Lecture 1 Flashcards
What is ionic bonding
- Metal + Non-metal
- Metal loses electron, becomes cation
- Non-metal gains electron, becomes anion
- Oppositely charged so attract by electrostatic forces of attraction
What is covalent bonding?
- Non-metal + Non-metal
- Their orbitals overlap, electrons are shared between the atoms
- Atoms gain full outer shell
- Very strong
What is metallic bonding?
- Metal + Metal
- Metals lose outer electrons forming sea of delocalised electrons
- Electrostatic forces of attraction occur between metal cations and free electrons
- Free electrons allow metals to carry charge, so conduct energy and electricity well
Order of strengths of Bonds table
4
Hydrogen bonding in water summarised + Keywords
Oxygen more electronegative than Hydrogen, e- in Hydrogen pulled closer to Oxygen, Oxygen gains δ- charge, Hydrogen gains δ+ charge
This causes POLARITY in H2O, hydrogen bonds can form (δ- O attracts δ+ H on adjacent water molecules)
Hydrophilic def
Area of a molecule with high charge (good H bonding potential, or low proportion of C atoms)
Tend to face towards water (eg, phosphate heads in phospholipid bilayer)
Hydrophobic / lipophilic def
Areas of molecule with NO charge, (or lots of C atoms), avoids water
Properties of Water due to polarity
- Good solvent
- High specific heat capacity
- High latent heat of vaporisation
- Less dense as a solid
- High surface tension and cohesive properties
- Reagent
Water as a Solvent
Ions such as NaCl and COVALENTLY BONDED POLAR SUBSTANCES (eg. Glucose) will dissolve in it
- This allows water to be an effective transport medium for METABOLITES (a substance formed in or necessary for metabolism)
- However only for polar molecules (non-polar are hydrophobic)
- Also allows chemical reactions to occur within cells (dissolved solutes are more chemically reactive when free to move about)
High Specific Heat Capacity
High Specific Heat Capacity
The specific heat capacity of a substance is the amount of thermal energy required to raise 1kg of the substance by 1°C without a change in state.
Water’s specific heat capacity is 4200°C
Water’s specific heat capacity is high due to the many HYDROGEN BONDS present. Lots of thermal energy is required to break these bonds, and lots of energy to build them.
Therefore the temperature of water does not fluctuate greatly, so :
- It can provide stable habitats
- Vital for maintaining optimal temperatures for enzyme activity
- because it can maintain a constant temperature because water can absorb a lot of heat without big temperature fluctuations
- Water in blood plasma is vital for transferring heat around body
- Blood passes through more active (warmer) regions of the body. Energy is absorbed out of these regions, regulating optimal temperature these regions, whilst temperature of the water remains fairly constant
- Water in tissue fluid does the same thing
Latent heat of vaporisation
Lots of energy is required to evaporate water (liquid to gas), due to hydrogen bonds being broken.
Specific latent heat of vaporisation is the energy required to change 1kg of liquid to gas at constant pressure.
This is advantageous to organisms because :
- It can provide a cooling effect
- Little water is required to evaporate for the organism to lose a great amount of heat energy
Cohesion and Adhesion
Hydrogen bonds between water molecules creates cohesion
This is advantageous because :
- Columns of water can move through xylem of plants and blood vessels of animals
- Enables surface tension, so water skippers can thrive
- hydrogen bonds on top later of water create a sort of film for insects to float
- Water molecules can move up xylem in the transpiration stream
- This is due to adhesion
- Water molecules hydrogen bond to other molecules such as CELLULOSE
- This is due to adhesion
Density
As a solid, water is less dense.
So ICE floats on the top of water.
This :
- Provides habitat for organisms, through :
- organisms being able to live below ice, eg. in Antarctic seas
- organisms being able to live on the ice, eg. in Antarctica
Types of amino acids table
How does an acid react if it is mixed with a polar solvent?
Acid will lose H+ and become negatively charged
Strong acids will completely dissociate
In less polar solvents, acid keeps H+
What happens when H2SO4 is mixed with a polar solvent?
Weak acid, so can dissociate to give anion and multiple protons (diprotic acid)
Energy difference between these states can be quite small (coz its a weak acid) and so going back and forth between forms is possible at physiological pH
What is pKa
Value indicating strength of acid
Low pKa = Strong acid = Ionises more easily in solution
What happens if pKa of acid is lower than physiological pH?
If pKa < pH, acid donates protons more easily and ionisation occurs
What happens if a base has a higher pKa than physiological pH?
pKa > pH, then more likely to be ionised
What determines an amide’s hydrophobicity / hydrophilicity?
Its R group, the amide itself is neutral across physiological pH range, so does not ionise.
What is an amide?
The backbone amines and carboxylic acids combine to form amides
Amides are neutral (at physiological pH), so DO NOT ionise.
So hydrophobic / hydrophilic nature of the protein is determined by the R groups within the amino acid sequence.
