W2 The Cell

Question 1

size of E.coli, bacillus megatherium and red blood cell

Answer 1

e.coli: 1.5 micrometers

BCM: 4 micrometers

rbc: 8 micrometers

Question 2

why do prokaryotes grow faster than eukaryotes

Answer 2

due to large surface area to volume ratio > allow greater uptake of systems

Question 3

definition of monomorphic and pleomorphic

Answer 3

monomorphic: one shape

pleopmorphic: multiple shapes
- changes during growth
- cells become smaller as they age
- response to environmental cues
- sporulation (nutrient limitation)

Question 4

properties of the bacterial membrane

Answer 4

permeability barrier: prevents leakage and functions as gateway for transport of nutrients in and out of cell

protein anchor: site of many proteins involved in transport, bioenergetics and chemotaxis

energy conservation: site of generation and use of proton motive force

Question 5

properties of the bilayer in bacteria

Answer 5

selective permeability barrier

macromolecules can transverse

no exo or endocytosis

head groups: phospatidyl ehtanolamine/serine/glycerol and cardiolipin

Question 6

functions of membrane proteins

Answer 6

nutrient transport

cell wall synthesis

signal transduction

protein secretion

chemotaxis

electron transport

lipid synthesis

Question 7

how does gram stain work

Answer 7

cells stained with crystal violet > iodine > complex formed > gram negative cells decolourised with alcohol while gram positive cell’s peptidoglycan too which for CV-I complex to be washed out > gram positive cells stained purple while gram negative colourless but becomes pink when counter stained with safranin

Question 8

difference between gram positive and negative cells

Answer 8

positive: single membrane with thick peptidoglycan

negative: double membrane with thin peptidoglycan

Question 9

what are the monomeric units of peptidoglycan in gram negative bacteria

Answer 9

amino acids

glycan = NAM + NAG disaccharide; beta(1,4) glycosidic bond

4 amino acids linked together by peptide bonds

Question 10

function of teichoic acid on gram positive cell walls

Answer 10

extends from surface of cell wall

gives cell wall a negative charge

provides flexibility to an otherwise rigid structure

Question 11

what is lipopolysaccharide (LPS) in gram negative bacteria cell wall

Answer 11

important barrier against host defenses

lipid A is an endotoxin to animals

o-specific polysaccharide varies from species to species

order of LPS is uniform: lipid A - ketodeoxyoctonate - core - o specific

Question 12

what is the periplasmic space

Answer 12

contains enzymes that participate in nutrient acquisition and metabolism

only in gram negative cells

contains chemolithotrophs: extensive arrays of electron transport proteins extending to the outer membrane for uptake and metabolism of inorganic ions

oxidation of toxic chemicals

Question 13

what are polyhydroxyaloanates

Answer 13

biodegradable polyesters produced by certain bacteria as a form of energy storage

Question 14

4 types of cellular inclusions

Answer 14

1. carbon storage beta hydroxybutyrate in both bacteria and archaea
2. sulfur storage in chromatium buderi (purple sulfur bacterium)
3. magnetosomes allow bacteria to orient and migrate along geomagnetic fields; usually associated with oxygen concentration
4. gas vesicles: important for aquatic microorganisms > allows them to float in large mats on water surface and sink to nutrient rich water at night

Question 15

types of flagella in bacteria

Answer 15

attached at one end

attached at both ends

tuft at one end

all around cell surface

Question 16

structure of flagella in gram negative bacteria

Answer 16

filament: flagellin

hook: hook protein

basal body: 3 rings

motor driven by proton motive force, not atp

Question 17

development process of flagellum

Answer 17

MS ring assembled in cytoplasmic membrane

P ring forms in periplasm

L ring forms in LPS

hook and cap form

flagellin protein flows through hook to form filament

Question 18

structure of gram positive flagellum

Answer 18

has filament-hook-basal body structure

proton motive force

homologous

only has two rings since there is no LPS

Question 19

how does chemotaxis work

Answer 19

bacteria sense attractants > flagella rotate counter clockwise > flagella bundle together and propel bacterium forward in a straight line

bacteria sense repellants > flagella rotate clockwise > flagella spread apart > bacterium randomly change direction away from repellant

Question 20

function of pili

Answer 20

cover surface and form conjugation bridges between bacterial cells for transferring DNA

Question 21

function of T4P and how it works

Answer 21

responsible for twitching mobility: pili extend and attach to surface > retract and pull bacterium forwards

Question 22

how do some bacteria move by slime extrusion from nozzles

Answer 22

bacteria secrete a slimy polysaccharide substance through nozzle > slime pushes against surface > allow bacteria to move

Question 23

what is sporulation

Answer 23

process where certain bacteria form spores when conditions are unfavourable to protect cell contents > spores are highly resistant, dormant structures designed to withstand environmental conditions

Question 24

process of sporulation

Answer 24

dna replication and asymmetric cell division > pre spore forms > mother cell engulfs pre spore > cortex formation (thick layer to protect spore) > spore adds additional layers and becomes metabolically inactive > mother cell breaks down and release mature spore > germination and growth into vegetative cell again once environmental conditions become favourable again

Question 25

properties of gram positive endospores

Answer 25

occurs as bacteria age due to nutrient deprivation

NOT triggered in response to environmental stress

extremely resistant to environmental stress

controlled by complex cascade of sigma factor gene expression events

Question 26

how do spores return to their vegetative state

Answer 26

activation: heat endospore to sublethal temperature

place in nutrient broth

germination: very rapid; synthesises RNA, protein, dna, breaks and discards spore coat

Question 27

what is dipicolinic acid

Answer 27

makes up 10% dry weight of endospores

high in calcium ion concentration > crosslinks DPA molecules

helps lower water content in spores so that they will become highly resistant to heat and other harsh conditions

Question 28

function of exoenzymes in gram positive cells

Answer 28

gram positive have no periplasmic space and which peptidoglycan layer > prevent molecules from directly entering cell

secrete exoenzymes to aid in transporting nutrients into cell