Lipids ,Water and Inorganic ions Flashcards
How to test for lipids in a sample?
- Dissolve solid samples in ethanol.
- Add an equal volume of water and shake.
- Positive result: milky white emulsion forms.
How do triglycerides form?
Triglycerides form through a condensation reaction between 1 molecule of glycerol and 3 fatty acids, forming 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 & 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.
Phospholipids are amphipathic molecules: glycerol backbone attached to 2 hydrophobic fatty acid tails & 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 & polyunsaturated fatty acids.
- Both contain the elements C, H, O.
- Both formed by condensation reactions.
Contrast phospholipids and triglycerides.
Phospholipids:
* 2 fatty acids & 1 phosphate group attached.
* Entire molecule is hydrophobic.
* Used primarily in membrane formation.
Triglycerides:
* 3 fatty acids attached.
* Hydrophilic head & hydrophobic tail.
* 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, forming O d- (slight negative charge) & H б+ (slight positive charge).
State 4 biologically important properties of water.
- Metabolite / solvent for chemical reactions in the body.
- High specific heat capacity.
- High latent heat of vaporisation.
- 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 & 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 & 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 porphyrin ring to form haem group in haemoglobin.
Haem group has binding site to transport 1 molecule of O2 around the 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 & amino 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
What is the structure of water
water is a dipolar molecule (di meaning two and pola referring to charges) water has an unevenly distributed charge due to the fct that the oxygen atom is slightly negative and the hydrogen atoms are slightly positive.
What are the five key properties of water
Hydrogen bonds form bteween different water molecules between the oxygen and hydrogen atom.
- It is a metabolite (e.g in condensation and hydrolysis)
- An important solvent in reactions
- Has a high heat capacity it buffers temperature
- Has a large latent heat of vaporisation providing a cooling effect with loss of water through evaporation
- has a strong cohesion between weater molecules this supports water collumns and provides surface tension
Describe how water is a metabolite
Water is involved in many reactions such as photosynthesis, hydrolysis and condensation reactions. This is one reason why approx 90% of plasma is the blood is water and the cytoplasms in cells is largely composed of water.
Describe how water is a solvent
Water is a good solvent meaning many substances dissolve in it. Polar or charged, molecules dissolve readily in water due to the fact water is dipolar. The slight positive charge on hydrogen atoms will attract any negative ions solutes and slight negative charge on the oxygen atoms of water will attracct any positive ions in solutes. These polar molecules are hydrophillic (attracted to water).
Non polar molecules such as lipids cannot disolve in water and are therefore described as hydrophobic (reppelled by water)
So many polar substances dissolve in water enables them to be transported easilyy around animals and plants.
Describe how water has a high specific heat capacity
A lot of energy is required to raise the temperature of water because of its many hydrogen bonds between water molecules which need to be broken.
This is useful to organisms as it means the temperature of water remains relatively stable even if the surroundkng temperature changes. Internal temperature of organisms should remain constant despite outside temp changes as large proportion of organism is water.
This prevents denaturing if enzymes and provides a stable enviroment for aquatic organisms
Descibe how water has a large latent heat of vaporisation
It requires alot of energy to convert water in its liquid state to a gaseous state. Due to the hydrogen bonds as energy is needed to break them for there to be a change of state.
This is advantageous to organisms as it means that water provides a specific cooling effect. E.g sweat (release water onto skin) large ammounts of heat energy from the skin is transfered to the water to evaporate it and therefore removing alot of heat and cooling the organsim
Describe how water has a strong cohesion
Cohesion is the term used to describe water molecules ‘sticking together’ by hydrogen bonds.
Due to water molecules sticking together when water moves up the xylem in plants due to transpiration it is as a continuous collumn of water allowing it to draw up the column easier rather than as individual molecules
It also provides surface tension to water enabiling small invertebrates to move and live on the surface providing them a habitat away from predators
