Biology of the Flu - Evolution through Influenza A

What Is Influenza?

• Influenza viruses are responsible for various types of flu, including bird flu and swine flu, and are classified under the broader category of influenza virus.

What Is a Virus?

• Definition: Viruses are parasites that depend on host cells to replicate.

• Structure:

  • Genetic Material: Can be either DNA or RNA, containing fewer genes than eukaryotic cells.

  • Capsid: A protein coat protecting the genetic material; may include proteins assisting in host attachment.

  • Envelope: Some viruses, like influenza, have a lipid envelope derived from the host cell, aiding entry into host cells.

Naming of Flu Viruses

• Influenza A virus classification is determined by surface spikes (glycoproteins) that facilitate identification and entry into host cells.

Are Viruses Alive?

• Viruses lack critical characteristics needed for life:

  • They cannot process energy independently.

  • They do not maintain homeostasis, reproduce, or respond to environmental stimuli on their own.

  • Therefore, viruses are not considered living organisms.

The Concept of Evolution

• What Is Evolution?: Change over time in biological populations, studied extensively by scientists.

• Biological Importance: Recognized as a unifying theory in biology linking various life forms and their adaptations over time.

Evolution and Influenza

• Influenza viruses evolve primarily through genetic exchanges with animal hosts (e.g., pigs, birds), leading to new strains capable of infecting humans.

• Impacts of Evolution:

  • Rapid changes in genetic information contribute to flu outbreaks and variations in virus behavior.

Mechanism of Evolution: Natural Selection

• Proposed independently by Charles Darwin and Alfred Russel Wallace.

• Key Components of Natural Selection:

  1. Variation: Presence of diverse traits within a population.

  2. Competition: More offspring produced than can survive creates a struggle for resources.

  3. Survival of the Fittest: Traits that enhance survival and reproduction become more common.

  4. Adaptation: Over time, populations adjust to their environments through advantageous traits.

Genetic Changes in Organisms

• Flow of Genetic Information: DNA → RNA → Protein.

• Mutations: Changes in the nucleotide sequence can alter protein structure and function, affecting traits.

Evidence of Evolution

• Fossil Record: Provides vital insights into organism morphology and evolutionary transitions.

  • Transitional fossils illustrate evolutionary links, e.g., Tiktaalik (fish to amphibian) and Archaeopteryx (reptile to bird).

• Comparative Anatomy:

  • Analogous Structures: Different species independently evolve similar traits due to adaptations (e.g., wings of birds and bats).

  • Homologous Structures: Similar structures due to common ancestry (e.g., limb bones across species).

• Genetic Material: DNA comparisons reflect evolutionary relationships, closer genetic sequences imply close evolutionary ties.

Summary Points

• Influenza viruses are vital in understanding evolutionary processes.

• Evolution is driven by natural selection, mutations, and genetic material exchanges.

• Evidence of evolution includes fossils, anatomical comparisons, and genetic similarities.

• Flow of Genetic Information: The process of gene expression involves the flow of genetic information from DNA to RNA to protein, which is fundamental for cellular function and is essential for the development and adaptation of organisms.

• Key Stages in Gene Expression:

  1. Transcription: The process where a segment of DNA is transcribed into messenger RNA (mRNA).

  • RNA polymerase binds to the promoter region of the gene, initiating transcription.

  • The DNA strands unwind, and RNA nucleotides complementary to the DNA template strand are added to form mRNA.

  • The transcription continues until a termination signal is reached, resulting in a primary mRNA transcript.

  1. RNA Processing: Before mRNA can be translated, it undergoes several modifications:

  • Capping: The addition of a 7-methylguanylate cap at the 5' end, which protects the mRNA from degradation and assists in ribosome binding.

  • Polyadenylation: The addition of a poly(A) tail at the 3' end, which also stabilizes the mRNA.

  • Splicing: Introns (non-coding regions) are removed, and exons (coding sequences) are joined together to produce a mature mRNA molecule.

  1. Translation: The process of decoding the mRNA into a polypeptide chain:

  • mRNA is transported to the ribosome, where translation occurs.

  • Transfer RNA (tRNA) molecules, which carry specific amino acids, recognize codons on the mRNA through their anticodon sequences.

  • The ribosome facilitates the binding of tRNA to mRNA and catalyzes peptide bond formation between amino acids.

  • Translation continues until a stop codon is reached, resulting in a newly synthesized protein.

• Mutations: Changes in the nucleotide sequence of DNA, which can affect protein structure and function, often leading to variations in traits. Mutations can be classified into several categories:

  • Point Mutations: A change in a single nucleotide base pair:

    • Silent Mutations: No change in the amino acid sequence.

    • Missense Mutations: Result in a different amino acid, which may alter protein function.

    • Nonsense Mutations: Create a premature stop codon, leading to a truncated protein.

  • Frameshift Mutations: Insertions or deletions of nucleotides that change the reading frame of the genetic code, often resulting in completely different amino acid sequences downstream of the mutation.

  • Large-scale Mutations: Adjustments that can affect entire genes or segments of chromosomes, such as duplications, deletions, inversions, or translocations, leading to significant changes in phenotype.

• Effects of Mutations on Traits:

  • Mutations can be beneficial, neutral, or harmful.

    • Beneficial Mutations: Provide an advantage in a specific environment (e.g., antibiotic resistance in bacteria).

    • Harmful Mutations: Lead to genetic disorders or decrease an organism's fitness (e.g., cystic fibrosis due to mutations in the CFTR gene).

    • Neutral Mutations: Have no apparent effect on the organism’s fitness, often occurring in non-coding regions.

• Adaptive Evolution: Genetic changes contribute to the process of evolution as organisms adapt to their environments over time.

  • Variation introduced by mutation creates a raw material for natural selection to act upon.

  • Populations accumulate advantageous traits while losing detrimental ones, leading to increased fitness and adaptation to changing environments.