AS Biology F212: DNA and RNA

DNA

The DNA needs to be stable and must be replicated accurately so daughter cells have the same genetic makeup.

When a cell divides into two,, the chromosomes have to replicate so hat each other the new cells still contains the original number of chromosome, e.g. 46 chromosomes in humans.

Because each chromosome consists of DNA, the DNA molecule has to REPLICATE. The parent cell produces a set of chromosomes identical to its own set. DNA replicates semi-conservatively.

Semi-conservative replication:

• Each parent strand acts as a template for a new strand
• Each new DNA double helix would then have one parent strand and one new strand 

Stages of DNA replication

• The whole  of the DNA molecule uncoils
• The DNA molecule unzips as the hydrogen bonds between the organic bases break
• The bases are now exposed
• In the nucleus individual DNA nucleotides are activated
• The bases of the free activated DNA nucleotides pair up with the complementary exposed bases on each original DNA strands
• The process of complementary base pairing ensures that C-G, A-T
• Covalent bonds form between the phosphate of one of the nucleotide and the sugar of the next to seal the sugar-phosphate backbone
• The whole process is controlled by the enzyme DNA POLYMERASE
• this continues all along the length of the DNA molecule until two DNA molecules are produced
• Both original strands are copied to give 1 old and 1 new strand.
• Two identical copies f the DNA are produced by the semi conservative method of replication

RNA

• RNA is found in three forms, (mRNA, rRNA, tRNA)

Difference between RNA and DNA

• (RNA
• DNA)

• RNA - found in the nucleus and cytoplasm
• DNA- found in the nucleus (small amounts in mitochondria and chloroplasts)
• Contains bases A, C, G, U
• Contains bases, A, C, G, T
• RNA molecule consists of a single strands
• DNA molecule consists of two strands running in opposite directions, twisted together to form a double helix
• Contains the pentose sugar ribose
• Contains the pentose sugar deoxyribose.

How DNA and RNA works together to produce a protein

The sequence of bases on DNA codes for particular polypeptide/protein molecules.

TRANSCRIPTION

• Part of the DNA uncoils and unzips 
• The hydrogen bonds break between the complementary base pairs
• The bases are exposed
• Only 1 of the DNA strand is used
• The particular sequence of bases for that gene form the template
• RNA nucleotide align next to the DNA template strand
• They join up individually using complementary base pairing, A with U, C with G
• A strand of mRNA is made when the backbone for the nucleotides are joined together
• DNA zips back up