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DNA & Protein Synthesis

DNA & Protein Synthesis . Chapter 3. DNA. Deoxyribonucleic acid is a nucleic acid (which is made up of nucleotides=sugar, phosphate and base) Made up of two strands that pair together by something called the complimentary rule DNA has specific pairing between the nitrogen bases:

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DNA & Protein Synthesis

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  1. DNA & Protein Synthesis Chapter 3

  2. DNA • Deoxyribonucleic acid is a nucleic acid (which is made up of nucleotides=sugar, phosphate and base) • Made up of two strands that pair together by something called the complimentary rule • DNA has specific pairing between the nitrogen bases: • ADENINE – THYMINE • CYTOSINE– GUANINE

  3. Phosphate Group O O=P-O O 5 CH2 O N Nitrogenous base (A, G, C, or T) C1 C4 Sugar (deoxyribose) C3 C2 Nucleotides

  4. DNA Double Helix 5 O 3 3 O P P 5 5 C O G 1 3 2 4 4 2 1 3 5 O P P T A 3 5 O O 5 P P 3

  5. DNA Replication • DNA MUST be copied!! • DNA produces two identical new complementary strands following the base pairing rules (A-T, G-C) • Each original strand of DNA serves as a template for each new strand

  6. Replication Step #1 • DNA Polymerase comes on the scene • UNWINDS the DNA upstream • UNZIPS the DNA • This site is known as the replication bubble

  7. Replication Step #2 • Complementary Bases begin adding into both sides of the DNA • A binds with T, C binds with G (no other possibility because of the shape of the bases!) • The DNA Polymerase precedes the paired bases and clips out any that are already added ahead of it

  8. Replication Step #3 • Finally you have 2 identical copies of DNA • The final job of the Polymerase is to Proofread the nucleotides after they are addedand to clip out any that are incorrectly paired

  9. The Code DNA molecules carry the code for all the genes of an organism Genes are pieces of the DNA molecule that code for specific proteins The process of making genes into proteins is called protein synthesis-which occurs OUTSIDE of the nucleus on the ribosome

  10. Steps of Protein Synthesis • The DNA code of the gene segment must be copied in the nucleus of the cell • The code must be carried from the nucleus into the cytoplasm and then to the ribosome • The protein is then assembled from the code and released • These steps are carried about by RNA (Ribonucleic acid)

  11. Carrying the Code Out RNA is a molecule that is used to translate the code from a DNA molecule into a protein It is very similar to DNA except: it is single stranded, it’s sugar is ribose and instead of thymine as a base, it uses Uracil (so A pairs with U in RNA only!) There are three types of RNA: messenger, ribosomal and transfer (ALL are involved in protein synthesis)

  12. Transcription • Step one of protein synthesis is the manufacturing of messenger RNA (mRNA) • This making of the mRNA is called transcription • Transcription begins when a region of the DNA unwinds and separates (this separated segment is a gene) • This unwound segment serves as a template for the soon to be mRNA strand

  13. mRNA The mRNA strand is assembled from individual RNA nucleotides that are present in the nucleus RNA polymerase (an enzyme) picks up these nucleotides and matches them to their DNA complement from the template that has just been unzipped At this point, the mRNA separates and leaves the nucleus-moving into the cytoplasm and settling on a ribosome-this is where translation begins

  14. Translation • Ribosomes are made up of ribosomal RNA (rRNA) • On these ribosomes mRNA is decoded (translated) and a corresponding polypeptide (amino acids) is formed • When we “decode” a chain of nucleotides we “read” it in a three base code called a codon • For example: our mRNA sequence could be AUGACAGAUUAG • The corresponding codon would be AUG ACA GAU UAG

  15. Codons • The three nucleotide codon has the specific function of corresponding to a particular amino acid • How does this work? • The mRNA is bound to the surface of the ribosome at the first nucleotide segment (called a start codon) • The cytoplasm in which the rest floats contains amino acids and a third kind of RNA, transfer RNA (tRNA)

  16. tRNA This molecule contains a three part nucleotide segment called an anticodon (this is the exact match of one mRNA codon) The anticodon corresponds exactly to one of the 20 kinds of amino acids Once the tRNA binds the amino acid it travels to the ribosome surface and there the three tRNA bases pair with their three complementary mRNA bases

  17. Finishing Up Translation The amino acid that is bound to the tRNA is then added to the growing polypeptide chain at the surface of the ribosome The ribosome facilitates this process by moving along the mRNA chain until it reaches a stop codon (a three nucleotide segment that tells the ribosome that the translation is complete) The ribosome then releases the newly-formed polypeptide chain which moves out into the cell as a fully functioning protein

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