2 Protein SynthesisProtein Synthesis is the process that cells use to produce protein.- it involves 2 distinct phasesTranscription – occurs in the nucleusinvolves the creation of mRNATranslation – occurs in the cytoplasmat a ribosome – the protein recipe is “read” and the correct protein is made
3 Proteins are chains of amino acids amino acid + amino acid + amino acid = proteinThe order of amino acids determines protein shapeShape determines functionDNA recipe consists of the order of amino acids for each protein- the recipes are known as genes
4 Recipe has to get from DNA to the ribosome which builds the protein
5 Transcription: makes a copy of the protein recipe This is necessary because:DNA cannot leave the nucleus!!!Proteins are made on ribosomes in the cytoplasm.mRNA provides the solutionMessenger ribonucleic acidmRNA is a copy of the protein recipe that can leave the nucleus
6 Knowledge CheckHow do transcription and translation work together to produce proteins?What is necessary for protein synthesis to occur?CRITICAL THINKING: What is the one time when DNA does leave the nucleus? (It is not in strands that can be copied at this time)
7 The Structure of RNAThere are three main differences between RNA and DNA:The sugar in RNA is ribose instead of deoxyribose.RNA is generally single-stranded.RNA contains uracil in place of thymine.
8 Types of RNA There are three main types of RNA: messenger RNA ribosomal RNAtransfer RNA
9 Messenger RNA (mRNA) carries copies of instructions for assembling amino acids into proteins, leaving the nucleus and traveling to the ribosome
10 Ribosomes are made up of proteins and ribosomal RNA (rRNA).
11 During protein construction, transfer RNA (tRNA) transfers each amino acid to the ribosome.
12 Critical ThinkingBased on their descriptions, hypothesize why you think each type of RNA is required for proteins synthesis to occur.
13 Transcription: Initiation The Process Begins The enzyme RNA polymerase finds the beginning of a protein recipe called the promoter- promotor = a series of nucleotides that indicate the start of a protein recipeThe RNA polymerase opens the DNA molecule at the promoter
14 Transcription: Initiation The RNA polymerase uses one DNA strand as a template to build the mRNA- only one of the DNA strands contains the protein recipe- the strand with the recipe is thetemplate strand- the strand without the recipe isthe non-template strand- it is not copied
16 Transcription: Elongation Building the mRNA Molecule RNA polymerase brings RNA nucleotides to the template strand-pairs them with their complements onthe original DNA molecule-this follows the base pairing rules except that uracil replaces thymine- Adenine on DNA is paired with Uracil (U)on the new mRNA
17 Transcription: Termination The Process Ends the RNA polymerase continues to add new nucleotides until it reaches the terminator- the terminator is a sequence of nucleotidesthat indicates the end of the recipethe mRNA drops off the DNA-this is pre-mRNA it needs furtherprocessing before it can be translated
18 Knowledge Check How does RNA polymerase assist in transcription? What role does the promoter play?Summarize the major steps of transcription (you should have at least 3)
19 RNA EditingIntrons – segments of nucleotides not involved in coding for proteinsExons – DNA sequences that code for proteinsIntrons get cut out and exons get spliced (added) together
21 Genetic Code The genetic code is the “language” of mRNA instructions. The code is written using four “letters” (the bases: A, U, C, and G).A codon consists of three consecutive nucleotides on mRNA that specify a particular amino acid.
22 The Genetic Code “Start” codon – AUG (methionine) 3 “stop” codons – do not code for amino acids; signify the end of a protein molecule
26 TranslationTranslation is the decoding of an mRNA message into a polypeptide chain (protein).Translation takes place on ribosomes.During translation, the cell uses information from messenger RNA to produce proteins.
27 Translation mRNA molecule attaches to a ribosome As each codon of the mRNA molecule moves through the ribosome, the proper amino acid is brought to the ribosome by the tRNAIn the ribosome, the amino acid is transferred to the growing protein molecule
28 Translation Each tRNA molecule carries only one kind of amino acid Each tRNA has 3 unpaired basesAnticodon – complementary to the one mRNA codon
29 Knowledge Check Where does translation occur? Summarize the major steps of translation (you should have at least 3).Critical Thinking: How does the anti-codon relate to the original DNA template strand?
30 The ribosome binds new tRNA molecules and amino acids as it moves along the mRNA, beginning with the “start” codon
31 The process continues until the ribosome reaches a stop codon.