Protein Synthesis Section 12.3

DNA’s Purpose DNA has genes that code for the synthesis (creation) of specific PROTEINS Here’s the problem… Where is DNA located? Nucleus

DNA’s Purpose Where does Protein synthesis occur? At ribosomes in the cytoplasm Can DNA ever leave the nucleus? NO!

RNA –Ribonucleic Acid 3 major types of RNA: Messenger RNA (mRNA) carries information from DNA to ribosome Transfer RNA (tRNA) Carries amino acids to ribosome to make protein Ribosomal RNA (rRNA) Makes up ribosomes; site of protein synthesis. located on Rough ER and in cytoplasm

3 Differences between DNA and RNA Structure: Double stranded Sugar: Deoxyribose Bases: Adenine Guanine Cytosine Thymine RNA Structure: Single-stranded Sugar: Ribose Bases: Adenine Guanine Cytosine Uracil

Copy the question to your notes! What are the three main types of RNA? What are three differences between RNA and DNA? messenger RNA, transfer RNA, ribosomal RNA Single stranded Ribose sugar Uracil replaces Thymine

How do you get from DNA to Proteins? TRANSCRIPTION – the synthesis of RNA under the direction of DNA TRANSLATION – the synthesis of a protein, under the direction of mRNA

Transcription From DNA to RNA

Transcription - Where does this happen? Where is the DNA? In the nucleus

Transcription - how RNA is made Location = nucleus RNA polymerase runs along DNA strand and makes messenger RNA (mRNA). Adds nucleotides in 5’ to 3’ direction.

Transcription – how RNA is made Adenine on DNA pairs with Uracil on RNA mRNA leaves nucleus through a nuclear pore and meets up with a ribosome (rRNA) in the cytoplasm

Practice making mRNA Transcript DNA code: TAC GTA AAC TTC ATT mRNA strand : AUG CAU UUG AAG UAA

RNA Processing Messenger RNA

RNA processing mRNA must be altered before it can be used to make a protein. 3 steps : Remove introns Add 5’ cap Add 3’ Poly A tail

Introns and Exons Exons – code for proteins Introns – intervening sequences that must be removed.

Translation From mRNA to Protein

Translation- Where does this happen? Protein synthesis – the manufacture of proteins Where are proteins made in the cell?

Translation - how proteins are made location= ribosome in cytoplasm Once mRNA is at a ribosome, amino acids are assembled to make proteins

Translation - how proteins are made Transfer RNA (tRNA) brings the correct amino acid to the growing protein chain

tRNA reads codons tRNA reads codons to assign the correct amino acid. Codon - found on mRNA; consists of three bases (triplet codon) 64 codons for 20 amino acids

Codons AUG – start codon or Methionine UAA, UAG, UGA – stop codons; code for nothing. Like the period on the end of a sentence.

Practice using codons mRNA: AUGCAUUUGAAGUAA Separate the codons Copy the codons to your notes then use Codon table to find amino acids!

Practice using codons Met (start) - His - Leu - Lys - STOP AUG – CAU – UUG – AAG – UAA Resulting amino acids: Met (start) - His - Leu - Lys - STOP

Protein formation Amino acids link together to form a protein

SUMMARY 1) mRNA is transcribed in the nucleus by RNA polymerase 2) mRNA is processed 3) mRNA attaches to the ribosome 4) tRNA brings the amino acid as it reads mRNA codons 5) The amino acids are joined together 6) When a stop codon is reached the protein synthesis ends.