General/Last year Flashcards
1
Q
What is % (w/v)?
A
- g/100ml
2
Q
What is M?
A
- mol/l
3
Q
What is accuracy?
A
- whether all values are close to true value
4
Q
What is consistency (precision)?
A
- whether all values are close to each other
5
Q
Why would you dilate bacteria in saline rather than water?
A
- saline has same Ψ as bacterial cells
- pure water would cause water to enter cells and burst
6
Q
What is the difference between viable cell count and total cell count?
A
- viable is actively growing cells
- total inc dead cells
7
Q
What is a streak plate culture and what does it allow?
A
- 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
8
Q
What is a spread plate culture?
A
- 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)
9
Q
What is a pour plate culture, and when is it a useful technique?
A
- 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
10
Q
What is an overlay culture?
A
- 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
11
Q
What are stages of a gram stain?
A
- heat fixed smear
- stain w/ methyl violet
- iodine to trap stain in peptidoglycan layer
- ethanol wash
12
Q
What do the results of a gram stain indicate about whether cells are gram +ve or -ve?
A
- +ve = purple
- -ve = pink/red
13
Q
What is the difference between gram +ve and gram -ve cells?
A
- gram +ve have thick cell wall, so retains methyl violet
- gram -ve have thin cell wall
14
Q
What does G banding do?
A
- stains gene-poor, heterochromatic regions
- leaving transcriptionally active regions unstained
- generates specific banding pattern for each chromosome
15
Q
Would you expect standard curve for spectrophotometer to be linear and how long for?
A
- 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
16
Q
What does absorbance equal?
A
- A = ECt
- E is extinction coefficient
- C is conc
- t is path length
17
Q
How is pH calculated from [H+]?
A
- -log[H+]
18
Q
What is the equation for Ka?
A
- Ka = [H+][A-] / [HA]
19
Q
What is the Henderson-Hasselbalch equation?
A
- pH = pKa + log( [A-] / [HA] )
20
Q
How is pKa calculated from [Ka]?
A
- -log[Ka]
21
Q
What is the relationship between pH and pKa when [A-] = [HA]?
A
- pH = pKa
22
Q
What are the limitations of Lineweaver-Burk plot?
A
- 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
23
Q
What is an autoclave?
A
- strong heated container used to sterilise equipment by subjecting them to high pressure steam at 138kPa, heated to 121º for 20 mins
24
Q
How can optical density be used to measure bacterial growth?
A
- 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
25
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
26
What % agarose gels do labs typically use and what can this resolve?
- 1%
| - can adequately resolve DNA fragments ~1-10kb
27
What factors can proteins be purified by?
- size
- shape
- charge
- solubility
- stability
- binding specificity
28
What is the formula for chi-squared?
Σ { (O-E)2 / E }
29
How is dilution factor calculated?
- total final vol / vol of original solution
| - starting conc / final conc
30
How is total dilution factor of serial dilutions calculated?
- multiply individual dilution factors together
31
What are doubling dilutions?
- series of 2 fold dilutions
32
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)
33
How can volumes in L be converted to volumes in m^3?
- 1L = 1dm^3
- 1ml = 1cm^3
- 1μl = 1mm^3
34
How do you calculate standard deviation?
- √ of Σ {(x – x)^2} / (n-1)
35
How is density calc?
- mass / vol
36
What is the density of water?
- 1g/mol
37
What is the mass of 1 mol C-12?
- 12g
38
What does Avogadro's no. tell you?
- = no. units in a mole
| - = atoms of 12C in 12g of 12C
39
What equation can be done if you know a vol and 2 concs (or a conc and 2 vols)?
- c1v1 = c2v2
40
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
41
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
42
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
43
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
44
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
