Protein Synthesis Notes

Protein Synthesis I. Protein synthesis is divided into two phases: phases: Transcription and translation. and translation. II. Transcription A. RNA polymerase polymerase unzips DNA 1. We are not making more DNA, we are just reading it. B. RNA polymerase reads in a 3' to 5' direction. 1. In which direction is RNA formed? C. Free RNA nucleotides are base base paired with the exposed DNA nucleotides and assembled assembled into a messenger RNA molecule by RNA polymerase.

D. The messenger RNA molecule molecule leaves the nucleus and moves to the ribosomes in the cytoplasm. E. After transcription, transcription, translation begins. III. III. Translation has four stages four stages.. A. Amino Acid Activation Stage. 1. The amino acids are acids are attached to their appropriate t-RNA molecules. t-RNA molecules. a. Specific enzymes bind each transfer RNA with only one specific amino acid. 2. This process process begins during transcription. 3. A molecule of  ATP transfers  ATP transfers its high energy bond to the activated t-RNA. B. Initiation Stage 1. The ribosome moves along the messenger RNA RNA molecule but nothing happens until the code for formyl-methionine formyl-methionine (AUG). (AUG). 2. When this code is reached, the elongation process begins. C. Elongation Stage (Three steps) 1. Step 1: New incoming t-RNA matches its anti-code with anti-code with the m-RNA code

a. For the first time this is repeated repeated twice.

2. Step 2: Then the amino acid (or acid (or chain of amino acids) on the first t-RNA is transferred to the amino acid on newly arrived t-RNA.

3. Step 3: The empty t-RNA leaves.

4. These three steps are repeated over and over again. 5. The ribosome continues along the m-RNA. m-RNA.

6. The Diphtheria toxin stops the elongation process!

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D. Termination phase 1. The elongation continues until a nonsense code is code is reached. 2. There will be no new incoming t-RNA t-RNA and therefore the protein is released and sent on its way. 3. One m-RNA can be read many many times by many ribosomes. A few more questions on protein synthesis A. What brought each animo acid to the growing protein? protein? B. What determined which t-RNA and amino acid would be place in order in the ribosome? C. What determined the m-RNA code? Central Dogma: DNA-> RNA->Protein. Proteins are not stable forever, so they must be synthesized as needed. Remember the operon theory and how cellular chemistry is controlled. m-RNA is also unstable and must be made as desired. Why is this good? A. One gene is usually transcribed transcribed many times B. One piece of m-RNA can be read many times Once synthesized, how do proteins find their destination? A. There are extra amino acids (hydrophobic (hydrophobic many times) that are not part of the active protein but have a role in delivery.

DNA, genes and chromosomes I. What is a gene? A. A length of DNA DNA that codes for a protein II. How many genes are in a DNA molecule? A. Depends on species, but can be tens of thousands. B. It is estimated that humans have over 100,000 genes. III. III. There are base sequences in DNA DNA that don't code for anything, these are called introns. introns. Exons code for the protein. A. The introns get transcribed transcribed into m-RNA but special molecules spliceosomes remove spliceosomes remove the unwanted information so the m-RNA can be correctly translated. IV. What are chromosomes A. Chromosomes are composed of DNA and protein. protein. B. There are two types of proteins proteins associated with the DNA in a chromosome chromosome 1. Histones- shown below, form the nucleosome. 2. Regulatory proteins make up about 50-70% of the rest. (Remember operon)

C. We only see chromosomes during cell division, and at at that time they have already doubled. D. So a chromosome is made of two two identical chromatids.

E. Between divisions the chromosomes are not visible because because they are stretched out in the form of chromatin.