3.3.13 Amino Acids, Proteins and DNA Flashcards
What is an amino acid?
A carbon atom bonded to a hydrogen, R group, amine group and carboxylic acid group
What properties do all amino acids have? (2)
Amphoteric (act as both a base and an acid)
Chiral (four different groups attached to carbon)
What is a zwitterion?
A dipolar ion where the amine group is protonated to NH3+ and the carboxylic acid is deprotonated to COO-
Only exist at isoelectric point (where overall charge is zero)
What happens to the zwitterion under acidic conditions?
NH3+
COOH
What happens to the zwitterion under basic conditions?
NH2
COO-
What are proteins?
Condensation polymers of amino acids - a sequence of amino acids connected by peptide links
What is the primary structure of proteins?
The sequence of amino acids in a chain
What is the secondary structure of proteins? (2)
The shape of the chain (α-helix / β-pleated sheet)
Due to hydrogen bonds
What is the tertiary structure of proteins?
The way the chain is coiled or folded
Due to hydrogen bonding, disulphides bridges and ionic attractions
Where do hydrogen bonds exist in proteins?
Between polar groups such as -OH and -NH2
What is disulphide bonding?
Bonding that occurs between two sulphur atoms present in amino acids, forming a covalent bond
What factors affect the shape of a protein? (2)
Temperature
pH
What are enzymes?
Proteins that act as biological catalysts
What is special about the active site of an enzyme? (2)
Lock and key model - active site only catalyses reactions with substrates of a specific shape
They are stereospecific - only work on one enantiomer of a substrate
How do inhibitors work? (2)
Molecules with a similar shape to the substrate act as inhibitors as they bond with the active site without reacting
No substrate can fit in the active site so the reaction is blocked
How are drugs designed? (2)
By using computers to model active sites and designing potential drug molecules to fit the specific shapes
This method is quick because hundreds of shapes can be tested before trying anything in a laboratory
What is a nucleotide?
The monomer that makes up DNA; made up of a phosphate group, pentose sugar (2-deoxyribose) and a base
What is the structure of a single strand of DNA like?
A polymer chain of nucleotides, linked by covalent bonds to form a sugar-phosphate backbone, with bases attached to the sugars in the chain
How does DNA exist? (2)
As two complimentary strands, arranged as a double helix
The bases pair up as AT or GC due to the arrangement of atoms allowing hydrogen bonding to exist between them
What is cisplatin?
A complex of platinum (II) containing two chloride ion ligands and two ammonia ligands in a square planar shape
The two chloride ions are next to each other (Z isomer)
How is cancer caused?
By the mutation and uncontrollable division of cells, forming tumours
How does cisplatin act as an anti-cancer drug? (4)
In order for a cell to divide, the DNA helix unwinds so it can be replicated
Cisplatin stops this from happening by forming a coordinate bond between the platinum ion and a nitrogen atom in guanine, replacing one of the chloride ion ligands
A second nitrogen atom from a different guanine molecule can replace the other chloride ion ligand
The presence of the cisplatin causes the strands to kink so they can’t unwind and be copied properly
Why can cisplatin cause adverse effects? (2)
It can also bind to DNA in normal cells, stopping healthy cells that normally replicate frequently from multiplying (e.g. hair and blood)
It can cause hair loss, suppress the immune system and cause kidney damage
How can the side effects of cisplatin be lessened? (2)
By giving low dosages
By targeting the tumour directly
