amino acids, proteins and dna Flashcards
What are the two functional groups of an amino acid?
An amine group (NH2) and a carboxyl group (COOH)
Define amphoteric:
Have both acidic and basic properties
This is because the amine group can accept a proton (basic) and a carboxyl group can donate a proton (acidic)
Why are amino acids chiral?
The central carbon usual has 4 different groups attached so can from enantiomers
What is a zwitterion?
A dipolar ion- has both a positive and negative charge
Only occur near the amino acids isoelectric point (pH where the charge overall is zero)
What charge will the amino acid carry in acidic conditions?
Positive because the NH2 group is likely to be protonated but the COOH group is likely to be unchanged
What charge will the amino acid carry in basic conditions?
Negative because the COOH group is likely to lose its proton but the NH2 group will be unchanged
How can we easily separate amino acids?
Using TLC because the amino acids will all have different solubilities in the same solvent due to the different R groups. Need to spray ninhydrin on the plate to view the amino acids on the plate
How do you calculate Rf values?
Rf= distance moved by spot ÷ distance moved by solvent
What are proteins?
Condensation polymers of amino acids, joined by peptide links
How do you break up proteins?
Hydrolysis under acidic conditions
What is the primary structure of a protein?
The sequence of amino acids in the polymer chain
What is the secondary structure of a protein?
The peptide links can form hydrogen bonds with each other so the chain can either form an alpha helix or a ßpleated sheet
What is the tertiary structure of a protein?
The secondary structure is folded or coiled more due to extra bonds between different parts of the polypeptide chain. This gives the protein a 3d shape
How do hydrogen bonds arise in proteins?
Exist between polar groups like NH2 and OH, as these groups contain electronegative atoms that will induce a partial positive charge on hydrogen so the hydrogen will then be attracted to lone pairs on adjacent polar groups
How do disulfide bonds arise in proteins?
Sulfur-sulfur bonding which only occurs between amino acids of cysteine. The thiol group (SH) in cysteine can lose its H atom and join together to form a disulfide bond with another thiol group
What does stereospecific mean in relation to enzymes?
They only work on one enantiomer of the substrate as the other enantiomer will not fit properly into the active site
What are the three components of DNA?
2-Deoxyribose sugar, a phosphate group and one of four bases: adenine, thymine, guanine and cytosine
What is cisplatin?
A complex of platinum(II) with two chloride ion ligands and two ammonia ligands in a square planar shape. The two chloride ions are next to each other. If the ions were opposite each other then the molecule would be transplatin which as different biological effects
How is cisplatin used as a drug?
Prevents the DNA double helix unwinding:
1. Nitrogen atom on a guanine base on DNA forms a co-ordinate bond with cisplatins platinum ion, replacing a chloride ion ligand
2. A second nitrogen atom from a nearby guanine (either on the same DNA strand or the opposite strand) can bond to the platinum and replace the other chloride ion
3. The presence of the cisplatin complex bound to the DNA strands causes the strands to kink so the DNA cant unwind and be copied properly, so tumour cant replicate
Why does cisplatin cause adverse effects?
Can bind to healthy cells and stop them replicating properly so causes hair loss, and suppresses the immune system and can also cause kidney damage
How can side effects of cisplatin be lessened?
Give patients very low doses or target the tumour cells directly so it doesn’t get a chance to attack healthy cells
