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Flashcards in General/Last year Deck (49):
1

What is % (w/v)?

- g/100ml

2

What is M?

- mol/l

3

What is accuracy?

- whether all values are close to true value

4

What is consistency (precision)?

- whether all values are close to each other

5

Why would you dilate bacteria in saline rather than water?

- saline has same Ψ as bacterial cells
- pure water would cause water to enter cells and burst

6

What is the difference between viable cell count and total cell count?

- viable is actively growing cells
- total inc dead cells

7

What are the types of microbial media?

solid:
- slope culture
- stab culture
- plate culture
- streak plate culture
- spread plate culture
- pour plate culture
- overlay culture

liquid:
- broth culture

8

What is a slope culture and when is it appropriate to use?

- tubes containing ~10ml agar or gelatin medium heated to melt medium
- allowed to set in sloping position
- increasing surface area
- inoculum spread over surface or applied in thin streak w/ sterile wire group
- approp for culturing small amounts of bacteria

9

What is a stab culture?

- tubes containing ~10ml agar medium, allowed to solidify in upright position
- inoculated by straight needle plunged vertically deep into medium

10

What is a plate culture?-

~20ml solid agar medium for each petri dish
- medium melted and cooled to 50ºC

11

What is a streak plate culture and what does it allow?

- cooled medium poured into petri dish and allowed to set in smooth even layer
- inoculum streaked onto surface of medium to prod well separated colonies after incubation
- allows cells to be spread more evenly , so individual colonies can be isolated

12

What is a spread plate culture?

- plate prepared like streak
- inoculum is drop of liquid bacterial culture
- transferred w/ pipette and spread using spreader dipped in alcohol and passed through bunsen flame (sterilising it)

13

What is a pour plate culture, and when is it a useful technique?

- inoculum added to melted and cooled agar medium
- gently mixed and poured into plates
- or inoculum placed into petri dish and liquid medium added
- to ensure even distribution, moved w/ rotating movement
- useful for isolation of bacterial cultures from mixed inoculum, or where heavy even growth needed

14

What is an overlay culture?

- similar to pour plates
- inoculum mixed w/ smaller amount of melted agar medium
- poured in thin layer to solidify on top of solid medium already in petri dish

15

What is a broth culture and what does it produce?

- inoculum transferred using sterile wire loop into liquid medium
- produces large no.s bacteria, but not discrete colonies

16

What are stages of a gram stain?

- heat fixed smear
- stain w/ methyl violet
- iodine to trap stain in peptidoglycan layer
- ethanol wash

17

What do the results of a gram stain indicate about whether cells are gram +ve or -ve?

- +ve = purple
- -ve = pink/red

18

What is the difference between gram +ve and gram -ve cells?

- gram +ve have thick cell wall, so retains methyl violet
- gram -ve have thin cell wall

19

What does G banding do?

- stains gene-poor, heterochromatic regions
- leaving transcriptionally active regions unstained
- generates specific banding pattern for each chromosome

20

Would you expect standard curve for spectrophotometer to be linear and how long for?

- in theory always linear
- in practise it wouldn't, as machine can't accurately measure v small amount of light being transmitted
- compound becomes more conc, will reach point where no longer be soluble

21

What does absorbance equal?

- A = ECt
- E is extinction coefficient
- C is conc
- t is path length

22

How is pH calculated from [H+]?

- -log[H+]

23

What is the equation for Ka?

- Ka = [H+][A-] / [HA]

24

What is the Henderson-Hasselbalch equation?

- pH = pKa + log( [A-] / [HA] )

25

How is pKa calculated from [Ka]?

- -log[Ka]

26

What is the relationship between pH and pKa when [A-] = [HA]?

- pH = pKa

27

What are the limitations of Lineweaver-Burk plot?

- difficult to find x-intercept as never any minus values
- bunching of lower values relied on to draw line to bigger values
- larger values unreliable as at low substrate conc

28

What is an autoclave?

- strong heated container used to sterilise equipment by subjecting them to high pressure steam at 138kPa, heated to 121º for 20 mins

29

How can optical density be used to measure bacterial growth?

- cells in suspension scatter light
- only proportion of light passes through to be detected by photocell in spectrophotometer
- as cell density increases w/ growth, more light scattered and optical density increases

30

What features do plasmids used as vectors generally have?

- contain origin of replication functional in E. coli
- multiple restriction sites, which can be used to insert foreign DNA
- encode gene for resistance for antibiotic as means of selection
- relatively small and present at high copy no. per cell so can be purified in large amounts

31

What % agarose gels do labs typically use and what can this resolve?

- 1%
- can adequately resolve DNA fragments ~1-10kb

32

What factors can proteins be purified by?

- size
- shape
- charge
- solubility
- stability
- binding specificity

33

What is the formula for chi-squared?

Σ { (O-E)2 / E }

34

How is dilution factor calculated?

- total final vol / vol of original solution
- starting conc / final conc

35

How is total dilution factor of serial dilutions calculated?

- multiply individual dilution factors together

36

What are doubling dilutions?

- series of 2 fold dilutions

37

What are the prefixes for the different powers of 10 from 6 to -15?

- 6 = mega (M)
- 3 = kilo (k)
- 2 = hecto (h)
- 1 = Deca (da)
- -1 = deci (d)
- -2 = centi (c)
- -3 = milli (m)
- -6 = micro (μ)
- -9 = nano (n)
- -12 = pico (p)
- -15 = femto (f)

38

How can volumes in L be converted to volumes in m^3?

- 1L = 1dm^3
- 1ml = 1cm^3
- 1μl = 1mm^3

39

How do you calculate standard deviation?

- √ of Σ {(x – x)^2} / (n-1)

40

How is density calc?

- mass / vol

41

What is the density of water?

- 1g/mol

42

What is the mass of 1 mol C-12?

- 12g

43

What does Avogadro's no. tell you?

- = no. units in a mole
- = atoms of 12C in 12g of 12C

44

What equation can be done if you know a vol and 2 concs (or a conc and 2 vols)?

- c1v1 = c2v2

45

How do you get ATP/EGTA/EDTA to dissolve in water?

- pH will drop to 3 --> stirring and heating will have no effect
- titrate w/ base to neutralise and dissolve acid, then correct to req pH after dissolved

46

When should serial dilutions be carried out, and why?

- when adding v small vols to v large vols
- as error would be too large and mixing not even

47

How do you calibrate a pH meter?

- remove cap and rinse in distilled water
- switch on (slide to right)
- calibrate in pH7 buffer and wait for it to settle
- take small screwdriver and adjust top left screw (ACW to decrease reading)
- calibrate in pH4 or 9.2 (whichever brackets pH aiming for)
- adjust right hand screw
- rinse w/ distilled water

48

How do you make a solution of 250ml w/ 2 solid components?

- weigh out and transfer to beakers
- add <250ml (as solids contribute to vol and need to add acid and alkali to get to desired pH) --> about 200ml
- put in magnetic stir bar
- make to desired pH (acid to lower) add dropwise w/ pasteur pipette, w/ stirrer still in
- rinse probe and replace cap
- make up to 250ml w/ distilled water, by pouring all back into cylinder
- mix in beaker

49

What is the difference between technical and biological repeats?

- technical repeats = repeated measurements of same sample --> look at measurement error w/ equipment etc.
- biological repeats = repeating whole experiment to get biologically distinct samples --> look at random biological variation