Chapter 4 - Functional Anatomy of Prokaryotic and ...



Chapter 4 - Functional Anatomy of Prokaryotic Cells

Be able to Compare and Contrast Prokaryotes and Eukaryotes (See Ch 5 )

| |Prokaryotes | |Eukaryotes |

|Genetic Material |DNA | |DNA |

| |Located in nucleoid region – not membrane bound | |Enclosed in membrane bound nucleus |

| |1 circular chromosome;loosely attached to plasma membrane | |Many linear chromosomes |

| | | | |

| |complexed with basic proteins | |DNA & histone protein complex = chromatin |

| | | | |

| | | | |

|Cell Division |Binary fission | |Mitosis |

|Membrane-Bound Organelles | | | |

| |None | |Nucleus, Smooth & Rough ER, Golgi, Mitochondria, Chloroplasts; |

| |Inclusions serve various functions, e.g. storage | |Lysosomes, Vesicles, Peroxisomes |

|Cytoskeleton | | | |

| |Some actin microfilaments | |Microtubules, Microfilaments, Intermediate filaments |

|Cell Wall | | | |

| |Bacteria all except Mycoplasma | |Plants – cellulose |

| |Contains peptidoglycan | |Green Algae – cellulose |

| | | |Fungi – chitin |

| |Archaea – cell wall is absent or lacks peptidoglycan | |Animals - NONE |

|Cell Membrane |Phospholipid bilayer | |Phospholipid bilayer |

| |Proteins | |Proteins |

| |No sterols | |Animal Cells – cholesterol |

| |Energy production | |Fungi - ergosterol |

|Ribosomes |70S | |80S |

| | | |70S found in mitochondria and chloroplasts |

|Organisms |Bacteria | |Protists ( algae, protozoa, ) |

| |Archaea | |Fungi |

| | | |Plants |

| | | |Animals |

II. Bacterial Cells – Size, Shape, Arrangement

A. Size -- 2-8 um long X 0.2 – 2 um wide

B. Shape ( Morphology) & Arrangement

1. Cocci – spherical, round-oval

• Diplococci - pairs

• Tetrads - in fours

• Sarcinae – groups of 8,16,32

• Streptococci - chains

• Staphylococci – clumps or clusters

2. Bacilli – rod shaped –

• Single

• Diplobacilli - pairs

• Streptobacilli - chains

• Pill shaped – regular with blunt ends

• Fusiform - pointed ends

• Coccobacilli - short, rounded like cocci

• Filamentous – long and branching

• Pallisade formation – lined up like the slats in a fence

• Spore formers

3. Spiral – helical or curved bacteria - Table 4.2 for comparison

• Vibrios – very short, curved like a comma

• Spirilla – wavy , coiled and rigid

• Spirochetes - tightly coiled – corkscrew – flexible

C. Monomorphic – maintains 1 shape; Pleomorphic – has multiple shapes

III. Organization of Prokaryotic Cells

A. External Structures - Outside the Cell Wall

1. Flagella

• Function – motility

• Arrangement

o Monotrichous – 1 at one pole

o Amphitrichous – a tuft at each end

o Lopotrichous – 2 or more at one end

o Peritrichous – many covering entire cell

• Structure

o Filament – a helical protein chain with a hollow core ; unique proteins exposed on the filament can be used to identify bacteria – called “H antigens”

o Hook – attached to the filament

o Basal Body – anchors to the cell wall & plasma membrane

• Motility

o Flagella rotate – propels bacterium

o Pattern – smooth movement in one direction ( runs) ( followed by tumbles which produce abrupt random changes in direction

o Swarming – on solid agar – characteristic of Proteus species.

o Taxis – Directional Movement in response to a stimulus

▪ Chemotaxis – response to chemical signal

▪ Phototaxis – response to light

▪ Attraction – movement toward a (+) signal ( the attractant)

▪ Repulsion – Movement away from a (-) signal (the repellent)

2. Axial Filaments – Periplasmic Flagella

o Like a flagella, but located beneath the outer sheath

o Spirals around the bacteria, producing a corkscrew motion

o Found in spirochetes – (Spirilla have flagella

3. Fimbriae and Pili

o Both are composed of a protein called pilin

o Shorter, straighter & thinner than flagella – Not Motility Structures

o Fimbriae

▪ Few – 100’s / cell

▪ Polar or evenly distributed

▪ Function -- Adherence ( e.g. to mucous membranes ) ; necessary for bacteria to colonize a surface

o Pili

▪ Only 1-2 / cell

▪ Longer than fimbriae

▪ Conjugation pilus – joins cells and facilitates transfer of DNA from a donor cell to a recipient cell during bacterial conjugation Fig 4.8

4. Glycocalyx ( sugar coat)

• Composition – polysaccharides, proteins or mixture of both

• Capsule – organized – attached to cell wall

o Virulence factor – e.g., Streptococcus pneumoniae, Bacillus anthracis - encapsulated strains are pathogenic; strains lacking capsules may be non-pathogenic

o Protects bacteria from phagocytosis

o Unique proteins or polysaccharides on the capsule are called “K” antigens – can be used to identify the bacteria

• Slime layer – unorganized – loosely attached to cell wall

▪ Formation of biofilms – dental plaque, on plastic tubing, etc.

• Other Functions of the Glycocalyx

o Serve as a reserve supply of nutrients

o Prevents dehydration

o Prevents loss of nutrients

o

The Cell Envelope ( The Cell Wall, Cell Membrane and Outer Membrane)

1. Function

o Semi-rigid – maintains shape of the cell

o Prevents rupture from osmotic pressure

o Anchors flagella

o Contributes to pathogenicity

o Site of action of some antibiotics

o Differentiates major types of bacteria

2. Gram Positive Cell Walls

o Peptidoglycan

• Carbohydrate (NAG and NAM) backbone with protein side-chains

• strands are cross-linked by peptide bridges between the protein chains

• Some antibiotics (Penicillins) prevent the cross-links from forming; cell lyses

o Thick layer of peptidoglycan – makes gram positives susceptible to antibiotics in the penicillin family

o Teichoic Acids – negatively charged – regulate movement of (+) ions in/out of cell; serve as specific identification markers for the type of cell

o Surface Polysaccharides – if they are unique antigens, they can also be used to ID a cell ( e.g., Streptococcus species)

o Lipids – mycolic acids – found in the Mycobacterium( includes the bacteria which cause tuberculosis and leprosy) -- make these bacteria Acid-fast

3. Gram Negative Cell Walls

o Fewer, thinner layers of peptidoglycan – located next to the plasma membrane

o Outer membrane – covers the peptidoglycan layer

▪ Lipoprotein

▪ Lipopolysaccharide (LPS)

• “O” polysaccharides – antigens – used to ID gram negative bacteria

• Lipid A – an endotoxin – causes fever and shock if released into the bloodstream

▪ Phospholipid

▪ Strong negative charge

▪ Helps bacteria evade immune system

▪ Acts as a barrier to antibiotics, digestive enzymes, detergents, heavy metals, dyes, bile salts

▪ Porins – protein channels which allow nutrients to cross – can also be a site where bacteria can be invaded

4. Gram Stain Mechanism – based on differences in structure of cell walls of gram positive and gram negative bacteria

o Primary Stain – Crystal Violet – both types accept the CV

o Mordant – Iodine – forms crystal complexes with the CV – fixes it to the peptidoglycan layer of the cell wall

o Decolorizer – Acetone/alcohol – washes out the lipid in the outer membrane of the gram negatives and they lose the CV/Iodine complex – become decolorized; Gram positives will not decolorize – retain the purple CV

o Counterstain – Safranin – will be accepted by the colorless gram negatives ; stains them pink

o Gram positives don’t decolorize; remain purple

o Gram negatives decolorize ; accept safranin; appear pink

5. Non-Typical Cell Walls

o Mycobacteria and Nocardia – waxy fatty acids ( mycolic acid) – “acid-fast”

o Mycoplasma – the smallest bacteria; lack cell walls ; cell membrane is stabilized by sterols

o Archaea – most lack cell walls ; a few have cell walls but lack peptidoglycan

o L-Forms – cell wall deficient variations – bacterial species that normally produce cell walls, but have lost them ; can be due to chemical exposure or mutation

6. Damage to Cell Walls

o Bacterial cell walls do not resemble those found in eukaryotic cells ( remember, animal cells NEVER have cell wall at all )

o Make good targets for controlling growth of bacteria ; agents that target the cell wall will kill bacteria, but not the host cells

o Weaken the cell wall ( cells rupture due to osmotic lysis

o Lysozymes – digestive enzymes found in tears, mucus, saliva, breat milk, sweat ; more effective against the gram positive cell wall ; weakly effective against gram negatives

o Antibiotics – Penicillins – prevent peptidoglycan from forming cross bridges and linking into a stable cell wall ; more effective against gram (+) bacteria

7. Plasma Membrane – Fluid Mosaic Model

• Encloses the cytoplasm

• Phospholipids, Proteins, No sterols

• Phospholipid bilayer

o Phospholipids – hydrophilic head; hydrophobic tail

o Bilayer – hydrophilic exterior; hydrophobic interior

• Proteins

o Peripheral – attached to surface of membrane – enzymes, support, movement

o Integral – embedded in the membrane – channels & transport proteins

• Membrane fluidity – like olive oil; self-sealing; proteins & phospholipids move freely within the layer; “flip-flop” from one layer to the other rarely occurs

• Functions

o Selective barrier ; semipermeable

o Location of enzymes that break down nutrients & produce ATP

o Site of photosyntheses

• Many antimicrobial agents act by damaging the membrane

C. Bacterial Internal Structure

1. The Cytoplasm

• Area inside the membrane

• About 80% water

• Proteins, carbohydrates, lipids, ions, DNA, ribosomes, inclusions

2. Nucleoid (Nuclear ) Region

• Single circular chromosome (most bacteria)– genetic information is DNA

• Coiled around basic proteins,

• Not enclosed within a nuclear membrane

• Loosely attached to plasma membrane

• Plasmids – small circular pieces of dsDNA found in the cytoplasm

o Independent of chromosomal DNA

o About 5-100 genes

▪ antibiotic resistance; tolerance for toxic metrals; production of toxins ; synthesis of enzymes

o Easily gained or lost ; transferred between bacteria during conjugation

o Used to transfer genes in biotechnology applications

3. Ribosomes

• Found in all cells – prokaryotic or eukaryotic

• Site of protein synthesis

• 2 subunits – large & small

• composed of proteins and ribosomalRNA ( rRNA )

• Bacterial ribosomes are 70 S; unique target for some antibiotics

• Eukaryotic ribosomes are 80S; eukaryotes have 70S ribosomes in their mitochondria

• Antibiotics which target 70S ribosomes may be toxic to eukaryotic mitochondria

4. Inclusions – reserve deposits in the cytoplasm

o Metachromatic Granules – phosphate reserves;

▪ stain red with methylene blue

▪ found in algae, fungi, protozoa, bacteria

o Polysaccharide Granules – store carbohydrates

▪ Stain with iodine

▪ Glycogen – stains reddish brown

▪ Starch – stains blue-purple

o Lipid Inclusions

▪ Found in Mycobacterium sp., Bacillus sp.

▪ Stain with the Sudan dyes

o Sulfur Granules – energy reserves of sulfur

▪ Some bacteria use sulfur for metabolism ( e.g. Thiobacillus)

o Carboxysomes

▪ Photosynthetic bacteria need these for C02 fixation

▪ Found in nitrifying bacteria, cyanobacteria, thiobacillus

o Gas Vacuoles – used to maintain buoyancy in aquatic prokaryotes

o Magnetosomes

▪ Iron oxide deposits – act like magnets; for movement and orientation

▪ Decompose toxic peroxide

▪ Used to make magnetite – magnetic coating for recording and data tapes

5. Actin Cytoskeleton – found in rod-shaped and spiral bacteria ; reinforce the cell membrane and help maintain shape of the cell

6. Endospores

o “resting” cells – unique to bacteria

o for survival in unfavorable environments – resist heat, drying, chemicals, UV radiation – persist for years in the soil

o formed by gram positive bacteria

o position – terminal, subterminal, central

o sporulation (spore formation) – can be triggered by lack of nutrients – takes hours

o DNA duplicates, a layer of peptidoglycan and a protein spore coat surround the DNA

o The vegetative cell eventually dies and only the spore remains

o Germination – return to the vegetative state – triggered by damage to spore coat

o NOT A MEANS OF REPRODUCTION – 1 cell ( 1 spore ( 1 cell

o Concern for food processing – spores are resistant to heating, freezing, drying

o Some spore producing species ( e.g., Clostridium botulinum, Clostridium tetani, Bacillus anthracis) produce toxins that can cause food poisoning or disease.

o Special Stain for Spores – Schaefer-Fulton Stain

IV. Classification Systems in the Prokaryotes

Aid in differentiation, identification, organizing, demonstrating origins and relationships

A. Classification by Phenotype

o Shape, arrangement, staining characteristics, growth characteristics, biochemistry and genetics

o Genetic and Molecular analysis is most helpful ( especially rRNA comparison)

o Bergey’s Manual of Determinative Bacteriology - provides identification schemes based on cell wall composition, morphology, differential staining, oxygen requirements, biochemical testing. Does NOT classify according to evolutionary relationships.

o Bergey’s Manual of Systematic Bacteriology – for classification – organized according to evolutionary relationships.

o Only about 10% of the 2600 species listed in the Approved Lists of Bacterial Names are human pathogens.

B. Taxonomic Scheme – Classification of Bacteria ( according to Bergey’s Manual of Determinative Bacteriology)

There are 4 divisions; each divided into classes; seven classes total

Division I -- Thin, gram-negative cell walls

1. non-photosynthetic bacteria

2. anaerobic photosynthetic bacteria

3. cyanobacteria

Division II -- Thick, gram positive cell walls

1. rods and cocci

2. filamentous branching cells

Division III -- without cell walls

1. Mycoplasmas

Division IV - Unusual cell walls

1. Archaeobacteria

Classification of Viruses

Not part of any of the kingdoms; obligate intracellular parasites – discussed in Ch 6

C. Diagnostic Scheme -- Medically Important Bacteria -

An adaptation of the phenotypic scheme – Bacteria are identified by morphology, arrangement, differential and structural staining, colony characteristics, biochemical analysis, serological typing and genetic and molecular identification methods.

D. Species and Subspecies in Bacteria

The bacterial species – a population of cells with similar characteristics.

All members of the same species may not be identical. A subspecies or strain is a group of identical bacteria that all belong to the same species, but may differ from other members of that same species. A serotype is a group within a species that can be differentiated by having distinct surface molecules (antigens) which stimulates a distinct pattern of antibody responses in their host’s serum.

V. Survey of Prokaryotic Groups with Unusual Characteristics

A. Obligate Intracellular Parasites

o Rickettsia – transmitted to mammals by bite of blood sucking arthropods ( fleas, ticks, lice, etc.) - Pathogenic – Rocky Mountain Spotted Fever; epidemic typhus

o Chlamydias - Sexually transmitted diseases; trachoma; pneumonia

B. Free-Living Non-Pathogenic Bacteria

▪ Photosynthetic Bacteria

• Cyanobacteria: Blue-Green Bacteria ; contain chlorophyll a; perform oxygenic photosynthesis; widespread in aquatic environments

• Green and Purple Sulfur Bacteria; do not contain chlorophyll a; do not give off oxygen as a result of photosynthesis; found in anaerobic environments – sulfur springs, freshwater lakes, swamps

C. The Archaea

o Form a separate Domain

o Share many characteristics with eukaryotic cells

o Methanogens, Extreme Thermophiles, Acidophiles, Extreme halophiles, sulfur reducers; Psychrophiles

Chapter 5 – Eukaryotic Cells

o Be able to describe the structure and function of the Eukaryotic cell and its organelles

o Be able to compare and contrast Eukaryotic cells and Prokaryotic Cells

o Be able to explain the Endosymbiont Theory of the Evolution of Eukaryotic Cells – See Insight 5.1

The Evolution of Eukaryotes - Endosymbiont Theory – Lynn Margulis

Explains how eukaryotic cells with cell organelles evolved.

Cell Organelles such as mitochondria and chloroplasts may have evolved from a relationship between two prokaryotic organisms.

Chloroplasts may have evolved from photosynthetic bacteria that invaded and lived inside larger heterotrophic cells.

Mitochondria may have evolved from aerobic bacteria that invaded & lived inside larger, anaerobic cells. Eventually, the smaller cells ( endosymbionts) lost the ability to live on their own, and the larger cells lost the ability to survive without the smaller endosymbionts.

Evidence : Mitochondria and Chloroplasts

• Contain some of their own DNA – which is circular like that of prokaryotes

• Have their own ribosomes – 70S like those in prokaryotes

• Can make their own proteins independent of nuclear DNA

• Replicate independently of nuclear DNA

• Are motile

• Have double membranes that resemble the plasma membrane

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