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

Question 1

what is the most abundant substance in all living organisms

Answer 1

water

makes up approximately 70% by mass

Question 2

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

Answer 2

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

Question 3

is water polar or non-polar

Answer 3

polar

Question 4

what does it mean that water is polar

Answer 4

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

Question 5

what are water soluble molecules said to be

Answer 5

hydrophilic (water loving)

Question 6

give examples of hydrophilic molecules

Answer 6

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

Question 7

what happens when sodium chloride is dissolved in water

Answer 7

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

Question 8

what are hydrophobic molecules

Answer 8

water hating

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

Question 9

what is the hydrophobic effect

Answer 9

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

Question 10

give examples of hydrophobic molecules

Answer 10

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

Question 11

what are amphipathic molecules

Answer 11

they contain both hydrophobic and hydrophilic parts

Question 12

are phospholipids hydrophobic, hydrophilic or amphipathic

Answer 12

amphipathic

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

Question 13

how are phospholipids arranged in water

Answer 13

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

Question 14

what is a micelle

Answer 14

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

Question 15

what is a phospholipid bilayer

Answer 15

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

Question 16

phospholipids can form liposomes, what are liposomes

Answer 16

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)

Question 17

many proteins are amphipathic, how are they arranged

Answer 17

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

Question 18

how are lipids transported in the blood

Answer 18

in a chylomicron

Question 19

what is a chylomicron

Answer 19

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

Question 20

what is the pH of water

Answer 20

7 - neutral

Question 21

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

Answer 21

equal

Question 22

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

Answer 22

greater [H+] and lower [OH-]

Question 23

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

Answer 23

lower [H+] and higher [OH-]

Question 24

what are strong acids and bases

Answer 24

acids and bases that fully dissociate

Question 25

give an example of a strong acid

Answer 25

HCl

Question 26

give an example of a strong base

Answer 26

NaOH

Question 27

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

Answer 27

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

Question 28

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

Answer 28

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

Question 29

how is optimal pH maintained

Answer 29

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

Question 30

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

Answer 30

H2PO4- ↔ H+ + HPO42-

Question 31

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

Answer 31

CO2 + H2O ↔ H2CO3 ↔ H+ + HCO3-

Question 32

how is the bicarbonate buffer system affected

Answer 32

Lung -> increase or decrease in ventilation will change CO2 | Kidney -> changes in bicarbonate reabsorption or secretion change overall plasma bicarbonate

Question 33

what can cause acid-base disorders

Answer 33

disease of lung and kidney

Question 34

what is the Henderson-Hasselbalch equation used for

Answer 34

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

Question 35

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

Answer 35

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!

Question 36

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

Answer 36

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-

Question 37

what is the blood's optimal pH

Answer 37

around 7.4

Question 38

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

Answer 38

can cause disastrous metabolic effects

Question 39

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

Answer 39

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