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.