Chapter 4 - Nucleic Acids Flashcards
Components of DNA
- 1 phosphate per nucleotide
- 1 deoxyribose (pentose sugar) per nucleotide
- 1 purine or pyrimidine per nucleotide (not uracil)
Which bases are purines and which are pyrimidines
Purines: adenine and guanine
Pyrimidine: thymine, cytosine and uracil(only in RNA)
Components of RNA
- 1 phosphate per nucleotide
- 1 ribose (pentose sugar) per nucleotide
- 1 purine or pyrimidine per nucleotide. (not thymine)
How a nucleotide forms
2 condensation reactions:
- 1 joins phosphate to pentose sugar (ester bond)
- 1 joins base to pentose sugar (glycosidic bond)
2 H20 molecules are formed for each nucleotide produced
DNA is …
- Macromolecule
- Polymer of nucleotides
- Double stranded helix
- Synthesised during interphase
- Located in nucleus
- 2 strands are antiparralel to each other.
- carries 1000’s of genes
Describe chromosomes
- linear structures
- consist of one molecule of DNA
- found in pairs
- carries 100-1000s of genes
- lengths of DNA wrapped around histone coat
What is a gene?
A length of DNA that codes for the production of enzymes.
What is a genome?
The total collection of all of the genes within an organism. Around 25000 genes in a human.
Properties of DNA
- Stable Molecule
- Carries huge amounts of information
- Complementary Base Pairing
- Passes information to mRNA
- If 1 strand of a DNA molecule is damaged, the info is not lost
- Double Helix
- Antiparralel strands
What were Chargaff’s 2 rules?
- In DNA, the amount of one purine always approx = the amount of the pyrimidine.
- The composition of DNA in terms of relative amounts of A,T,C and G varies between species.
Why are hydrogen bonds important within DNA?
- Hold polynucleotide strands together
- helps maintain 3D structure
- prevent unwinding and strand separation
- give stability to DNA molecule
- can be broken when required
- can easily reform
Process of Semi Conservative Replication
- Histone coat is removed
- DNA is unwound by DNA helicase
- H-bonds between bases break
- free DNA nucleotides are activated by + 2 phosphate groups.
- Activate nucleotides diffuse close to the strands and join with H-bonds
- Both strands act a templates and are copied
- DNA polymerase catalyses synthesis of 2 new strands.
- 2 new phosphate groups on the activated DNA-nucleotides are hydrolysed = releases energy for bonding.
- Sugar phosphate backbone is joined by phosphodiester bonds by DNA polymerase.
- DNA rewinds
- Histone coat is replaced.
Why is DNA polymerase important?
- ensure there are no mutations:
this would lead to altered proteins, different antigens, cells can’t function together, uncontrolled mitosis, unregulated apoptosis.
DNA purification procedure
- dissolve salt in distilled water. Add the washing up liquid and mix gently.
- Break up onion cells in a hand blender and add to solution.
- put beaker in water bath at 60 degrees for 15 mins.
- cool mixture - put in ice bath.
- blend mixture
- filter mixture
- add 2-3 drops of protease to about 10cm^3 of onion extract.
- pour ice cold ethanol down side of boiling tube.
- Leave for a few mins, DNA will form a white precipitate.
