Intro To Prokaryotes #2

Question 1

what are the 3 broad groups of archaea?

Answer 1

1. Methanogens (produce methane)
2. Halophiles (salt loving)
3. Thermophiles (heat loving)

Question 2

how do archaeal cell envelopes differ from bacterial envelopes? (4)

Answer 2

• s layer may be only component outside plasma membrane
• some lack a cell wall
• capsules & slime layers rare
• lack peptidoglycan
• s layer may be outside membrane separated by pseudomurein

Question 3

what feature of the cell wall in archaea make them not susceptible to certain antibiotics (2)

Answer 3

no peptidoglycan so not susceptible to lysozyme, beta-lactam or glycopeptide antibiotics

Question 4

what are some key features of archaeal membranes? (5)

Answer 4

• have distinct membrane lipids (diff from bacteria & euks)
• branched chain hydrocs (alkyl isoprenoids) bonded to glycerol by ether bonds, not FAs linked by ester bonds
• contain diglycerol tetraethers (not in bacteria or euks)
• some have monolayer structure instead of bilayer (due to diglycerol ethers)

Question 5

what evidence is there that archaea are in a distinct group and are not eukaryotes or bacteria ?

Answer 5

contain diglycerol tetraethers
have distinctive membrane lipids

(not in bacteria or euks)

Question 6

how does pseudo murein differ from peptidoglycan (3)

Answer 6

• contains L-aa rather than D-aa;
• has β(1-3) glycosidic bonds and not β(1-4) glycosidic bonds
• contains NAT & NAG not NAM & NAG

Question 7

what are archaeal chromosomes like?

Answer 7

similar to eubacteria, single closed DNA circle per cell

Question 8

what do archaeal ribosomes have in common with bacteria?

Answer 8

ribosomes are 70S but shape is variable

Question 9

what is the protein synthesis of archaea sensitive and resistant to?

Answer 9

• sensitive to anisomycin
• resistant to chloramphenicol and kanamycin (like euks)

aniso affects archaea
chlorine and kites resistant to archaea

Question 10

what is the EF-2 (elongation factor) in archaea sensitive to?

Answer 10

diphtheria toxin (like euks)

archaea elongates dippy (dipper)

Question 11

drugs

in what way is archaeal rna polymerase similar to that in eukaryotes?

Answer 11

insensitive to rifampicin and streptolydigin (usually inhibit bacterial transcription)

Question 12

drugs

what effect does streptolydigin have on prokaryotes?

Answer 12

bacteria: inhibit transcription
archaea: rna polymerase insensitive to streptolydigin

archaea like eukaryotes

Question 13

drugs

what effect does rifampicin have on prokaryotes?

Answer 13

bacteria: inhibit transcription
archaea: rna polymerase insensitive to rifampicin

archaea like eukaryotes

Question 14

how is the small subunit rrna in archaea similar to bacterial (1)

Answer 14

is 16S and similar in length to bacteria

Question 15

which group was archaea more closely related to upon phylogenetic analysis?

Answer 15

eukaryotes

Question 16

what reasons are there to consider archaea prokaryotic ? (4)

Answer 16

• similar cell sizes to bacteria
• no nuclear membrane & cellular organelles
• possess single, large, circular chromo
• may have plasmids

Question 17

what is a protoplast ?

Answer 17

plasma membrane & everything within it

Question 18

what are plasmids? (2)

Answer 18

• extrachromosomal DNA found in bacteria, archaea, some fungi
• usually small, closed circular DNA molecules

Question 19

what are episomes ?

Answer 19

a type of plasmid that may integrate into chromosome

Question 20

what is curing ?

Answer 20

the loss of a plasmid

Question 21

what is refractive index?

Answer 21

a measure of how greatly a substance slows the velocity of light

Question 22

focal point ? (F)

Answer 22

the specific place where lenses focus light rays at

Question 23

focal length (f) ?

Answer 23

the distance between centre of lens & focal point

Question 24

what does a short focal length mean?

Answer 24

more magnification

Question 25

what does a bright-field microscope do?

Answer 25

produces a **dark image** against a **brighter background**

Question 26

what is resolution ?

Answer 26

ability of a lens to **separate (distinguish) small objects** that are close together

Question 27

what is the relationship between **wavelength of light** and **resolution**?

Answer 27

shorter wavelength → greater resolution

Question 28

what is the numerical aperture ?

Answer 28

ability of the lens to gather light (n sin θ)

Question 29

what two factors is numerical aperture determined by?

Answer 29

1. **refractive index** of the medium 2. **theta** (1/2 the angle of the cone of light entering the objective lens)

Question 30

can any lens working in air have a numerical aperture greater than 1.0 ?

Answer 30

no, because air has a refractive index of 1.0

Question 31

how to increase numerical aperture in air ?

Answer 31

increase **n** by changing the medium in which the objective lens works from air to immersion oil

Question 32

what is the **working distance** ?

Answer 32

the **distance between the front surface of lens & the surface of cover glass or specimen** when it's in sharp focus

Question 33

what is heat fixation ?

Answer 33

routine use with bacteria & archaea preserves overall morphology but not internal structures

Question 34

what is chemical fixation ?

Answer 34

used with larger, more delicate organisms protects fine cellular substructure & morphology

Question 35

what are **chromophore groups** ?

Answer 35

chemical groups with conjugated double bonds and **gives dye its colour**

Question 36

what is differential staining used for ?

Answer 36

to detect presence or absence of structures (e.g. gram staining)

Question 37

what causes the colour change in gram staining?

Answer 37

shrinkage of pores of thick peptidoglycan layer of gram-positive cells prevents loss of crystal violet during decolourisation step

Question 38

what is the **terminus** ?

Answer 38

site at which **replication is terminated** | located opposite of origin

Question 39

what is the **replisome** ?

Answer 39

group of proteins needed for DNA synthesis

Question 40

what is the **growth curve**?

Answer 40

* observed when microorgs are cultivated in batch culture (in closed vessel w single batch of medium), * plotted as log of cell nr vs time

Question 41

what are the **four distinct phases** of the growth curve ?

Answer 41

1. **lag** 2. **exponential** 3. **stationary** 4. **death**

Question 42

explain the **lag phase** in the growth curve (2)

Answer 42

during this phase, cells are synthesising new components to replenish spent materials and **adapt** to the new medium

Question 43

describe the **exponential phase** in the growth curve (3)

Answer 43

* **rate of growth & division is constant** & maximal, * cell pop is most uniform in terms of chemical & physical properties during this phase, * cells exhibit **balanced growth** | (aka log phase)

Question 44

what is **balanced growth** ?

Answer 44

cellular constituents are manufactured at constant rates relative to each other

Question 45

under what conditions does **unbalanced growth** occur?

Answer 45

- **change in nutrient levels** shift up = poor to rich medium shift down = rich to poor medium - **change in env conditions**

Question 46

describe the **stationary phase** in the growth curve (3)

Answer 46

* pop growth eventually ceases & total **nr of viable cells remains constant** * active cells stop reproducing or **reproductive rate is balanced by cell death rate**

Question 47

what are possible reasons for the stationary phase ? (4)

Answer 47

- nutrient limitation - limited oxygen availability - toxic waste accumulation - critical pop density reached

Question 48

what are the two alternative hypotheses for the senescence and death phase in the growth curve ?

Answer 48

1. cells are **temporarily** unable to grow (viable but not culturable VBNC) = cells are alive but **dormant**, capable of new growth when conditions are right 2. **programmed cell death** (fraction of the pop genetically programmed to die i.e. commit suicide)