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Chapter 25

Chapter 25. Protein synthesis. A Gene is a segment of DNA that has information on how to make a polypeptide DNA codes for proteins. But DNA is only in the nucleus and proteins are made by ribosomes in the cytoplasm. RNA occurs in both the nucleus and the cytoplasm. RNA. Review on RNA

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Chapter 25

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  1. Chapter 25 Protein synthesis

  2. A Gene is a segment of DNA that has information on how to make a polypeptide • DNA codes for proteins. But DNA is only in the nucleus and proteins are made by ribosomes in the cytoplasm. • RNA occurs in both the nucleus and the cytoplasm

  3. RNA • Review on RNA • Nitrogen bases are • Adenine • Cytosine • Guanine • Uracil • Strands • Single Stranded • Sugar Used • Ribose

  4. RNA • Three Main Types of RNA • Messenger RNA  mRNA  takes a message from DNA in nucleus to the ribosomes in cytoplasm • Ribosomal RNA  rRNA  this is what makes a ribosome. Two parts, one is rRNA and the other is a protein • Transfer RNA tRNA  this brings or transfers amino acids to the ribosome

  5. Making mRNA • An Enzyme called RNA polymerase ‘unzips’ the DNA. • The RNA polymerase starts ‘unzip’ the DNA at a location called the initiation site. • The initiation site is a specific area on the DNA that has a unique sequence of nucleotides • This is called Initiation • The RNA polymerase starts to create a RNA strand by using the DNA strand as a template • This step is called elongation • The RNA polymerase then reaches a specific section of DNA called the termination site • This is called Termination

  6. Making mRNA out of DNA is called Transcription • There are 3 steps to transcription • Initiation • Elongation • Termination

  7. mRNA  Some of the information is useless • The newly made mRNA has two parts • Introns • Exons • The introns are pieces of the mRNA that does not have any information to make protein. So the introns are removed from the mRNA • They are removed with a non-protein enzyme called Ribozyme • Only the exons remain

  8. mRNA • The mRNA then leaves the nucleus by going through one of the nuclear pores. • The ‘mature’ mRNA has only exons • The mRNA determines the order of the amino acids in the polypeptide

  9. mRNA gets translated into a polypeptide • This is called Translation Step 1 • Initiation the mRNA attaches to the small subunit of the ribosome. It attaches at the “start codon” AUG. The very first tRNA attaches to this start Codon Step 2 • Elongation the polypeptide lengthens. The tRNA continues to bring in amino acids. The tRNA brings in amino acids based on what the mRNA.

  10. Hydrogen Bonds This tRNA comes in Condensation Synthesis occurs This tRNA then leaves

  11. Translation always start with the start codon AUG • Every three nucleotides on the mature mRNA are called codons • The tRNA has a section that combines with the codon called the Anticodon

  12. Translation Step 1 • Initiation Step 2 • Elongation Step 3 • Termination  the ribosome reaches a section of the mRNA that has a Stop Codon. No tRNA combines with this. The polypeptide leaves the ribosome

  13. Question: What is the result of the translation of the DNA sequence CCGTATCTT mRNA is GGCAUAGAA Glycine, Isoleucine, Glutamate

  14. What are the possible mRNA codons that would code for the dipeptide Lysine and Glutamine? AAACAA AAACAG AAGCAA AAGCAG What are the possible tRNAanticodons that would code for the same dipeptide? UUUGUU UUUGUC UUCGUU UUCGUC

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