Mutations lead to changes in the DNA base sequence, which might lead to a change to the primary structure and hence the tertiary structure of a protein. This could lead to a non-functional form of an enzyme, for example.
Totipotent stem cells can differentiate into any type of cell. Pluripotent stem cells can differentiate into most types of cells. Multipotent stem cells are found in adults and can differentiate into a limited number of specialised cells. Unipotent stem cells can only differentiate into 1 type of cell, one example of it are cardiomyocytes.
In eukaryotes, transcription of target genes can be stimulated or inhibited when specific transcriptional factors move from the cytoplasm into the nuclues. Activators stimulate rate of transcription by helping RNA polymerase bind to the start of the target gene whereas repressors do the reverse.
In addition, oestrogen starts transcription by combining with a receptor site on the transcriptional factor. This causes a conformation change so that the transcription factor is now complementary to the target gene to start transcription.
siRNA and miRNA both inhibit translation by preventing mRNA from binding to the ribosomes.
Epigenetics are heritable changes to DNA without changing the DNA base sequence. Increased acetylation and decreased methylation both inhibit tranlsation by preventing transcription factors from binding and increasing association of histones and DNA respectively.