Genetics and Evolution - Molecular Basis of Inheritance

  • Introduction to the molecular basis of inheritance
  • Understanding the role of genes and DNA
  • Importance of genetic information for evolution

DNA Structure

  • Double-helix structure
  • Complementary base pairing (adenine-thymine, guanine-cytosine)
  • Sugar-phosphate backbone

Central Dogma of Molecular Biology

  • DNA replication
  • Transcription (DNA to mRNA)
  • Translation (mRNA to protein)

Gene Expression

  • Importance of gene expression
  • Regulation of gene expression
  • Role of transcription factors

Genetic Code

  • Codons and triplets
  • Role of amino acids in protein synthesis
  • Start and stop codons

Initiation Codon

  • The initiation codon is AUG
  • Encodes for the amino acid methionine
  • Signals the start of protein synthesis

Importance of Initiation Codon

  • Initiates the assembly of ribosomes on mRNA
  • Determines the reading frame for protein synthesis
  • Essential for the proper functioning of genes

Examples of Initiation Codons

  • AUG is the most common initiation codon
  • Other initiation codons include GUG and UUG
  • Different organisms may have variations in initiation codons

Mutations and Initiation Codons

  • Mutations in initiation codons can lead to genetic disorders
  • Non-functional initiation codons can disrupt protein synthesis
  • Frameshift mutations can also affect the initiation codon

Summary

  • The initiation codon is an essential component of the genetic code
  • It signals the start of protein synthesis
  • Mutations in initiation codons can have detrimental effects on gene expression and protein synthesis
  1. Which Codon is Called Initiation Codon?
  • The initiation codon is the codon that signals the start of protein synthesis.
  • In the standard genetic code, the initiation codon is AUG.
  • AUG codes for the amino acid methionine, which is often the first amino acid in a protein sequence.
  1. Importance of the Initiation Codon
  • The initiation codon plays a crucial role in protein synthesis.
  • It determines the reading frame for translation.
  • It helps assemble ribosomes on the mRNA molecule.
  1. Initiation Codon Variations
  • While AUG is the most common initiation codon, there are some exceptions.
  • In specific organisms, initiation codons like GUG and UUG can also be used.
  • However, AUG is by far the most prevalent and widely recognized initiation codon.
  1. Examples of Initiation Codons
  • In humans, the vast majority of protein-coding genes start with the AUG initiation codon.
  • However, there are exceptions where alternative initiation codons may be used.
  • For example, the gene for the growth hormone receptor starts with the initiation codon CUG.
  1. Mutations in Initiation Codons
  • Mutations in the initiation codon can have severe consequences.
  • A mutation that changes the initiation codon can prevent the proper initiation of translation.
  • This can lead to the production of non-functional or incomplete proteins.
  1. Non-Functional Initiation Codons
  • Non-functional initiation codons can arise due to point mutations or indels (insertion or deletion of bases).
  • They can prevent ribosome binding or disrupt the reading frame, resulting in non-functional protein production.
  • Non-functional initiation codons can lead to genetic disorders or impaired cellular processes.
  1. Frameshift Mutations and Initiation Codons
  • Frameshift mutations can also affect the initiation codon.
  • Addition or deletion of nucleotides can shift the reading frame, altering the entire sequence downstream of the mutation.
  • This can cause a different codon to be interpreted as the initiation codon, leading to abnormal protein synthesis.
  1. The Role of Initiation Codon in Translation
  • The initiation codon plays a dual role in translation - it defines the start site for protein synthesis and establishes the reading frame.
  • Initiation factors aid in the recognition and binding of the initiation codon by the ribosome.
  • Once the initiation codon is identified, the ribosome assembles and begins the process of protein synthesis.
  1. Initiation Codons in Different Organisms
  • Different organisms may have variations in initiation codons.
  • For example, in bacteria, the initiation codon can be either AUG or GUG.
  • Mitochondria in some organisms also use alternative start codons like AUA or AUU.
  1. Summary
  • The initiation codon, typically AUG, is the codon that signals the start of protein synthesis.
  • It determines the reading frame for translation and is crucial for proper initiation of translation.
  • Mutations in the initiation codon can lead to genetic disorders or impaired protein synthesis.

Genetic Code Variations

  • Some organisms have variations in the genetic code
  • Example: Mitochondria in certain species use alternative initiation codons like AUA or AUU
  • These variations can have implications for protein synthesis and gene expression

Silent Mutations

  • Silent mutations do not result in a change in the amino acid sequence
  • They occur when a different codon still codes for the same amino acid
  • Example: GCU, GCC, GCA, and GCG all code for the amino acid alanine

Nonsense Mutations

  • Nonsense mutations introduce a premature stop codon
  • This leads to the production of a truncated and non-functional protein
  • Example: UAA, UAG, and UGA are stop codons

Frameshift Mutations

  • Frameshift mutations occur due to insertions or deletions of nucleotides that are not in multiples of three
  • This shifts the reading frame and alters the entire sequence downstream of the mutation
  • Example: Insertion of an extra base - AGGCGA –> AGGACGA

Missense Mutations

  • Missense mutations result in the substitution of one amino acid for another in the protein sequence
  • This can impact protein structure and function
  • Example: GAG (glutamic acid) to GTG (valine) in the beta-globin gene causes sickle cell anemia

Mutagens and Mutations

  • Mutagens are agents that can induce mutations
  • Examples: Radiation, chemicals, and certain viruses
  • Mutations can have harmful, neutral, or occasionally beneficial effects on an organism

Gene Mutations and Inheritance

  • Gene mutations can be inherited from parents
  • If a mutation occurs in germ cells (sperm or egg), it can be passed on to offspring
  • Example: Mutations in the BRCA1 gene can increase the risk of breast and ovarian cancer

Genetic Disorders

  • Genetic disorders are caused by mutations in specific genes
  • Examples: Cystic fibrosis, Down syndrome, Huntington’s disease
  • These disorders can result from different types of mutations and have varying inheritance patterns

Genetic Testing

  • Genetic testing helps identify mutations and genetic disorders
  • Examples: Carrier screening, prenatal testing, diagnostic testing
  • Testing allows for early detection, treatment, and informed reproductive decisions

Gene Therapy

  • Gene therapy aims to correct or replace faulty genes to treat genetic disorders
  • Different approaches include gene addition, gene editing, and gene silencing
  • This field holds promise for potential medical advancements and therapies