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General Biology: DNA Structure and Protein Synthesis

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  • Two primary functions of DNA

    Genetic inheritance and protein synthesis.

  • What is a mutation? Why are transcription mistakes not mutations?

    A mutation is a change in the DNA sequence. Mistakes in transcription are not mutations because they do not alter the DNA, only the RNA copy.

  • Four DNA nucleotides and their types

    Adenine (A) and Guanine (G) are purines (two rings). Cytosine (C) and Thymine (T) are pyrimidines (one ring).

  • Complementary base pairs in DNA and bond type

    A-T and G-C pairs held together by hydrogen bonds.

  • What does DNA antiparallel mean?

    DNA strands run in opposite directions: one 5’ to 3’, the other 3’ to 5’ along the sugar-phosphate backbone.

  • Difference between 3’ and 5’ ends of DNA

    3’ end has a hydroxyl group on the sugar; 5’ end has a phosphate group attached to the sugar.

  • Why does DNA use Thymine instead of Uracil?

    Thymine is more stable and protects DNA from enzymatic degradation; Uracil is used in RNA.

  • Where do transcription and translation occur in prokaryotes and eukaryotes?

    In prokaryotes, both occur in the cytoplasm and are coupled. In eukaryotes, transcription occurs in the nucleus and translation in the cytoplasm.

  • Role of RNA polymerase in transcription

    RNA polymerase synthesizes mRNA by adding RNA nucleotides complementary to the DNA template strand.

  • DNA to RNA complementary base pairs

    DNA A pairs with RNA U, T with A, C with G, and G with C.

  • How does mRNA processing differ in eukaryotes vs. bacteria?

    Eukaryotic mRNA undergoes extensive processing (5’ cap, splicing, poly-A tail); bacterial mRNA usually does not.

  • What is coupled transcription and translation?

    In prokaryotes, transcription and translation occur simultaneously on the same mRNA, making protein synthesis faster.

  • Roles of mRNA, tRNA, rRNA, and codons in translation

    mRNA carries the code, tRNA brings amino acids, rRNA forms the ribosome, and codons specify amino acids.

  • Functions of the ribosome sites E, P, and A

    A: tRNA entry, P: peptide bond formation, E: tRNA exit.

  • What catalyzes peptide bond formation?

    The ribosomal RNA (rRNA) acts as a ribozyme catalyzing peptide bond formation.

  • Why is the genetic code universal?

    All organisms use the same codon-to-amino acid rules, indicating a common ancestor.

  • Why can a jellyfish gene be expressed in a plant?

    Because the genetic code is universal, the plant can translate jellyfish mRNA into protein correctly.

  • Template strand vs. coding strand of DNA

    RNA polymerase reads the template strand. The coding strand matches the mRNA sequence (except T is U in RNA).

  • How to determine mRNA sequence from DNA

    Use the template strand and replace T with U to get the mRNA sequence.

  • How does RNA polymerase know where to start transcription?

    It binds to the promoter region; eukaryotes require transcription factors to initiate.

  • Functions of 5’ methyl cap and 3’ poly-A tail on mRNA

    5’ cap protects mRNA and helps ribosome binding; 3’ poly-A tail increases mRNA stability.

  • What is RNA splicing and where does it occur?

    Removal of introns by the spliceosome in eukaryotes; exons are joined to form mature mRNA.

  • What is alternative splicing?

    Different combinations of exons are joined to produce multiple protein variants from one gene.

  • Why are codons three nucleotides long?

    Three nucleotides allow 64 codons, enough to code for 20 amino acids with redundancy.

  • Role of tRNA anticodon in translation

    tRNA anticodon pairs with mRNA codon to deliver the correct amino acid during protein synthesis.

  • Difference between free and bound ribosomes

    Free ribosomes synthesize cytosolic proteins; bound ribosomes make proteins for secretion or membranes.

  • What is a signal peptide?

    A sequence that directs a protein to its proper cellular location, like a zip code.

  • What happens to ribosome and mRNA after translation ends?

    They dissociate; ribosome subunits separate and mRNA may be degraded or reused.

  • Types of mutations and their effects

    Silent: no amino acid change; missense: different amino acid; nonsense: early stop codon; frameshift: shifts reading frame, altering protein.