Chapter 13.2 (Pgs. 366-371): Ribosomes and Protein Synthesis

The Genetic Code- A gene is a section of DNA that codes

for a trait, usually a protein

- This code specifies the order of amino acids in a protein

- This code is made of 3-letter “words” called codons

- Codons in mRNA have 3 RNA nucleotides (A, C, G or U)

- Each codon stands for an amino acid

Protein Synthesis- Is also called translation

- Occurs in the cytoplasm

- Is the process of assembling a protein using the sequence of codons in mRNA

- Also requires ribosomes and tRNA- Ribosomes help bond amino acids together- tRNA has anticodons that are

complementary to mRNA codons

Steps in Translation1) A ribosome attaches to mRNA molecule, and

begins reading the mRNA at the “start” codon

2) tRNA brings in an amino acid that matches the mRNA codon

3) The ribosome helps amino acids bond to each other, and moves the growing polypeptide over to make room for the next amino acid

4) When the ribosome reaches a “stop” codon, it releases the mRNA and the protein

http://vimeo.com/25051231

The Central Dogma of Molecular Biology- Information is transferred from DNA

to RNA to proteinDNA -> RNA -> Protein

- Proteins create traits

- This is called gene expression

- This process is found in all organisms

Differences in Transcription and Translation

Transcription- Occurs in the nucleus- Makes RNA- Uses DNA as a template- Uses RNA polymerase- Uses RNA nucleotides as

the building blocks

Translation- Occurs in the cytoplasm- Makes a protein- Uses mRNA as a template- Uses ribosomes and tRNA- Uses amino acids as the

building blocks