Gene Expression and Protein Synthesis Quiz

Learning Outcomes

• Reinforce knowledge from a previous session.
• Apply knowledge through exercises.
• Understand why studying gene expression is important.
• Recognize the medical significance.
• Identify techniques used to study DNA, RNA, and proteins.
• Explore the possibility of synthesizing DNA, RNA, and proteins in vitro.

The Genetic Code

• There are 64 codons that code for 20 amino acids.
• Third base in a codon is degenerate meaning multiple codons can code for the same amino acid.
• Start codon is AUG, which codes for methionine, the first amino acid in a polypeptide.

One Gene - One Protein Hypothesis

• Proposed by Beadle and Tatum in 1941.
• Not always true as some genes can make multiple proteins through alternative splicing.

Alternative Splicing

• Process where exons are joined together in different combinations to produce various mRNA isoforms.
• Example: Drosophila Dscam gene can produce up to 38,016 isoforms through alternative splicing.

Medical Importance of Gene Expression Errors

• Errors in gene expression can lead to various disorders, including:
  • Duchenne Muscular Dystrophy
  • Spinal Muscular Atrophy
  • Cystic Fibrosis
  • Pulmonary Arterial Hypertension
• Can also influence the predisposition to common diseases, such as:
  • Breast cancer
  • Lung cancer
  • Prostate cancer
  • Blood cancer

Errors in Genes Causing Diseases

• Duchene Muscular Dystrophy: mutation in the DMD gene
• Spinal Muscular Atrophy: mutation in the SMN1 gene
• Cystic Fibrosis: mutation in the CFTR gene
• Pulmonary Arterial Hypertension: mutation in the BMPR2 gene
• Breast cancer: mutation in the BRCA1 and BRCA2 genes.

Transcription Errors

• Over-expression of the transcription factor (TF) MYC is found in various cancers.
• Mutations in one copy of the gene encoding the TF can also lead to diseases:
  • Haploinsufficiency: one copy of the gene is not enough (e.g., p53 gene).
  • Dominant mutation: change in the gene sequence alters protein function and dominates over the wild-type (e.g., TFCP2L3 gene and genetic deafness).

Splicing Errors

• Errors in alternative splicing are common.
• In Cystic Fibrosis: mutation in exon 7 of the SMN1 gene leads to its skipping and a non-functional protein.

Translation Errors

• Mutations can affect translational efficiency.
• Mutations in key translation proteins can lead to disease, including:
  • Translation initiation factors (e.g., eIF2 gene - Vanishing White Matter disease).
  • Release factors (e.g., eRF3 gene - gastric cancer).
  • tRNA transfer proteins or the ribosome itself (rare anemias and several neurodegenerative diseases).

Techniques for Detecting Gene Expression

• Gel Electrophoresis of DNA/RNA:
  • DNA is negatively charged and moves towards the cathode in an electric field.
  • Used to separate DNA or RNA fragments based on size.
• Western blotting:
  • Used to detect specific proteins.
  • Steps:
    • Gel Electrophoresis
    • Blotting
    • Blocking
    • Antibody Probing
    • Detection/Visualisation
• PCR: polymerase chain reaction
  • Amplifies specific regions of DNA.
  • Used for:
    • Gene expression profiling (qPCR)
    • Diagnostics
    • Gene cloning
    • Legal disputes

Making DNA, RNA, and Protein in a Tube

• There are protocols available for synthesizing RNA in vitro.
• Researchers have successfully created pre-mRNA for splicing in a tube.

This quiz assesses your understanding of gene expression, its significance in medicine, and the techniques used to study DNA, RNA, and proteins. Additionally, it covers concepts like the genetic code, the one gene-one protein hypothesis, and alternative splicing. Test your knowledge on these critical topics in molecular biology!