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microbiology > cell morphology 9/19 > Flashcards

cell morphology 9/19 Flashcards

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Biology 101 flashcards
1
Q

most prokaryotes (bacteria and archaea) have a…

A

cell wall

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2
Q

cell walls are

A

–exterior to cell membrane, rigid and mostly structural polysaccharides and peptides or protein

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3
Q

For unicellular and colonial prokaryotes, the primary function of the cell wall is to

A

prevent osmotic lysis

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4
Q

what is osmotic lysis

A

•pressure from water entering cell causes a rupture of the cell membrane and death of the cell

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5
Q

does a cell want to be hypertonic or hypotonic

A

hypertonic to environment

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6
Q

what are hypotonic environments

A

–solute concentration outside the cell is less than inside the cell, and water concentration is higher

–water moves into cell and cell swells

–cell wall protects from lysis

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7
Q

what are hypertonic environments

A

–solute concentration outside the cell is greater than inside, water concentration lower

–water leaves the cell

–plasmolysis occurs

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8
Q

what is a lysozyme

A

• breaks the bond between N-acetyl glucosamine and N-acetylmuramic acid in cell wall

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9
Q

what does penicillin do

A

•inhibits peptidoglycan synthesis

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10
Q

what will happen to cells if a lysozyme or penicillin is used

A

they will lyse if they are in a hypotonic solution

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11
Q

what are characteristics of mycoplasma

A

–does not produce a cell wall

–plasma membrane stronger ( has sterols (rare in prokaryotes) more resistant to osmotic pressure

–Hyper regulates internal solute conc. to stay just slightly hypertonic

–Has sterols

–Very small; 0.2 microns

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12
Q

gram positive

A

•stain purple; thick layer of peptidoglycan

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13
Q

gram negative

A

•stain pink or red; thin peptidoglycan and outer membrane

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14
Q

what is peptidoglycan or murein

A

the structural polysaccharide in the cell walls of domain Bacteria prokaryotes

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15
Q

what is the structure of peptidoglycan

A

•Mesh-like polymer of identical subunits forming long strands; a structural polysaccharide with amino acids that surrounds the cell

–Basic subunit - disaccharide of two alternating modified sugars joined by Beta glycosidic bonds

  • N-acetylglucosamine (NAG)
  • N- acetylmuramic acid (NAM)

–And alternating D- and L- amino acids in a tetrapeptide (4 amino acids) attached to muramic acid that forms cross links with other tetrapeptides

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16
Q

what shape are peptidoglycan strands and what are the chains crosslinked by

A
  • Peptidoglycan strands have a helical shape
  • Peptidoglycan chains are crosslinked by covelent bonds between the tetrapeptides for strength
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17
Q

what is the difference between gram positive and negative bacteria in terms of crosslinks

A

•In gram negative bacteria, crosslinks are directly between amino acids in the tetrapeptide

In gram positive bacteria, there is often an interbridge (indirect) of additional amino acids between the tetrapeptides

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18
Q

what type of connections can be made when peptidoglycan chains are crosslinked by peptides for strength

A

–interbridges may form

–peptidoglycan sacs – interconnected networks

–various structures occur

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19
Q

what are characteristics of gram positive cell walls

A
  • Composed primarily (~90 %) of peptidoglycan
  • Also contains large amounts of teichoic acids (negatively charged) embeded in wall

–help maintain cell envelop

–may bind to host cells

–may store PO4; may attract cations

  • Some gram-positive bacteria have layer of proteins on surface of peptidoglycan
  • Also have lipoteichoic acid which attaches wall to cell membrane
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20
Q

what is the periplasmic space of the gram and bacteria

A
  • Lies between plasma membrane and cell wall and is smaller than that of gram-negative bacteria
  • Periplasm has relatively few proteins
  • Enzymes secreted by gram-positive bacteria are called exoenzymes

–aid in degradation of large nutrients

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21
Q

what are characteristics of gram negative cell walls

A
  • More complex than Gram- positive
  • Consist of a thin layer of peptidoglycan surrounded by an outer membrane
  • Braun’s lipoproteins connect outer membrane to peptidoglycan
  • other adhesion sites reported
  • Outer membrane composed of phospholipids, lipoproteins, and lipopolysaccharide (LPS)
  • No teichoic acids
  • Peptidoglycan is ~5-10% of cell wall weight and in periplasmic space (less peptidoglycan)
  • Periplasmic space differs from that in gram-positive cells

–may constitute 20–40% of cell volume

–many enzymes present in periplasm

•hydrolytic enzymes, transport proteins and other proteins

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22
Q

what is the difference between the top and bottom of the gram negative cell wall

A

Top – lipid bilayer and lipo-polysaccharides on top

Cell membrane/bottom layer – phospholipid bilayer

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23
Q

Lipopolysaccharide (LPS) characteristics

A

•Consists of three parts

–lipid A (endotoxin)

–core polysaccharide

–O side chain (O antigen) – differs

  • Lipid A embedded in outer membrane
  • Core polysaccharide, O side chain extend out from the cell
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24
Q

importance of LPS

A
  • Contributes to negative charge on cell surface
  • Helps stabilize outer membrane structure
  • May contribute to attachment to surfaces and biofilm formation
  • Creates a permeability barrier
  • Protection from host defenses (O antigen)
  • Can act as an endotoxin (lipid A)
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25
Q

gram negative outer membrane permeability

A

•More permeable than plasma membrane due to presence of porin proteins and transporter proteins

–porin proteins form channels to let small molecules (600–700 daltons) pass

26
Q

mechansim of gram stain reaction

A
  • Gram stain reaction due to nature of cell wall
  • Shrinkage of the pores of peptidoglycan layer of gram-positive cells

–constriction prevents loss of crystal violet during decolorization step

•Thinner peptidoglycan layer and larger pores of gram-negative bacteria does not prevent loss of crystal violet

27
Q

what is a glycocalyx

A

•polysaccharide rich (glucose or modified glucose subunits) material exterior to cell wall; sometimes has protein component (2 types – capsule; slime layer)

28
Q

what is a capsule

A

–dense; tightly attached; regular arrangement of polysaccharides; visible to light microscope

-helps prevent virus from binding

29
Q

what is a slime layer and its functions

A

•Slime layer – diffuse; loosely attached; irregular arrangement of polysaccharides

–Functions: attachment to solid surfaces (such as on your teeth if don’t brush them), anti-dessicant, reserve source of energy, anti-phagocytic for some pathogens, prevents virus attachment;

•Slime layer may aid in motility

30
Q

what is the s layer

A

regularly structured layers of protein or glycoprotein that self-assemble (s layer not cell wall in bacteria)

31
Q

difference between gram negative and positive S layer

A

–in gram-negative bacteria the S layer adheres to outer membrane

–in gram-positive bacteria it is associated with the peptidoglycan surface

32
Q

what are the functions of the s layer

A
  • Protect from ion and pH fluctuations, osmotic stress, enzymes, and predation
  • Maintains shape and rigidity
  • Promotes adhesion to surfaces
  • Protects from host defenses
  • Potential use in nanotechnology

–S layer spontaneously associates

33
Q

what are structures beyond the cell envelope in bacteria and archaea and their functions

A
  • Fimbriae
  • Pili
  • Flagella

–protection, attachment to surfaces, horizontal gene transfer, cell movement

34
Q

what are fimbriae

A

•short, thin, hairlike, proteinaceous appendages (up to 1,000/cell)

–mediate attachment to surfaces – type 4

–some (type IV fimbriae) required for motility or DNA uptake

35
Q

sex pili

A

–similar to fimbriae except longer, thicker, and less numerous (1-10/cell)

–genes for formation found on plasmids

–required for conjugation (gene transfer)

36
Q

what are flagella and their functions

A
  • Threadlike, locomotor appendages extending outward from plasma membrane and cell wall
  • Functions:

–motility and swarming behavior

–attachment to surfaces

–may be virulence factors

37
Q

what are characteristics of domain bacteria flagella

A
  • Thin, rigid protein structures that cannot be observed with bright-field microscope unless specially stained
  • Pattern of flagellation varies
38
Q

Monotrichous

A

one flagellum

39
Q

Polar flagellum

A

• flagellum at end of cell

40
Q

Amphitrichous

A

•one flagellum at each end of cell

41
Q

Lophotrichous

A

•cluster of flagella at one or both ends

42
Q

Peritrichous

A

flagella spread over entire surface of cell

43
Q

what are the three parts of the flagellum

A

filament (longest part), hook, basal body (motor)

44
Q

what is the filament of the flagellum

A

–extends from cell surface to the tip

–hollow, rigid cylinder

–composed of the protein flagellin

–some bacteria have a sheath around filament

45
Q

what is the hook of the flagellum

A

–links filament to basal body; made of protein

46
Q

what is the basal body of the flagellum

A

–series of rings that drive flagellar motor

47
Q

what is flagellar synthesis

A
  • complex process involving many genes and proteins
  • new flagellin molecules transported through the hollow filament to tip
  • filament subunits self-assemble with help of filament cap at tip, not base
48
Q

what are the types of mobility in domain bacteria and archaea

A

Flagellar movement

Spirochete motility

Twitching motility

Gliding motility

49
Q

bacteria and archaea have what kind of motility

A

directed movement

50
Q

what is taxis

A

–directed cell movement in response to some stimulus

51
Q

what is chemotaxis

A

–move toward chemical attractants such as nutrients, away from harmful substances

52
Q

what can many bacteria and archaea move in response to

A

temperature, light, oxygen, osmotic pressure, and gravity

53
Q

Changing concentrations of chemical attractants and chemical repellents bind

A

chemoreceptors (molecules that can detect stimulus) of chemo sensing system

54
Q

what does the flagellum rotate like

A

a propeller–very rapid rotation up to 1100 revolutions/sec

55
Q

what is not the main source of energy in flagellar movement

A

ATP

56
Q

spirochete motility

A
  • Have corkscrew shape which allows them to move in viscous media
  • Multiple flagella form axial fibril which winds around the cell
  • Flagella remain in periplasmic space inside outer sheath
  • Corkscrew shape exhibits flexing and spinning movements
57
Q

what do twitching and gliding motility involve in general

A
  • Involves contact with surface
  • May involve Type IV pili and slime
58
Q

twitching

A

–pili at ends of cell

–short, intermittent, jerky motions

–cells are in contact with each other and surface

59
Q

gliding

A

–smooth movements

–Secretes mucus to cut back on friction

60
Q

what are prokaryotic cytoplasmic structures

A

Cytoskeleton

Intracytoplasmic membranes

Inclusions

Ribosomes

Nucleoid and plasmids

microbiology (11 decks)

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