Genetic Information

• A gene is a base sequence of DNA on a chromosome coding for a protein
• The triplet code is non overlapping, degenerate and universal
• The degenerate nature of the genome means that many triplets can code for the same amino acids
• The universal nature of the genetic code means that most organisms share the same base code for the same amino acids
• The non overlapping nature of the genetic code means that each triplet is read separately
• An exon will code for a protein whereas an intron will not
• MRNA is a linear sequence of complimentary bases to the template DNA strand
• PreMRNA leaves the nucleus via a nuclear pore where it is spliced to become MRNA
• During transcription, a helicase breaks hydrogen bonds between complimentary nucleotides, separating the strands
• The exposed DNA template strand's nucleotides then attract complimentary nucleotides in the nucleoplasm
• Once the complimentary base pairs are lined up, RNA polymerase will bind them together with phosphodiester bonds
• Uracil replaced thymine in RNA
• The MRNA strand will travel to a ribosome where it will be translated into an amino acids by TRNA molecules
• Each TRNA molecule has a complimentary anticodon to the MRNA sequence carrying the corresponding amino acid
• ATP is used to bind amino acids together via peptide bonds at the ribosome
• Gene point mutations are where a base is substituted for another
• Substitutions can be silent, missense or nonsense
• A missense mutation is where a base is substituted, changing the amino acid that the codon codes for
• A nonsense mutation is where a triplet becomes a STOP codon preventing the rest of the polypeptide from forming
• Non disjunction is where there is not an even amount of chromosomes in each cell
• Base deletions or additions cause a frameshift which can prevent the protein from forming correctly
• Crossing over occurs at chaismata during prophase 1 of meiosis
• Paired homologous chromosomes are known as bivalents in prophase 1 and can become recombinant if crossing over occurs
• In metaphase and anaphase 1, homologous chromosomes align at the equator and spindle fibres attach to their centromeres, pulling one of each homologous chromosome pair to either pole, this is known as random assortment
• 2^n is the formula for the combination of homologous chromosomes
• In telophase and cytokinesis 1, the nuclear membrane reforms and the cytoplasm cleaves leading to two haploid cells
• In prophase 2, new spindle fibres form and the nuclear envelope breaks down
• In metaphase 2, sister chromatids line up at the centre of the cell and spindle fibres attach to their centromere
• As the spindle fibres contract, each sister chromatid is pulled to the opposite pole
• In telophase 2, the chromosomes lengthen and the nuclear membrane reforms, the cell willsplit into 2 more haploid cells resulting in 4 genetically variated daughter cells
• (2^n)^2 is the formula for fertilisation
• Mutagenic agents such as smoking increase the frequency of genetic mutation
• n is the number of pairs of homologous chromosomes