Gene Expression aka Protein Synthesis
Transcription Transcription begins when RNA polymerase unwinds and separates the 2 strands of the double helix, exposing the DNA nucleotides on each strand. RNA polymerase adds and then links complementary RNA nucleotides as it reads the gene. Transcription follows the base-pairing rules for DNA replication except that in RNA, uracil, rather than thymine, pairs with adenine. U – A G – C
Transcription DNA: ATA-GGC mRNA: UAU-CCG Enzyme unwinds & separates DNA strands. Gene Promoter One strand is used as a template to make mRNA DNA: ATA-GGC mRNA: UAU-CCG m m
Transcription Transcribe the following DNA strand into an mRNA molecule. U G C U A DNA RNA
Three-Nucleotide “Words” mRNA – (messenger RNA) carries the instructions for making a protein from a gene and delivers it to the site of translation (ribosome); the information is translated into the amino acids that make the protein Codon – a series of 3 nucleotide sequences on the mRNA; each codon corresponds to an amino acid or start and stop signal for translation Genetic Code – are the amino acids or “start” and “stop” signals that are coded for by each of the possible 64 mRNA codons (Genetic Code = Codon Chart) Three-Nucleotide “Words”
Genetic Code codon
Genetic Code Examples ALL organisms use the same genetic code to translate nucleic acid sequences into proteins. This strongly suggests that all life forms have a common ancestry.
II. Translation Translation takes place in the cytoplasm. During translation, the mRNA molecule binds to a ribosome, and the tRNA’s carry amino acids to the ribosome according to the codons on the mRNA. Each codon codes for a specific amino acid. The amino acids are then joined to make a protein. tRNA – (transfer RNA) is a small strand of RNA that carries a specific amino acid on one end; each tRNA is folded into a compact shape and has an anticodon anticodon – a 3 nucleotide sequence on a tRNA that is complementary to an mRNA codon rRNA – (ribosomal RNA) are RNA molecules that are part of the structure of ribosomes
Codons & Anticodons (mRNA) (tRNA) Amino Acids Anticodons Codons tRNA
Transcription & Translation Transcription occurs in the nucleus! Translation occurs on a ribosome in the cytoplasm!
Transcription vs. DNA Replication *makes copies of DNA molecules *both strands of DNA are used as a template *makes RNA molecules *only 1 strand is used as template
2 1. Which step below represents transcription? 2. Which step below represents translation? 3. Which step below represents DNA replication? 3 1 (Proteins)
Anticodons: AAU AUG GUC 5. What are the codons that correspond to the following segment of DNA? DNA: CAG TAT GAT 6. What are the anticodons that correspond to the following segment of mRNA codons? mRNA: UUA – UAC – CAG Codons: GUC AUA CUA Anticodons: AAU AUG GUC