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foundations of medicine 1 > life at the cellular level (3) - water and pH > Flashcards

life at the cellular level (3) - water and pH Flashcards

1
Q

what is the most abundant substance in all living organisms

A

water

makes up approximately 70% by mass

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2
Q

why has evolution been shaped by water more than any other substance

A 
because It bathes our cells
Dissolves and transports compounds
Allows compounds to move within and between cells
Participates in chemical reactions
Dissipates heat
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3
Q

is water polar or non-polar

A

polar

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4
Q

what does it mean that water is polar

A

the charge within the molecule is not evenly distributed, giving it a slight +ve charge at the H end and a slight -ve charge at the O end

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5
Q

what are water soluble molecules said to be

A

hydrophilic (water loving)

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6
Q

give examples of hydrophilic molecules

A 
Sugars
Alcohols
Aldehydes
Ketones
Compounds with N-H groups
Charged particles such as ions
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7
Q

what happens when sodium chloride is dissolved in water

A

the water forms ‘screens’ around each ion keeping the Na+ and Cl- ions in solution once dissolved
this type of ‘screening’ also works for more complicated biomolecules

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8
Q

what are hydrophobic molecules

A

water hating

do not dissolve readily in water, but do dissolve in lipid

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9
Q

what is the hydrophobic effect

A

when hydrophobic molecules arrange themselves in water so as to minimise contact with surrounding water molecules

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10
Q

give examples of hydrophobic molecules

A 
Fat soluble vitamins (A, D, E, K)
Lipids
Cholesterol
Steroid hormones
Oxygen
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11
Q

what are amphipathic molecules

A

they contain both hydrophobic and hydrophilic parts

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12
Q

are phospholipids hydrophobic, hydrophilic or amphipathic

A

amphipathic

The phosphate head is hydrophilic and the fatty acid tail is hydrophobic.

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13
Q

how are phospholipids arranged in water

A

phospholipids form micelles or bilayers such that the hydrophobic tail is directed away from contact with the water.

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14
Q

what is a micelle

A

sphere of phospholipid with hydrophobic part orientated to the centre, away from the water

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15
Q

what is a phospholipid bilayer

A

hydrophobic part orientated towards centre of the “sandwich”, away from the surrounding water

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16
Q

phospholipids can form liposomes, what are liposomes

A

If you put lots of phospholipids with water, you get a sphere with a lipid bilayer outer shell and a hollow core (as opposed to a micelle which is a single layer of phospholipid with no core)

17
Q

many proteins are amphipathic, how are they arranged

A

such that hydrophobic regions of the protein chain are on the inside and hydrophilic regions on the outside
this allows them to be water soluble

18
Q

how are lipids transported in the blood

A

in a chylomicron

19
Q

what is a chylomicron

A

A chylomicron is a like a liposome with protein embedded in the shell, and lipid stored in the core
The phospholipid heads and outer edges of the proteins form a hydrophilic outer shell
The hydrophilic shell is essential to allow the chylomicron to be transported in the aqueous plasma of the blood

20
Q

what is the pH of water

A

7 - neutral

21
Q

how do the concentrations of [H+] and [OH-] compare in water

A

equal

22
Q

how do the concentrations of [H+] and [OH-] compare in acidic solutions

A

greater [H+] and lower [OH-]

23
Q

how do the concentrations of [H+] and [OH-] compare in basic (alkaline) solutions

A

lower [H+] and higher [OH-]

24
Q

what are strong acids and bases

A

acids and bases that fully dissociate

25
Q

give an example of a strong acid

A

HCl

26
Q

give an example of a strong base

A

NaOH

27
Q

what is more important in biological systems and why, weak acids and bases or strong acids and bases

A

weak acids and bases as they are only partially dissociate, this gives them some unique properties, particularly the ability to act as “buffers”

28
Q

how are many biomolecules (proteins,DNA) affected by pH

A

their shape is dictated by the pH of their environment, so for optimal activity they must be at an optimal pH

29
Q

how is optimal pH maintained

A

by using weak acids and their bases as buffer systems within cells and organisms

30
Q

in cells, the phosphate buffer system is important, what is the equation

A

H2PO4- ↔ H+ + HPO42-

31
Q

in plasma, the bicarbonate buffer system is important, what is the equation

A

CO2 + H2O ↔ H2CO3 ↔ H+ + HCO3-

32
Q

how is the bicarbonate buffer system affected

A

Lung -> increase or decrease in ventilation will change CO2

Kidney -> changes in bicarbonate reabsorption or secretion change overall plasma bicarbonate

33
Q

what can cause acid-base disorders

A

disease of lung and kidney

34
Q

what is the Henderson-Hasselbalch equation used for

A

to calculate how the pH of a physiological solution will respond to changes in either the conjugate acid or base

35
Q

what is the Henderson-Hasselbalch equation in it’s simplified form

A

pH α [buffer]
————
[H-buffer]

pH is proportional to the ratio of buffer to H-buffer or for example proportional to the ration of HCO3- (buffer) to H2CO3 (H-buffer)
the more buffer you have, the more pH goes up (increases alkalinity) and the more H-buffer you have, the more pH goes down (increases acidity)
Alternatively, if pH goes down, either buffer has gone down or H-buffer has gone up, and vice versa!

36
Q

what would happen if blood did not have the bicarbonate buffer system

A

the pH would fluctuate wildly as cellular products of acids (e.g. lactic acid) would cause marked drops in blood pH
Instead, as these acidic products are released into the blood, the bicarbonate ions act to buffer the H+ to prevent a rapid fall in blood pH. As free [H+] rises so does H2CO3 as the equation is pushed to the left. The bicarbonate “mops up” free H+ and limits (but does not completely prevent) the fall in pH.
H2CO3 ↔ H+ + HCO3-

37
Q

what is the blood’s optimal pH

A

around 7.4

38
Q

what happens if small deviations from the blood’s optimal pH occurs

A

can cause disastrous metabolic effects

39
Q

what can measuring blood pH, [HCO3-] and [CO2] check

A

the Henderson-Hasselbalch equation can be used to check how much buffering capacity a patient has

foundations of medicine 1 (7 decks)

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