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Protein Synthesis (Chapter 3 – Part 4 )

Protein Synthesis (Chapter 3 – Part 4 ). Eukaryotic vs. Prokaryotic DNA. Eukaryotic DNA DNA is located in the nucleus in the form of a number of chromosomes. Eukaryotic vs. Prokaryotic DNA. Prokaryotic DNA Lack nucleus and many of the organelles found in eukaryotes.

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Protein Synthesis (Chapter 3 – Part 4 )

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  1. Protein Synthesis (Chapter 3 – Part 4 )

  2. Eukaryotic vs. Prokaryotic DNA • Eukaryotic DNA • DNA is located in the nucleus in the form of a number of chromosomes.

  3. Eukaryotic vs. Prokaryotic DNA • Prokaryotic DNA • Lack nucleus and many of the organelles found in eukaryotes. • DNA is located in the cytoplasm. • Have a single circular DNA molecule (usually referred to as the cell's chromosome).

  4. Some Terms • Chromosome - Very long, continuous piece of DNA (a single DNA molecule), which contains many genes. • Genes - Sequence of DNA that codes for a protein and thus determines a trait.

  5. Chromosome Structure • DNA molecules are surprisingly long. • The chromosome of the prokaryote E. coli, which can live in the human colon, contains 4,639,221 base pairs! • Analogy: Imagine trying to pack a 300-meter length of rope into your school backpack! • DNA must be dramatically folded and tightly packed to fit within the cell.

  6. More Terms • Chromatin - Granular material visible within the nucleus; consists of DNA tightly coiled around proteins

  7. Proteins • Proteins are made up of a chain of amino acids. • Proteins are enzymes, which catalyze and regulate chemical reactions.

  8. 2 Steps to Make a Protein 1. Transcription DNA → RNA 2. Translation RNA → Protein (Chain of amino acids)

  9. Step 1: Transcription • Transcription - Process in which part of the nucleotide sequence of DNA is copied into a complementary sequence in RNA. • The DNA strands are separated. • One strand of DNA is used as a template from which nucleotides are assembled into a strand of RNA.

  10. Transcription: DNA → RNA

  11. Transcription Animation • http://www.ncc.gmu.edu/dna/mRNAanim.htm • http://www.johnkyrk.com/DNAtranscription.html • http://www-class.unl.edu/biochem/gp2/m_biology/animation/gene/gene_a2.html • http://207.207.4.198/pub/flash/26/transmenu_s.swf (very good but need to skip some parts)

  12. After Transcription • The mRNA leaves the nucleus and travels to the ribosomes in the cytoplasm.

  13. Codons • Codon - Three-nucleotide sequence on messenger RNA that codes for a single amino acid.

  14. The Genetic Code • The “language” of mRNA instructions is called the genetic code. • The genetic code is read three letters at a time, so that each “word” of the coded message is three bases long.

  15. Step 2: Translation • Translation - Decoding of a mRNA message into a protein (amino acid chain) • Takes place on Ribosomes

  16. Steps of Translation • Begins when an mRNA molecule in the cytoplasm attaches to a ribosome. • As each codon of the mRNA molecule moves through the ribosome, the proper amino acid is brought into the ribosome by tRNA.

  17. Anticodon • Each tRNA molecule has three unpaired bases called the anticodon, which are complementary to one mRNA codon.

  18. Anticodon Example • In the case of the tRNA molecule for methionine: • The anticodon UAC codes for the amino acid methionine • The anticodon bases are UAC • The codon bases are AUG You Try It: List the codon, anticodon, and the amino acid coded for the 2nd codon.

  19. Translation Animations • http://207.207.4.198/pub/flash/26/transmenu_s.swf (very good animation!)

  20. Mutations • Mutation - Change in a DNA sequence that affects genetic information; error or mistake in copying DNA.

  21. Types of Mutations • Point Mutations - Mutation that affects a single nucleotide, usually by substituting one nucleotide for another. • Substitution – one base is changed to another Original: AUGUAC→ Met – Tyr Mutated: AUGUAG→ Met – Stop (causes the amino acid chain to stop protein production early)

  22. Types of Mutations • Frameshift Mutations - Mutation that shifts the “reading” frame of the genetic message by inserting or deleting a nucleotide. • Insertions – A base is inserted into the DNA sequence. • Deletions - A base is removed from the DNA sequence. Original: The fat cat ate the wee rat. Frame Shift: The fat caa tet hew eer at. (Frame shift mutations affect all subsequent amino acids!)

  23. Significance of Mutations • Many mutations have little or no effect on the expression of genes. • Mutations may be harmful and may be the cause of many genetic disorders and cancer. • Source of genetic variability in a species (may be highly beneficial).

  24. What Varies in Our DNA • Mutations - Occur by changing the sequence of the nitrogen bases or the order of nucleotides. • Differences Between Organisms - Occur because the sequence of the nitrogen bases or the order of nucleotides are different.

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