3.8 amino acids, proteins and DNA Flashcards
what is the structure of an amino acid?
NH2 group and COOH group
all same structure apart from R group
amino acids are amphoteric. what does this mean?
they have acidic and basic properties
COOH = COO- + H+
NH2 + H+ = NH3+
why are amino acids chiral molecules?
what does this mean happens?
c has 4 diff groups attached
so solution of single amino acid enantiomer rotates polarised light
what is a zwitterion?
a dipolar ion- both + and - charge in diff parts of the molecule
what is an isoelectric point?
where zwitterions exist on an amino acid
the pH where the overall charge is 0- depends on R group
when does an amino acid become a zwitterion?
when its amino group is protonated to NH3+ and its COOH group is deprotonated to COO-
what happens to an amino acid in conditions more acidic than its isoelectric point?
Nh2 group is likely to be protonated but COOH stays same so amino acid has + charge
what happens to an amino acid in conditions more basic than its isoelectric point?
COOH point likely to lose proton but NH2 unchanged so amino acid has - charge
what happens on/ near isoelectric point?
COOH and NH2 likely to be ionised, forming a zwitterion
how can you separate amino acids?
diff r groups have diff solubilities in same solvent so can use thin-layer chromatography
amino acids arent coloured so how can we see them on TLC plates?
use plate with fluorescent dye and UV lamp
how can you identify amino acids?
rf value (distance travelled by spot/ distance travelled by solvent)
what are proteins?
condensation polymers of amino acids
lots of amino acids joined by peptide links
what happens if the 2 amino acids that are joining are different?
2 diff dipeptides are produced as they can join either way round
how do you split protein into its amino acids?
hydrolysis using harsh conditions
(eg HCl and heat under reflux)
what is the primary structure of a protein?
sequence of amino acids
what is the secondary structure of a protein?
peptide links form H bonds with each other so the chain isnt straight
alpha-helix or beta- pleated sheet
what is the tertiary structure of a protein?
chain of amino acids coiled and folded in characteristic way- extra bonds form
what intermolecular forces are present in proteins?
hydrogen bonding- between polar groups that contain electronegative atoms which induce + charge on H atom which is then attracted to lp on adjacent polar groups
disulphide bridges- occurs between cysteines. cysteine contains thiol group (SH) which can lose its H and join to form -S-S- with another thiol
what are enzymes?
proteins that are biological catalysts and act upon substrates
what is specificity?
what is stereospecific?
enzymes can be explained by lock and key- only work if active site and substrate are complimentary
active sites are stereospecific so only work on 1 enantiomer of a substrate
what are inhibitors?
molecules with a similar shape to the substrate
they bind to active site so no substrate can fit
amount of inhibition depends on relative conc of inhibitor and substrate/ how strongly the inhibitor binds
eg of inhibitors as drugs
problems
antibiotics can block active site of enzyme in bacteria that helps them make cell wall so cell wall weakens and bacteria burst
hard to find drug that fits- very specific- found by trial and error/ using computers to model active site
what are nucleotides made up off?
phosphate group (ion)
pentose sugar- 2 deoxyribose
base- A,C,T,G
see data sheet for how nucleotides are put together
what are the structures of the nucleotides?
see poster
what are polynucleotides?
nucleotides joined by condensation reaction that forms covalent phosphodiester bonds between phosphate group of one and sugar of another
what is complimentary base pairing due to?
arrangement of atoms in base molecules that are capable of forming h bonds
atoms have to be right distance apart for h bonds to form
A and T can each form 2 H bonds and C and G can each form 3 so these are the base pairings- others would put them at diff distances so can form h bonds
double helix has to twist so bases are in correct alignment
what is cisplatin?
complex of platinum II with 2 chloride ion ligands and 2 ammonia ligands in a square planar shape
the 2 chloride ions are next to each other making it cisplatin not transplatin
how is cisplatin an anticancer drug?
1) N atom on G base form coordinate bond with cisplatins pt ion, replacing one of the cl ion ligands
2) 2nd N from nearby G can bond and replace 2nd chloride ion
3) presence of cisplatin complex bound to DNA causes strands to kink so DNA cant unwind and be copied properly so cant replicate properly
adverse effects of cisplatin
how can you lessen the side effects?
why is it still used?
can bind to DNA in normal cells too so problem for any healthy cells that replicate frequently such as hair and blood cells- leads to hair loss and poor immune system and kidney damage
give patients low dosages, target tumour directly
long term positive effects outweigh negative short term effects
draw the structure of cisplatin
make/ see poster
