PROTEIN SYNTHESIS

1. RNA carries DNA’s instructions. The central dogma states that information flows in one direction from DNA to RNA to proteins.

2.RNA differs from DNA in three major ways. RNA has a ribose sugar. RNA has uracil instead of thymine. RNA is a single-stranded structure.

3. Protein synthesis is the cellular process in which the DNA code is read, copied and then the instructions are used at the ribosomes to synthesize (make) the correct proteins. 4. Protein synthesis has 2 parts: Transcription and translation.

5. Transcription is catalyzed by RNA polymerase. a. RNA polymerase and other proteins form a transcription complex. b. The transcription complex recognizes the start of a gene and unwinds a segment of it. start site nucleotides transcription complex

RNA polymerase moves along the DNA c. Nucleotides pair with one strand of the DNA. d. RNA polymerase bonds the nucleotides together. e. The DNA helix winds again as the gene is transcribed. DNA RNA polymerase moves along the DNA

RNA (m-RNA) because it carries the DNA’s “message” to the ribosome. f. The RNA strand detaches from the DNA once the gene is transcribed. This is called messenger RNA (m-RNA) because it carries the DNA’s “message” to the ribosome. RNA

6. Transcription can actually make three different types of RNA. Messenger RNA (mRNA) carries the message that will be translated to form a protein. Ribosomal RNA (rRNA) forms part of ribosomes where proteins are made. Transfer RNA (tRNA) brings amino acids from the cytoplasm to a ribosome.

The two processes have different end results. 7. Transcription and replication are similar. They both involve complex enzymes and complementary base pairing. The two processes have different end results. Replication copies all the DNA; transcription copies a gene. Replication makes one copy; transcription can make many copies. growing RNA strands DNA one gene

Introns (junk DNA) are also removed in transcription process.

TRANSLATION

1. Amino acids are coded by mRNA base sequences. 2. Translation converts mRNA messages into polypeptides (proteins). 3. A codon is a sequence of three nucleotides that codes for an amino acid. codon for methionine (Met) leucine (Leu) EACH CODON CODES FOR 1 AMINO ACID. THERE ARE 20 AMINO ACIDS, THEREFORE THERE ARE MULTIPLE CODES FOR EACH AMINO ACID. There are a total of 64 possible codes.

4.The genetic code matches each codon to its amino acid or function. one start codon, codes for methionine three stop codons The genetic code matches each RNA codon with its amino acid or function.

5. A change in the order in which codons are read changes the resulting protein. 6. Regardless of the organism, codons code for the same amino acid.

7. Amino acids are linked to become a protein. 8. An anticodon is a set of three nucleotides that is complementary to an mRNA codon. An anticodon is carried by a transfer RNA (tRNA). When the t-RNA is carrying its amino acid it is said to be “charged”.

9. Ribosomes consist of two subunits. The large subunit has three binding sites for tRNA. The small subunit binds to mRNA.

10. For translation to begin, tRNA binds to a start codon and signals the ribosome to assemble. 11. A complementary tRNA molecule binds to the exposed m-RNA codon, bringing its amino acid close to the first amino acid.

12. The ribosome helps form a polypeptide bond between the amino acids. 13. The ribosome pulls the mRNA strand the length of one codon.

14. The now empty tRNA molecule exits the ribosome. 15. A complementary tRNA molecule binds to the next exposed m-RNA codon. 16. Once the stop codon is reached, the ribosome releases the protein and the ribosome disassembles.

17. Now the new protein has been synthesized following the precise code from the DNA.

ANIMATION #1 http://www.ncc.gmu.edu/dna/ANIMPROT.htm ANIMATION WEBSITE #2 http://omega.dawsoncollege.qc.ca/ray/protein/panim.htm ANIMATION WEBSITE http://tidepool.st.usm.edu/crswr/protsynthmov.html