genes and genetic code

• the order of bases in a gene determines the order of amino acids in a protein
• each amino acid is coded for by a sequence of 3 bases (this is called a codon)
• A gene may also code for a section of functional DNA
• functional RNA are RnA molecules other than messenger RNA (involved in protein production)
• examples of functional RNA molecules include tRNA (transfer RNA) and rRNA (ribosomal RNA)
• mRNA is a section of DNA that codes for a protein
• In the genome, there are sections of DNA that code for tRNA and rRNA
• a universal genetic code is one in which each triplet codes for the same amino acid in all organisms
• a non-overlapping genetic code is one in which each base in the sequence is read only once
• a degenerate genetic code is one in which most amino acids are coded for by more than one triplet
• the genetic code is degenerate, universal and non-overlapping
• the start codon is a series of three bases at the start of a gene + initiates translation
• The start codon codes for the amino acid methionine and is removed from the protein if not actually needed for the structure
• The start codon is TAC in DNA and AUG in mRNA
• The stop codon is a series of three bases at the end of every gene that do not code for an amino acid
• The stop codon marks the end of the polypeptide chains and causes ribosomes to detach and therefore translation to stop
• The stop codons are ATT, ACT and ATC in DNA
• 20 amino acids that the genetic code has to be able to code for
• degenerate -> each amino acid is coded for by more than one triplet of bases
• the code is degenerate as 64 possible combinations (4x4x4 because 4^3) is more than is needed to code for 20 amino acids
• Introns are sections of DNA that do not code for amino acids and therefore polypeptide chains
• the true purpose of introns is currently unknown
• introns are removed during protein synthesis
• prokaryotic DnA does not contain introns
• exons are regions of genes that do code for a protein
• Eukaryotic DNA also contains repeating regions of DNA located outside of genes (called short tandem repeats or microsatelillites) which are also non-coding
• A gene can exist in multiple forms
• These are called alleles
• Humans usually have 2 alleles of the same gene - one for each chromosome
• The base sequence of two alleles of the same gene may be slightly different to one another
• This difference may lead to slightly different proteins being made
• a gene is a section of DNA that contains a code for making a polypeptide and functional RNA
• polypeptides make proteins so genes determine the proteins of an organism