DNA

what is a nucleotide? draw the structure of a nucleotide":

monomer made up of PO₄^3- bonded to 2-deoxyribose in turn bonded to 1 of 4 bases

draw 2 nucleotides bonded together by covalent bonds (and trailing bonds):

describe the structure of DNA:

• ssDNA = polymer of nucleotides linked by covalent bonds between the PO₄^3- group of one nucleotide and the 2-deoxyribose of another nucleotide

• 2 complementary strands arranged in the form of a double helix

• CBP between H bonds - 2 between adenine and thymine, 3 between cytosine and guanine

• complementary strands have base sequences that match adenine to thymine and cytosine to guanine

• sugar-phosphate-sugar-phosphate polymer chain w/ bases attached to the sugars in the chain

this is the structure of adenine - mark where on the molecule adenine bonds to deoxyribose and its base partner:

(when bonding to deoxyribose - H is lost as part of condensation reaction)

this is the structure of thymine - mark where on the molecule thymine bonds to deoxyribose and its base partner:

(when bonding to deoxyribose - H is lost as part of condensation reaction)

this is the structure of cytosine - mark where on the molecule cytosine bonds to deoxyribose and its base partner:

(when bonding to deoxyribose - H is lost as part of condensation reaction. only one of H atoms in NH₂ forms H bond)

this is the structure of guanine - mark where on the molecule guanine bonds to deoxyribose and its base partner:

(when bonding to deoxyribose - H is lost as part of condensation reaction. only one of H atoms in NH2 forms H bond)

give the structure of cisplatin and explain why transplatin would be unsuitable as an anticancer drug:

not transplatin - Cl ligands must be on same side to substitute so that Pt can bind to guanine bases

describe how cisplatin is used as an anti-cancer drug:

• the bonding of Pt to N atom in guanine displaces the Cl^- ligands, resulting in crosslinking which causing kinks in the DNA structure

• so altered DNA cannot unwind or replicate as it normally would

explain why drugs such as cisplatin can have adverse effects - suggest how these can be controlled and why cisplatin is still used for chemotherapy:

• can bind to DNA in normal cells as well as cancer cells

• can cause side effects especially in rapidly /ing cells e.g. hair loss due to damage to hair follicle cells

• can be controlled by giving small doses/targeting cisplatin to the tumour

• still used - balance of long-term +ve effects (curing cancer) outweigh -ve short term effects

draw how a cytosine unit H bonds to a guanine unit:

draw how a thymine unit H bonds to an adenine unit: