Lipids, Water, Inorganic ions

Describe how to test for lipids in a sample

1. Dissolve solid samples in ethanol

2. Add an equal volume of water and shake

3. Positive result: milky white emulsion forms

How do triglycerides form?

Condensation reaction between 1 molecule of glycerol and 3 fatty acids forms ester bonds

Contrast saturated and unsaturated fatty acids

Saturated

• contain only single bonds

• Straight chain molecules have many contact points

• Higher melting point = solid at room temperature

• Found in animal fats

Unsaturated

• contain c=c double bonds

• Kinked molecules have fewer contact points

• Lower melting point = liquid at room temperature

• Found in plant oils

Relate the structure of triglycerides to their functions

High energy:mass ratio = high calorific value from oxidation (energy storage)

Insoluble hydrocarbon chain = no effect on water potential of cells and used for waterproofing

Slow conductor of heat = thermal insulation e.g adipose tissue

Less dense than water = buoyancy of aquatic animals

Describe the structure and function of phospholipids

Amphipathic molecule: glycerol backbone attached to 2 hydrophobic fatty acid tails and 1 hydrophilic polar phosphate head

• forms phospholipid bilayer in water = component of membranes

• Tails can splay outwards = waterproofing

Compare phospholipids and triglycerides

Both have glycerol backbone

Both may be attached to a mixture of saturated, monounsaturated and polyunsaturated fatty acids

Both contain the elements C, H, O

Both formed by condensation reactions

Contrast phospholipids and triglycerides

Phospholipids

• 2 fatty acids and 1 phosphate group attached

• Hydrophilic head and hydrophobic tail

• Used primarily in membrane formation

Triglycerides

• 3 fatty acids attached

• Entire molecule is hydrophobic

• Used primarily as a storage molecule (oxidation releases energy)

Are phospholipids and triglycerides polymers?

No, they are not made from a small repeating unit. They are macromolecules.

Why is water a polar molecule

O is more electronegative than H, so attracts the electron density in the covalent bond more strongly

Forms O s- (slight negative charge) and H s+ (slight positive charge)

State 4 biologically important properties of water

Due to polarity and intermolecular H-bonds

• metabolite/solvent for chemical reactions in the body

• High specific heat capacity

• High latent heat of vapourisation

• Cohesion between molecules

Explain why water is significant to living organisms

• Solvent for polar molecules during metabolic reactions

• Enables organisms to avoid fluctuations in core temperature

• Cohesion-tension of water molecules in transpiration stream

What are inorganic ions and where are they found in the body

• ions that do not contain carbon atoms

• Found in cytoplasm and extracellular fluid

• May be in high or very low concentrations

Explain the role of hydrogen ions in the body

• high concentration of H+ = low (acidic) pH

• H+ ions interact with H-bonds and ionic bonds in tertiary structure of proteins, which can cause them to denature

Explain the role of iron ions in the body

Fe2+ bonds to porphyria ring to form haem group in haemoglobin

Haem group has binding site to transport 1 molecule of O2 around body in bloodstream

4 haem groups per haemoglobin molecule

Explain the role of sodium ions in the body

Involved in co-transport for absorption of glucose and animal acids in lumen of gut

Involved in propagation of action potentials in neurons

Explain the role of phosphate ions in the body

Component of:

• DNA

• ATP

• NADP

• cAMP