Cellular Evolution
— prokaryotes: appear 3.5 billion years ago
— eukaryotes: appear 2.5 billion years ago
— Endosymbiotic Theory states that eukaryotic cells evolved from a cooperation of prokaryotic cells
— -large prokaryotes lost their walls and engulfed smaller ones which specialized to become organelles
Evidence:
— both mitochondria and chloroplasts have features similar to bacteria:
— -circular loop of DNA
— -70s ribosomes
— -similar size and shape
— -can replicate independent of host cell via binary fission
— -double membrane: cell membrane plus endosome/phagosome from being internalized
— Cyanophora paradoxa:
— Living example of a prokaryote inside a eukaryote
— (both require each other for survival)
Cell Size and the Significance of Smallness
- The small size of prokaryotic cells affects their physiology, growth rate, and ecology.
- There are advantages to being small
— Small cells contain more surface area relative to cell volume than large cells (i.e., higher S/V)
— Support greater nutrient exchange per unit cell volume
— Tend to grow faster than larger cells
— Rate of flow in/out cell is inversely proportional to cell size
Prokaryotic & Eukaryotic Cells
The Prokaryotic Cell
“pre-nucleus” --bacteria and archaea
“pre-nucleus” --bacteria and archaea
Size:
- 0.2-2.0μm diameter, 2-8 μm length
Shape: Three basic shapes
· coccus = sphere
· bacillus = rod
· spiral = twisted
· Other shapes are- star, (Stella) rectangular,flat (Haloarcula), triangular shape
· Monomorphic/Pleomorphic
· Division by binary fission:
Can result in daughter cells remaining loosely adhered along the division plane resulting in characteristic arrangements
Arrangement:
1. Cocci
· Single coccus: daughter cells separate
· Diplococcus: 2, flat on adjacent sides, e.g. Neisseria
· Streptococci: chain, all cells divide in same plane. e.g. Enterococcus faecalis, Streptococcus, Lactococcus.
* Tetrad: 4, division occurs in two planes, e.g. Micrococcus
* Sarcinae: 8, division occurs in three planes, e.g. Sarcina
* Staphylococci: group, cluster, cells dividein random planes. e.g. Staphylococcus aureus
2. Bacilli
l rods of various length
l rods divide only along the short axis
l single bacillus: daughter cells separate
l diplobacilli: 2 cells
l streptobacilli: chain, e.g. Bacillus megaterium
l coccobacillus: short oval,
l cocci are perfectly spherical, any ovalish shape = bacillus
3. Spiral
l one or more twists
a) vibrio: curved rod
b) spirillum: rigid helical shape, move via flagella
l Most bacteria are monomorphic: always one shape
l Some are genetically pleomorphic: have varied shapes within the population of a single species
Structure of the Prokaryotic Cell
l Glycocalyx
l Flagella
l Cell wall
l Cell membrane
l Cytoplasm
l Nuclear area
l Ribosome
l Inclusion body Endospore
1) Glycocalyx
l external, outermost surface layer of secreted carbohydrate-rich gelatinous material, usually sticky or slimy
l capsule = organized glycocalyx, firmly attached to cell wall
l slime layer = unorganized glycocalyx, loosely attached to cell wall
Functions
l -promote biofilm formation
l -allow cell adhesion to substrate
l or host tissues
l -protect cell from dehydration
l -protect cell from nutrient loss
l -protect cell from phagocytosis
2) Flagella
l -long, filamentous appendages
l -used for motility
Arrangements:
A. monotrichous: one on one end
B. amphitrichous: one or more on each end
C. lophotrichous: two or more on one end
D. peritrichous: all over cell
Structure
a. filament:
-made up of intertwined chains of flagellin protein
-hollow core
-sticks out beyond plasma membrane and cell wall
b. hook:
-provides rotational movement of flagella
-solid, composed of hook protein
c. basal body:
-rod and disc structure
-anchors flagellum to cell wall flagellum rotates to cause taxis of bacteria taxis = movement, usually toward or awayfrom a stimulus (chemotaxis, phototaxis)
Axial Filaments
-endoflagella
-used by spirochetes for taxis
-Consist of flagella-like structures
l wound around spirochete under the outer sheath
l rotation of filaments produces cork-screw rotation of sheath and thus whole spirochete
l rotation allows penetration of secretions and tissues
Fimbriae and Pili
l -short, hair-like appendages
l -composed of pilin protein
l Fimbriae:
-at poles or all over surface
l -up to few hundred
l per cell
l -“fuzzy” coat used
l for adherence
l Pili/Pilus:
l -usually one, if present
l -used to transfer DNA to neighboring cell
l -more rarely, some types used for movement
3) Cell Wall
l -located outside the cell/plasma membrane
l -gives cell its shape
l -provides protection
l -resists osmotic lysis
l -provides anchorage point for flagella
l composition:
-in bacteria = peptidoglycan (aka murein):
-lattice of disaccharides and polypeptides
-repeating disaccharide chains formed by
two monosaccharides linked end to end:
l NAG (N-acetylglucosmine)
l NAM (N-acetylmuramic acid
l -disaccharide chains are held together by polypeptides to form a tight wall
l -Two common cell wall types in bacteria:
1. Gram Positive Cell Walls
l -thick, many layers of peptidoglycan,
l strong, rigid-also contain teichoic aci
2. Gram Negative Cell Wall
l -has an outer membrane
l -periplasmic space between outer membrane and cell membrane
l Houses the peptidoglycan in periplasm
l -few layers of peptidoglycan, thinner,
l weaker
l -no teichoic acid
*G-wall = outer membrane + thin peptidogycan in periplasm
l -outer membrane:
l -composed of phospholipids, lipoproteins and lipopolysaccharide (LPS)
l -has porins to allow exchange with environment
l functions of outer membrane:
-evade phagocytosis
-avoid action of complement
l -chemical barrier: resist antibiotics, digestive enzymes detergents, heavy metals, dyes, etc.
-LPS is toxic to animals (Lipid A portion) causes endotoxic shock
Unusual wall structures
a. Mycobacterium species:
l -Gram+ structure with mycolic acids
l - (waxy) resists dehydration
b. Mycoplasma species:
l -smallest bacteria
l -no cell wall
l -have sterols in membrane (resist osmotic lysis)
c. Archaea
l -either no walls or
l -walls consisting of pseudomurein (different carbohydrate)
l Many antimicrobial drugs target bacterial cell walls:
l safe target, chemical structure not found in animals e.g. Penicillin: prevents peptide crosslinking, prevents formation of functional wall in growing cells e.g. Lysozyme:
l enzyme produced by some eukaryotes
l found in human secretions
l digests the NAG-NAM linkages
l weak wall = osmotic cell lysis
l most effective against Gram+ve (outer membrane protects Gram-ve)
4) PlasmaMembrane/CellMembrane/Cytoplasmic Membrane
l -located inside the cell wall
l -functions to enclose the cytoplasm
l composed of a dynamic phospholipid bilayer:
l phosphate + glycerol = hydrophilic end
l fatty acid tails = hydrophobic end
l membrane self forms into bilayer to protect hydrophobic regions from water inside and outside the cell
l membrane has associated proteins
l peripheral proteins: at surface
-enzymes for metabolic reactions
-support, communication
l integral proteins / transmembrane proteins:
-span width of bilayer
-channels for transport
5) Cytoplasm
l The substance contained by the plasma membrane
l ~80% water with proteins (enzymes), carbohydrates, lipids, ions
l includes some solid structures:
-nucleoid
-ribosomes
-Inclusions
6) Nuclear Area / Nucleoid
-location of the bacterial chromosome:
-long loop of DNA, attached to the plasma membrane genetic info of cell
l Some bacteria also contain plasmids
l Plasmid = small circular DNA element
-separate from the genome
-does not contain any essential genes
-has 5-100 “bonus” genes (e.g. drug resistance, capsules, toxins, enzymes...)
-plasmids replicate independent of the host genome, can be passed to other cells
-plasmids can be found throughout the cytoplasm
7) Ribosomes
-site of protein synthesis
-composed of rRNA and protein
-consist of 2 subunits:
30s + 50s = 70s prokaryotic ribosome
(ribosomes are another common antimicrobialdrug target because the prokaryotic 70sribosome is very different from the eukaryotic 80s ribosome)
8) Inclusions
l All tend to be storage deposits
a. Metachromatic granules:
-inorganic phosphate (for ATP)
b. Polysaccharide granules:
-glycogen and starch (energy)
c. Lipid droplets
-fats (energy)
d. Sulfur granules
-in sulfur bacteria only
-use sulfur in ATP production
e. Carboxysomes
-contain the enzyme to fix CO2 during photosynthesis
f. Gas vaculoles
-air bags, provide buoyancy in water
g.Magnetosomes
l iron oxide deposits
l allow detection of earth’s magnetic field (orientation)
l break down hydrogen peroxide
Bacterial Endospores
-formed by some Gram + bacilli (e.g Clostridium & Bacillus species)
-Endospore = dehydrated, thick wall structure for survival: resistant to heat, toxins,radiation, etc
-Formation occurs when the environment becomes unfavorable: process called sporulation
-sporulation is NOT reproduction
-endospores can remain dormant for thousands of years
-upon return of favorable conditions, endospores germinate into vegetative cells
Eukaryotic cells
Structure and function
The Eukaryotic Cell = “true nucleus”
ž algae, protozoa, fungi, plants and animals
ž up to 100μm variable sizes and shapes
1. Flagella and Cilia
ž projections used for cellular locomotion
ž contain cytoplasm, surrounded by plasma membrane (not outside the cell)
ž move via beating or waving (no rotation)
ž internal structure: 9+2 array of microtubules (straw-like tubes composed of tubulin)
ž anchored in the cytoplasm by basal bodies composed of microtubules (no rod/disk)
ž Flagella- long, wave like motion, few on cell
ž Cilia- short, beating motion, numerous
2. Cell Wall
ž algae: wall composed of cellulose (simple polysaccharide)
ž fungi: wall composed of chitin (simple polysaccharide)
ž protozoa: no wall: either flexible pellicle or no covering
ž eukaryotes that lack a wall usually have glycocalyx instead: sticky carbohydrate layer exterior to the plasma membrane for strength, attachment, and cell recognition
ž No eukaryotes have peptidoglycan or pseudomurein (prokaryote polymers only)
3. Plasma Membrane
ž phospholipid bilayer: basic structure
ž sterols: resist osmotic lysis
ž carbohydrates on surface: receptors
ž integral and peripheral proteins: transport and metabolism (enzymes)
4. Cytoplasm
ž substance between the plasma membrane and the nucleus contains:
-cellular components (organelles)
-cytosol = fluid portion of cytoplasm
-cytoskeleton
ž Cytoskeleton
-composed of three types of filaments that form a scaffold:
a. microfilaments
b. intermediate filaments
c. microtubules
Functions:
-provide support and shape of cell
-assist in transporting substances inside cell
-assist in cell motility
ž cytoplasmic streaming = movement of cytoplasm inside the cell along the cytoskeleton.
5. Nucleus
ž large, spherical
ž houses the cell’s hereditary information
ž double-membrane bound:
ž membrane = nuclear envelope
-Two layers of phospholipid bilayer
-has nuclear pores that control the movement of materials between the nucleus and the cytoplasm
ž Location-inside nucleus
-in non-dividing cells DNA appears as a loose mass called chromatin
-in dividing cells, DNA is tightly packaged as separated DNA elements called chromosomes
ž eukaryote chromosome numbers differ but all have more than one, all are linear
DNA is always organized
-when not being used for RNA synthesis,DNA is wound around histone proteins forming repeating nucleosomes
ž nucleosome = 165 bp DNA wound around 8 histone proteins
6. Endoplasmic Reticulum
Network of membrane sacs called cisterns
-continuous with nuclear envelope
ž Two forms-
A. Rough ER
-flattened sacs of membrane
-studded with ribosomes
-proteins manufactured on RER ribosomes are fed into the cisterns to be modified
-the proteins are ultimately for use outsidethe cytoplasm (in membrane or secreted)
B. Smooth ER
-more tubular, no ribosomes
-synthesizes fats and sterols and detoxifies harmful substances
7. Ribosomes
Site of protein synthesis
-eukaryotic ribosome = 80s
-consists of two subunits: 60s and 40s
-attached to the RER or free in the cytoplasm:
-free ribosomes: in the cytoplasm
ž manufacture proteins to be used in the cytoplasm
-fixed ribosomes: attached to the RER
ž manufacture proteins to be used in the plasma membrane or for exocytosis (export out of the cell)
8. Golgi Complex
ž 3-20 large cisterns, stacked, not connected
ž not attached to the nuclear envelope or ER
ž functions to modify and sort proteins
ž Proteins synthesized in the RER are packaged into transport vesicles which bud off the RER and fuse with the Golgi
ž The proteins are modified by the Golgi and pass from one cistern to the next in transport vesicles (modifications: addition of lipids or carbohydrates, protein refolding)
ž The proteins are sorted according to final
destination and packed into vesicles
ž Three possible fates:
1. Secretory vesicles:
-carry exocytosis proteins,
-vesicle fuses with the plasma membrane dumping the protein contents outside of the cell
2. Membrane renewal vesicles:
-carry new integral or peripheral proteins to be added to the plasma membrane
3. Lysosomes: digestive enzymes temporarily housed in a storage vesicle
9. Lysosomes
ž formed by the Golgi
ž single membrane bound sphere
ž contain digestive enzymes to break down large molecules, organelles or bacteria
ž upon completion of digestion, residual body (waste) is exocytosed
10. Vacuoles
ž membrane enclosed space in the cytoplasm
ž -derived from the Golgi
ž -some serve as temporary storage compartments (for proteins, carbohydrates, toxins, etc.)
ž -some fill with water to provide rigidity to the cell
11. Peroxisomes
ž membrane spheres smaller than lysosomes
ž -come from pre-existing peroxisomes, not
Golgi or ER
ž -contain:
ž -enzymes for oxidation reactions
ž -catalase to break down toxic peroxide
ž oxidation of organics during metabolism generates peroxide and other free radicals
12. Centrosome
-located near the nucleus
-important for nuclear division during mitosis
-consists of two parts:
a. pericentriolar material
ž cytosol + protein fibers
ž organizes the mitotic spindle for cell division
b. pair of centrioles
ž 2 cylinders, at right angles to each other
ž composed of 9+0 arrangement of microtubules
ž source of microtubules to form the mitotic spindle
13). Mitochondria
ž “powerhouse of the cell”
ž -rod shaped, enclosed in double membrane:
ž -outer membrane: smooth
ž -inner membrane: folded into cristae
ž -open middle = matrix, where cellular respiration occurs
ž -most of the ATP in a cell is generated in a reaction called electron transport which occurs along the surface of the cristae
ž Mitochondria contain their own circle DNA and 70s ribosomes and can replicate by binary fission independent of the cell
14. Chloroplasts
ž -found only in algae and plants
ž -used to carry out photosynthesis reactions
ž -double membrane:
-outer smooth
-inner = flattened
ž membrane sacs called thylakoids
ž thylakoids are arranged in stacks called grana
ž Chloroplasts contain their own circle DNA and 70s ribosomes and replicate independent of the cell via binary fission
The Algae
Study of algae= Phycology
Morphology, size and shape
• Eukaryotic, motile or non motile
• Unicellular, filamentous, or multicellular (thallic)
• Wide range of sizes and shapes
• Single cell- spherical, rod, club or spindle shaped
• Multicellular-branched and unbranched
• Cell wall- thin and rigid but diatoms have silica in their wall making them thick and very rigid
• Discrete nucleus. Other inclusions are starch grains, oil droplets and vacuoles
• Algal pigments- chlorophylls, carotenoids, phycobilins
Vegetative structure
• Relatively simple eukaryotes lacking the tissues (roots, stem, leaves) of plants
• Body of a multicellular alga is called a thallus
• Larger algae (sea weeds) contain branched holdfasts which anchor them to rock, stem like hollow stipes and leaf like blades.
• Cells covering the thallus carry out photosynthesis
• Thallus lacks conductive tissue (xylem/phloem) characteristics of vascular plants
Unicellular alga
Comparison between unicellular algal, fungal and protozoal cell
Habitat and Nutrition
• Mostly live in aquatic environment, also thrive as terrestrial algae
• Ocean, salt lake, fresh water, damp soil, rocks, stones, tree bark etc.
• They are found in places where there are sufficient light, moisture and simple nutrients to sustain them
• Majority are photoautotrophs, contain chlorophyll and other pigments
• Algae absorb nutrients from the water over their entire surface
• Red Tide/Algal Bloom
Reproduction
• Both sexual and asexual
• Differ from plants in having simple reproductive structures for sexual reproduction
• Unicellular algae may function as gametes
• Asexual reproduction carried out by producing flagellated spores and/or nonmotile spores in sporangia
Selected phyla of algae
• Brown algae (Phaeophyta)
• Red algae (Rhodophyta)
• Green algae (Chlorophyta)
• Diatoms (Bacillariophyta)
· Dinoflagellates (dinoflagellata
1. Phaeophyta
• Brown algae (kelp)
• Cellulose + alginic acid cell walls
• Multicellular
• Chlorophyll a and c, xanthophylls
• Store carbohydrates
• Harvested for algin
2. Rhodophyta
• Red algae
• Cellulose cell walls
• Most multicellular
• Chlorophyll a and d, phycobiliproteins
• Store glucose polymer
• Harvested for agar and carrageenan
3. Chlorophyta
• Green algae
• Cellulose cell walls
• Unicellular or multicellular
• Chlorophyll a and b
• Store glucose polymer
4. Bacillariophyta
• Diatoms
• Pectin and silica cell walls
• Unicellular
• Chlorophyll a and c, carotene, xanthophylls
• Store oil
• Fossilized diatoms formed oil
· Produce domoic acid
5. Dinoflagellata
• Dinoflagellates
• Cellulose in plasma membrane
• Unicellular
• Chlorophyll a and c, carotene, xanthins
• Store starch
• Some are symbionts in marine animals
Neurotoxins cause paralytic shellfish poisoning
Biological and Economic Importance
• Primary producer- they form the base of most aquatic food chains because of their photosynthetic activities
• Water algae increase the O2 conc through photosynthesis, help to reduce hardness of water and removes salts
• Produce undesirable taste and odor in water supplies, heavy growth (mat) prevent oxygen and light penetration into water, cause suffocation to fish and marine animals
• Commercial products from algae
• From cell wall- agar, alginic acid and carrageenan are obtained
• Agar, carrageenan- polymer of galactose, used to make gel or viscous materials, as stabilizer/emulsifier in food products (icecream), as binder in toothpaste or pharmaceutical products, ulcer therapy, finishing compound in textile and paper industry, thickening agent in shaving cream, lotoin, in soap industry
• agar used as solidifying agent in microbiological media. Obtained from red alga Gelidium and Gracilaria.
• Alginic acid obtained from brown algae eg. Laminaria, Fucus etc. Used in icecream, cheese industry, bakery, dentistry.
Algae as food
• Mostly red and brown algae are used as food in the Far East
• Porphyra is used as food in Japan, where it is called ‘Nori’
• Other red algae Chondrus, Nemalion etc are used as vegetables or in soups or prepared as sweetened jellies.
• Gracilaria used in China as food
• Chlorella as food/source of protein for human and domestic animal
Algae and Disease
• Prototheca- probable pathogen of Human causes systemic or subcutaneous infections/ inflammation of joints
• Parasitic on higher plants. e.g. Cephaleuros attacks leaves of tea, coffee, pepper etc. (Irish potato blight)
• Toxin produced by aquatic algae which are lethal to fish and animals. e.g. dinoflagellate release neurotoxin cause death of aquatic shellfish. Domoic acid intoxication due to diatoms in shellfish, diarrhea & memory loss
Poisoning of human occurs after ingesting shilfish, scallops or mussels infected with dinoflagellate.
Red tide
• A phenomenon known as an algal bloom- an event in which estuarine, marine, or fresh water algae accumulate rapidly in the water column and results in discoloration of the surface water
• Red tides are caused by increase in nutrients that algae need, usually due to farm runoff, causing an overpopulation
• Their occurrence in some locations appear to be entirely natural, a seasonal occurrence resulting from coastal upwelling, a natural result of the movement of certain ocean currents while, in others they appear to be a result of human activities
• It is usually found in coastal areas
• The growth of marine phytoplankton is generally limited by the availability of nitrates and phosphates, which can be abundant in agricultural run-off as well as coastal upwelling zones
• Coastal water pollution produced by humans and systematic increase in sea water temperature have also been implicated as contributing factors in red tides
• When the algae are present in high concentrations, the water appears to be discolored or murky, normally being red or green.
• Some red tides are associated with the production of natural toxins, depletion of dissolved oxygen or other harmful effects, and are generally described as harmful algal blooms
• The most conspicuous effects of red tides are the associated wildlife mortalities among marine and coastal species of fish, birds, marine mammals, and other organisms.
• In the case of Florida red tides, these mortalities are caused by exposure to a potent neurotoxin called brevetoxin which is produced naturally by the marine algae Karenia brevis.
Archaea
General Characteristics
• Constitute third Domain Archaea
• Seem more closely related to Domain Eukarya than to bacteria
• Contain unique genetic sequences in their rRNA
• Have unique membrane lipids (Fatty acid attached by ether not ester links) & cell wall (contain pseudomurein) construction
• Live in the most extreme habitats in nature, extremophiles
• Adapted to heat, salt, acid pH, pressure & atmosphere
• Includes: methane producers, hyperthermophiles, extreme halophiles, and sulfur reducers
Similarities to prokaryotes
* Size
• Shape
• Lack nucleus
• Single chromosome
Similarities to eukaryotes
• Few plasmids
• RNA
• Translation machinery
• ribosome and tRNA
*Sequencing of Methanococcus jannaschii in 1992, 56% of genes not similar to bacteria or eukaryotes!
Morphological Diversity
• Tiny, usually less than one micron long
• Shapes are quite diverse: coccus, bacillus, triangular, square shaped
• May have one or more flagella attached to them, or may lack flagella altogether
• Archaeal cells have an outer cell membrane that serves as a barrier between the cell and its environment
• Cell wall is a semi-rigid layer that helps the cell maintain its shape and chemical equilibrium
Physiological Diversity
• Phototrophs: energy is obtained from light
-heterotrophs: carbon is obtained from organic compounds (halophilic Archaea and others)
-autotrophs: carbon is obtained by fixing CO2 (most cyanobacteria, photosynthetic bacteria)
• Chemotrophs: energy is obtained from chemicals
• lithotrophs: inorganic chemicals (sulfur, iron, hydrogen)
- autotrophs: carbon is obtained by fixing CO2 (sulfur-reducing Archaea, methanogens)
- heterotrophs: carbon is obtained from organic compounds (sulfur-reducing Archaea)
• organotrophs and heterotrophs: carbon and energy are obtained from organic chemicals (heterotrophs, E.coli, pathogens)
Major groups of Archaea
• Methanogenic archaea
• Archaeal sulfate reducers
• Extremely halophilic archaea
• Cell wall-less archaea
• Extremely thermophilic S metabolizers
Methanogens
• Largest group of Archaea
• Form methane (CH4) from CO2 or other compounds (e.g. formate, methanol, acetate)
• Strict anaerobes
• Found in a variety of anaerobic environments rich in organic matter
• Ex: Methanococcus sp, Methanobacterium sp
Extremely halophilic archaea
• Require high salt concentration
• Brightly colored due to purple pigments (bacteriorhodopsin)
Use light energy to make ATP.
