3.3.13- Amino acids, proteins and DNA (PAPER 2) Flashcards
Draw the structure of an amino acid
What is the structure of amino acids?
Amino group -NH2
Carboxylate group -COOH
Organic side chain represented with R
Chiral molecules- 4 diff groups around central C which rotate plane polarised light
How to name amino acids?
1- find longest C chain (including carboxylic acid)
2- number carbons ( Carbon 1 is COOH)
3- which number carbon is the NH2 group(s) on- if carbon 2 it would be 2-amino
4- name any other groups normally like OH=hydroxy
What is a zwitterion?
A molecule with both positive and negative ions- only exist at the amino acids isoelectric point
What is the isoelectric point?
The pH at which overall charge is 0: dependant on R group
How is a zwitterion formed?
When at a pH at the isoelectric point
Carboxyl and amino groups are ionised- H goes from carboxyl group to NH2 to form C=O, O- and NH3+
What happens at low pH to a zwitterion?
If pH is lower than isoelectric point, COO- is likely to accept an H+ to reform COOH
NH3+ remains
What happens to zwitterion at high pH?
If pH is higher than the isoelectric point then NH3+ is likely to lose an H+ to form NH2
COO- remains
What are proteins?
Polymers made up of amino acid monomer units. Joined together by condensation reactions forming peptide bonds. Chain can be broken through hydrolysis (using water)
How is a dipeptide formed?
H from one amino acid, HO from another amino acid so N and C are bonded together. Water eliminated.
What are the conditions needed for the hydrolysis of protein?
6 moldm-3 HCl
110 degrees C
Reflux for 24 hours
Break the peptide link bond in the middle between C and N, add OH and H to each amino acid unit
What is the primary structure of a protein?
The individual sequence of amino acids in the polypeptide chain. Free COOH on one end and NH2 on other.
What is the secondary structure of a protein?
When the straight chain is pulled into a coiled or pleated structure due to H bonds between peptide links in polymer chain. A helix chain or B pleated sheet
What is the tertiary structure of a protein?
When the protein chain coils up and forms a particular structure- additional bonds hold this together (ionic , hydrogen and disulfide bridges)
How does a disulfide bond hold a protein shape together?
Cysteine is an amino acid with a thiol group (-SH). They can lose this H atom and the sulfur atoms can bond together form a disulphide (S-S) bond.
How do hydrogen bonds hold together a protein shape?
Exists between highly electronegative elements like O and N with H.
In amino acids- this is -NH2 and -OH
What are enzymes?
Proteins and biological catalysts which speed up chemical reactions. They catalyse metabolic reactions within living organisms.
How are enzymes specific?
They have a 3D active site which is part of tertiary protein structure- where chemical reactions occur and substrates bind.
How is the active site stereospecific?
Only one enantiomer in the substrate will fit into the active site- substrate fits into enzyme and is split into 2 products. Enzyme is unchanged.
What is an inhibitor?
Substance with similar shape to substrate- binds to active site, if it binds poorly the ROR is not reduced as much. Higher conc= more active sites blocked so lower ROR
How can drugs work as inhibitors?
Some antibiotics block the active site of the enzyme responsible for making the cell wall of a bacterial cell- it will burst and die.
Why is it difficult to find drugs that fit the active site?
Active site is stereospecific, if drug is chiral only one of enantiomers will work. Trial and error in drugs. Scientists use computer modelling to design new drugs that act as inhibitors for specific active sites - quicker and cheaper
