Intro To Prokaryotes (Lecture1-2)

Question 1

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what are the 6 shapes prokaryotes can be?

Answer 1

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

Question 2

what is the cell envelope ?

Answer 2

plasma membrane + all layers outside it

Question 3

function of plasma membrane in prokaryotes (5)

Answer 3

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

Question 4

nucleoid

Answer 4

localisation of genetic material

Question 5

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

Answer 5

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

**GRAM + **
smaller or absent

Question 6

function of fimbriae & pili (3)

Answer 6

• attachment to surfaces,
• bacterial conjugation & transformation,
• twitching & gliding

Question 7

flagella function

Answer 7

swimming motility

Question 8

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

Answer 8

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

Question 9

what is the phospholipid often found in membrane ?

Answer 9

phosphatidylethanolamine

Question 10

what is the structure of phosphatidylethanolamine ? (4)

Answer 10

• 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)

Question 11

briefly describe peripheral proteins (2)

% of total proteins

Answer 11

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

Question 12

briefly describe integral proteins (3)

% of total membrane proteins

Answer 12

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

Question 13

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

an example

Answer 13

conditions reflected in saturation levels

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

Question 14

what are hopanoids and their function ? (2)

Answer 14

sterol-like molecules in bacterial membranes that stabilise the membrane

Question 15

what is similar about sterols & hopanoids ?

Answer 15

they are synthesised from the same molecular precursors

Question 16

where in the cell is peptidoglycan found ?

Answer 16

the bacterial cell wall

Question 17

what is peptidoglycan ? (2)

aka murein

Answer 17

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

Question 18

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

Answer 18

it’s gram-positive

thick layer of peptidoglycan of 20 - 80 nm

Question 19

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

Answer 19

it’s gram-negative

thin peptidoglycan of 2-7nm PLUS an outer membrane

Question 20

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

Answer 20

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

PoSPoC

Question 21

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

Answer 21

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

Question 22

how are NAM & NAG linked?

Answer 22

by β(1→4) glycosidic bonds

Question 23

why use D-amino acids?

Answer 23

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

Question 24

describe peptidoglycan’s shape (3)

Answer 24

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

Question 25

what does peptidoglycan's shape mean for its chains ?

Answer 25

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

Question 26

what are the 2 ways peptidoglycan can be linked?

Answer 26

* direct **crosslinking** * crosslinking using bridging peptide (**interbridge**)

Question 27

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

Answer 27

beta-lactam (penicillins + cephalosporins) glycopeptide (vancomycin) | **beta glooms peptidoglycan beta team = ceph & penn van glydes**

Question 28

what kills growing cells ? (2)

Answer 28

beta lactam antibiotics, glycoproteins

Question 29

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

Answer 29

**lysozyme** (aka muramidase) * hydrolyses the β(1→4) glycosidic bonds in glycan chains * makes bacteria susceptible to lysis by osmotic effects

Question 30

what is lysozyme?

Answer 30

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

Question 31

where is lysozyme found ?

Answer 31

human secretions

Question 32

against which pathogens is lysozyme most effective against ?

Answer 32

**gram-positive** like streptococcus

Question 33

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

Answer 33

* mostly peptidoglycan * contains **teichoic acids** (negatively charged) * some have layer of proteins on surface | + = t eichoic acids

Question 34

what are the functions of teichoic acids ? (3)

Answer 34

* help maintain **structure** of cell envelope * **protection** from env substances * help **pathogens bind to host tissues** (to initiate infection)

Question 35

describe the structure of **teichoic acids** (3)

Answer 35

* polymers of **glycerol/ribitol** linked by **phosphate groups** * **aa or sugars** attached to glycerol/ribitol units (R groups)

Question 36

where does the periplasmic space of gram+ lie?

Answer 36

between plasma membrane & cell wall

Question 37

what are **exoenzymes**?

Answer 37

enzymes secreted by **gram-positive** bacteria | + = x oenzymes

Question 38

what is the function of exoenzymes ?

Answer 38

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

Question 39

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

Answer 39

* thin peptido surrounded by outer membrane (5-10% of cell wall weight) * no teichoic acids

Question 40

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

Answer 40

**lipids, lipoproteins, lipopolysaccharide (LPS)** | L = -

Question 41

what is the function of Braun's lipoproteins?

Answer 41

connect outer membrane to peptidoglycan | (in gram-negative)

Question 42

what are the 3 parts LPS consists of?

Answer 42

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

Question 43

what is the O side chain?

Answer 43

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

Question 44

what is the importance of LPS ? (6)

Answer 44

- 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)

Question 45

what's the difference between the permeability of the outer membrane and the plasma membrane ? (3) | and why

Answer 45

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

Question 46

what are S layers ?

Answer 46

regularly structured layers of protein or glycoprotein that self-assemble

Question 47

where is the s layer in gram-negative bacteria ?

Answer 47

adheres to outer membrane

Question 48

where is the s layer in gram-positive bacteria ?

Answer 48

associated with the peptidoglycan surface

Question 49

functions of the s layer (3)

Answer 49

- **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