DNA def? Stand for?
- DNA is a polynucleotide.
- Exists as two complementary strands arranged in double helix.
- Stands for: deoxyribonucleic acid.
What is a nucleotide?
- Phosphate ion bonded to 2-deoxyribose which is in turn to one of the 4 bases.
Where is bond formed between phosphate group and 2-deoxyribose?
1.) Between bottom OH group of phosphate and top HOCH₂ group of 2-deoxyribose.
2.)OH removed from phosphate group/ H removed from sugar group.
3.) Then… CONTINUES so bond formed between top OH group of phosphate and bottom OH group of 2-deoxyribose.
4.) OH removed from phosphate and H removed from sugar.
- Trailing bonds.
Where is bond formed between 2-deoxyribose and base?
- OH group on top right of 2-deoxyribose….
Joins to specific N on base. - Refer to “DNA word dox” to test you know which one for each base!!
What does a single strand of DNA consist of?
- A single strand of DNA is a polymer of nucleotides linked by covalent bonds between phosphate group of one nucleotide and 2-deoxyribose of another nucleotide.
- This creates sugar-phosphate polymer chain (ie. sugar-phosphate backbone.)
How is sugar-phosphate backbone formed in DNA?
- Formed by condensation polymerisation.
- Monomers: nucleotides.
- OH groups on phosphate and 2-deoxyribose further react to extend polymer chain.
- For each covalent, phosphodiester bond formed –> molecule of water eliminated.
How do 2 complementary strands of DNA twist to form double helix?
- Polynucleotide strands held together by H bonds between bases.
- Adenine forms H bonds w/ thymine.
- Cytosine forms H bonds w/ guanine.
How many hydrogen bonds between A and T? How about C and G?
- Between A and T: 2 hydrogen bonds.
- Between C and G: 3 hydrogen bonds.
Where do H bonds form between the bases?
- Refer to “DNA worksheet dox. “ for these answers!
Conditions for H bonds to form?
- S+ hydrogen interreacts with lone pair of electrons on electronegative N, O,F.
- S+ hydrogen and electronegative N, O,F must be correct DISTANCE APART.
Why do H bonds only form between A and T and C and G?
- Both A/ T contain TWO POINTS where H bonds form.
- Both C/ G contain THREE POINTS where H bonds form.
(ie. fit perfectly.)
**- Different base pairing: **
1.) Partially-charged atoms would be too close to each other –> repel OR bases can’t get close enough for H bonds to form.
() - extra info for clarification
Why can’t A and G form hydrogen bonds between each other?
- Partially-charged atoms, on each base, would be too close to each other so bases would either:
1.) Repel.
2.) Not get close enough for H bonds to form.
Name of common anticancer drug. Structure?
- Cisplatin.
- Square planar complex with Pt (II) metal, 2 ammonia ligands and 2 chloride ligands.
(ensure you can draw structure of this. Refer to “DNA worksheet dox.”)
True or False
CIS-platin must have the two chloride ions on the RIGHT-HAND SIDE in the Pt (II) complex.
- False!!
- The chloride ions must be adjacent to each other.
- Could be both on the top!
(refer to “DNA worksheet” for both ways to draw.)
True or False
Both cis-platin and trans-platin have the same effect on the body.
- False.
- Trans-platin have Cl- ions on opposite sides of molecule and has different effect on body (not anticancer drug.)
Role of cisplatin?
- Anticancer drug.
- Binds to DNA in cancer cells.
- As complex attached to DNA, prevents DNA replicating –> therefore, prevents cell divison.
How does cisplatin bond to cancer cell DNA?
- Chloride ions are easy to displace with N atoms.
- Chloride ions dettach from Pt (II) complex.
- Pt bonds to N atoms on guanine base within DNA.
- Another guanine base does same with second chloride in cis-platin.
- Cis-platin bonds to DNA.
What happens once cis-platin bonds to cancer cell’s DNA?
- Cis-platin bonds to DNA.
- Creates distortion in DNA strand
- This prevents unwinding of DNA strands.
- This prevents DNA replication (no copying of DNA)
- Prevents cell division of cancer cells.
Why does cisplatin have adverse side effects?
- Prevents healthy cells from dividing as well as cancer cells.
- Affects blood cells –> can suppress immune system/ increased risk of infection/ kidney damage.
- Affects hair follicle cells –> hair loss.
What type of healthy cells does cisplatin affect–> leading to adverse side effects?
- Cells that replicate frequently ie. blood cells/ hair follicle cells.
How can adverse side effects of cis-platin be reduced?
- Give low doses.
- Targetted delivery (ie. nanotechnology) to reduce attack of healthy cells.
What is name of reaction that cisplatin uses to prevent DNA replication in cancer cells?
- Ligand replacement reaction.
Why is cisplatin still used in chemotherapy despite its adverse side effects?
- Short-term side effects VS long-term benefits of eliminating cancer.
You have DNA polymer chain. On what number carbons in 2-deoxyribose will the phosphates be bonded to?
- Carbon 3.
- Carbon 5.
