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Genetics > Intro To Prokaryotes (Lecture1-2) > Flashcards

Intro To Prokaryotes (Lecture1-2) Flashcards

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Biology 101 flashcards
1
Q

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what are the 6 shapes prokaryotes can be?

A
  • Cocci (divided into streptococci and staphylococci),
  • bacilli (also coccobacilli),
  • Vibrios (comma shaped),
  • Spirilla (rigid helices),
  • Spirochetes (flexible helices),
  • Filamentous
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2
Q

what is the cell envelope ?

A

plasma membrane + all layers outside it

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3
Q

function of plasma membrane in prokaryotes (5)

A
  • selectively permeable barrier
  • mechanical boundary of cell
  • nutrient &
  • waste transport,
  • location of many metabolic processes
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4
Q

nucleoid

A

localisation of genetic material

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5
Q

describe the periplasmic space (in gram positive and gram negative)

A

GRAM -
contains hydrolytic enzymes & binding proteins for nutrient processing & uptake

**GRAM + **
smaller or absent

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6
Q

function of fimbriae & pili (3)

A
  • attachment to surfaces,
  • bacterial conjugation & transformation,
  • twitching & gliding
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7
Q

flagella function

A

swimming motility

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8
Q

how thick are the plasma membranes in prokaryotes and what is the structure like (5)

A
  • 5-10 nm
  • lipid bilayers with membrane proteins
  • lipids = amphipathic
  • polar ends
  • non polar tails
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9
Q

what is the phospholipid often found in membrane ?

A

phosphatidylethanolamine

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10
Q

what is the structure of phosphatidylethanolamine ? (4)

A
  • polar & hydrophilic end -> ethanolamine
  • glycerol (3C molecule)
  • long, nonpolar hydrophobic FA chains
  • 2 hydroxyl groups were used to make bonds w forming ester linkage (each FA forms ester linkage)
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11
Q

briefly describe peripheral proteins (2)

% of total proteins

A
  • 20 - 30% of total membrane proteins
  • loosely connected to membrane & easily removed
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12
Q

briefly describe integral proteins (3)

% of total membrane proteins

A
  • 70 - 80% of membrane protein
  • amphipathic
  • carry out nb functions
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13
Q

what is the effect of environment conditions on membrane lipids ? (2)

an example

A

conditions reflected in saturation levels

e.g. at lower temperature = more FAs with more unsaturation

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14
Q

what are hopanoids and their function ? (2)

A

sterol-like molecules in bacterial membranes that stabilise the membrane

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15
Q

what is similar about sterols & hopanoids ?

A

they are synthesised from the same molecular precursors

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16
Q

where in the cell is peptidoglycan found ?

A

the bacterial cell wall

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17
Q

what is peptidoglycan ? (2)

aka murein

A

a rigid structure that lies outside cell membrane and keeps bacteria in shape

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18
Q

remember: purple = good = thick

if a gram stain is purple, what does it say about the type of bacteria and its cell wall? (2)

describe layer of peptidoglycan

A

it’s gram-positive

thick layer of peptidoglycan of 20 - 80 nm

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19
Q

if a gram stain is pink or red, what does it say about the type of bacteria and its cell wall? (2)

A

it’s gram-negative

thin peptidoglycan of 2-7nm PLUS an outer membrane

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20
Q

what are the functions of the cell wall ? (4)

A
  • maintains shape
  • protection from osmotic lysis
  • protection from toxic molecules
  • contribute to pathogenicity

PoSPoC

21
Q

what does each subunit of peptidoglycan consist of ? (3)

A
  • 2 sugars (NAG or NAM)
  • short peptides consisting of 4 alternating D and L amino acids
22
Q

how are NAM & NAG linked?

A

by β(1→4) glycosidic bonds

23
Q

why use D-amino acids?

A

protects against most peptidase enzymes (which only recognise aa in L-isomeric form)

24
Q

describe peptidoglycan’s shape (3)

A

helical with short peptides extending from glycan backbone at right angles to each other

25
Q

what does peptidoglycan’s shape mean for its chains ?

A

each peptido strand can be crosslinked to peptido above it, below it & to left and right

26
Q

what are the 2 ways peptidoglycan can be linked?

A
  • direct crosslinking
  • crosslinking using bridging peptide (interbridge)
27
Q

2 types of antibiotics that target peptidoglycan synthesis ? (4)

A

beta-lactam (penicillins + cephalosporins)
glycopeptide (vancomycin)

beta glooms peptidoglycan
beta team = ceph & penn
van glydes

28
Q

what kills growing cells ? (2)

A

beta lactam antibiotics, glycoproteins

29
Q

what enzyme targets peptidoglycan, and how does it do this? (3)

A

lysozyme (aka muramidase)

  • hydrolyses the β(1→4) glycosidic bonds in glycan chains
  • makes bacteria susceptible to lysis by osmotic effects
30
Q

what is lysozyme?

A

antimicrobial enzyme produced by humans & animals (part of innate immune system)

31
Q

where is lysozyme found ?

A

human secretions

32
Q

against which pathogens is lysozyme most effective against ?

A

gram-positive like streptococcus

33
Q

describe the structure of gram-positive cell wall (3)

A
  • mostly peptidoglycan
  • contains teichoic acids (negatively charged)
  • some have layer of proteins on surface

+ = t eichoic acids

34
Q

what are the functions of teichoic acids ? (3)

A
  • help maintain structure of cell envelope
  • protection from env substances
  • help pathogens bind to host tissues (to initiate infection)
35
Q

describe the structure of teichoic acids (3)

A
  • polymers of glycerol/ribitol linked by phosphate groups
  • aa or sugars attached to glycerol/ribitol units (R groups)
36
Q

where does the periplasmic space of gram+ lie?

A

between plasma membrane & cell wall

37
Q

what are exoenzymes?

A

enzymes secreted by gram-positive bacteria

+ = x oenzymes

38
Q

what is the function of exoenzymes ?

A

aid in degradation of polymeric nutrients (e.g. starch & proteins)

39
Q

describe the structure of gram-negative cell wall (3)

A
  • thin peptido surrounded by outer membrane (5-10% of cell wall weight)
  • no teichoic acids
40
Q

what is the outer membrane of gram-negative bacteria composed of ?

A

lipids, lipoproteins, lipopolysaccharide (LPS)

L = -

41
Q

what is the function of Braun’s lipoproteins?

A

connect outer membrane to peptidoglycan

(in gram-negative)

42
Q

what are the 3 parts LPS consists of?

A
  • **lipid A **(in outer membrane)
  • core polysaccharide
  • O side chain
43
Q

what is the O side chain?

A

the O antigen that varies between bacterial strains and extends out from cell

44
Q

what is the importance of LPS ? (6)

A
  • contributes to negative charge on cell surface
  • helps stabilise outer membrane
  • contribute to attachment to surfaces & biofilm formation
  • creates permeability barrier
  • protection from host defences (O antigen)
  • lipid A can act as endotoxin (toxic to host)
45
Q

what’s the difference between the permeability of the outer membrane and the plasma membrane ? (3)

and why

A

outer membrane is more permeable due to presence of porin & transporter proteins

46
Q

what are S layers ?

A

regularly structured layers of protein or glycoprotein that self-assemble

47
Q

where is the s layer in gram-negative bacteria ?

A

adheres to outer membrane

48
Q

where is the s layer in gram-positive bacteria ?

A

associated with the peptidoglycan surface

49
Q

functions of the s layer (3)

A
  • protection from ion & pH fluctuations, osmotic stress, enzymes & predation
  • maintains shape & rigidity
  • promotes adhesion to surfaces
  • protects from host defenses
  • potential use in nanotech

other points not as nb

Genetics (14 decks)

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