State the names of two enzymes directly involved in synthesizing or joining DNA strands during DNA replication and repair.
In response to cellular stress, an enzyme called PKA phosphorylates a transcription factor called CREB. This phosphorylation allows CREB to bind to specific promoter sequences on DNA and initiate gene transcription.
Use your knowledge of protein structure to explain how the phosphorylation of CREB allows it to bind to DNA.
The synthesis of a new DNA strand requires nucleoside triphosphates (such as dATP) rather than nucleoside monophosphates.
Explain, in terms of energy changes, why nucleoside triphosphates are required for this polymerisation reaction.
Double-strand DNA breaks are normally detected by a sensor protein called ATM. Upon activation, ATM phosphorylates p53, which upregulates the inhibitor p21 to arrest the cell cycle at the G1/S G_1/S\,G1/S checkpoint, allowing time for DNA repair. A mutation could result in a person having a non-functional form of the ATM gene.
Predict the biological consequences of having a homozygous mutation that produces a completely non-functional ATM protein.
