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Protein Synthesis
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PROTEIN SYNTHESIS
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Protein synthesis involves two types of nucleic acids:
DNA (deoxyribonucleic acid) RNA (ribonucleic acid)
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Differences Between DNA and RNA
DNA RNA double-stranded single-stranded sugar = deoxyribose sugar = ribose bases = A,T,C,G bases = A,U,C,G (uracil takes the place of thymine)
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RNA RNA, like DNA, is a polymer formed by a sequence of nucleotides
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Free Nucleotide
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Protein Synthesis involves two processes:
Transcription: the copying of the genetic instructions (DNA) into a molecule of mRNA Translation: mRNA is used to assemble an amino acid sequence into a polypeptide (protein)
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Pathway to Making a Protein
DNA mRNA Protein Transcription Translation
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Transcription Process in which genetic instructions are transcribed (rewritten) to form an RNA molecule. occurs in the nucleus of eukaryotic cells Transcription occurs in 3 major steps:
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RNA polymerase (enzyme) binds to the promoter.
Step 1: RNA polymerase (enzyme) binds to the promoter. Promoter – a specific nucleotide sequence of DNA that initiates transcription. (“START” sequence) DNA strand unwinds and separates
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Step 2: RNA polymerase adds free RNA nucleotides that are complementary to the nucleotides on one of the DNA strands.
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Complementary Pairings:
EXAMPLE: DNA RNA A = U T = A C = G G = C
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Step 3: RNA polymerase reaches the “termination signal” sequence of nucleotides that marks the end of transcription. RNA polymerase releases both the DNA strand and the newly formed RNA strand.
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The RNA made during transcription can be any of the three types of RNA:
messenger RNA (mRNA) transfer RNA (tRNA) ribosomal RNA (rRNA)
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Transcription Animation
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Translation (Protein Synthesis)
RNA protein
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Translation occurs in the cytoplasm of the cell, at the ribosome
All RNAs needed in translation mRNA, tRNA, and rRNA
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Messenger RNA (mRNA) Carries coded instructions for protein synthesis (translation) From the DNA in the nucleus to the ribosome
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The genetic code Codons instructions for making a
protein, a series of three nucleotides on the mRNA Each codon signifies start, stop, or an amino acid
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The genetic code
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Transfer RNA (tRNA) Brings amino acids to the ribosome so it can build proteins It has Anticodons 3 nucleotide sequence complementary to the mRNA codon
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Ribosomal RNA (rRNA) Makes up ribosomes
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Translation Step 1: mRNA from nucleus Through cytoplasm to the ribosome mRNA start codon AUG signals beginning of protein
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Translation Step 2: tRNA with the complementary anticodon carries amino acid (a.a.) to bind to the codon
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Translation Step 3: Enzymes help form peptide bonds between amino acids Peptide bond
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Translation Step 4: This continues until a stop codon is reached
Protein is released into the cell
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Translation Animation
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