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Protein Synthesis

Protein Synthesis. The Link Between Genes and Proteins. Gene -portion of DNA that codes for a protein that controls a trait Two types of proteins Structural proteins : determine how we look EX: Hair & skin pigments; ear lobe shape Enzymes : determine how we function

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Protein Synthesis

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  1. Protein Synthesis

  2. The Link Between Genes and Proteins • Gene -portion of DNA that codes for a protein that controls a trait • Two types of proteins • Structural proteins: determine how we look • EX: Hair & skin pigments; ear lobe shape • Enzymes: determine how we function • Control every chemical reaction in the body • EX: Sucrase breaks down sucrose (table sugar) Detached ear lobes Attached ear lobes

  3. Overview • Sequenceof bases determines the “genetic code” • DNA NEVER leaves the nucleus • RNA copies DNA code of a gene. • RNA carries the copied code out of the nucleus to the ribosomewhere protein is made DNA code

  4. Types of RNA mRNA • Messenger RNA = mRNA • Copies instructions from DNA code; carries code out of nucleus to ribosome 2. Ribosomal RNA = rRNA • Ribosomes are made of protein and RNA 3. Transfer RNA = tRNA • Carries and transfers a specific amino acid to the ribosome • T-shape rRNA tRNA

  5. Step 1: Transcription • Transcription: a single strand of mRNA is copied from DNA in the nucleus • DNA unwinds – helicase • RNA polymerase uses DNA template to make mRNA strand • If DNA is TACCAGTTT • mRNA will be AUGGUCAAA • mRNA is removed and DNA strands will join & recoil

  6. Slide # 8 Step 2: mRNA editing • mRNA editing: cutting and splicing mRNA before it leaves the nucleus • Introns- (interfere) are cut out by enzymes • Exons- (expressed) are left • spliced together to create an edited version • Poly-A tail added to end • Edited mRNA is sent to ribosome Introns are removed and exons are spliced together. This is the message that is translated.

  7. Slide # 9 Step 3: Translation • How the mRNA is read: • Every 3 bases on mRNA represents a code for an amino acid (codon) • Amino acids are abbreviated (usually first 3 letters). • Met = methonine (start) • Leu = leucine

  8. Slide # 11 Step 3: Translation • Occurs at a ribosome • Codon on mRNA specifies which tRNAbrings the designated amino acid • Anticodonon tRNA“reads” the codon on mRNA • Ribosome joins the amino acids together with peptide bonds to build a polypeptide (protein) • DNA (gene)  RNA  Protein Trait

  9.  Translation Slide # 12 Nucleus mRNA  Lysine Phenylalanine t RNA Methionine  Anticodon Ribosome mRNA  Start codon Go to Section:

  10. Translation Slide # 13 Growing polypeptide chain The Polypeptide “Assembly Line” Ribosome tRNA Lysine tRNA mRNA Completing the Polypeptide mRNA Translation direction Ribosome Go to Section:

  11. Reading the Codon Chart Slide # 10 Examples: AUG = Methionine CAU = Histidine UAG = Stop First Position Third Position Try these: GCU: UAC: CUG: UUA: Answers: Alanine Tyrosine Leucine Leucine This chart only works for mRNA codons.

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