BIO2041: Lecture 2

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  • Created by: LMoney
  • Created on: 14-05-14 09:56
what proportion of water do cells contain?
usually >70%
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why is an aqueous environment required in cells?
Utilisation of nutrients/metabolites requires them to be in aqueous solution
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how are cells separated from their environment?
by a selectively impermeable membrane
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define osmosis?
The movement of solvent (water) across a semi-permeable membrane from an area of low osmotic pressure to an area of high osmotic pressure
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what is tonicity?
proportion of the potential osmotic pressure that is due to solutes to which the cell membrane is impermeable
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what is Total Water equal to?
Free Water + Bound Water
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what is bound water?
Water sufficiently strongly associated with another molecule that it is not available to act as an independent water molecule
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what are bound water molecules trapped in?
molecular matrix
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what does the amount of bound water influence?
osmotic pressure and water activity (Aw)
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what is water activity equal to?
P/Po, P= vapour pressure of total water when some of it is bound water, Po= vapour pressure of total water when none bound
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what is the range of Aw
has range between 0.0 (no free water) to 1.0 (no bound water)
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what is the relationship between Aw and osmotic pressure?
inverse
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Most microbes maintain cell Aw slightly (blank) than surroundings?
Less
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what does this maintain?
turgor pressure - the result of high tonicity of the cytoplasm
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why is turgor pressure important?
needed to permit elongation before binary fision
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what prevents the cell from bursting due to turgor pressure?
presence of cell wall exterior to membrane
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what is the cell's response to a drop in external turgor pressure?
accumulation of small organic molecules in cytoplasm (compatible solutes)
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describe compatible solutes?
They are very soluble, have no net charge, do not alter enzyme activity and have specific cell transport mechanisms to permit their accumulation
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what are some examples of compatible solutes in bacteria?
amino acids and their derivatives
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what are some examples of compatible solutes in fungi?
glycerol, arabitol and mannitol
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what happens if the cell is unable to maintain difference in Aw?
water flows out of cell causing shrinkage and osmotic shock
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what happens if water flows out of the cell?
1) As water flows out of cell it reduces metabolic activity within the cell 2) Eventually metabolism stops 3) may get cell death 4) May get cessation of growth but survival
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which is more likely to kill the cell- Aw slightly lower than minimum for growth or Aw considerably lower?
Aw slightly lower
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what are halophiles?
grow in presence of high salt concentrations
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what are osmophiles?
grow in presence of high concentrations of sugar
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what are xenophiles?
grow in very dry conditions
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what are the effects of minimum Aw on the growth curve of cells?
1) increased lag 2) decreased slope 3) shorter plateau 4) less cells produced 5) rapid decline
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what does enzyme activity (overall metabolic activity and growth) and membrane stability depend on?
temperature- Microbes have optimum temperature for growth - stable membrane and optimum enzyme activity
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can microbes maintain their cell temperature different from surroundings?
no
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what is the temperature range for psychrophiles?
min: -10, optimum: 10-15, max: 20
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what is the temperature range for psychrotrophs?
min: -10, optimum: 20-30, max: 42
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what is the temperature range for mesophiles?
min: 5, optimum: 28-43, max: 52
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what is the temperature range for thermophiles?
min: 30, optimum: 55-75, max: 100
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as temperature decreases below optimum what happens to lag and log phases?
1) The length of lag phase increases 2) The slope of log phase decreases
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what is the pH range for bacteria?
Opt: 6-8, Range: 4-9
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what is the pH range for yeasts?
Opt: 4.5-6, Range: 2-8.5
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what is the pH range for moulds?
Opt: 3.5-4.0, Range: 1.5-9.0
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what happens to the growth curve of cells if the conditions are of minimum pH?
1) increase lag 2) shorter plateau 3) decreased slope 4) more rapid decline 5) less cells produced
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what happens if there are strong acids but the pH outside below optimum but within growth range?
1) no effect on cytoplasmic activity as H+ and OH- cannot cross cell membrane 2) may denature proteins associated with outside of cell membrane 3) may disrupt ATP production via trans-membrane potentials (chemiosmotic hypothesis)
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what happens if there are strong acids and there are extreme of pH on the outside of the cell?
1) Cell membrane damaged so H+ and OH- enter cytoplasm 2) Denature enzymes, damage DNA, cell death
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describe weak acids?
Mostly small, organic acids, lipophilic
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what happens when weak acids are undissociated (uncharged) and what happens when they're dissociated (charged)?
1) undissociated: pass across membrane by simple diffusion 2) dissociated: do not cross membrane
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which form does lower pH favour?
favours undissociated form
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is there higher or lower pH in the cytoplasm?
1) Higher- causes dissociation and increase in [H+] (and decrease in pH) in cytoplasm 2) Damage to cell contents 3) Wastes energy pumping H+ out of cell
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lukashi true or false?
true
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Other cards in this set

Card 2

Front

why is an aqueous environment required in cells?

Back

Utilisation of nutrients/metabolites requires them to be in aqueous solution

Card 3

Front

how are cells separated from their environment?

Back

Preview of the front of card 3

Card 4

Front

define osmosis?

Back

Preview of the front of card 4

Card 5

Front

what is tonicity?

Back

Preview of the front of card 5
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