life at the cellular level (3) - water and pH Flashcards
what is the most abundant substance in all living organisms
water
makes up approximately 70% by mass
why has evolution been shaped by water more than any other substance
because It bathes our cells Dissolves and transports compounds Allows compounds to move within and between cells Participates in chemical reactions Dissipates heat
is water polar or non-polar
polar
what does it mean that water is polar
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
what are water soluble molecules said to be
hydrophilic (water loving)
give examples of hydrophilic molecules
Sugars Alcohols Aldehydes Ketones Compounds with N-H groups Charged particles such as ions
what happens when sodium chloride is dissolved in water
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
what are hydrophobic molecules
water hating
do not dissolve readily in water, but do dissolve in lipid
what is the hydrophobic effect
when hydrophobic molecules arrange themselves in water so as to minimise contact with surrounding water molecules
give examples of hydrophobic molecules
Fat soluble vitamins (A, D, E, K) Lipids Cholesterol Steroid hormones Oxygen
what are amphipathic molecules
they contain both hydrophobic and hydrophilic parts
are phospholipids hydrophobic, hydrophilic or amphipathic
amphipathic
The phosphate head is hydrophilic and the fatty acid tail is hydrophobic.
how are phospholipids arranged in water
phospholipids form micelles or bilayers such that the hydrophobic tail is directed away from contact with the water.
what is a micelle
sphere of phospholipid with hydrophobic part orientated to the centre, away from the water
what is a phospholipid bilayer
hydrophobic part orientated towards centre of the “sandwich”, away from the surrounding water
phospholipids can form liposomes, what are liposomes
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)
many proteins are amphipathic, how are they arranged
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
how are lipids transported in the blood
in a chylomicron
what is a chylomicron
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
what is the pH of water
7 - neutral
how do the concentrations of [H+] and [OH-] compare in water
equal
how do the concentrations of [H+] and [OH-] compare in acidic solutions
greater [H+] and lower [OH-]
how do the concentrations of [H+] and [OH-] compare in basic (alkaline) solutions
lower [H+] and higher [OH-]
what are strong acids and bases
acids and bases that fully dissociate
give an example of a strong acid
HCl
give an example of a strong base
NaOH
what is more important in biological systems and why, weak acids and bases or strong acids and bases
weak acids and bases as they are only partially dissociate, this gives them some unique properties, particularly the ability to act as “buffers”
how are many biomolecules (proteins,DNA) affected by pH
their shape is dictated by the pH of their environment, so for optimal activity they must be at an optimal pH
how is optimal pH maintained
by using weak acids and their bases as buffer systems within cells and organisms
in cells, the phosphate buffer system is important, what is the equation
H2PO4- ↔ H+ + HPO42-
in plasma, the bicarbonate buffer system is important, what is the equation
CO2 + H2O ↔ H2CO3 ↔ H+ + HCO3-
how is the bicarbonate buffer system affected
Lung -> increase or decrease in ventilation will change CO2
Kidney -> changes in bicarbonate reabsorption or secretion change overall plasma bicarbonate
what can cause acid-base disorders
disease of lung and kidney
what is the Henderson-Hasselbalch equation used for
to calculate how the pH of a physiological solution will respond to changes in either the conjugate acid or base
what is the Henderson-Hasselbalch equation in it’s simplified form
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!
what would happen if blood did not have the bicarbonate buffer system
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-
what is the blood’s optimal pH
around 7.4
what happens if small deviations from the blood’s optimal pH occurs
can cause disastrous metabolic effects
what can measuring blood pH, [HCO3-] and [CO2] check
the Henderson-Hasselbalch equation can be used to check how much buffering capacity a patient has
