Life at the Cellular Level 4 Flashcards
What does water being a polar molecule allow it to do?
Bathe our cells
Dissolve and transport compounds
Allows compounds to move within and between our cells
Participate in chemical reactions
Dissipate heat
Why is water polar?
Because O is more electronegative than H so it attracts the electrons of the covalent bond towards it causing partial charges
What kind of bonds can water form due to being polar?
Hydrogen bonds
What kind of molecules can form hydrogen bonds?
Any that contain electronegative atom bonded to H which is electropositive
What do hydrogen bonds determine due to linking molecules in precise patterns in space?
3D structure
Are bent or linear hydrogen bonds the strongest?
Linear
Are molecules that can form hydrogen bonds water soluble or insoluble?
Water soluble
What are some examples that can form hydrogen bonds?
Sugars
Alcohols
Aldehydes
Ketones
Compounds with N-H groups
What happens when molecules with hydrogen bonds are dissolved in water?
Water-water hydrogen bonds and solute-solute hydrogen bonds are replaced with more energetically favourable solute-water hydrogen bonding
Why are O2 and CO2 poorly water soluble?
O=O and O=C=O have no polarity
End molecules in the straight line are the same so no partial charge
Why is O2 carried by haemoglobin and CO2 floats around as bicarbonate?
Because they are poorly water soluble
Are charged molecules water soluble?
Yes, water forms ‘screens’ around each ion
What is the hydrophobic effect?
Tendency of nonpolar substances to aggregate in an aqueous solution and exclude water molecules
How do non polar molecules arrange themselves in water?
To minimise disruption of hydrogen bonding amount surrounding water molecules, because this is the most energetically favourable arrangement
What does amphipathic mean?
Contains both hydrophobic and hydrophillic parts
How do phospholipids minimise water-water hydrogen bonding?
By forming bilayers
Why do proteins fold in on themselves?
So hydrophobic regions are on the inside and hydrophillic are on the outside, allowing them to be water soluble
How are hydrophobic lipids transported in the blood?
In a chylomicron (phospholipid surface, triacylglycerols stored inside)
How does water weakly dissociate?
H2O ⇔ H+ + OH-
What does dissociate mean?
Molecule splits into smaller pieces
What equation describes the equilbrium of water?
Why can the equilbrium of water equation be expressed as this?
Kw = [H+][OH-]
Because the concentration of H2O is very high and essentially constant so it can be removed from the original equilbrium of water equation
What is Kw known as?
The ionic product of water
What is the value of Kw?
1x10-14
The ratio of H+ and OH- in pure water is 1:1 so:
[H+] = [OH-] = 1x10-7mol/L
Why do we use the log to express the concentration of H+ in water?
Because the concentration is so small, we use the negative log to avoid negatives:
-log[H+] = -log[OH-] = 7
The negative log is appreciated to pH and pOH
pH = pOH = 7
Why does water have a neutral pH?
Because the concentration of H+ and OH- is the same
What is an acid?
A molecule capable of donating a proton
pH < 7
Greater concentration of H than OH
What is a base?
Molecule capable of accepting a proton
pH > 7
Greater concentration of OH- than H+
What does an increase or decrease of 1pH represent?
A ten fold increase or decrease of [H+]
What does pH + pOH equal?
pH + pOH = 14
What is a strong acid/base, giving an example of each?
One which fully dissociates
HCl is a strong acid
NaOH is a strong base
What is a weak acid/base, giving an example of each?
One which partly dissociates
Lactic acid is a weak acid
Ammonium hydroxide is a weak base
What is a congugate acid?
Spieces after a base accepts a proton
What is a congugate base?
Spieces after an acid donates a proton
What makes up the conjugate acid/base pair?
A proton donor and the corresponding acceptor
Does a strong or weak acid have a greater tendency to lose its proton?
The stronger an acid the greater its tendency go give up its proton
HA⇔H+ + A-
The tendency of an acid to lose its proton is defined by what? What expression describes this?
The equilbrium constant (Keq) or acid dissociated constant (Ka)
What are pKa values?
The negative log of Ka value
pKa = -logKa
What is a buffer?
Mixture of a weak acid and its conjugated base which can resist pH changes from the addition of an acid or base
What two equilbriums are going on in a solution of a weak acid?
H2O ⇔ H+ + OH-
HA ⇔ H+ + A-
What are the steps of a titration curve of a weak acid?
- As NaOH is added the OH- combines with free H+ to make H2O
- HA dissociates further to replace the lost H+ and maintain equilbrium
- Process continues and more HA ionises to A-
- At midpoint pH = pKa, beyond this HA continues to be used up until all of it is ionised to A-
What happens to the pH during the buffering region?
pH barely changes with a large input of an acid or base
The Henderson-Hasselbalch equation relates the acid dissociation equiation to the bufffering ability of a week acid/conjugate base, what does this look like?
What are important buffers in the body?
Phosphate
Bicarbonate
Why are buffers important in the body?
They maintian physiological pH when acids and bases are added
