Nisa Rachmania Mubarik Major Microbiology Department of Biology, IPB Nisa RM 1 1212 Microbial Physiology - Nisa RM What Are Cells? All living things are

Nisa Rachmania Mubarik

Major Microbiology

Department of Biology,

IPB

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Microbial Physiology -

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What Are Cells?All living things are constructed of cells; at least one (unicellular) or

many (multicellular).

Cell Theory, goes as follows:All organisms are composed of one or more cells.Cells are the basic unit of structure and function in organisms.All cells come only from other cells.

Two Basic Types of CellsAll cells fall into one of the two major classifications:prokaryotes or eukaryotes.


Features of ProkaryotesPro = “before”, karyon = “nucleus”Prokaryotes, the first living organisms to evolve, are primarilydistinguished by the fact that they lack a membrane bound nucleus.Their genetic material is naked within the cytoplasm, ribosomes theironly type of organelle.

Prokaryotes are most always single-celled, except when they exist incolonies. These ancestral cells, now represented by members of thedomains Archaea and Eubacteria, reproduce by means of binaryfission, duplicating their genetic material and then essentially splittingto form two daughter cells identical to the parent.

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Features of EukaryotesEu = “true”, karyon = “nucleus”The most noticeable feature that differentiates these more complexcells from prokaryotes is the presence of a nucleus, a doublemembrane-bound control center separating the genetic material,DNA (deoxyribonucleic acid), from the rest of the cell.

Eukaryotic cells also contain internal membrane-bound structurescalled organelles. Organelles, such as mitochondria andchloroplasts, are both believed to have evolved from prokaryotesthat began living symbiotically within eukaryotic cells (EndosimbionHypothesis)

Eukaryotic cells can reproduce in one of several ways, includingmeiosis (sexual reproduction) and mitosis (cell division producingidentical daughter cells).


Major Characteristics of Eukaryotes and Prokaryotes

Characteristic Eukaryote Prokaryote

Major Groups Algae, fungi, protozoa, plants,

animals.Bacteria.

Size (approximate) >5 um. 0.5 to 3 um.

Nuclear Structures

- Nucleus Classic membrane. No nuclear membrane.

- Chromosomes Strands of DNA; diploid genome. One circular DNA; haploid genome.

Cytoplasmic Structures

- Mitochondria Present. Absent.

- Golgi Bodies Present. Absent.

- Endoplasmic Reticulum Present. Absent.

- Ribosomes 80S (60S + 40S). 70S (50S + 30S).

- Cytoplasmic Membrane Contains sterols. Does not contain sterols.

Cell Wall Absent of composed of chitin. Complex structure.

Reproduction Sexual and asexual. Asexual (binary fission).

Movement Complex flagellum, if present. Simple flagellum, if present.

Respiration

Microbial Physiology -Via mitochondria. Via cytoplasmic membrane.

Microbial Physiology - 5

Structure of Bacteria Cell

Prokaryote andEukaryote CellStructure

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Acellular Particles: Viruses, Viroids & Prions

Viruses, viroids and prions are not considered to be livingorganisms because they are incapable of carrying out alllife processes.

What Is a Virus?

Viruses infect living cells and once inside, transform the cellessentially into a factory for making more viruses.

Viruses are composed of nucleic acid, proteins and, in somecases, lipids as well. Nucleic acid, which can be either DNAor RNA, encodes the genetic information that is necessaryto make copies of the virus.

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SARS: The First New Virus of the 21st Century

http://learn.genetics.utah.edu/features/sars/ (3-9-2008)


http://www.ncbi.nlm.nih.gov/ICTVdb/Ictv/fs_avsun.htm

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Viruses reproduce via four basic steps, asfollows:Delivery if the viral genomes into a host cell

Commandeering the host cell’s transcriptionand translation machinery

Utilization of host cell building blocks to copyviral genomes and synthesize viral proteins.

Viral genomes and proteins self-assembleand exit host cells as new infectiousparticles.


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What Is a Viroid?

Viroids are smallest known agents of infectious disease. Whereas virusesare made up of nucleic acid encapsulated in protein (capsid), viroids areuniquely characterized by the absence of a capsid.In spite of their small size, viroid ribonucleic acids (RNAs) can replicate andproduce characteristic disease syndromes when introduced into cells.This type of acellular particle has only been identified in association withplants and is not currently a threat to humans.

FamilyGenus

80.002. Avsunviroidae

80.002.0.01. Avsunviroid

Type Species 80.002.0.01.001.

Avocado sunblotch viroid

Features:

-Circular ssRNA between 246 and 250 nt

-The most stable secondary structure is a rod-like or quasi-rod-like conformation

-It is unique in having a base composition rich inA+U (62%) in contrast to the other viroids whichare rich in G+C (53-60%).


What Is a Prion?

A prion is a disease-causing agent responsible for various fatalneurodegenerative diseases called Transmissible SpongiformEncephalopathies.

Prions are an abnormal form of a normally harmless protein found inmammals and birds.

These abnormal proteins can enter the brain through infection or it canarise from a mutation in the gene that encodes the protein.

Once present in the brain, prions cause normal proteins to refold intoabnormal shapes. As these abnormal proteins multiply, they destroyneurons and eventually cause brain tissue to become riddled withholes.


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Misfolded Proteins & Disease

PRION: a defective protein agent (PrPsc) due to mis-coded gene(PRNPc) native prion protein is PrPc & resides on nerve cell surfaces.Defective protein PrPsc accumulates forming aggregates that lead to CJD& SE's.

CJD: Creutzfeld-Jacob disease, genetic based or acquired - (by eating"mad cow" tissue) fatal neurological disease due to presence of misfoldedPRPc protein.

Spongiform Encephalopathy (SE) - vacuolation (holes) in brain nervetissue (http://fig.cox.miami.edu/~cmallery/255/255prot/255proteins.htm)

Both PRION proteins can have identical aasequence, but may fold differently[are conformers = proteins differ only inconformation]A. normal (PrPc) protein...

mostly α-helix foldings - remains solubleB. abnormal PrPsc protein...

45% β-sheet - insoluble & protease insensitiveproduces cell surface aggregates that kill cells


The cytoplasmic membranes of most prokaryotes are surrounded by rigidpeptidoglycan (murein) layers. The exceptions are Archaeobacteriaorganisms (which contain pseudoglycans or pseudomureins related topeptidoglycan) and mycoplasmas (which have no cell walls at all).

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External Structures

Some bacteria (Gram positive or Gram negative) are closely surrounded byloose polysaccharide or protein layers called capsules.

In cases in which it is loosely adherent and nonuniform in density orthickness, the material is referred to as a slime layer.

The capsule and slime layers are also called the glycocalyx.

Bacillus anthracis, the exception to this rule, produces a polypeptide capsule.

Capsules and slimes are unnecessary for the growth of bacteria but are veryimportant for survival in the host.

The capsule is poorly antigenic and antiphagocytic and is a major virulencefactor (e.g., Streptococcus pneumoniae). The capsule can also act as abarrier to toxic hydrophobic molecules, such as detergents, and can promoteadherence to other bacteria or to host tissue surfaces. For Streptococcusmutans, the dextran and levan capsules are the means by which the bacteriaattach and stick to the tooth enamel.

Synthesis of the capsule takes energy and will not be effected by thebacteria after continued growth under laboratory conditions away from theselective pressures of the host.


Transmission electron micrographs ofPorphyromonas (formerly Bacteroides)gingivalis and Pseudomonasaeruginosa revealing the surfaceassociated capsule.

Both strains were isolated from humanpatients, P. gingivalis from an adult withperidontitis and P. aeruginosa from apatient with cystic fibrosis.

C = capsule; OM = outer membrane;PG = peptidoglycan; CM = cytoplasmicmembrane; R = ribosome; PP =polyphosphate. Bar = 0.1 um.

http://micro.digitalproteus.com/morphology2)

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Bacteria may have the following appendages:

Flagella are ropelike propellers composed of helically coiled proteinsubunits (flagellin) that are anchored in the bacterial membranes throughhook and basal body structures and that are driven by membranepotential.

Bacterial species may have one or several flagella on their surfaces, andthey may be anchored at different parts of the cell.

Flagella provide motility for bacteria, allowing the cell to swim (chemotaxis)toward food and away from poisons.

Bacteria approach food by swimming straight and then tumbling in a newdirection. The swimming period becomes longer as the concentration ofchemoattractant increases. The direction of flagellar spinning determineswhether the bacteria swim or tumble. Flagella also express antigenic andstrain determinants.


Fimbriae (pili) (Latin for "fringe") are hairlike structures on the outside ofbacteria; they are composed of protein subunits (pilin).

Fimbriae can be morphologically distinguished from flagella because theyare smaller in diameter (3 to 8 nm versus 15 to 20 nm) and usually are notcoiled in structure. Generally, several hundred fimbriae are arrangedperitrichously (uniformly) over the entire surface of the bacterial cell.

They may be as long as 15 to 20 nm, or many times the length of the cell.

Fimbriae promote adherence to other bacteria or to the host (alternativenames are adhesins, lectins, evasins, and aggressins). As an adherencefactor (adhesin), fimbriae are an important virulence factor for E. colicolonization and infection of the urinary tract, for Neisseria gonorrhoeaeand other bacteria.

The tips of the fimbriae may contain proteins (lectins) that bind to specificsugars (e.g., mannose). F pili (sex pili) promote the transfer of largesegments of bacterial chromosomes between bacteria. These pili areencoded by a plasmid (F).

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Peptidoglycan Structure and Function

Peptidoglycan is a huge polymer of interlocking chains of identicalmonomers. The backbone of the peptidoglycan molecule iscomposed of two derivatives of glucose: N-acetylglucosamine(NAG) and N-acetlymuramic acid (NAM). The NAG and NAMstrands are connected by interpeptide bridges.

From the peptidoglycan inwards all bacterial cells are very similar.Going further out, the bacterial world divides into two majorclasses: Gram positive (Gram +) and Gram negative (Gram -).



Gram-positive CellsIn Gram-positive cells, peptidoglycan makes up as much as 90% of thethick, compact cell wall, which is the outermost structure of Gram +cells.Gram-negative CellsThe cell walls of Gram - bacteria are more chemically complex, thinnerand less compact. Peptidoglycan makes up only 5 – 20% of the cellwall, and is not the outermost layer, but lies between the plasmamembrane and an outer membrane.This outer membrane is similar to the plasma membrane, but is lesspermeable and composed of lipopolysaccharides (LPS). LPS is aharmful substance classified as an endotoxin, The space between thecell wall and the plasma membrane is called the periplasm. Periplasmcontrols molecular traffic entering and leaving the cell.


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Gram positive and Gram negative bacteria. A Gram positive bacteriumhas a thick layer of peptidoglycan (left). A Gram negative bacterium has athin peptidoglycan layer and an outer membrane (right). Structures in ()are not found in all bacteria (http://micro.digitalproteus.com/morphology2)

Bacterial Membrane Structures

Structure Chemical ConstituentsPlasma Membrane Phospholipids, proteins, enzymes for energy, membrane potential,

transport.

Cell Wall

Gram +ve Bacteria

Peptidoglycan Glycan chains of GlcNAc and MurNAc cross linked by peptide bridge.

Teichoic Acid Polyribitol phosphate or glycerol phosphate cross linked to

peptidoglycan.

Lipoteichoic Acid Lipid linked teichoic acid.

Gram -ve Bacteria

Peptidoglycan Thinner version of that found in Gram positive bacteria.

Periplasmic Space Enzymes involved in transport, degradation, and synthesis.

Outer Membrane Phospholipids with saturated fatty acids.

Proteins Porins, lipoprotein, transport proteins.

LPS (lipopolysaccharide) Lipid A, core polysaccharide, O antigen.

Other Structures

Capsule Polysaccharides (disaccharides and trisaccharides) and polypeptides.

Pili Pilin, adhesins.

Flagellum Motor proteins, flagellin.

Proteins M proteins of streptococci (for example).

Comparison of the Grampositive and Gramnegative bacterial cellwalls.


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Function Component(s)

Structural Rigidity All.

Packaging Of Internal Contents All.

Permeability Barrier Outer membrane or plasma membrane.

Metabolic Uptake Membranes and periplasmic transport

proteins, porins, permeases.

Energy Production Plasma membrane.

Adhesion To Host Cells Pili, proteins, teichoic acid.

Immune Recognition By Host All outer structures.

Escape From Host Recognition Capsule, M protein.

Antibiotic Sensitivity Peptidoglycan synthetic enzymes.

Antibiotic Resistance Outer membrane.

Motility Flagella.

Mating Pili.

Adhesion Pili.


Functions of the Bacterial Envelope


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Internal Structure of Bacteria

Bacteria have a very simple internal structure, and no membrane-boundorganelles.

Nucleoid DNA in the bacterial cell is generally confined to this central region.Though it isn't bounded by a membrane, it is visibly distinct (by transmissionmicroscopy) from the rest of the cell interior.

Ribosomes give the cytoplasm of bacteria a granular appearance in electronmicrographs. Though smaller than the ribosomes in eukaryotic cells, theseinclusions have a similar function in translating the genetic message inmessenger RNA into the production of peptide sequences (proteins).

Storage granulesNutrients and reserves may be stored in the cytoplasm in the form ofglycogen, lipids, polyphosphate, or in some cases, sulfur or nitrogen.endospore(not shown) Some bacteria, like Clostridium botulinum, formspores that are highly resistant to drought, high temperature and otherenvironmental hazards. Once the hazard is removed, the spore germinatesto create a new population.


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Documents

Nisa Rachmania Mubarik Major Microbiology Department of Biology, IPB Nisa RM 1 1212 Microbial Physiology - Nisa RM What Are Cells? All living things are