2.3 Nucleotides and Nucleic acids

• The structure of DNA is double-stranded, with two antiparallel strands held together by hydrogen bonds between complementary base pairs.
• RNA molecules are single-stranded and do not form double helix structures like DNA.
• DNA and RNA are polymers of nucleotides.
• nucleotides are composed of a phosphate group, a pentose sugar, and a nitrogenous base.
• Nitrogenous bases can be purines (adenine or guanine) or pyrimidines (cytosine, thymine, uracil).
• nitrogenous bases in RNA are adenine, guanine, cytosine, and uracil.
• nitrogenous bases in DNA are adenine, thymine, cytosine, and guanine.
• nucleotides are joined together by phosphodiester bonds, which are formed by condensation reactions.
• adenosine triphosphate (ATP) is a nucleotide derivative that consists of ribose, adenine, and three phosphate groups.
• energy releases when ATP is hydrolysed - forming an ADP molecule and a phosphate molecule.
• phosphorylation is when a phosphate group is added to a molecule, (eg ADP + phosphate -> ATP).
• semi-conservative replication process: the double helix unwinds using gyrase and the hydrogen bonds between base pairings are broken by helicase creating the replication fork. The original strands (lagging and leading) act as templates and complementary base pairing occurs with the templates and free nucleotides in the nucleoplasm. Phosphodiester bonds join adjacent nucleotides in condensation reactions using DNA polymerase. Then the helix is rewound by gyrase.
• semi-conservative replication: each new strand is a combination of the original strand and the newly synthesised strand.
• the genetic code is the order of bases on DNA containing triplets of bases (codons) that code for a particular amino acid.
• a gene is a section of DNA that codes for a protein.
• amino acids are joined together by peptide bonds to form polypeptides.
• introns are the non-coding sections of DNA. They are removed from the mRNA before it is translated
• exons are the coding regions of a gene and are the parts of the gene that are transcribed into mRNA.
• a genome is the entire set of genetic material in an organism, including all the genes and the DNA that controls them.
• the genetic code is non-overlapping, meaning that each codon is read only once.
• genetic code is degenerate meaning that more than one type of codon can code for the same amino acid.
• a stop codon is a codon that codes for a stop signal and stops translation.
• a mutation is a random change in the DNA sequence of a gene that can lead to a change in the amino acid sequence of a protein.
• the genetic code is universal because it is common to all forms of life.
• Stages of protein synthesis (transcription): the hydrogen bonds between complementary base pairings break and the DNA strands separate. then one of the strands is used as a template by RNA polymerase to make mRNA. Free nucleotides then line up by complementary bases and adjacent nucleotides are joined by phosphodiester bonds using RNA polymerase. The mRNA molecule then moves out of the nucleus via pores in the envelope and attaches to a ribosome where translation occurs.
• Stages of protein synthesis (Translation): mRNA attaches to the ribosome and tRNA carries free amino acids in the cytoplasm to the ribosome. tRNA can only carry one amino acid at a time and a triplet of bases. It then attaches to the mRNA by complementary base pairings and the amino acid detaches from tRNA and adds to the growing polypeptide chain. The process is repeated until a stop codon is reached on the mRNA.