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DNA Replication and Protein Synthesis
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DNA Replication and Protein Synthesis


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  • 1. Processes of DNA Replication and Protein Synthesis
  • 2. DNA Replication
  • 3. Replication • Makes duplicate copies of DNA in the process of replication • DNA replication involves separating the DNA molecule into 2 strands. • Each strand than serves as a pattern, or template, to make a new DNA molecule. • The result is 2 identical double-stranded molecules of DNA
  • 4. Replication (con’t) • Because each of these double-stranded molecules of DNA consists of a single strand of old DNA (the template) and a single strand of new, replicated DNA (the complement), this is called semi- conservative replication.
  • 5. Steps 1. Helicase unwinds DNA, creating a replication fork. Proteins bind to the single strand to keep the DNA from recombining. 2. RNA primase starts replication at special base sequences by adding RNA primers. 3. DNA polymerase attaches to the RNA primers and begins elongation. (Elongation = the adding of DNA nucleotides to the complement strand)
  • 6. Steps (con’t) 4. The leading complementary strand is assembled continuously as the DNA uncoils. 5. The lagging complementary strand is assembled in short pieces called Okazaki fragments. The pieces are joined together by DNA ligase. 6. The RNA primers are replaced by DNA nucleotides.
  • 7. Protein Synthesis
  • 8. Protein Synthesis • Proteins can function as: – Enzymes – Repairing agents for the cell • Proteins determine the shape and function of organisms. • Each gene is responsible for one protein. So, the message of the DNA code is information for building proteins.
  • 9. Protein Synthesis (con’t) • How do genes code for proteins? THE GENETIC CODE!!! • Genetic code: sequence of nitrogen bases along one of the two strands that codes for the synthesis of proteins. • The nitrogen bases set up in sets of 3 that are known as codons.
  • 10. Protein Synthesis (con’t) • Because the sequence of 3 nitrogen bases forms the code for an amino acid, the DNA code is often called the triplet code. • 64 combinations are possible when a sequence of 3 bases is used. So, 64 different codons are in the genetic code. • 61 of the codons code for amino acids, and the other 3 code for protein synthesis to start or stop.
  • 11. Protein Synthesis (con’t) • More than one codon can code for an amino acid; however, for any one codon, there can only be one amino acid. • The genetic code is universal. Universal means that the codons represent the same amino acids in all organisms. • Protein synthesis: process that describes how enzymes and other proteins are made from DNA.
  • 12. Protein Synthesis (con’t) • Steps of Protein Synthesis: – Transcription – RNA processing – Translation • There are 3 types of RNA: – mRNA (messenger): provides the instructions for assembling amino acids into a polypeptide. – tRNA (transfer): delivers amino acids to a ribosome for their addition into a growing polypeptide chain – rRNA (ribosomal): combines with proteins to form ribosomes
  • 13. Transcription: From DNA to RNA RNA is transcribed from a DNA template by a process that resembles DNA replication.
  • 14. Steps of Transcription: • Initiation – The “start transcribing” signal is a nucleotide sequence called the promoter, located in the DNA at the beginning of the gene. Promoter is a specific place where RNA polymerase attaches. – RNA polymerase attaches to the promoter – Start of RNA synthesis
  • 15. Steps of Transcription (con’t) • RNA Elongation – During the 2nd phase of transcription, elongation, the RNA grows longer. – As RNA synthesis continues, the RNA peels away from DNA and allows the DNA strand to rejoin.
  • 16. • Termination – The 3rd and final phase, RNA polymerase reaches the terminator sequence of bases in DNA. – This sequence signals the end of the gene and the polymerase molecules detaches from the RNA molecule and the gene. Steps of Transcription (con’t)
  • 17. RNA Processing The RNA copy that is formed is called mRNA. The mRNA carries the information for making the protein chain to the ribosomes, where it goes through RNA processing.
  • 18. Translation Conversion between different languages – from nucleic acid to protein. Occurs on the ribosomes and uses tRNA. End product is a very long protein chain.
  • 19. tRNA • Composed of about 75 nucleotides • Each tRNA recognizes only one amino acid. • The amino acid becomes bonded to the top of the tRNA. • Located on the bottom of the tRNA are 3 nitrogenous bases, called an anticodon, which pairs with mRNA codons during translation.
  • 20. Steps of Translation • Initiation – 1st phase brings together: • mRNA • 1st amino acid with its attached tRNA, and • The 2 subunits of a ribosome
  • 21. Steps of Translation (con’t) • Elongation – Amino acids are added one by one in a 3-step process • Step 1 – Codon recognition • Step 2 – Peptide bond formation • Step 3 – Translocation
  • 22. • Termination – Elongation continues until a stop codon (UAA, UAG, or UGA) is reached. – Polypeptide is released. – Ribosome splits into subunits and falls off. Steps of Translation (con’t)