2-Water and pH Flashcards
Life at the Cellular Level
Describe the interactions between water molecules and polar molecules that determine solubility.
Water is a polar molecules, this means that the charge within it is not evenly distributed, giving it a slight positive charge at the H end, and a slight negative charge at the O end. This means that any polar molecule will dissolve readily.
Define a hydrogen bond.
A hydrogen bond is a chemical bond that occurs due to a rise in polarity, and molecules that form H bonds tend to be soluble in water.
Describe the interactions between water molecules and proteins that determine solubility.
An ordered layer of water surrounds all the solutes, “screens” both the substrate and the enzyme.
When the substrate and an enzyme interact, ordered water molecules are displaced.
This increase in disorder, energetically speaking, favours the formation of the enzyme-substrate complex.
Describe the interactions between water molecules and hydrophobic molecules that determine solubility.
Hydrophobic molecules do not dissolve in water, however they can dissolve in lipid.
Hydrophobic molecules arrange themselves in water so as to minimise contact with surrounding water molecules. This is the hydrophobic effect.
Describe the interactions between water molecules and lipids that determine solubility.
Lipids: Triglycerides.
1 glycerol and 3 fatty acids
These are non-polar and do not dissolve in water.
*storage lipids - in adipocytes.
Describe interactions between water molecules and amphipathic molecules that determine solubility.
Amphipathic molecules contain both hydrophilic and hydrophobic parts.
Many proteins are amphipathic.
The hydrophilic parts of the chain are on the outside as phosphate heads and the hydrophobic parts are on the inside as fatty chains (lipids)
This allows them to be water soluble.
In water, amphipathic molecules form micelles or bilayers, such that the hydrophobic tail is directed away from the water.
If you put lots of phospholipids within water, you get liposomes, which is a sphere with a lipid bilayer outer shell with a hollow core.
Describe sickle cell anaemia in relation to polarity/solubility.
Haemoglobin is the protein in red blood cells, and is the oxygen and carbon dioxide carrier.
Sickle cell anaemia starts from the exchange from a hydrophilic amino acid to a hydrophobic amino acid. (glutamic - > valine).
This creates a hydrophobic region in the surface of the protein causing it to react with other Haemoglobin molecules by hydrophobic interactions.
This causes the haemoglobin to clump together and form rigid fibres. Final cause is sickling of the red blood cell.
Describe the transport of lipids within the body.
Lipids are transported in the blood by a chylomicron.
A chylomicron is essentially a liposome with a protein embedded in the surface and lipid stored in the core.
The hydrophilic core composed of phospholipid heads is essential to allow the chylomicron to be transported in the aqueous plasma of the blood.
Define the term pH.
pH is the method of determining the H+ concentration in a substance.
Explain the importance of the Henderson-Hasselbalch equation.
The Henderson-Hasselbalch equation can be used to calculate how the pH of a physiological solution will respond to changes in either the conjugate acid or base.
pH is proportional to the ratio of conjugate base to weak acid.
Describe what is meant by the term ‘Buffer’
Buffers are solutions that can resist changes to pH. They are composed of a mixture of a weak acid or base and the salt of that weak acid or base.
Describe the buffers of the body.
In the cytoplasm of all cells, the phosphate buffer system is used.
In the plasma, the bicarbonate buffer system is used to maintain the pH of the plasma at around 7.4.
The bicarbonate buffer system is affected by two organ systems; lungs, where an increase in ventilation will change CO2 levels; and the kidneys, where changes in bicarbonate reabsorption or secretion change overall plasma bicarbonate.
Drastic changes in pH can lead to irreparable cell damage, disastrous metabolic effects and death.
Diseases of lung and kidney can cause acid-base disorders.
