Chapter 10 How Proteins are Made

Gene Expression: DNA is transcribed into RNA – happens in nucleus RNA is translated into protein – happens in cytoplasm

Transcription: RNA Polymerase binds to promoter. RNA Polymerase unwinds and separates double helix. RNA Polymerase adds complimentary RNA nucleotides until the stop signal.

Many identical RNA molecules are made from the same gene at the same time.

RNA Processing: Introns – long segments of nucleotides that have no coding information (need to be cut out of RNA) Exons – portions of DNA that will be expressed (pieces of RNA spliced together) Result is messenger RNA (mRNA)

Messenger RNA carries the genetic code in codons - Three nucleotide groupings that code for a specific amino acid or a start or stop signal.

Translation: Ribosome, mRNA and tRNA (methionine) come together. Codon in A site (attachment site) receives a tRNA with a complementary anticodon carrying the specified amino acid.

Translation: A peptide bond forms between the two amino acids. tRNA in the P site (peptide site) is ejected.

Translation: The tRNA with the growing chain moves from the A site to the P site, mRNA moves with it. - The A site receives a tRNA with the amino acid for the next codon which is bonded to the growing chain. 6. The P site tRNA is ejected.

Translation: 7. The 6 steps repeat until a stop codon is reached, then the ribosome and RNA disassemble and the protein is released.

Gene Regulation: Genes are only expressed when needed in order to save energy and resources.

Prokaryote example: Lac-Operon A repressor binds to the operator, blocking the RNA polymerase. When lactose is present, the repressor lets go and binds to the lactose instead (unlocks the gate) The RNA polymerase is free to transcribe the genes for the proteins that digest lactose.

Eukaryote example: Transcription Factors Transcription factors – proteins that regulate transcription The enhancer and promoter regions of DNA need to be brought together by an activator protein before transcription can begin.

Point Mutations: Changing even one nucleotide can cause mutations in the protein created. Substitution – One nucleotide is incorrect. - can cause: no effect, one wrong amino acid, or a stop codon.

Point Mutations: Insertion or deletion of a nucleotide causes a frameshift mutation. Codons are read in the wrong groupings. All amino acids after that point will be wrong.