Section 8-5 “Translation”

Transcription KEY CONCEPT Translation converts an mRNA message into a polypeptide, or protein. Translation

The basic building block of a protein is the amino acid. There are 20 amino acids; each one differs in its R group. Below are four amino acids showing the differences in R groups

20 Amino Acids

Amino acids are joined together in proteins by peptide bonds. A peptide bond forms between the carboxyl group of one amino acid (amino acid 1 in the figure below) and the amino group of the adjacent amino acid (amino acid 2)

Amino acids are coded by mRNA base sequences A codon is a sequence of three nucleotides that codes for an amino acid. codon for Methionine (Met) Leucine (Leu)

START codon – signals the start of translation. One START codon: AUG (methionine) START codon for Methionine (Met) codon for Leucine (Leu)

STOP codon – signals the end of translation. Three STOP codons: UAA, UAG, UGA

mRNA (Messenger RNA) Messenger RNA consists of leader, reading frame, and trailer sequences. mRNAs vary in length. Sequences of mRNAs vary because amino acid coding sequences (reading frames) differ, and because leader and trailer sequences differ

A three-nucleotide sequence that codes for an amino acid - three stop codons signal the end of the amino acid chain Signals start of translation always begins with amino acid: methionine. (AUG)

Codons are read, without spaces, as a series of three nonoverlapping A change in the order in which codons are read changes the resulting protein READING FRAME Codons are read, without spaces, as a series of three nonoverlapping nucleotides. Regardless of the organism, codons code for the same amino acid

COMMON LANGUAGE: The genetic code is shared by almost all organisms—and even viruses. The “language” of proteins uses 20 amino acids Each code word is a unique combination of three letters (like the ones shown above) that will eventually be interpreted as a single amino acid in a polypeptide chain. There are 64 code words possible from an 'alphabet' of four letters Translation 2

The genetic code shared by almost all organisms— “language” of proteins uses 20 amino acids Codons are read, without spaces, as a series of 3 nonoverlapping nucleotides.

Amino acids are linked together to become a protein An anticodon is a set of three nucleotides that is complementary (opposite) to an mRNA codon An anticodon is carried by a tRNA Codon Translation 3

Ribosomes consist of two subunits The large subunit has three binding sites for tRNA The small subunit binds to mRNA

For translation to begin, tRNA binds to a start codon and signals the ribosome to assemble A complementary tRNA molecule binds to the exposed codon, bringing its amino acid close to the first amino acid

The ribosome helps form a polypeptide bond between the amino acids The ribosome pulls the mRNA strand the length of one codon

The tRNA molecule (now empty) exits the ribosome A complementary tRNA molecule binds to the next exposed codon Once the stop codon is reached, the ribosome releases the protein and disassembles (gets taken apart)

large subunit binds to tRNA small subunit binds to mRNA Type of RNA that carries amino acids from cytoplasm to ribosome. One end has specific anticodon and the other a specific amino acid Matching set of 3 nucleotides complementary to an mRNA codon. large subunit binds to tRNA small subunit binds to mRNA

Use the chart in textbook on page 244 to decode the mRNA. Group in sets of 3’s then use chart to determine what amino acid each would be.

Use the chart in textbook on page 244 to decode the mRNA. Group in sets of 3’s then use chart to determine what amino acid each would be. Ile ____ ____

Use the chart in textbook on page 244 to decode the mRNA. Group in sets of 3’s then use chart to determine what amino acid each would be. Ile ____ ____ Gln

Use the chart in textbook on page 244 to decode the mRNA. Group in sets of 3’s then use chart to determine what amino acid each would be. stop Ile ____ ____ Gln

Amino acid (start – methionine. AUG Peptide bond tRNA Large ribosomal subunit Anticodon mRNA Small ribosomal subunit codons

Ribosome assembles at the start codon Ribosome assembles at the start codon. Complementary tRNA molecule pairs with exposed codon Ribosome helps bond the new amino acid to start codon and breaks bond between the amino acid and first tRNA Ribosome pulls the mRNA strand the length of one codon. The first tRNA strand returns to cytoplasm as another codon is exposed (opened up) for tRNA binding