Protein Synthesis The Making of Proteins Using the Genetic Information Stored in DNA

Central Dogma of Molecular Biology Genetic information flows in one direction – from DNA to RNA to proteins.

Relationship between DNA, Genes, Proteins Genetic information passed from parent to offspring is DNA

Each DNA molecule has hundreds of sections known as genes Gene - section of DNA that provides the instructions for making a protein

 Protein molecules are polymers formed by joining amino acids

 The type of protein made is determined by the order of amino acids.

 1,000’s of different protein molecules are made by the cell every minute

Protein Synthesis - process of using DNA’s code to make proteins.  Two-part process: 1. Transcription 2. Translation

Part 1 Transcription - DNA code used to make RNA Occurs in the cell nucleus. DNA is too big to leave the nucleus. So its “message” is rewritten in the language of RNA molecules which are smaller and can leave the nucleus

How Transcription Works  Enzymes unwind DNA to expose bases in a specific gene. start site nucleotides transcription complex

Transcription RNA polymerase attaches complementary RNA bases to the exposed DNA strand RNA polymerase bonds the nucleotides together to form RNA. DNA RNA polymerase moves along the DNA

Transcription – rewriting DNA into RNA

Transcription The newly made RNA strand detaches from the DNA after the gene is transcribed. The small RNA strand exits the nucleus through pores in the nuclear membrane RNA

Transcription – DNA code rewritten in the “Language” of RNA DNA RNA C G G C T A A U Uracil replaces Thymine in RNA

Transcription – DNA code rewritten in the “Language” of RNA GTC ABC ATG ACT AAT GCT AC DNA CAG UCG UAC UGA UUA CGA UG RNA DNA RNA C G G C T A A U Uracil replaces Thymine in RNA

Transcription makes 3 types of RNA: Messenger RNA (mRNA) –carries DNA’s protein making code to ribosomes Ribosomal RNA (rRNA) –forms ribosomes, the cell’s “protein factories” Transfer RNA (tRNA) – carries amino acids to the ribosome to make proteins.

Messenger RNA Carries the message of a DNA’s gene needed to make a protein. Each group of 3 nucelotides in mRNA is called a codon. Each codon specifies a particular amino acid. A codon must be read in the right order sequence called a reading frame.

mRNA codon Amino Acid Abbreviation Amino Acid

mRNA codon Amino Acid Abbreviation Amino Acid AUG ACG GAG CUU CGG AGC UAG

How messenger RNA’s code is used to make proteins Protein MET START Methionine THR Threonine GLU Glutamate LEU Leucine ARG Arginine SER Serine STOP

8.4 Transcription

Transcription compared to replication. Transcription and replication both involve 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