| what is a mutation | change in sequence of nucleotide bases in DNA, may alter a codon causing it to code for a different amino acid, resulting in differfent polypeptide and different primary structure in protein. |
| what if the protein was an enzyme | it could mean a change in shape of the active site, the substrate may no longer fit the active site, preventing the enzyme from functioning. if the altercation to the codon produces a STOP codon, then the polypeptide may be shortened and the final protein may be non-functional |
| what is insertion 1 | occurs when one or more extra nucleotides are added into the normal sequence of nucleotides in a DNA molecule. |
| what is insertion 2 | in transcription, this sequence is copied to form mRNA. The nucleotdides are 'read' in threes (triplet code) when they are translatied into a sequence of amino acids. the insertion of an axtra base can completely alter the sequnce of amino acids from the point of mutation onwards. meaning that the primary structure is altered and this will affect the secondary and tertiary protein structure |
| insertion 3 | as a result of the inserted nucleotide, every triplet of bases that follows the insertion is altered by one nucleotide. This type of mutation, where the whole 'reading frame' is changed, is called a frame shift |
| what is the frame shift do | may alter the nucleotdie sequence so that a STOP codon is created and the polypeptide chain that results will be shorter. meaning that enzymes cannot be made |
| insertions 4 | more than one nucleotide insertion is possible, where therre is an insertion of 3 nucleotides there will be a change at the site of insertion but the sequence of amino acids following this will be the same, can still alter the tertiar structure of the protein formed |
| deletions | when one of more nucleotides are lost from the normal DNA sequence. Again this causes a frame shift that results in a completely different sequence of amino acids in the polypeptide from that orginally coded for. deletion of 3 nucleotides result in the loss of one or more amino acids from the chain. with the rest of the chain having the same sequence. enzymes are often not formed |
| substitutions 1 | when a nucleotide in a DNA is replaced by another that has a different base. If we take the triplet of bases in the DNA template strand guanine - thymine - cytosine (GTC) that codes for the amino acid glutamine, a change to a single base could result in one of the following |
| a nonsense mutations | if the base change results in the formations of one of the three STOP codons that mark the end of a polypeptide chain, so if guanine is substituted by adenine becomes ATC codes for one of three STOP codons on mRNA. so the final protein would be shortened and not function properply |
| a mis-sense mutations | occurs when a base change results in a different amino acid being coded for. if cytosine is substituted by guanine then it GTG, the amino acid histidine is coded for by the GTG and this then replaces the original amino acid glutamine.
the polypeptide produced will be different, if the amino acid changed is important then the protein may not function, active site might not work anymore |
| silent mutations | substituions results in a different base occuring in a DNA triplet but one that still codes for the same amino acid, the final polyppetide producted is identical to the oragincal |
