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General Biology: DNA Structure, Gene Function, and Viral Biology

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Termini in questo insieme (28)

  • DNA structure

    DNA is a nucleic acid with two antiparallel, complementary strands forming a double helix. Bases pair A–T and C–G via hydrogen bonds.

  • Nucleotide components

    A nucleotide consists of a phosphate group, a 5-carbon sugar (deoxyribose in DNA), and a nitrogenous base.

  • Central dogma of molecular biology

    Genetic information flows as DNA → RNA → Protein.

  • Types of RNA

    mRNA carries protein instructions; tRNA transfers amino acids; rRNA forms ribosomes.

  • Difference between DNA and RNA

    DNA is double-stranded with deoxyribose and bases A, T, C, G; RNA is single-stranded with ribose and bases A, U, C, G.

  • Transcription process

    RNA polymerase binds promoter, synthesizes mRNA from DNA template strand by complementary base pairing (A→U, T→A, C→G, G→C), then terminates at terminator.

  • RNA processing in eukaryotes

    Pre-mRNA is modified by adding a 5′ cap, poly-A tail, and removing introns to form mature mRNA.

  • Translation initiation

    mRNA binds small ribosomal subunit; initiator tRNA pairs with start codon AUG; large subunit joins to form functional ribosome.

  • Codon and anticodon

    A codon is 3 mRNA bases encoding an amino acid; an anticodon is 3 tRNA bases complementary to the codon.

  • Peptide bond formation

    During elongation, amino acids carried by tRNAs are joined by peptide bonds to form a polypeptide chain.

  • Translation termination

    Ribosome reaches a stop codon (UAA, UAG, UGA); release factor binds; polypeptide is released and folds into a functional protein.

  • Gene expression regulation in prokaryotes

    Operons control groups of genes; e.g., lac operon is off when lactose absent (repressor bound), on when lactose present (repressor released).

  • Gene expression regulation in eukaryotes

    Regulation via DNA packaging, transcription factors, alternative splicing, mRNA export/degradation, and protein activity control.

  • Mutation types

    Mutations include substitution, insertion, deletion, and frameshift, affecting protein function variably.

  • Frameshift mutation effect

    Insertion or deletion not in multiples of 3 shifts reading frame, altering many codons and often disrupting protein function.

  • Causes of mutations

    Mutations arise from spontaneous DNA replication errors or mutagens like chemicals, radiation, and X-rays.

  • Virus structure

    Viruses contain DNA or RNA (never both) and a protein coat; lack nucleus, organelles, ribosomes, and cytoplasm.

  • Why viruses need host cells

    Viruses hijack host transcription/translation machinery to replicate because they lack cellular equipment.

  • Lytic viral infection cycle

    Virus enters host, replicates immediately, causes host cell lysis, and releases new viruses.

  • Lysogenic viral infection cycle

    Viral genes integrate and replicate with host DNA; stress can trigger switch to lytic cycle.

  • Viroids vs prions vs viruses

    Viroids are circular RNA without protein; prions are misfolded proteins; viruses have genetic material plus protein coat.

  • Start and stop codons in translation

    Start codon is AUG (methionine); stop codons are UAA, UAG, UGA, which signal translation termination.

  • Genome vs chromosome

    Genome is all genetic material in a cell; chromosome is a DNA package coiled around proteins.

  • Complementary base pairing rules

    In DNA, A pairs with T; C pairs with G. In RNA, A pairs with U; C pairs with G.

  • Role of ribosome in translation

    Ribosome, made of rRNA and proteins, facilitates mRNA decoding and peptide bond formation between amino acids.

  • Alternative splicing

    Different exon combinations from the same mRNA produce multiple protein variants.

  • Function of 5′ cap and poly-A tail

    They protect mRNA from degradation and assist in nuclear export and translation initiation.

  • Operon repressor function

    Repressor binds DNA to block RNA polymerase and prevent transcription when specific molecules are absent.