gene expression : gene to protein

• Expression


  The appearance in a phenotype of a characteristic or effect attributed to a particular gene. Expression happens in a sequence (DNA→mRNA→protein)

  
• Gene expression


  The process by which the information encoded in a gene is used to direct the assembly of a protein molecule

  
• Gene expression


  Genes are expressed by being transcribed into RNA, and this transcript may then be translated into protein

  
• Our genes encode around 20,000 proteins. Proteins have a great variety of functions (defense, transport, support, motion, regulation, etc)
• Central dogma of molecular biology

  Transcription, Translation
• Transcription

  1. Transcription factors bind to DNA sequence to control transcription

  2. RNA polymerase produces pre-mRNA

  3. ATP provides energy for transcription

  4. TATA box is a binding site for transcription factors

  5. TFIID positions TFIID over TATA box

  6. Other transcription factors attach

  7. Transcription complex prepares DNA for RNA polymerase

  8. RNA polymerase unwinds DNA and synthesizes pre-mRNA

  9. Most transcription factors are released after transcription begins

  10. Typical transcription rate is 20 bases per second

  11. Terminator sequence indicates end of gene's RNA-encoding region

  
• DNA

  Usually double-stranded, thymine (T) as a base, deoxyribose as the sugar, stores genetic information, more stable than RNA
• RNA

  Usually single stranded, uracil (U) as a base, ribose as the sugar, controls how genetic information is used, less stable than DNA
• Types of RNA

  • mRNA, rRNA, tRNA
• mRNA


  Carries information that specifies a particular protein, each three mRNA base (codon) specifies certain amino acid, most mRNA is 500 to 4,500 bases long

  
• Ribosome


  An organelle in cell composed of rRNAs and certain proteins, has two subunits that are separated in the cytoplasm but joined at the site of initiation of protein synthesis
• mRNA processing

  1. Methylated cap added to 5' end

  2. Polyadenylation adds poly A tail

  3. Final product is mRNA with cap and poly A tail
• mRNA splicing

  1. Primary transcript contains exons and introns

  2. Spliceosome assembles and cuts out introns, joins exons

  3. Mature mRNA has methylated cap, joined exons, and poly A tail

  
• Translation

  1. Small ribosomal subunit attaches to mRNA

  2. Start codon codes for methionine

  3. tRNA molecules bring amino acids to ribosome

  4. Large ribosomal subunit attaches

  5. Ribosome has A, P, and E sites for tRNA

  6. Amino acid from P site attaches to A site tRNA

  7. Ribosome moves along mRNA, adding amino acids

  8. No tRNA recognizes stop codon, ribosome dissociates

  9. Peptide chain is released from tRNA and leaves ribosome

  
• Protein folding


  Proteins fold into 1D, 2D, 3D, and 4D structures based on chemistry<|>Mutations can alter primary structure<|>Protein folding begins immediately after synthesis<|>Smaller proteins fold faster<|>Proteins begin moving to destinations as they are synthesized
• Chaperone proteins


  Stabilize partially folded regions, prevent proteins from getting stuck in intermediate forms
• Proteasome


  A multi-protein structure that can degrade unneeded or misfolded proteins
• Ubiquitin

  Escorts misfolded proteins to the proteasome