Protein synthesis
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Protein Synthesis. 12-3. 2 Steps of Protein Synthesis. Transcription Translation. Transcription. DNA is coded (transcribed) into the RNA “language” The DNA sequence is copied into a complementary RNA sequence G  C C  G T  A A  U. Transcription.

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2 steps of protein synthesis
2 Steps of Protein Synthesis

  • Transcription

  • Translation


  • DNA is coded (transcribed) into the RNA “language”

  • The DNA sequence is copied into a complementary RNA sequence

    • G  C

    • C  G

    • T  A

    • A  U


  • Transcription requires RNA polymerase, an enzyme a lot like DNA polymerase

  • RNA polymerase binds to DNA, separates the strands, and uses one strand as a template for making mRNA.

  • RNA polymerase “polymerizes” (links together) the nucleotides that make up mRNA

Where to start
Where to Start?

  • RNA polymerase doesn’t randomly bind to DNA.

  • It will only bind to sites known as promoters—regions of DNA that have specific sequences.

  • Promoters are signals that say “START RNA HERE!”

  • Similar signals also tells transcription to stop.

Rna editing
RNA Editing

  • Some RNA molecules need to be edited before they are ready for making proteins.

  • Sometimes large sequencesmust be removed so that the RNA can make a functional protein. These intervening sequences are called introns.

  • The remaining portions or expressed sequences are called exons. They are spliced back together to form the final draft of mRNA.

The genetic code
The Genetic Code

  • There are 20 different amino acids found in nature.

  • Proteins are made by joining amino acids into long chains called polypeptides.

  • The genetic code is read 3 letters at a time. Each set of 3 nucleotides is called a codon.

  • Each codon specifies a specific amino acid.

The genetic code1
The Genetic Code

  • There are 64 different codons.

  • Some amino acids have more than one codon.

  • The START codon is AUG. It occurs at the beginning of EVERY protein.

  • There are 3 STOP codons—UAA, UAG, and UGA.


  • mRNA carries the coded message to the ribosome. The message must then be decoded or translated so the ribosome can build the protein.

  • During translation, the ribosome uses information from mRNA to produce proteins.

  • Translation is carried out by tRNA and rRNA.


  • Each tRNA molecule has an amino acid attached to one end and 3 nucleotide bases at the other end.

  • The 3 nucleotide bases attached to tRNA are called an anticodon because they are complementary to the codon for that amino acid.

  • Example: codon = AAG anti = UUC (AAG codes for Lysine)


  • tRNA can then give the correct amino acid to the ribosome.

  • The ribosome, which is made of rRNA, attaches the amino acids together to make the polypeptide chain (protein).

Dna rna and proteins
DNA, RNA, and Proteins

  • DNA is like the master copy.

  • RNA is like the blueprint the workers use.

  • The workers are ribosomes.

  • Proteins are the finished product.

  • Proteins are the keys to almost EVERYTHING that living cells do!