Course review
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Learning objective
• Transcription makes mRNA as a mobile copy of gene information • RNA polymerase synthesizes RNA complementary to the DNA template strand
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Learning objective
• Free RNA nucleotides align by complementary base pairing and hydrogen bonding • DNA adenine pairs with RNA uracil, while cytosine pairs with guanine
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Learning objective
• DNA template strands are transcribed without altering the base sequence • Sugar-phosphate backbone and base pairing preserve genetic information
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Learning objective
• Transcription is the first stage of gene expression • Cells regulate which genes are transcribed according to tissue, stage, and signals
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Learning objective
• Translation decodes mRNA at ribosomes to synthesize polypeptides • mRNA codon order determines amino acid sequence
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Learning objective
• mRNA provides codons; tRNA carries activated amino acids with anticodons • Ribosomes hold mRNA and tRNAs so peptide bonds can form
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Learning objective
• tRNA anticodons pair with complementary mRNA codons by hydrogen bonding • Specific tRNA-amino acid attachment helps ensure correct amino acid addition
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Learning objective
• The genetic code is triplet, degenerate, and almost universal • Codons specify amino acids, a start signal, or stop signals
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Learning objective
• Genetic code tables use mRNA codons, not DNA triplets • Convert template DNA to mRNA first, then read codons 5' to 3'
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Learning objective
• Ribosomes move along mRNA one codon at a time from start to stop • Peptide bonds join amino acids; multiple ribosomes can form a polysome
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Learning objective
• Mutations can change codons and therefore amino acid sequence • Changed primary structure may alter folding and function, such as sickle-cell haemoglobin
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Learning objective
• RNA polymerase reads template DNA 3' to 5' and synthesizes RNA 5' to 3' • Ribosomes translate mRNA codons in the 5' to 3' direction
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Learning objective
• Promoters mark transcription start regions and orientation • Transcription factors help RNA polymerase bind and initiate in eukaryotes
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Learning objective
• Non-coding DNA does not code for polypeptide amino acid sequences • Includes introns, regulatory sequences, telomeres, rRNA genes, and tRNA genes
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Learning objective
• Eukaryotic pre-mRNA is modified before export and translation • Processing adds a 5' cap and poly-A tail and removes introns by splicing
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Learning objective
• Alternative splicing joins different exon combinations from one pre-mRNA • One gene can produce multiple protein variants in different cells or stages
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Learning objective
• Translation initiation assembles ribosomal subunits at the start codon AUG • Initiator tRNA enters the P site; A, P, and E sites organize tRNA movement
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Learning objective
• Newly made polypeptides may be folded, cleaved, or chemically modified • Preproinsulin processing to active insulin is a key example
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Learning objective
• Proteasomes degrade tagged, damaged, or unneeded proteins • Amino acid recycling supports new protein synthesis and proteome quality control
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