Gene Expression & Regulation

DNA, RNA, & Gene Expression
1. Converting the information encoded by a gene into its product starts with RNA synthesis, during which enzymes use the gene's DNA sequence as a template to assemble a strand of RNA.
2. RNA usually occurs in a single-stranded form that is similar to a single strand of DNA
  1. the fourth base in RNA is uracil (U), not thymine as it is in DNA
3. DNA's only role is to store genetic information
4. rRNA assembles amino acids into polypeptide chains
5. tRNA delivers amino acids to ribosomes
6. mRNA functions as the "messenger" between DNA and protiens
7. Transcription and translation are part of the process called gene expression
Transcription: DNA to RNA
1. The same base-pairing rules also govern RNA synthesis in transcription
2. DNA as a Template
  1. DNA replication begins with one DNA double helix and ends with two DNA double helices
  2. An RNA strand is structurally so similar to a DNA strand that the two can base-pair if their nucleotide sequences are complementary (U pairs up with A)
  3. A strand of DNA acts as a template upon which a strand of RNA is assembled from
  4. Only part of one DNA strand (not the whole molecule) serves as the template
  5. Produces a single strand of RNA, and DNA replication produces two DNA double helices
3. Process of Transcription
  1. In eukaryotic cells, transcription occurs in the nucleus; in prokaryotes, it occurs in cytoplasm
  2. The polymerase starts moving along the DNA, over the gene region
  3. The polymerase unwinds and joins free RNA nucleotides in the order dictated by that DNA sequence
  4. DNA and RNA are released. RNA polymerase follows base-pairing rules, so the new RNA strand is complementary to the DNA strand from which it was transcribed
4. RNA Modification
  1. Introns are removed in chunks from a newly transcribed RNA before it leaves the nucleus
  2. A tail of 50 to 300 adenines is added to the end of a new mRNA (poly-A tail)
  3. mRNA carries DNA's protein-building information which consist of codons
  4. All codons make the genetic code
  5. Each tRNA has an anticodon that can base-pair with a codon, and it binds to the amino acid specified by that codon
  6. Enzymatic rRNA and proteins make up the two subunits of ribosomes
RNA Players in Translation
1. In eukaryotic cells, RNA is transcribed in the nucleus
2. Finished RNA moves into the cytoplasm through nuclear pores
3. Ribosomal subunits and tRNA converge on an mRNA
4. A polypeptide chain forms as the ribosome moves along the mRNA, linking amino acids together in the order dictated by the mRNA codons
5. The ribosome then begins to assemble a polypeptide chain as it moves along the mRNA
6. The first tRNA is released and the ribosome moves to the next codon
7. The second tRNA is released and the ribosome moves to the next codon
8. The new polypeptide chain continues to elongate
Translating the Code: RNA to Protein
Mutated Genes & Their Protein Products
Eukaryotic Gene Controls

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Gene Expression & Regulation

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