Characteristics of Life and Microbe Distribution

Characteristics of Life and Microbe Distribution

• Growth is an increase in size that occurs in bacteria, archaea, and eukaryotes, but not in viruses.
• Reproduction is an increase in number that occurs in bacteria, archaea, and eukaryotes; for viruses, the host cell replicates the virus.
• Responsiveness is the ability to react to environmental stimuli, seen in bacteria, archaea, eukaryotes, and some viruses (reaction to host cells).
• Metabolism involves controlled chemical reactions and it occurs in bacteria, archaea, eukaryotes, and viruses (viruses use the host cell's metabolism).
• Cellular structure is a membrane-bound structure, present in bacteria, archaea, and eukaryotes, but viruses lack a cytoplasmic membrane or cellular structure.

Two Types of Cells

• Prokaryotes do not have a nucleus.
• Bacteria and Archaea are prokaryotes.
• Eukaryotes have a nucleus.
• Fungi, protozoa, helminths, animals, plants and algae are eukaryotes.

Similarities Between Prokaryotes and Eukaryotes

• Both cell types are similar in their chemical composition.
• Both contain cellular entities, nucleic acids (DNA and RNA), and proteins.
• Similar chemical reactions occur in both cell types.
• Both carry out metabolism, protein production, and energy storage.
• Both cell types may also use flagella for motility.

Differences Between Prokaryotes and Eukaryotes

• Prokaryotic DNA is not enclosed by a membrane, thus lacking a nucleus.
• Eukaryotic DNA is enclosed by a nuclear membrane, and a nucleus is present.
• Prokaryotes have a single circular chromosome.
• Eukaryotes have multiple linear chromosomes.
• Prokaryotes lack membrane-enclosed organelles.
• Eukaryotes contain various membrane-enclosed organelles.
• Mitochondria, ER, Golgi apparatus, lysosomes, and chloroplasts are examples of eukaryotic's membrane-enclosed organelles.
• Prokaryotic cell walls almost always contain peptidoglycan.
• Eukaryotic cell walls, if present, do not contain peptidoglycan.
• Prokaryotes divide by binary fission.
• Eukaryotes divide by mitosis.
• Prokaryotic division is less complex than eukaryotic cell division.

The Prokaryotic Cell

• Thousands of species of bacteria exist.
• Species of bacteria are identified by their morphology, chemical composition (staining), nutritional requirement, biochemical activities, and energy source.

The Prokaryotic Cell: Morphology

• Morphology refers to the appearance (form).
• The size of prokaryotic cells ranges from 0.2 to 2.0 μm in diameter and 2.0 to 8.0 μm in length.
• The most common shapes of prokaryotic cells include cocci, bacilli, and spiral.
• Some bacteria can have other shapes and are pleomorphic.
• Morphology is hereditary, and bacteria are generally monomorphic.

Bacterial Shapes

• Cocci are spherical.
• Bacilli are rod-shaped.
• Spiral bacteria have a twisted shape.

Typical Bacterial Cell Features

• Prokaryotic cell structures include the cell wall, cytoplasmic membrane, cytoplasm, nucleoid, ribosomes, plasmids, and inclusions.

Glycocalyx

• The glycocalyx is made up of sugar, protein, or both.
• There are two types of glycocalyx: capsule and slime layer.
• A capsule is firmly attached to the cell surface.
  • Capsules protect cells from desiccation and may prevent them from being recognized and destroyed by the host.
  • Capsules are important in bacterial virulence.
  • The presence of a capsule can be determined by staining.

Slime Layer

• A slime layer is loosely attached to the cell surface.
• The slime layer allows prokaryotes to attach to surfaces and protect cells from desiccation.
• The slime layer is water-soluble.

Prokaryotic Flagella

• Prokaryotic flagella are whip-like structures used for motility.
• The filament, hook, and basal body are parts of the flagella.
• Movement occurs by rotation of the hook, which propels the cell.
• Flagella do not have a membrane/sheath.
• Some bacteria can be identified by their flagellar proteins, such as E. coli O157: H7 (H protein = flagellar protein).
• Eukaryotic flagella are more complex.

Arrangements of Bacterial Flagella

• Arrangements of bacterial flagella include monotrichous, amphitrichous, lophotrichous, and peritrichous.

Motility and Taxis

• Motility refers to self-directed movement.
• Motility involves a series of "runs" and "tumbles".
• Taxis is movement in response to a stimulus and includes chemotaxis and phototaxis.
• Chemicals and light can act as attractants or repellents.
• Positive taxis is the movement toward an attractant.
• Negative taxis is the movement away from a repellent.

Axial Filaments

• Axial filaments are similar to flagella but wrap around the cell.
• These filaments are found only in spirochetes; create corkscrew-like movement.
• Axial filaments are also called "endoflagellum."

Fimbriae and Pili

• Fimbriae are short, hairlike appendages that are shorter, straighter, and thinner than flagella.
• Fimbriae are sticky, bristle-like projections used by bacteria to adhere to surfaces and to each other.
• Fimbriae are shorter than flagella and are present in >100s/cell.
• Fimbriae serve an important function in biofilms for adherence to various surfaces.
• N. gonorrhoeae uses fimbriae to attach to mucous membranes.
• Pili are tubules composed of pilin and adhesins; they're longer than fimbriae but shorter the flagella.
• Bacteria typically only have 1-2 pili per cell.
• Pili mediate the conjugation of DNA from one cell to another.
• F pili act as conjugation or sex pili.
• Ordinary pili mediate adhesion to mucous membranes.

Cell Wall

• The cell wall surrounds the plasma membrane.
• It is semi-rigid, providing cell shape and shields the cell interior from environmental changes.
• The cell wall also protects against changes in water pressure (osmosis).
• The complex cell wall structure contains peptidoglycan.
• A significant feature is that the bacterial cell wall is very different from the host cell wall.
• Good drugs damage the invader but not the host.

Peptidoglycan

• Peptidoglycan is composed of sugars such as N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM).
• Chains of NAG and NAM are attached to other chains by tetrapeptide crossbridges.
• Bridges may be covalently bonded to one another, or held together by short connecting chains of amino acids.

Gram Positive and Gram-Negative Bacteria

• Cell wall composition is important in differentiating bacteria.
• There are 2 main types of bacterial cell walls: Gram-positive and Gram-negative, based on cell wall characteristics.
• Gram stain is the first test used to narrow down possible bacterial species.
• Gram stain is used only for bacteria.

Gram-Positive Cell Wall

• The gram-positive cell wall contains many layers of peptidoglycan.
• Teichoic acids and lipoteichoic acids exists within the gram-positive cell wall.
• The wall is thick and rigid.
• Gram-positive organisms are less sensitive to mechanical damage than Gram-negative organisms.
• Gram-positive bacteria is also more sensitive to penicillin than Gram-negative.

Gram-Negative Cell Wall

• A Gram-negative cell wall is a peptidoglycan sandwich.
• It consists of the outer membrane, a thin layer of peptidoglycan, and the plasma membrane.
• The outer membrane has a negative charge, preventing phagocytosis by host cells.
• The outer membrane also acts as barrier against certain antibiotics and chemicals.
• Porins allows nutrients in Gram-negative cell walls.
• The Gram-negative wall contains lipopolysaccharide (LPS), an endotoxin causing fever and shock.

Atypical Cell Walls

• Mycoplasma is a bacterial genus that naturally lacks cell walls and cannot be Gram stained.
• Mycobacteria has an abundance of mycolic acids in the cell wall, so also cannot be Gram stained.
• Corynebacterium and Nocardia also produce mycolic acids.
• Archaea lack peptidoglycan and have pseudomurein instead.

Plasma Membrane

• The plasma membrane, also known as the cytoplasmic membrane, is inside of cell wall and encloses the cytoplasm.
• The plasma membrane is a phospholipid bilayer composed of lipids and proteins, described by the fluid mosaic model.
• Approximately half of the plasma membrane consists of proteins that act as recognition proteins, enzymes, receptors, carriers, and channels.
• Integral proteins, peripheral proteins, and glycoproteins are the proteins in the plasma membrane.
• The main functions are to control what enters the cell by selective permeability through pores and transporters and is the site for energy production and nutrient breakdown.

Movement Across Plasma Membrane

• Passive processes include simple diffusion, facilitated diffusion, and osmosis.

Simple and Facilitated Diffusion

• It is easier to move substances from areas of high concentration to areas of low concentration.
• Down a concentration gradient.

Osmosis

• Osmosis is the net movement of solvent molecules across a semi-permeable membrane from an area of lower solute concentration to an area of higher solute concentration.
• Solvent (H2O) moves from high to low concentration.

Tonicity

• Tonicity is the ability of a surrounding solution to cause a cell to gain or lose water.
• Isotonic solution: The solution has equal osmotic pressure across the cell membrane.
• Hypertonic solution: The solution has a higher solute concentration than an isotonic solution.
• Hypotonic solution: The solution has a lower solute concentration than an isotonic solution.

Active Transport

• Material moves from low to high concentration by transporter proteins.
• It's useful when a bacterial cell is in an environment with low nutrients.
• The cell uses an active process to gain needed substances.
• It expends energy to go against the concentration gradient.

Cytoplasm

• Cytosol: Liquid portion of cytoplasm.
• 80% water.
• Containing proteins, enzymes, carbohydrates, lipids, inorganic ions, low MW compounds, inorganic ions.
• Nucleoid Area: DNA.
• Ribosomes: Sites of protein synthesis.
• Inclusions: Reserve chemical deposits.

Nucleoid

• The nucleoid is not membrane enclosed.
• It contains genetic information.
• Bacterial chromosomes are single circular dsDNA, no proteins.
• Eukaryotes have multiple linear chromosomes versus the single linear chromosome.
• Carries all information required for the cell's structure and function.
• Is up to 20% of cell volume in actively growing bacteria.

Plasmids

• Plasmids are extrachromosomal genetic elements.
• Replicate independently of main chromosome.
• Contain genes not crucial to survival.
• Genes give antibiotic resistance, tolerance to toxic elements, and toxin production.
• Can be transferred from one bacteria to another.

Ribosomes

• Ribosomes are the site of protein synthesis.
• Prokaryotic and eukaryotic ribosomes are different.
• Prokaryotic = 70S.
• Some antibiotics inhibit prokaryotic ribosomes with no effect on eukaryotic ribosomes.

Endospores

• Endospores are unique resting structures produced by some bacteria
• They are a defensive strategy for survival against unfavorable adverse environmental conditions and are are not metabolically active.
• Endospores are highly durable, dehydrated cells with thick walls.
• Survive heat (boiling), dehydration, toxic chemicals, radiation, etc and are a problem in the food industry (under processing).
• Located terminally, sub-terminally or centrally in cells.
• Only certain bacteria create endospores.

Formation of Endospores by Sporulation

• DNA is replicated.
• DNA aligns along the cell's long axis.
• Cytoplasmic membrane grows and engulfs forespore within a second membrane.
• Cytoplasmic membrane invaginates to form the forespore.
• A cortex of calcium and dipicolinic acid is deposited between the membranes.
• Spore coat forms around endospore.
• Maturation of endospore; completion of spore coat and increase in resistance to heat and chemicals by unknown process.
• Endospore released from original cell.
• Vegetative cell's DNA disintegrates.

Endospore Variations in Morphology

• Variations in endospore morphology: (1, 4) central endospore; (2, 3, 5) terminal endospore; (6) lateral endospore.

The Eukaryotic Cell

• Organelles contained within Include the: nuclear envelope, nuclear pore, lysosome, mitochondrion, centriole, secretory vesicle, ribosome, transport vesicles, rough endoplasmic reticulum, cell membrane, smooth endoplasmic reticulum, and cytoskeleton .

Flagella and Cilia

• Flagella in eukaryotes are few, and long relative to cell size.
• The shaft is composed of arranged tubulin (microtubules).
• There is a “9+2” microtubule arrangement in flagellated eukaryotes.
• Flagella may be single or multiple and are generally are found at one pole of cell.
• Cilia in eukaryotes are numerous and short (like hairs).
• Cilia are shorter and more numerous than flagella.
• Cilia consists with “9+2” and “9+0” arrangements.
• Coordinated beating propels cells through their environment.
• Cilia move substances past the cell surface with wave-like movement.
• Ciliated cells are in the respiratory tract.

Cell Wall and Glycocalyx (Eukaryotic)

• Eukaryotic cell walls have no peptidoglycan.
• Eukaryotic cell wslls are clinically significant and much simpler than prokaryotic cell walls.
• Cell walls are made of carbohydrates (sugars)
• Algae have cellulose.
• Fungi contains chitin.
• Yeast: contains glucan and mannan.
• Protozoa has no typical cell wall; flexible outer coating called a pellicle.
• Animal cells: consist of glycocalyx, a layer of sticky carbohydrates to strengthen cells and provide means of adherence to other cells

Plasma Membrane (Eukaryotic)

• Eukaryotic plasma membranes are similar to prokaryotic.
• Eukaryotic plasma membrane has a phospholipid bilayer containing proteins like prokaryotics.
• The membrane has carbohydrates attached to proteins and sterols.
• It exhibits similar passive and active processes to move materials across plasma membrane.

Cytoplasm & Organelles

• Cytoplasm: inside of plasma membrane and outside of nucleus.
• There is very complex internal structure in Cytoskeleton, made up of support, shape, intracellular transport, cellular movement, phagocytosis.
• Ribosomes are larger and denser (80S) than prokaryotic ribosomes.
• Organelles are membrane-bound.
• Organelles are a characteristic of eukaryotic cells.
• Structures contain w/ specific shapes and specialized functions Nucleus, Smooth and Rough Endoplasmic Reticulum, Golgi, Lysosomes, Peroxisomes, Mitochondria.

Nucleus

• Nucleus are characteristic of eukaryotes.
• Is often the largest cellular structure
• Contains DNA.
• -DNA associated with proteins.
• Chromatin = DNA + proteins.
• Consists of linear chromosomes.
• Surrounded by nuclear envelope consisting of double membrane composed of two phospholipid bilayers. Nuclear envelope contains nuclear pores.

Endoplasmic Reticulum

• It's a network of flattened sacs/ tubules connected to nuclear envelope.
• Smooth consists of no ribosomes and perform lipid synthesis, glycogen breakdown, store Ca2+, detoxification.

Ribosomes - Eukaryotic

• Synthesize proteins by inhibiting bacterial protein synthesis

Golgi Complex

• Protein from the ER, are sorted in the Golgi complex.
• Consists of flattened sacs called cisterns
• Functions membrane formation and protein protein secretion

Vesicles, Lysosomes & Peroxisomes

• Vesicles: Store and transfer substances with cells.
• May store nutrients in cell.
• Lysosomes contain catabolic enzymes capable of digesting bacteria.
• Are important in host immune response.
• White blood cells contains lots of lysosomes.
• Peroxisomes contain enzymes the degrade poisonous.

Mitochondria

• Has two membranes composed of phospholipid bilayer
• Produce most of cells energy and are known as powerhouses
• Mitochondria possess an interior matrix with their own DNA & ribosomes in 70S
• Circular molecule of dsDNA
• Reproduce like bacterial cells by binary fission

Comparison: Prokaryotic and Eukaryotic cells

• Prokaryotic cells are commonly 0.2-2.0 µm in diameter, while Eukaryotic cells are commonly 10-100 µm in diameter
• Eukaryotes possess a nucleus, while prokaryotes do not
• Eukaryotes posses free organelles bound with phospholipid membranes.
• Both cell types may contain glycocalyx, motility, and flagella though their composition differs.
• Some possess fimbriae and pili. Some have a cell wall.
• The cytosol is usually lacks carbohydrates in prokaryotes and commonly contains glycolipids, glycoproteins, and sterols in eukaryotes.
• Inclusions are more common in prokaryotes and are mostly present in Eukaryotes.
• Only some prokaryotes contain endospores but are absent in Eukaryotes.
• Ribosomes are smaller (70S) in prokaryotes and larger (80S) in eukaryotes.
• Prokaryotes have a single, circle chromosome without histomes, while Eukaryotes commonly have multiple lined chromosome with histomes.

Concept Check

• Function of glycocalyx.
• The properties of the cell walls and makeup of bacteria composed on peptidoglycan.
• Organisms that are associated with prokaryotic organisms.