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General Biology: Gene Expression, Evolution, and Speciation

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  • Differentiated cell

    A cell that expresses specific genes to perform specialized functions, despite having the same DNA as other cells.

  • Bridge molecule between DNA and protein synthesis

    mRNA acts as the messenger carrying genetic information from DNA to the ribosome for protein synthesis.

  • Transcription and its location

    Process of copying DNA into RNA; occurs in the nucleus with RNA polymerase as the key enzyme.

  • Role of the promoter

    A DNA sequence where RNA polymerase and transcription factors bind to initiate transcription.

  • Transcription factors

    Proteins that bind to the promoter or other DNA sequences to regulate transcription initiation.

  • Three stages of transcription

    Initiation: RNA polymerase binds promoter; Elongation: RNA strand is synthesized 5’ to 3’; Termination: RNA polymerase detaches at terminator sequence.

  • TATA box

    A DNA promoter sequence where transcription factors bind to help position RNA polymerase for transcription start.

  • mRNA processing modifications

    5’ cap addition, poly-A tail addition, and RNA splicing occur in the nucleus to produce mature mRNA.

  • Introns and exons

    Introns are non-coding sequences removed during RNA splicing; exons are coding sequences joined to form mature mRNA.

  • Role of spliceosome

    A complex that removes introns and joins exons during RNA splicing.

  • Alternative splicing

    Process allowing a single gene to code for multiple proteins by splicing RNA in different ways.

  • One gene, one protein hypothesis

    Original idea that one gene codes for one protein; challenged by alternative splicing and multifunctional proteins.

  • Triplet code, codon, anticodon

    Triplet code: three-nucleotide sequences in mRNA; codon: mRNA triplet; anticodon: complementary tRNA triplet.

  • Start codon and amino acid

    AUG is the start codon and codes for methionine.

  • Stop codons

    Codons that signal translation termination; examples include UAA, UAG, UGA.

  • Genetic code redundancy

    Multiple codons can code for the same amino acid, providing redundancy.

  • Role of tRNA in translation

    tRNA carries specific amino acids and has an anticodon that pairs with mRNA codons during translation.

  • Wobble position

    The third nucleotide in a codon that allows flexible base pairing, contributing to genetic code redundancy.

  • Aminoacyl-tRNA synthetase function

    Enzyme that attaches the correct amino acid to its corresponding tRNA.

  • Ribosome structure and binding sites

    Ribosomes are made of rRNA and proteins; have P (peptidyl), A (aminoacyl), and E (exit) sites for tRNA binding during translation.

  • Stages of translation

    Initiation: assembly of ribosome and start codon recognition; Elongation: amino acid chain elongation; Termination: release at stop codon.

  • Free vs bound ribosomes

    Free ribosomes synthesize proteins for cytosol; bound ribosomes synthesize proteins for membranes or secretion.

  • Point mutation types

    Silent (no amino acid change), missense (amino acid change), nonsense (premature stop codon).

  • Insertion and deletion mutations

    Addition or loss of nucleotides causing frameshift mutations that alter protein reading frame.

  • Operon components

    Includes promoter, operator, structural genes, repressor, and regulatory gene controlling gene expression in prokaryotes.

  • Trp operon regulation

    Repressor binds operator to turn off operon when tryptophan (corepressor) is abundant; operon is on when tryptophan is low.

  • Lac operon function

    Produces enzymes to metabolize lactose; turned on when lactose is present and glucose is low.

  • Evolution definition

    Change in allele frequencies in a population over time.

  • Natural selection requirements

    Variation, heritability, and differential reproductive success.

  • Homologous vs analogous structures

    Homologous: shared ancestry; analogous: similar function but different ancestry (convergent evolution).

  • Speciation

    Process by which new species arise from existing ones.

  • Prezygotic barriers

    Reproductive isolating mechanisms preventing fertilization (e.g., temporal, behavioral, mechanical isolation).

  • Postzygotic barriers

    Barriers after fertilization causing hybrid inviability or sterility.

  • Allopatric vs sympatric speciation

    Allopatric: geographic isolation; sympatric: speciation without geographic separation.

  • Punctuated equilibrium

    Evolutionary model with long periods of stasis interrupted by rapid change.