Protein Synthesis Chapter 16, section 2

The sequence (order) of bases in a strand of DNA makes the code for building proteins. EX: The three bases “CCA” form the code for the amino acid proline. A long string of amino acids forms a protein. Each gene is usually a set of instructions for making a protein. Proteins are responsible for most of the differences in organisms that we see. EX: height, curly or straight hair, etc.

RNA is needed to produce proteins. It is so similar to DNA that it serves as a temporary copy of a DNA sequence. Three different types of RNA are involved in the making of a protein. 1. mRNA (messenger RNA): mRNA creates a complementary strand from DNA and carries it out of the nucleus into the cytoplasm. It replaces thymine with uracil.

For example: A G C G T A A GDNA strand U C G C A U U CRNA strand 2. rRNA (ribosomal RNA): makes up part of the ribosome. 3. tRNA (transfer RNA): brings the correct amino acids to the ribosome for protein construction.

Protein Synthesis Occurs in Two Steps 1.Transcription: Produces a single-stranded molecule of RNA. STEPS: 1.The DNA molecule opens up along a gene. 2.RNA nucleotides (A,U,C,G) match up and join the open DNA strand. 3.The complete RNA strand is released and moves to the cytoplasm.

2. Translation: occurs at the ribosome. The ribosome is the “protein factory” of the cell. STEPS: 1.A ribosome attaches to the beginning of a mRNA molecule. 2.The mRNA is fed through the ribosome three bases at a time. 3.Molecules of tRNA deliver amino acids from the cytoplasm to the ribosome. 4.The tRNA molecules are released after the amino acids they carry are attached to the growing chain of amino acids.

5. The ribosome completes the translation when it reaches the end of the mRNA strand and the newly made protein molecule is released.