3.8 Control of gene expression

• What is a gene mutation?

  A change in the base sequence of DNA
• What is one type of gene mutation?

  Substitution
• What is another type of gene mutation?

  Deletion
• How does a substitution mutation affect the amino acid sequence?

  It may or may not change the sequence
• What is the effect of a deletion mutation?

  It leads to a frameshift mutation
• How can a mutation in a proto-oncogene lead to cancer?

  It can cause the proto-oncogene to become an oncogene
• What is the consequence of excessive protein production from an oncogene?

  It stimulates excessive cell division
• What happens to the cell cycle when cells divide uncontrollably?

  The cell cycle is disrupted
• What can uncontrolled cell division lead to?

  Formation of a tumor
• How does a deletion mutation affect the polypeptide produced?

  It alters the reading frame of codons
• What is the result of most amino acids being incorrect after a deletion mutation?

  It can produce a non-functional protein
• Why do not all mutations result in a change to the amino acid sequence?

  The genetic code is degenerate
• What is a silent mutation?

  A substitution that results in the same amino acid
• How can mutations in non-coding regions affect protein production?

  They may not affect protein production
• What can some mutations not affect?

  The folding or function of the protein
• What are transcription factors?

  Proteins that bind to specific DNA sequences
• Where do transcription factors interact?

  With the promoter region of a gene
• What do activator transcription factors do?

  Help RNA polymerase bind to DNA
• What do repressor transcription factors do?

  Block RNA polymerase, preventing transcription
• What influences the binding of transcription factors?

  Hormones and environmental factors
• Why is the regulation of transcription factors important?

  Ensures genes are expressed only when needed
• How does oestrogen activate gene transcription?

  It binds to an oestrogen receptor
• What does the oestrogen-receptor complex act as?

  A transcription factor
• Where does the oestrogen-receptor complex bind?

  To the promoter region of a target gene
• What is the effect of the oestrogen-receptor complex on transcription?

  It increases transcription by allowing RNA polymerase to bind
• How does siRNA inhibit gene expression?

  It binds to a complementary mRNA sequence
• What does siRNA form with mRNA?

  A siRNA-mRNA complex
• What happens to the siRNA-mRNA complex?

  It is recognized and broken down by RISC
• What is the result of the mRNA being broken down by RISC?

  It cannot be translated, preventing protein synthesis
• What does transcriptional control regulate?

  Whether mRNA is produced from a gene
• What does post-transcriptional control regulate?

  mRNA processing, stability, or translation
• What are epigenetic changes?

  Modifications that do not alter the DNA sequence
• How does DNA methylation affect gene expression?

  It adds methyl groups to cytosine bases
• What is the effect of DNA methylation on transcription factors?

  It prevents them from binding to the promoter region
• How does histone modification affect DNA?

  It makes DNA more tightly packed
• What do both DNA methylation and histone modification do?

  Reduce transcription, silencing the gene
• How does increased DNA methylation affect gene expression?

  It silences the gene and prevents protein production
• What is the difference between benign and malignant tumors?

  Benign tumors do not spread, malignant tumors do
• How do benign tumors grow compared to malignant tumors?

  Benign tumors grow slowly and remain localized
• What is the role of tumor suppressor genes?

  They regulate the cell cycle and prevent uncontrolled division