30.1 and 30.2 Amino acids Flashcards
What are amino acids
What are they made of
Building blocks of proteins
They have two functional groups: A carboxylic acid and a primary amine
Chiral carbon bonded to 4 different things so almost all amino acids exist as enantiomers, usually the - one
Why do amino acids act as an acid and a base
- The carboxylic acid group can lose a proton to act as an acid
- The amine group has the tendency to accept a proton to act as a base
What are zwitterions
. Amino acids exist as these.
. Ions like these have a permanent positive charge and a permanent negative charge.
. Compound is neutral overall because these cancel out
Are amino acids soluble in water?
What about in other solvents
Do they have high or low boiling points
. They are ionic so amino acids have high boiling points.
. They dissolve well in water but poorly in non polar solvents
How do amino acids act in strongly acidic conditions
What about in strongly basic conditions
. The lone pair on H2N group accepts proton to form positive ion
. So it is protonated
. The COOH loses a proton to form the negative ion so is deprotonated
What is formed by a group of amino acids
What structure of a protein does this form
A polypeptide has many amino acids bonded together with peptide bonds
This forms the primary structure of a protein
What kind of polymers are polypeptides
Condensation polymers because a molecule of water is produced for each bond that forms
How do you hydrolyse a polypeptide
- Boil with HCl conc 6moldm-3 for around 24 hours
- This breaks it down to a mixture of amino acids as it breaks the peptide bonds
Why is wool stretchy
- Wool is a protein fibre with a helix held together by hydrogen bonding
- When it is stretched the hydrogen bonds stretch and the fibre extends
- Then releasing the tension allows the hydrogen bonds to return to the original shape
Why would washing wool at high temperatures misshape it
Very high temperatures will break the hydrogen bonds holding the helix together
What are the 3 types of bonding in proteins
- Hydrogen bonding between C=O and N-H groups
- Ionic attractions between groups on side chains of amino acids such as
-COO- and -NH3+ - Sulfur-sulfur bonds form in amino acid cysteine which has a side chain containing sulfur, so two cysteine molecules can react forming sulfur-sulfur bonds. This makes cystine which is a double amino acid.
What is primary structure of a protein
- Sequence of amino acids is primary structure
- Held together by covalent bonding so it is relatively stable
- Requires harsh conditions eg boiling with HCl to be broken apart
What is the secondary structure of a protein
How can it be broken
- Protein chain may form an alpha helix or a pleated beta sheet
- This is the secondary structure and is held in place by hydrogen bonding between C=O and N-H groups
Hydrogen bonds are much weaker than covalent bonds and this level of structure can be disrupted by change in PH or gentle heating
Describe tertiary structure of protein
- Alpha helix or beta pleated sheet can be folded into a 3D shape called tertiary structure
- This is held in place by hydrogen bonding, sulfur- sulfur bridges and ionic bonding
What is an example of a technique used to determine secondary and tertiary structure of protein
First step is determining primary structure to find out number of each type of amino acid
So reflux with HCl at 6moldm-3 which is called hydrolysis
Then do thin layer chromatography
What is thin layer chromatography and how is it different to normal
- After hydrolysis, amino acids can then be separated and identified by this technique
- Instead of paper chromatography, a thin flexible plastic sheet is used
Describe experiment
- Dot of amino acid mixture is placed on line (not touching water so it is above)
- Lid is placed on tank so the inside is saturated with solvent vapour. Solvent rises up the paper and carries amino acids with it
-Different amino acids travel different amounts depending on its affinity for the solvent compared with its affinity for the stationary phase
- When solvent has almost reached the top of the plate it is removed from the tank and position the solvent moved to is marked
Find RF values for each amino acid spot
Why is the plastic layer thing sprayed with ninhydrin
Amino acids are colourless so this reacts with amino acids to make purple compound
