Protein Synthesis Unit 6 Goal: Students will be able to describe the processes of transcription and translation.
Types of RNA Messenger RNA (mrna) makes a copy of DNA, carries instructions for making proteins, Transfer RNA (trna) decodes mrna and transfers amino acids to the ribosome Ribosomal RNA (rrna) build the protein by bonding amino acids together. Ribosomes are made of rrna.
Central Dogma DNA RNA Protein DNA is the instructions for making the protein RNA copies the instructions & builds the protein The protein is built by the ribosome and used either by that cell or transported to other cells.
DNA RNA Protein DNA Nuclear membrane Eukaryotic Cell Transcription RNA Processing Pre-mRNA mrna Translation Ribosome copyright cmassengale Protein 4
Codons & Amino Acids Codon = 3 base (letter) sequence on mrna Amino Acid = monomer of protein 1 codon CODES FOR 1 amino acid Some amino acids have multiple codons. 64 possible codons; 20 Amino Acids in nature
Codon Chart Chart tells which Amino Acid that codon means Find the correct letter in the 1 st position 2 nd position 3 rd position (where do those meet?) Example: AUG codes for Met (Methionine) 6
Name the Amino Acids GGG? UCA? CAU? GCA? AAA? copyright cmassengale 7
Start/Stop Codons There will always be a Start codon (AUG) at the beginning. It is like capitalizing the 1 st letter of a sentence. There will always be a Stop codon (UGA, UAA, UAG) at the end. It is like a period at the end of a sentence.
Protein Synthesis: Protein synthesis uses the information in genes to make proteins. 2 Steps 1.Transcription Copying the DNA into mrna 2.Translation trna decodes mrna & delivers the amino acids rrna bonds the amino acids together to build the protein
Transcription: Where? mrna is made in the NUCLEUS mrna will leave the nucleus through the pores in the nuclear membrane (DNA does NOT leave the nucleus)
Transcription: Involved Molecules DNA (instructions for making the protein) mrna (copy of the instructions) RNA polymerase (enzyme that builds mrna)
RNA Polymerase = The Enzyme responsible for Transcription 12
Transcription: Produces? mrna (messenger RNA) Long Straight chain of Nucleotides Made in the Nucleus Copies DNA & leaves through nuclear pores Contains the Nitrogen Bases A, G, C, U ( no T ) 13
Remember the Complementary Bases On DNA: A=T C=G On RNA: A=U DNA RNA G C C G T A A U C=G 14
Transcription: What Happens? Big Idea: DNA is copied into a complementary sequence of mrna. 1.RNA polymerase is the enzyme that is responsible for transcription 2.RNA polymerase reads the gene and adds the correct complementary RNA base to make a new strand of RNA. DNA = GCCATT mrna = CGGUAA 3. The mrna gets processed (edited and packaged) 4. mrna leaves the nucleus and goes to the cytoplasm.
Adenine (DNA and RNA) Cystosine (DNA and RNA) Guanine(DNA and RNA) Thymine (DNA only) Uracil (RNA only) RNA polymerase RNA DNA
Transcription: Goes to? mrna leaves the nucleus through the pores in the nuclear membrane, travels through the cytoplasm, and goes to the ribosomes 17
Translation
Translation: Where? Ribosome Free floating ribosome in cytoplasm (makes proteins for that cell) OR attached ribosome on the Rough ER (makes proteins to be exported to other cells)
Translation: Involved Molecules mrna (copy of the instructions) trna (translates the instructions) rrna (builds the protein)
Transfer RNA Decodes (translates) the mrna Delivers (transfers) amino acids to the ribosome amino acid attachment site copyright cmassengale U A anticodon C 21
Codons and Anticodons The 3 bases of an anticodon are complementary to the 3 bases of a codon Ex: Anticodon UGA Codon ACU UGA ACU copyright cmassengale 22
Ribosomal RNA (rrna) Ribosomes are made of rrna Site of Protein Synthesis Forms peptide bonds between amino acids copyright cmassengale 23
Translation: Produces? Chain of amino acids Polypeptide (protein)
Translation: What Happens? Big Idea: The mrna is then TRANSLATED by trna at the RIBOSOME (made of rrna). The RIBOSOME then BUILDS the protein by bonding amino acids together.
Translation: What Happens? 1. trna translates the mrna using anticodons. (complementary to the codon) Each trna molecule has an anticodon on one end and an amino acid on the other. 2. trna transfers the amino acids to the ribosome in the correct sequence. 3. rrna forms peptide bonds between the amino acids. This links them together to build the protein.
Translation: Where does it go? The protein will do one of 2 things Stay inside the cell to carry out functions for that cell OR Be exported to other cells Rough ER Golgi Exocytosis
Messenger RNA Messenger RNA is transcribed in the nucleus. Nucleus Ribosome Methionine Phenylalanine trna Lysine Transfer RNA mrna The mrna then enters the cytoplasm and attaches to a ribosome. Translation begins at AUG, the start codon. Each transfer RNA has an anticodon whose bases are complementary to a codon on the mrna strand. The ribosome positions the start codon to attract its anticodon, which is part of the trna that binds methionine. The ribosome also binds the next codon and its anticodon. mrna Start codon
The Polypeptide Assembly Line The ribosome joins the two amino acids methionine and phenylalanine and breaks the bond between methionine and its trna. The trna floats away, allowing the ribosome to bind to another trna. The ribosome moves along the mrna, binding new trna molecules and amino acids. trna Growing polypeptide chain Ribosome Lysine trna mrna mrna Ribosome Translation direction Completing the Polypeptide The process continues until the ribosome reaches one of the three stop codons. The result is a growing polypeptide chain.