Applicable for A-Level, IB, DSE, AP-Level Exams

Biological Molecules    Cell Structure    Cell Transport    Immunology    Exchange    Mass Transport    DNA, Genes & Protein Synthesis    Genetic Diversity    Biodiversity    Photosynthesis    Respiration    Energy & Ecosystems    Stimuli and Response    Nervous Coordination & Muscles    Homeostasis    Inheritance    Populations & Evolution    Ecosystems    Gene Expression    Recombinant DNA Technology   


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.

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Stem Cells and Totipotency

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.

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Regulation of Transcription

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.

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Regulation of Translation

siRNA and miRNA both inhibit translation by preventing mRNA from binding to the ribosomes.

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Epigenetic Control of Gene Expression

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.

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