DNA and semiconservative replication

• Chromosomes are made up of large molecules of DNA which have a double helix structure. DNA is made up of bases that pair together (A with T and C with G).
• Nucleotides are nitrogen containing substances that form the bases of the nucleic acids DNA and RNA. Nucleotides are made up of a phosphate group, a pentose sugar and a nitrogen containing base. In DNA the sugar is deoxyribose whereas in RNA it's ribose.
• Adenine (A) and guanine (G) are purine bases. Whereas thymine (T) and cytosine (C) are pyrimidine bases. DNA contains A,G,T and C whereas RNA contains A,G,U and C.
• Semi-conservative replication involves the DNA molecule unzips as the hydrogen bonds between bases are broken. Free nucleotides pair up with their complementary base pair on the original DNA strand. DNA polymerase joins the strong chemical bond between the sugar and the phosphate molecule of adjoining nucleotides on the new strand of DNA. An enzyme rewinds the double helix and 2 DNA molecules are created consisting of one parent strand and one new strand.
• There are 20 different types of amino acids.
• RNA contains ribose not deoxyribose and contains uracil instead of Thymine. Sequence of bases are complementary to small sections of DNA molecules.
• mRNA (messenger RNA) is a single strand and is a nucleic acid. It contains ribose not deoxyribose and uracil instead of thymine.
• Transcription involves the relevant gene in the DNA in the nucleus being copied into a molecule of mRNA.
• The first part of transcription involves DNA's double helix unzipping as hydrogen bonds between complementary bases break and the two polynucleotide strands separate. 1 strand called the sense strand acts as a template . Free RNA nucleotides (mRNA) complementary base pair to the exposed bases on this strand by forming hydrogen bonds.
• Transcription then involves RNA polymerase forming sugar-phosphate bonds between nucleotides. The mRNA detaches from the sense strand. The two DNA strands join together by complementary base pairings and the DNA molecules wind back up into a double helix.
• In transcription the sequences of 3 bases on the mRNA coding for amino acids are called codons. Not all bases in the DNA code for amino acids so mRNA just transcribed contains non-coding regions called introns.
• Introns in are removed by enzymes before the mRNA leaves the nucleus leaving just the exons.
• A codon is a sequence of three bases on the mRNA that codes for a specific amino acid.