PROTEIN SYNTHESIS

Review: DNA contains genes or a set of instructions. These genes code for a certain sequence of amino acids, that form polypeptides, which come together and fold into a 3D shape to form proteins.

Review: Proteins are used for/as: -repair & maintenance -hormones -enzymes -antibodies -transport -regulatory molecules.

. Review: Three Types of RNA Messenger RNA (mRNA) copies DNA’s code & carries the genetic information to the ribosomes.Messenger RNA (mRNA) copies DNA’s code & carries the genetic information to the ribosomes. Ribosomal RNA (rRNA), along with protein, makes up the ribosomes and bind mRNA for translation.Ribosomal RNA (rRNA), along with protein, makes up the ribosomes and bind mRNA for translation. Transfer RNA (tRNA) transfers amino acids to the ribosomes where proteins are synthesized.Transfer RNA (tRNA) transfers amino acids to the ribosomes where proteins are synthesized.

Messenger RNA (mRNA) Carries the information for a specific protein.Carries the information for a specific protein. Typically nucleotides in length.Typically nucleotides in length. Sequence of 3 bases called a codon.Sequence of 3 bases called a codon. AUG – Methionine or “Start” codonAUG – Methionine or “Start” codon UAA, UAG or UGA – “Stop” codons.UAA, UAG or UGA – “Stop” codons.

Ribosomal RNA (rRNA) rRNA ranges from nucleotides in lengthrRNA ranges from nucleotides in length Globular in shapeGlobular in shape Made inside the nucleolus of the cellMade inside the nucleolus of the cell Associates with proteins to help form ribosomes and bind mRNA for translationAssociates with proteins to help form ribosomes and bind mRNA for translation

Transfer RNA (tRNA) Clover-leaf shape Single stranded molecule with attachment site at one end for an amino acid Opposite end has three nucleotide bases called the anticodon, where it binds to the corresponding codon on the mRNA

Transfer RNA amino acid attachment site UAC anticodon

The Genetic Code A codon designates an amino acid. An amino acid may have more than one codon. There are 20 amino acids, but 64 possible codons. Some codons tell the ribosome to start or stop translating.

Codons and Anticodons The 3 bases of an anticodon are complementary to the 3 bases of a codon. Example: Codon ACU Anticodon UGA UGA ACU

DNA  mRNA  Protein

Promoters Promoters are regions on DNA that are utilized to show where RNA Polymerase must bind to begin the creation of mRNA This starting location for transcription is called the TATA box

mRNA Processing After the DNA is transcribed into mRNA, editing must be done to the nucleotide chain Introns, non-coding segments of DNA, are edited out

mRNA Processing Exons, segments of mRNA that will be expressed as amino acids and, ultimately, proteins; are then rejoined by the enzyme ligase. The mRNA can then leave the nucleus and head out into the cytoplasm to the ribosomes.

New Transcript Result of Transcription

Translation Translation is the process of decoding the mRNA into a polypeptide chain At the ribosomes, mRNA is “read” 3 bases, or 1 codon, at a time and to construct 3D proteins

Step 1- Initiation mRNA translation starts as the codon, AUG, attaches to the small ribosomal subunit

Step 2 - Elongation As the ribosome moves along the mRNA strand, two tRNA, with their amino acids, move into sites A and P of the ribosome for attachment of the coded amino acids Peptide bonds join the amino acids

Ribosomes P Site A Site Large subunit Small subunitmRNA AUGCUACUUCG

Demo of Initiation mRNA AUGCUACUUCG 2-tRNA G LEU AU A 1-tRNA UAC MET anticodon hydrogen bonds codon

mRNA AUGCUACUUCG 1-tRNA2-tRNA UACG MET LEU AU A anticodon hydrogen bonds codon peptide bond 3-tRNA GAA LEU Demo of Elongation

mRNA AUGCUACUUCG 1-tRNA 2-tRNA UAC G MET LEU AU A peptide bond 3-tRNA GAA LEU Ribosomes move over one codon (leaves)

mRNA AUGCUACUUCG 2-tRNA G MET LEU AU A peptide bonds 3-tRNA GAA LEU 4-tRNA GCU ARG ACU

mRNA AUGCUACUUCG 2-tRNA G MET LEU AU A peptide bonds 3-tRNA GAA LEU 4-tRNA GCU ARG ACU (leaves) Ribosomes move over one codon

mRNA GCUACUUCG MET LEU A peptide bonds 3-tRNA GAA LEU 4-tRNA GCU ARG ACU UGA 5-tRNA THR

mRNA GCUACUUCG MET LEU A peptide bonds 3-tRNA GAA LEU 4-tRNA GCU ARG ACU UGA 5-tRNA THR Ribosomes move over one codon

mRNA ACAUGU MET LEU U primarystructure of a polypeptide LEU 200-tRNA ARG UAG THR CU VAL HIS terminator or stop or stop codon codon Termination

29 End Product – The Polypeptide Chain The end products of protein synthesis is the primary structure of a protein, also known as a Polypeptide Chain. A sequence of amino acid bonded together by peptide bonds. MET LEU ARG THR VAL HIS