Chapter 17 Notes

From Gene to Protein

Concept 17.1

The study of metabolic defects provided evidence that genes specify proteins- (1909) Garrod suggests that genes dictate phenotypes that catalyze specific chemical reactions in the cell

- ex. alkaptonuria

Concept 17.1

One Gene- One Enzyme- mutations that affect eye color in Drosophila block pigment synthesis at a specific step by preventing production of the enzyme that catalyzes that step-b/c each mutant was defective in a single gene, the function of a gene is to dictate the production of an enzyme

Concept 17.1

One Gene- One Polypeptide- after researchers discovered that not all proteins are enzymes, they revised their hypothesis- many proteins are made from two or more polypeptide chains, and each chain is specified by its own gene

Concept 17.1

Transcription and Translation are the two main processes linking genes to proteins- transcription is the synthesis of RNA under the direction of DNA- translation is the actual synthesis of a polypeptide, which occurs under the direction of mRNA

Concept 17.1

Concept 17.1

Nucleotide triplets specify amino acids- there are only 4 nucleotides to code for the 20 amino acids- triplet code: the genetic instructions for a polypeptide chain are written in the DNA as a series of three nucleotide words

Concept 17.1

Concept 17.1

During transcription, the gene determines the sequence of base triplets along an mRNA molecule- template strand: the one of the two possible DNA strands that is transcribed

Concept 17.1

- the mRNA strand is complementary, not identical, since the RNA bases are assembled on the template according to the base-pairing rules - the mRNA base triplets are called codons

Concept 17.1

- the codon AUG has a dual function: it codes for the amino acid Methionine (Met) and it functions as a “start” signal, or initiation codon- information is extracted by reading symbols in the correct reading frame

- ex. the big red dog ate the cat- ex. heb igr edd oga tet hec at

Concept 17.2

Messenger RNA (mRNA), a carrier of information from DNA to the ribosome, is transcribed from the template strand of a gene - RNA polymerase: connects the RNA nucleotides as they base-pair along the DNA template

Concept 17.2

- like DNA replication, RNA polymerases can only add nucleotides to the 3’ end of a polymer. RNA elongates in the 5’ 3’ direction.- promoter region: DNA sequence where the RNA polymerase attaches to begin transcription

Concept 17.2

- terminator region: sequence that signals the end of transcription- special proteins, called transcription factors, mediate the initiation of transcription

Concept 17.2

Concept 17.2

Concept 17.3

After transcription, RNA processing occurs- primary RNA transcript becomes mRNA- the 5’ cap is added to the front of the mRNA (acts to help in the translation process)- the poly(A) tail is added to the 3’ end

Concept 17.3

- RNA splicing: the introns, the noncoding segments, are removed and the exons are fused together

Concept 17.3

Concept 17.4

In translation, the cell interprets the genetic message and builds a protein accordingly- transfer RNA (tRNA): transfers amino acids from the cytoplasm’s amino acid pool to a ribosome

- contains an anticodon that is complementary to the mRNA codon

Concept 17.4

Concept 17.4

Ribosomes are made of 2 subunits that are constructed of proteins and ribosomal RNA (rRNA)- contains a binding site for mRNA- contains 3 binding sites for tRNA

- P site: holds the tRNA carrying the growing peptide chain

Concept 17.4

- A site: holds the tRNA carrying the next amino acid that is to be added to the chain

- E site: location for tRNA to leave the ribosome

Concept 17.4

Concept 17.6

Mutations can affect protein structure and function- mutations: changes in the genetic material of a cell- point mutations: chemical changes in just one base pair of a gene

Concept 17.6

Concept 17.6

Types of point mutations- substitutions: the replacement of one nucleotide with another nucleotide - missense mutations: the altered mutations still codes for the amino acid and the protein functions- nonsense mutations: change an amino acid to a stop signal;

Concept 17.6

Frameshift mutations- insertions: additions of nucleotide pairs in a gene- deletions: losses of nucleotide pairs in a gene- frameshift mutation: all nucleotides that are downstream are affected