A2 biology new spec control of gene expression


Control of gene expression

·         Gene mutations are cause by a change in the base sequence of DNA.

·         Substitution of bases can result in a stop codon being formed so the polypeptide is shorter, significantly different and non-functioning, it can code for another amino acid which may alter the shape and make the polypeptide non-functional like in sickle cell anaemia, or as the code is degenerate, it may code for the same amino acid and so it will have no effect.

·         Deletion of bases= frame shift, so every triplet after this point is read differently = considerable impact on phenotype, impact does depend where the deletion occurred along an exon.

·         Addition of bases= frame shift, sometimes multiple can be added, if 3 is added, frame shift will not occur, there will just be an added amino acid.

·         Duplication of bases= bases are repeated= frame shift to the right.

·         Inversion of bases= group of bases become separated, and re-join back to front, only the triplets in the group are affected.

·         Translocation of bases= a group of bases off 1 chromosome become separated and are inserted on to another chromosome. It brings significant effects on phenotype= abnormal like cancer and reduced fertility.

·         Mutations can be spontaneous so happen without influence, mutagenic agents increase the basic rate of mutations- they can disrupt the structure of DNA by altering the shape of bases so DNA polymerase can’t act on them like UV light or x rays, UV light also causes thymine to form bonds with bases next to it= disrupts replication, can alter structure or interfere with transcriptions like NO2 and benzopyrene in tobacco smoke inactivates TP53 by inserting large amounts of guanine in which DNA polymerase just binds anything with= cancer. – nitrous acids remove an NH2 of cytosine making it uracil

·         Mutations can be good as they help in natural selection, but the vast majority are harmful= cancer

·         All the cells in the body have the same genes, but some are permanently switched off so cells become more specialised for a function. Some are permanently switched on e.g. enzymes for respiration. different proteins are produced = visibly different

·         Totipotent cells can mature into any body cell. after a cell has matured, it cannot differentiate into another type of cell.

·         To prevent genes being expressed, transcription or translation is stopped.

·         Stem cells retain the ability to differentiate

·         Totipotent step cell= any type of cell- early embryo and zygote

·         Pluripotent stem cells= almost any type of cell- embryonic and foetal stem cells

·         Multipotent stem cells= can differentiate into a limited number of cells- bone marrow= any blood cell, adult stem cells and umbilical cord blood stem cells.

·         Unipotent stem cells= only into 1 type of cell and are derived from multipotent, found in adult tissue

·         Induced pluripotent stem cells


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