Amoeba Sisters Understanding Protein Synthesis

Protein Synthesis Notes

Overview

• PROTEIN SYNTHESIS is the overall process of making proteins. It can be broken down into the following:

• DNA -> RNA -> Protein

Protein Synthesis - Overiew

• The DNA in the nucleus has the information to make the proteins, but the proteins are actually made outside of the nucleus on the ribosomes.  

• DNA cannot leave the nucleus. Therefore, DNA must be changed into another similar molecule called mRNA through a process called TRANSCRIPTION.

• Then, the mRNA code must be read and tRNA molecules must use it to transfer amino acids to build a protein through the process of TRANSLATION.

Closer Look at Transcription

• Transcription is the process that copies the instructions in the DNA onto a strand of messenger RNA (mRNA). 

• This occurs in the nucleus.

• 1) A portion of DNA is unzipped so that the mRNA can be made from DNA like a template. 

• 2) Nucleotides of mRNA will match with one strand of DNA and make mRNA. Since RNA does not have thymine and instead contains uracil, adenine will pair with uracil, and cytosine will still pair with guanine.

Let’s practice transcribing!

• A T C G T A C T G A T T A C A C C G T A

• U A G C A U G A C U A A U G U G G C A U

Closer Look at Transcription

• 3) After the mRNA is formed, it moves out of the nucleus through a pore and into the cytoplasm of the cell.

• The nitrogen bases in the mRNA form groups of three called CODONS. 

• Each codon has the “code” for an amino acid (which are the building blocks of proteins.)

Closer Look at Translation

• Translation occurs in the cytoplasm of the cell wherever there is a ribosome. 

• 1)    mRNA attaches to a ribosome and a start codon must be read. (The start codon is usually AUG). 

• 2)    The first amino acid is brought in by tRNA (transfer RNA). The function of tRNA is to carry amino acids to the ribosome.

• 3)    tRNA has a three-nucleotide sequence called an anticodon. The anti-codon matches up to the codon on mRNA. 

Closer Look at Translation

• 4)    The tRNA carries a specific amino acid that is determined by the anticodon sequence. 

• 5)    As the amino acids are placed by the tRNA, a peptide bond forms between the two amino acids, and the tRNA is released.

• 6)    This process is repeated over and over and builds a chain of amino acids called a polypeptide (a protein).

• 7)    When the rRNA reads a special stop codon, translation stops, and the chain/protein is released into the cytoplasm. 

Diagram of Protein Synthesis as a Whole

• A. DNA

• B. Transcription

• C. mRNA

• D. Nucleus

• E. Nuclear pore

• F. Translation

• G. Ribosome

Diagram of Protein Synthesis as a Whole

• H. mRNA

• I. anticodon

• J. codon

• K. tRNA

• L. amino acid

• M. polypeptide/protein