Download Unit 2: Cell Structure, Growth and Biochemistry Chapters 4-7

Unit 2: Cell Structure,
Growth and Biochemistry
Chapters
4-7
Prokaryotes
• Bacteria are Prokaryotes – No nucleus or
organelles bound in membranes
• DNA is usually a single circular chromosome
• No Histones associated with DNA
• Cell Walls of peptidoglycan (polymer of NAG
and NAM cross-linked with polypeptide chain)
• Smaller ribosome unit
• Usually divide by binary fission (not mitosis)
Typical Bacteria makeup
I) Prokaryotic Cells
Binary Fission
Bacterial chromosome and an extra-chromosomal “plasmid”
Eukaryotes-
review material in Chapter 4 on own
Eukaryotes – “true nucleus”, and membrane bound organelles
DNA is membrane bound, inside nucleus, nuclear membrane is a double
membrane
Chromosomes are usually multiple (paired), and have special histone protein
associated with the DNA molecules
Membrane bound “organelles”: packages where specialized functions take place:
mitochondria, lysosome, ER, Golgi, etc.
Cell wall if present is chemically simple (cellulose, or chitin)
Slightly larger ribosome
Cells divide by a process like mitosis (and can have meiosis too)
• Cell shape is determined by the genetic
character of the organism. Its genes code for
the synthesis of the CW material and the cell
division mechanism that results in a “round” or
“rod” or “spiral” shape
• One of the criteria used in ID of bacteria
• Coupled with gram reaction = helpful
• Ex. Gram + cocci in clusters is “Staphylococcus”
Gram (-) bacilli, motile, green sheen on EMB is E.coli
Morphology & Arrangement
Varieties
1)Coccus
diplo = 2
strepto = chain of
tetrads = 4
sarcinae = cubed (8)
staphylo = cluster of
gndc
Tetrads!
Sarcina!
2) Bacillus
two meanings in
Microbiology-can refer to
shape or genus
3) Spirillum
vibrio = comma
spirillum = helical
(use true flagella)
spirochete = often more
spirals
(use axial filaments)
4. Also Star-shaped &
5. Rectangular-shaped
Stella
Haloarcula
Structures External to the Cell
Wall
• Glycocalyx
• Flagella
• Axial Filaments
• Fimbriae
• Pili
• Glycocalyx
• Glycocalyx – sugar coat, if tightly bound = capsule
• Protects and prevents from drying, also protects from phagocytes
(believed to be a virulance factor)
• Bacillus anthracis, Streptococcus pneumoniae, Klebsiella
• Not often seen in clinical lab (in vitro)-bacteria do not have a need to
form a capsule
• Slimy, and often a significant component of “biofilms”unorganized and loosely attached to the cell
• Extracellular polymeric substance (EPS)
Flagella
Flagella: complex organ of motility, a “motor”
A = monotrichous B = amphitrichous C = lophotrichous D = peritrichous
Gram negative bacteria contain 2 pairs of rings (outer pair
of rings attaches to cell wall; inner pair anchored to cell
membrane)
Gram positive bacteria contain only the inner pair
Flagella not as complex as those of the eukaryotes
Axial Filaments
Spirochetes have unique
structure and motility.
Anchored at one end of the
spirochete
Similar structure to flagella
Propel in a spiral motion
Similar to how a corkscrew
moves through a cork
Allows to move effectively
through body fluids
Fimbriae and Pili
Pili (sex pilus) = used to transfer
DNA from one cell to another by
conjugation
Taxis-movement of a bacterium toward a favorable
environment or away from an adverse one
Chemotaxis-chemical
Phototaxis-light
Bacterial Cell Envelope
•
•
•
•
Complex, multi-layered structure
Protects organism from outside environment
Gives bacteria shape
2 Types:
• Gram-positive
• Gram-negative
• Cell Wall, Outer membrane, Plasma
Membrane, etc.
Cell Wall
• Complex, semi-rigid structure
• Almost all prokaryotes have cell wall (excpetion-mycoplasma)
• Bacterial Cell Wall – macromolecule, polysaccharide, repeating sugars,
NAG and NAM, cross-linked with short chains of amino acids
• Composed of macromolecular network called peptidoglycan, aka:
murein; present alone or with other substances
• PRIMARY FUNCTION-prevents rupture from internal osmotic pressure
• protects cell, gives it its distinct shape; as volume of cell increases,
plasma membrane/cell wall expand
• Point of anchorage for flagella
Cell Wall
• Clinically-cell wall important-contributes to
ability of some species to cause disease
• Certain antibiotics work by inhibiting cell wall
synthesis (penicillins)
• Cell wall composition used to differentiate
many types of bacteria
Peptidoglycan makeup
• Repeating disaccharides connected by
polypeptides to form a lattice that surrounds
and protects the entire cell.
• One, large molecule
• Disaccharide portion is made up of
monosaccharides called N-acetylglucosamine
(NAG) and N-acetylmuramic acid (NAM) from
murus which means wall, which are related to
glucose.
• Components of peptidoglycan assembled in the
cell wall
• Alternating NAM and NAG molecules are linked
in rows of 10-65 sugars to form a carbohydrate
“backbone” (this is the glycan portion of
peptidoglycan)
• Adjacent rows are linked to polypeptides
• Tetrapeptide chains consist of 4 amino acids
attached to NAMSs in the backbone.
• Amino acids occur in alternating pattern of D
and L forms
• ***Unique: Amino acids found in other proteins
are L forms.
• Penicillin interferes with the final linking of
the peptidoglycan rows by peptide crossbridges
• Cell wall is greatly weakened and the cell
undergoes lysis, caused by the rupture of the
plasma membrane and the loss of cytoplasm
• Bacterial Cell Wall
• Bacterial Cell Wall
Gram-Positive Cell Walls
• Peptidoglycan: In most gp’s- cell wall is many layers
peptidoglycan
• Plasmic Space- area between cell wall and plasma membrane
Includes granular layer which is made of lipoteichoic acid
• Teichoic Acids-made up of mostly alcohol (glycerol phosphate
or ribitol phosphate)
• Two classes: lipoteichoic acid-spans the peptidoglycan layer and is
linked to plasma membrane
• Wall Teichoic acid-linked to peptidoglycan layer
Gram-Positive Cell Wall
• Teichoic Acids
• Negatively charged because of phosphate groups
• Therefore, may bind & regulate movement of cations into & out of cell
• Can also be involved in cell growth, preventing extensive wall
breakdown and possible cell lysis
• Provide much of cell wall’s antigenic specificity-therefore, help with
identification gram-positive bacteria
• Cell walls of GP streptococci are covered with polysaccharides that
allow grouping of types
Gram-negative cell wall
•
•
•
•
Consists of:
1.) Peptidoglycan
2.) Periplasm
3.) Outer membrane
Gram-negative cell wall
• Peptidoglycan:
• One or very few layers of peptidoglycan-bonded to
lipoproteins in the outer membrane & is in the
periplasm (gel-like fluid in periplasmic space)
Gram-negative cell wall
• Periplasm• High concentration of degradative enzymes
• Transport Proteins
• GN’s cell walls contain NO teichoic acids
Gram-negative cell wall
• Outer Membrane made up of• Lipopolysaccharides (LPS)
• Lipoproteins
• Phospholipids
• Several, specialized functions:
• Strong, negative charge important factor in avoiding
phagocytosis and actions of complement (lyses cells and
promotes phagocytosis)-2 important host defenses
• Barrier to detergents, heavy metals, bile salts, certain dyes,
antibiotics (i.e. pencillin), & digestive enzymes (i.e. lysozyme)
• Doesn’t block all environmental substances-nutrients must enter
Gram-negative cell wall
• Outer membrane permeability due in part to porins, that
form channels.
• Porins permit passage of molecules like nucleotides,
disaccharides, peptides, amino acids, vitamin B12, & iron
Gram-negative cell wall
• Lipopolysaccharide (LPS)
• Large, complex molecule of lipids and carbohydrates
• 3 components• Lipid A- lipid portion; embedded in top layer of O.M. **when GN
bacteria die, they release lipid A, which is an endotoxin-causes
symptoms associated with gn infections: fever, dilation of blood
vessels, shock, blood clotting
• a core polysaccharide- attached to lipid A; contains unusual sugars;
provides structure/stability
• an O polysaccharide- extends outward from core polysaccharide;
made up of sugar molecules; serves as an antigen-useful in ID (i.e. E.
coli 0157:H7-distinguished from other serovars through Ag testing)
***comparable to teichoic acid in gp’s.
Atypical Cell Walls
• L-form (phase) bacteria- certain prokaryotic cells have NO
wall or very little cell wall material. Mycoplasma genus
(smallest known bacteria that can grow and reproduce
outside living host cells). Pass through most bacterial
filters; were first thought to be viruses. Plasma membranes
are unique-have lipids called sterols, thought to help
protect from lysis
• Archaea- may lack cell walls, or have unusual cell walls
composed of pseudomurein
• Acid Fast Cell Walls- cell walls contain high concentration
of mycolic acid (hydrophobic, waxy lipid)
Damage to Cell Wall
• Chemicals that damage bacterial cell wallsunique to prokaryotes, therefore, often do
NOT harm animal host cells
• Cell Wall Synthesis is often target for some
antimicrobial drugs
• One way to damage cell wall-exposure to
digestive enzyme lysozyme
Susceptible to lysozyme
• Found in saliva, tears, & mucus
• Breaks down peptidoglycan wall- so, effective against most GP’s
• Catalyzes hydrolysis of bonds between sugars in repeating
disaccharide “backbone” of peptidoglycan.
• If cell doesn’t lyse, still surrounded by plasma membrane, could
still carry on metabolism- Protoplast
• Some Proteus and other genus’ can lose their cell walls and swell to
irregularly-shaped cells called L-forms (may also form in response to
penicillin or lysozyme).
• GN’s-usually does not destroy cell wall like in GP’s; some of outer
membrane also remains-Spheroplast
The Plasma (Cytoplasmic) Membrane
•
•
•
•
•
•
•
Also known as Inner Membrane
Thin structure
Located inside cell wall
Encloses cytoplasm
In prokaryotes-primarily phospholipids (mostly) & proteins
Lack sterols (eukaryotic membranes have), so not as rigid
**Exception: Mycoplasma (walless bacteria; have sterols)
Plasma Membrane
Plasma membrane
• Many proteins/some lipids on outer surface have
carbohydrates attached to them.
• Glycoproteins-proteins attached to carbohydrates
• Glycolipids-lipids attached to carbohydrates
• Function: protect/lubricate cell
•
cell-to-cell interactions (i.e. influenza virus & the
toxins which cause cholera & botulism enter their target cells by
first binding to glycoproteins).
• Phospholipids & proteins move freely within membrane-fluidmosaic model-allows molecules to move about without damaging
membrane
Plasma Membrane
• Functions:
• 1. Selective barrier- *most important function
• (selective permeability/semipermeability)
• Certain ions/molecules allowed to pass, but others are
stopped
• Large molecules (proteins) cannot pass
• Smaller molecules (water, oxygen, carbon dioxide, some simple
sugars pass-these are substances which dissolve easily in lipids)
• Ions penetrate slowly
Plasma Membrane
•
•
•
•
Functions continued:
2. breakdown of nutrients/production of energyContain enzymes which breakdown nutrients - ATP
In some bacteria, pigments/enzymes for photosynthesis
Plasma Membrane
•
•
•
•
Structure is vital to bacterial cell
Chemicals/compounds specifically damage plasma membranes.
Disinfectants-Alcohols/quaternary ammonium compounds
Polymyxins-group of antibiotics disrupt phospholipids; cause
leakage of intracellular contents--cell death
• Bacterial cell membrane: regulates what moves in and
out of the cytoplasm
• Diffusion –concentration gradients > high to low
• Osmosis – diffusion of water across a semipermeable
membrane
• Isotonic
• Hypertonic
• Hypotonic
•
•
•
•
***REVIEW ON YOUR OWN***
Passive transport
Active transport
Engulfment (phagocytosis, pinocytosis)
Specialized group translocation
Structures Inside the Cell Wall
1) Cytoplasm ~ 80% Water
•
Also contains metabolic enzymes
2) Nuclear Area (Nucleoid)
• 1 circular double-stranded DNA chromosome
• No histones
•Attached to the
plasma membrane
• May also contain PLASMIDS
• Also circular dsDNA
• Smaller: carry 5-100 genes (not critical for
survival)
• May be gained or lost without harming cell
• Often important in antibiotic resistance
• Used by us in genetic engineering
• Where F factor is contained if present
• Inside the bacterial cytoplasm
• Inclusions: granules of sugar, lipid storage, etc. (storage)
• Endospores (Genus: Bacillus and Clostridium) Hardiest of bacterial
structures. Difficult to kill with heat or chemical. Autoclave: 121
degree C, 15 lbs/sq. in. pressure – to penetrate thick coat and
destroy genome of bacteria. Purpose: survival not reproduction
• Inclusions:
3) Ribosomes = site of protein
synthesis
• Composed of ribosomal RNA (rRNA) & proteins
Actually 2 subunits:
30S & 50S
-S=Svedberg units
smaller and less dense than eukaryotic ribosomes-70s
(think of as size not weight; don’t add up to 70)
-Eukaryotic ribosome is 80s
Certain antibiotics work by inhibiting
protein synthesis at the ribosomes
• Streptomycin
• Gentamycin
• Erythromycin
• Chloramphenicol
4) Endospore = ‘resting
cells’
• Clostridium & Bacillus
• Can survive in boiling H2O 19
hours
SPORULATION
GERMINATION
•Location of endospore within cell is
useful in identification