
Duplicated and passed on to offspring
Not essential to bacterial growth and metabolism
May encode antibiotic resistance, tolerance to toxic
metals, enzymes, and toxins
– Used in genetic engineering - readily manipulated
and transferred from cell to cell
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• Ribosomes
– Made of 60% ribosomal RNA and 40% protein
– Consist of two subunits: large and small
– Prokaryotic differ from eukaryotic ribosomes in
size and number of proteins
– Site of protein synthesis
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Endospores
• Occurs in members of genera Bacillus and
Clostridium
• Dormant cell produced by a process called
Sporulation
• Germination- when they exit the dormant
state and then become a vegetative cell
• Several species of endospore formers can
cause disease