Ch. 3 - Cell Structure & Function in Bacteria & Archae (Ch. 4 -- 12 ed.)

Question 1

Central Dogma of Molecular Bio

(pp. 176, 252)

Answer 1

• Genetic material in the cell specifies the organization of the cell & its activity
• Molecular processes (underlying genetic info flow) can be dividied into 3 stages:

1. Replication - DNA is duplicated, producing two double helices
2. Transcription - DNA participates in protein synthesis through an RNA intermediate (mRNA)

• -> some genes contain info for other types of RNA: tRNA & rRNA
  3. Translation - sequence of amino acids in a polypeptide (making up a protein) is determined by the specific sequence of bases in mRNA

–> In Eukaryotes…each gene transcribed to give a single mRNA

–> in Prokaryotes…a signle mRNA may carry genetic info from several genes

Question 2

Mimi Virus exception(s)?

Answer 2

• Viruses contain only a single form of nucleic acid – either DNA or RNA

–> Mimi virus contains both RNA & DNA

Question 3

Major Cell Morphologies

Answer 3

–> several morphologies are known among prokaryotes…

• Coccus – spherical or ovoid
• Bacillus (rod) – cylindrical shape
• Spirilla – some rods twist into spiral shapes

–> several groups possess unusual shapes…

• Spirochets – tightly coiled shape
• Appendaged – possess extensions of their cells (hypha/stalks)
• Filamentous bacteria – long, thin cells/chains
• Vibrio – half-moon shaped

**Cell morphology is easily recognized…but generally a poor predictor of a cell’s other properties**

Question 4

Describe Cell Size of Prokaryotes

• Esherichia coli?
• Thiomargarita namibiensis?
• Mycoplasma pneumoniae

Answer 4

• Prokaryotes vary in size from ~ 0.2 µm to ~ >700 µm (in diameter)
• -> 1 µm (micrometers) = 10^-6 m (meters)
• E. coli = 2 µm
• -> considered base volume for prokaryotic cells
• -> E. coli vol. = 2 µm³ –> (EC vol. = 1)
• T. namibiensis = 750 µm
• -> T. namibiensis vol. = 200,000,000 µm³ –> (EC vol. = 10⁸
• M. pneumonia = 0.2 µm
• -> M. pneuonmia vol. = 0.005 µm –> (EC vol = 2.5 x 10^-3)

Question 5

Significance of Small size of Prokaryotes

Answer 5

• prokaryotic cells generally very small cells compared to eukaryotes
• -> very large…not common
• rate at which nutrients/waste products transport in/out of cell is generally **inversely proportional to cell size**
• -> higher S/V (surface are/volume) ratio of smaller cells supports greater nutreint exchange per unit of cell volume…vica versa…
• -> cell’s growth rate depends (among other important things) on the rate of nutrient exchange

**S/V = 3/r** (for spherical coccus..)

⇒ larger the cell…smaller the S/V ratio –> results in a lesser efficient exchange with environment

Question 6

Structure of Viruses

Answer 6

Viruses come in numerous sizes & shapes…most smaller than prokaryotic cellsg

• Acellular…thus “nonliving”
• -> rely on host cells to provide E & materials needed for replicationg their genomes & synthesizing their proteins…**Obligate intracellular parasites**
• Nucleic acids – contain either DNA or RNA.. (NOT both)
• -> (exception)…Mimi Virus contains both DNA & RNA
• Capsids – protein shell which surrounds nucelic acid of virion
• -> made up of Capsomers (structural subunits)
• -> Nucelocapsid – complete complex of nucelic acid & protein packaged in virion

Question 7

Viriods

Answer 7

• infectious RNA molecules that differ from viruses…lack capsids (protein coat)
• consist of single-stranded (covalently-closed) circular RNA that forms a seemingly double-stranded structure by intra-strand base pairing
• -> makes it stable to exist outide of host cell… (NOT an obligate intracellular parasite)
• -> enters through wound in plant cells… (does not use a receptor to enter host like viruses)
• **interferes with regulatory RNA in plants**…
• -> viriods possess no protein-encoding genes…basically totally dependent on host function (for replication)
• -> viroid replicated in host cell nucleus or chloroplast by plant RNA polymerases
• NO animal diseases known

Question 8

Prions

Answer 8

• thought to be small replicating polypeptides
• -> contain neither RNA or DNA
• Mechanism of Prion misfolding:
• -> neuronal cells produce normal form of prion protein (PrP^C)
• -> Pathogenic form (PrP^Sc) catalyzes refolding of normal prions into abnormal form… (PrP^C into PrP^Sc)
• PrP^Sc is protease resistant & insoluble…aggregates in host neural cells (brain cells)
• infectious in animals only
• -> Mad Cow Disease in cattle
• -> Creutzfeldt-Jakob disease (CJD) in humans

Question 9

General structure of Phospholipid Bilayer

Answer 9

• main constituent of cytoplasmic membrane
• -> separates cytoplasm from environment
• -> highly selective permeability barrier
• -> if broken…integrity of cell is destroyed
• possess both hydrophobic (fatty acids) & hydrophilic (glycerol-phosphate) components
• -> hydrocarbon chains (of fatty acid) points inward
• -> glycerol-phosphates point outward toward environment & cytoplasm
• 6-8 nm wide
• viewed from electron microscope…appears as 2 light-colored lines separated by a darker area

Question 10

Describe in-depthly composition of Phospholipids
–> chemical make-up…

Answer 10

• consists of hydrophobic fatty acids (hydrocarbon chains) *esterified* to glycerol
• -> **removal of H20 between alcohol group (from glycerol) & caroxyl group (from 2 fatty acids OR 1 phosphoric acid)**

Question 11

Cytoplasmic membrane Proteins
–> 2 types…

Answer 11

1. Peripheal Proteins (extrinsic proteins)

• not embedded…but still associated with membrane surface
• some easily removed from changes in environment (pH, ionic strenght, etc…)
• typically on surface of membrane
• some may be bound to integral proteins…important cellular processes (energy metabolism, transport, etc…)
• -> some are *Lipoproteins*… proteins containing lipid tail that can anchor integral proteins

2. Integral Proteins (intrinsic proteins)

• firmly embedded in membrane
• many span entire membrane but not all…possessing external & internal surfaces
• -> must be *ampipathic* (both hydrophilic & hydrophobic regions)…hydrophobic inside membrabe & hydrophilic internal/external surfaces of membrane

**Cytoplasmic proteins are arranged in clusters** (NOT being distributed evenly)

• -> allows grouping of proteins that interact or that have similar function
• -> Lipid bilayer varies in thickness (from 6 - 8 nm) to accommodate various patches of proteins

Question 12

Cytoplasmic Membrane Function

Answer 12

1. Permeability Barrier

• prevents leakage (which would distruct integrity of cell)
• functions as a gateway for transport of nutrients into and out of cell

2. Protein Anchor
   - site of many proteins involveed in transport, bioenergetics, signaling, & chemotaxis
3. Energy Conservation

• site of generation & use of proton motive force
• -> *Proton Motor Force* – membrance possesses a charge separation (in which protons & hydroxyl ions are separate across surface)… results in form of energy
• -> responsible for driving many energy-requiring functions in cell
• -> includes some forms of transport, motility, and biosynthesis of ATP

Question 13

Proton Motive Force

Answer 13

• factor that gives cytoplasmic membrane ability to function as major site of E conservation in cell
• **membrane possess an energetically charged form in which protons (H⁺) are separated from hydroxyl ions (OH^-) across its surface**
• -> charge separation is a form of E…analogous to potential E
• -> responsible for driving many E-requiring functions in cell…some forms of transport, motility, biosynthesis of ATP
• bc of charged membrane…charged molecules (even as small as a proton H⁺) canNOT passivle transport across membrane

Question 14

Sterols

Answer 14

• Eukaryotes possess **Sterols** in their membranes (while almost all prokaryotes do NOT)
• -> (exceptions… 2 prokaryotes that do possess Sterols – Mycoplasmas)
• -> Mycoplasmas lack cell walls…require Sterols to stabilize their membrane
• Steroles make up anywhere from 5% - 25% of total lipids in eukaryotic membranes
• Sterols are rigid planar molecules & the association of these with the membrane serves to *stabilize* its structure making it less flexible
• -> Fatty Acids are more flexible

Question 15

Hopanoids

Answer 15

• similar to Sterols…rigid, planar molecules which strengthen & stabilize membrane making it less flexible
• ***present in many Bacteria***
• -> NOT present in Archaea
• widely distributed example = *Diplotene (C₃₀)*

Question 16

Achaeal Membranes

Answer 16

• Archaea lipids are chemically unique
• -> possess ***Ether*** linkages between L-glycerol & their hydrophobic side chains…
• -> …Bacteria & Eukarya possess *Ester* linkages between D-glycerol & fatty acid hydrocarbon chains
• Archaea lipids lack fatty acids…
• -> … possess side chains of repeating units of parent 5-carbon hydrocarbon **Isoprene** [(c) of image @ bottom]

***it was 16S rRNA sequence differences that led Woese to discover Archaea as a new domain…distinct from Bacteria & Eukarya***

Question 17

Major Lipids of Archaea

Answer 17

(both still possess repeating units of Isoprene side chains)

• ***Glycerol diethers***
• -> possess 20-C side chains… (4 linked Isoprene units)
• -> …*Phytanyl* – 20-C side chains
• ***Diglycerol Tetraethers***
• -> possess 40-C side chains… (8 linked Isoprene units)
• -> …*Biphytanyl* – 40-C side chains
• -> 2 phytanyl from each glycerol molecule are covalently bonded together – Tetraether actually called Di-biphytanyl diglycerol tetraether
• (in Tetraether lipids)…
• -> within a membrane, this structure yields a lipid ***monolayer***
• Lipid Monolayers are resistant to peeling apart
• -> monolayer membranes widespread among hyperthermophilic Archaea, prokaryotes…prevents cell lysis

Question 18

Necessary Properties of Transport Proteins

Answer 18

1. transport systems demonstrate **Saturation Effect**

• -> carrier proteins are saturable sometime even at low [solute]
• -> rate of uptake becomes maximal @ substrate saturation & addition of more solute does not increase the rate

2. has high specificity

• -> many carrier protons react only with a single molecule
• -> others show affinities for closely related class of molecules (such as sugars; amino acids)

3. biosynthesis of transport proteins is typically regulated by cell

• -> function of both nutrients present in environment & their concentrations
• -> particular nutrient may need to be transported by one transporter when at high [given nutrient]….and by a different (higher-affinity) transporter when at low [given nutrient]

Question 19

Rate of Solute Entry

Answer 19

**Y axis : S_i
**X axis: Time

• Initial velocities of transport: /\S_i/ /\T
• velocities meased when S_i is initially 0 & S₀ is varied & rate is measured @ early times
• each line represents a different initial [solute] on outside, S₀
• eventually *max velocity* is achieved
• -> arrow line would be same for S₄, S₅, S₆, etc…
• -> V_max of transport reached

Question 20

Types of Passive Transport

Answer 20

**do not utilize source of E**
–> solute travels down conc. gradient…
…from [high] to [low]
- **Net transport internally when [S]o > [S]i**
–> if [S]o = [S]i then v = 0

1. Simple Diffusion
   - non-saturable
2. Facilitated Diffusion

• saturation @ high [solute]
• -> carrier proteins possess specificity for solute

Question 21

Types of Active Transport

Answer 21

**use E to accumulate solute against conc. gradient**
–> transports from [low] to [high]

1. Simple Active

• utilize Ion gradients/*Proton Motice Force*
• consists of only a membrane-spanning integral protein

2. ATP-binding Cassette (ABC) System

• E from ATP
• consists of 3 components: 1) substrate-binding protein; 2) membrane-integrated transport; 3) ATP-hydrolyzing protein

–> 2 ATP → 2 ADP + 2 P_i

3. Group Translocation

• E from chemical modification of transported substance (phosphorylation) driven by Phosphoenopyruvate
• involved series of proteins in transport event

Question 22

Membrane Spanning Proteins & their structural similarities which correspond to their ability to act as Transporter membranes

–> 3 classes of transport events?

Answer 22

• contain 12 alpha-helix domains that weave back & forth forming channels which solutes enter cell
  –> transport event involves protein *conformational change* upon solute binding…
  …this shuttles solute across membrane

3 clases of transport events:

1) Uniporter
- proteins that transport a molecule unidirectionally across membrane

2) Antiporter
- proteins that transport a molecules across membrane while simultaneously transporting a second molecule in *opposite* direction

3) Symporter
- proteins that transpot a molecule across membrane while simultaneously transporting a second molecule in *same* direction
- -> frequents a proton (H⁺)
- -> function as *cotransporters*

Question 23

Phosphotransferase System

Answer 23

• best studied model of *group translocation*
  –> type of active transport – requires E…
  …energy from PEP (Phosphoenol-pyruvate)
  –> results in phophorylation (chemically modification) of substance being transported
• **Phosphotransferase Sys. transports the sugars glucose, mannose, & fructose in E. coli**
• consists of a family of proteins…5 of which are necessary for given sugar
• (before transport of sugar) these proteins are alternately phosphoylated & then dephosphorylated in cascading fashion … until the actual transporter (Enzyme II_C) phosphorylates the sugar
• Enz I; HPr; Enz II_a are all cytoplasmic proteins
• Enz II_b lies on the inner surface & Enz II_c is an integral protein
• Enz I & HPr are non-specific components
• all Enz II proteins are specific components…
• -> specific Enz II exists for each sugar (glucose, fructose, & mannose)

***phosphorylation of Glucose to Glucose-6-P is 1st step in its intracellular metabolism – Glycolysis***

Question 24

The ABC System

Answer 24

ATP-binding Cassette
–> necessary for uptake of organic compounds (sugars, amino acids) & inorganic compounds (sulfate & phosphate) & trace metals

**Gram- (-) bacteria possess Periplasmic region**

• -> Periplasm – lies between cytoplasm & peptidoglycan
• -> periplasm contains many different periplasmic-binding proteins
• Gram- (+) bacteria also have ABC systems
• -> substrate-binding protein anchored to external surface of cytoplasm

ABC System:

• ATP hydrolyzing protein (Kinase) provides E
• 3 components
  1) Periplasmic (substrate) - binding protein
  –> located in periplasm
  –> typically high substrate affinity
  2) membrane-spanning transporter protein
  3) ATP-hydrolyzing protein (Kinase)
  2 ATP → 2 ADP + P_i

Question 25

Protein Transport

Answer 25

- cell to function properly...proteins transported through cytoplasmic membrane or inserted into membrane - -\> possible by \*\*Translocases\*\* - many bacterial enzymes function as exoenzymes - Preproteins -- presecretory proteins which synthesize transported proteins - -\> preproteins possess a signal peptide at amino terminus...recognized by Sec System - -\> Chaperon -- proteins that bind to signal peptides & delay protein folding (keeping it in necessary conformation for transport) - -\> Signal Peptidase -- remove signal peptide & protein folds into shape - key example -- \*Sec (secretory) System\* - -\> both exports/inserts into membrane - consists of 7 proteins: 1) Sec Y, E, G -- transmembrane transporter proteins 2) Sec A -- ATP hydrolyzing enzyme (energy) 3) Sec B -- prevents folding of protein in cytoplasm 4) Sec D, F -- assists in translocation - -\> also consumes E from Proton Motive Force

Question 26

Function of Cell Wall of Bacteria

Answer 26

\*bc of activities of transport systems...cytoplasm of bacterial cells maintains a high [dissolved solutes]\* - protects cell from Osmotic Pressure & prevents Cell Lysis - -\> bacteria tend to live in environments typically hypotonic to cell...thus H20 tends to move into cell - -\> this causes significant Osmotic Pressure...would cause cell lysis if it were not for rigid cell wall - confers shape & regidity to cell

Question 27

Gram + vs Gram - Bacteria cell walls

Answer 27

- \*\*Peptidoglycan is rigid layer primarily responsible for strength of cell wall\*\* - Gram + : - -\> 1 thicker layer of peptidoglycan - -\> Gram stain test results in Purple stained cells - -\> B. subtilis - -\> S. aureus - Gram - : - -\> 2 layers -- thin peptidoglycan + LPS - -\> Gram stain test results in Pink stained cells - -\> E. coli

Question 28

Composition of Peptidoglycan

Answer 28

- rigid layer or sheet - -\> thick in Gram + - -\> thin in Gram - - composed of 2 sugar derivatives: N-acetylglucosamine (G) & N-acetylmuramic acid (M) - -\> always connected in Beta-1,4 glycosidic bond - also composed of small group of amino acids: L-alanine & D-alanine, D-glutamic acid; either Lysine (gram +) or Diaminopimelic acid (DAP) (gram -)

Question 29

DAP vs Lysine

Answer 29

- 2 of numerous amino acids found in peptidoglycan cell wall of bacteria - identical in chemical structure besides terminal end - Gm (-): - -\> possess DAP (Diaminopimelic Acid) - -\> E. coli - -\> - COOH - Gm (+): - -\> possess Lysine - -\> B. subtilis - -\> S. aureus - -\> - H

Question 30

Peptidoglycan variations: Cross-links & interbridge connections

Answer 30

\*\*Glycan backbone portion constant among all species of Bacteria\*\* - -\> G-M-G-M (N-acetylglucosamine & N-acetylmuramic acid) - -\> beta 1,4 Glycosidic bond - Tetrapeptide variation only in 1 amino acid in \*\*\*position 3\*\*\* -- DAP/Lysine - Gm (-): - -\> amino group (- NH2) of DAP cross-linked to carboxy group (- COOH) of terminal D-alanine via \*\*peptide bond\*\* - -\> NO interbridge - Gm (+): - -\> cross-linkage occurs via \*\*peptide interbridge\*\* - -\> kinds & numbers of amino acids in interbridge vary from organism to organism - -\> interbridge in S. aurerus...consists of Glycine pentapeptide bridge

Question 31

Peptidoglycan Sheet

Answer 31

- Glycosidic bonds confer strength in X direction - Peptide bonds confer strength in Y direction

Question 32

Diversity of Peptidoglycan --\> Defining characteristics...?

Answer 32

- only present in species of Bacteria - sugar N-acetylmuramic acid (M) & amino acid Diaminopimelic acid (DAP) never found in cell walls of Archaea or Eukarya - most Gm (+) possess Lysine instead of DAP - -\> 3rd molecule distal from M - (unusual feature) presence of 2 amino acids that are D-configuration (D-alanine & D-glutamic acid) - greatest diversity in peptide crosslinks & interbridge - -\> Gm (+) -- Lysine -- cross-linkage @ peptide interbridge bond (Lysine & varying amino acid bridge of adjacent glycan chain) - -\> Gm (-) -- DAP -- cross-linkage @ peptide bonds (DAP & D-alanine of adjacent glycan chain) - Gm (+) possess more cross-links - Gm (-) possess cross-links that are "longer"

Question 33

Teichoic Acids

Answer 33

- acid substances embedded in cell wall - -\> of Gm (+) Bacteria - bc of (-) charge of Teichoic acids...partially responsible for (-) charge on Gm (+) cell surface as whole - encompasses all cell wall, cytoplasmic membrane, & capsular polymers containing \*polyalcohols\* - -\> Polyalcohols -- glycerophosphate; ribitol phosphate residues - (in wall) covalently bound to N-acetylmuramic acid via \*\*Phosphate Esters\*\* - -\> usually possess D-alanine & other sugars attached - \*\*Lipoteichoic acids\*\* -- teichoic acids covalently linked to membrane lipids (Lipoproteins)

Question 34

Lysozyme

Answer 34

- Peptodoglycan can be destroyed by certain agents - -\> causes weakening of cell & possibly eventual cell lysis - -\> such as \*\*Lysozyme\*\* - -\> Lysozyme -- protein that breaks the B-1,4-glycosidic bond between N-acetlymuramic acid & N-acetyl glucosamine - -\> Lysozyme function as major line of defense against bacterial infections via this mechanism

Question 35

Protoplasts

Answer 35

- a Gm (+) bacterium that has lost its cell wall - -\> did not under cell lyses - -\> destruction of peptidoglycan caused from agents such as Lysozyme - Lyses occurs.... ...in dilute solution bc cell wall is structurally very weak - Lyses does NOT occur... ...in solutation containing an \*\*isotonic\*\* concentration of a solute (such as Sucrose) ...H20 does NOT enter cell ⇒ \*\*\*Protoplasts only possess cytoplasmic membrane & internal constituents\*\*\* --\> devoid of cell wall; no residual wall left

Question 36

Spheroplasts

Answer 36

- Gm (-) bacteria produce Spheroplasts when treated with Lysozyme - (similar to protoplasts)...but possess residual wall attached

Question 37

Examples of Cells that lack Cell Walls

Answer 37

- Mycoplasmas - -\> group of pathogenic bacteria that cause variety of infectious diseases in humans & other animals - -\> like protoplasts & live in osmotically protected environment - -\> Sterols add strength to membrane - -\> ...Lysozyme found in animal secreations... - Thermoplasmas - -\> species of Archaea that naturally lack cell wall - -\> unusually tough cytoplasmic membranes

Question 38

Pseudomurein

Answer 38

- found in some Archaea cell wall - -\> Methanogenic Archaea - constructed of a polysaccharide very similar to Peptidoglycan - backbone composed of alternating repeats of N-AcGlu & N-acetyltalosaminuronic acid (T) - -\> Glycosidic bonds are B-1,3 (instead B-1,4) - -\> Lysozyme-insensitive - possess Lysine as 3rd position on Glycan Chain - possess only L steroisomer - some archae have S layers

Question 39

Penicillin

Answer 39

- type of Beta-lactam ring antibiotic - potent inhibitors of cell wall synthesis - -\> disrupts formation of cross-links - -\> bind to Transpeptidase enzymes - Archae naturally resistant to Penicillin (& Lysozyme) - Bacteria affected by both Penicillin & Lysozyme

Question 40

S layer

Answer 40

- most common cell wall type among Archaea - Paracrystalline surface layer (or S layer) - -\> showed ordered appearance under microscope - -\> typically hexagonal symmetry - consists of protein or glycoprotein - provides some protection from osmotic lysis - -\> many organisms possess both S layer & peptidoglycan -- (S layer being the outermost) - selective sieve - -\> not alloweing large molecules in (such as viruses) - may retain proteins near surface

Question 41

Lipopolysaccharide layer (LPS)

Answer 41

- Gm (-) bacteria possess outer LPS in addition to peptidoglycan - contains polysaccharides & phospholipids... - -\> ... linked in outer membrane to form lipopolysaccharide structures

Question 42

Structure of LPS

Answer 42

- 3 components: 1) O-specific polysaccharides - often branched - most external facing component 2) Core polysaccharides 3) Lipid portion (Lipid A) - most internal portion of LPS - is endotoxic (toxicity to animals) - embedded in phospholipid portion - -\> lipoproteins present on inner side of LPS anchor outer membrane to peptidoglycan - considered lipid bilayer but distinct from cytoplasmic membrane

Question 43

Endotoxin

Answer 43

- LPS layer [Gm (-)] bacteria commonly toxic to animals - toxic properties associated with Lipid A - -\> Innermost portion of LPS - produce fever, decrease B.P., activation of inflammation, coagulation of blood presence in blood can lead to \*\*septicemia\*\*

Question 44

LPS Permeability & Porins

Answer 44

- LPS not permeable to large molecules (proteins) - -\> major function -- prevent proteins from diffusing - O-specific polysaccharides prevent hydrophobic molecules from diffusing pass LPS - -\> hydrophobic antibiotics not effective to Gm (-) - Lipid A phspholipid layer prevent hydrophilic small molecules from diffusing pass LPS - \*\*Porins\*\* -- proteins present in LPS - -\> function as channels for entrance/exit of hydrophilic low-molecular-weight substances - -\> H20 filled channels - -\> several different porins exist...both specific & nonspecific - consists of 3 identical subunits

Question 45

Capsules vs. Slime Layers

Answer 45

both may be thick/think; rigid/flexible depending on chemical makeup & hydration 1. Capsules - material organized in tight matrix (like an envelope around cell) - exclused small particles -- such as india ink 2. Slime layers - material more easily deformed; organized in loose matrix - will not exclude particles; more difficult to see

Question 46

Functions of Capsules

Answer 46

- attachment of microbes to solid surfaces - -\> pathogens typically first bind to surface components on human tissues - -\> nonpathogenic often bind to surfaces in nature -- forming Biofilm ( -- thick layer of cells) - encapsulated pathogenic bacteria more difficult for phagocytic cells to engulf & destroy - polysaccharide layers bind water & may make cells resistant to desiccation (drying)

Question 47

Fimbriae & Pili

Answer 47

- both filamentous structures composed of protein that extend from surface of cell - -\> not typically involved in motility even though similar to flagella - allow cells to stick to surfaces - -\> including animal tissue - Fimbriae are considerably shorter than flagella & are more numerous - Pili are similar to fimbriae but typically longer & only 1 or a few present on cell surface

Question 48

Functions of Pili

Answer 48

pili often receptors for certain types of viruses... --\> can best be seen under electron microscope when they have become virus-coated pilus - \*Congugation\* -- facilitation of genetic transfer between prokaryotic cells - -\> F+ (donar) x F- (recipient) ⇒ F- becomes F+ - -\> F factor (Plamid) transferred while replicated - \*Adhesion of pathogens\* to specific host tissue - \*Cell Twitching\* -- unusual form of cell motility