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Making Proteins!!!

Making Proteins!!!. Objectives: 1. Explain the structure of RNA 2. Explain how proteins are made in the cell. 3. Explain the function of mRNA, rRNA and tRNA. Quiz. In your investigation yesterday, you mixed banana with dish detergent. What was the purpose of this?

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Making Proteins!!!

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  1. Making Proteins!!! Objectives: 1. Explain the structure of RNA 2. Explain how proteins are made in the cell. 3. Explain the function of mRNA, rRNA and tRNA

  2. Quiz • In your investigation yesterday, you mixed banana with dish detergent. What was the purpose of this? • In this experiment how did I break apart the cell wall? • Why is DNA considered to be the source of diversity among all living things? • Copy this DNA sequence and write its complementary sequence. GAA TTA ACA • What is the purpose of DNA replication?

  3. The DNA Code – Genetic Code • all the codes located on the DNA of the 23 pairs of chromosomes are referred to as the genetic code • the genetic code consists of the lengthwise sequence of nitrogen bases found along a DNA molecule e.g. ATTGCAGGCCTAATT • the genetic code is written in triplets of nitrogen bases (three letter words or codons) e.g. ATT GCA GGC CTA ATT • each triplet represents one amino acid in the final protein

  4. RNA • RNA is a type of nucleic acid • It is a three part molecule including a phosphate, sugar and nitrogen-containing base component. • The sugar is ribose and the nitrogen-containing base is one of the following four: adenine, cytosine, guanine or uracil • It is single stranded • It is a helper to DNA allowing protein synthesis to occur.

  5. in the genetic code, more than one codon can be used to code for a particular amino acid; e.g. serine is coded for by UCU, UCC, UCA, or UCG • there are three “STOP” codons, which do not code for any amino acids, but which indicate the end of the protein chain • the genetic code for amino acids is universal in all living organisms • a gene from one species may be inserted into another species, and be fully functional e.g. bacteria, using a human gene to produce insulin – aprotein

  6. Overview of Gene Expression – Protein Synthesis • Protein synthesis (building of a protein in the cell) is a 2 step process: • Transcription (copying DNA in the nucleus) • Translation (building a protein in the cytoplasm)

  7. 1) Transcription • Transcription occurs in the nucleus • it involves DNA and mRNA • one DNA gene is “transcribed” (copied) to form a complementary copy referred to as messenger RNA (mRNA)

  8. STEPS: • DNA unwinds or unzips at a specific gene site • remember, a gene is a short segment of DNA coding for a single protein • one side of the DNA gene, the template strand, will be copied • free RNA nucleotides in the nucleus form complementary base pairs with the template DNA strand

  9. STEPS(cont’d) • the new mRNA molecule formed is a single linear strand • mRNA then leaves the nucleus and enters the cytoplasm • mRNA attaches itself to a ribosome

  10. NOTE: • a sequence of 3 nitrogen bases on mRNA is referred to as a codon. • these codons are complementary to the triplets of the original DNA gene • thus, a mRNA molecule is a complementary copy of a gene on the DNA molecule and carries the genetic information on how to build a particular protein

  11. 2) Translation • Translation occurs in the cytoplasm • it involves mRNA, the ribosome, tRNA and amino acids • the codons on mRNA are “read” and “translated” by theribosome into a sequence of amino acids that will form a protein molecule

  12. STEPS: • mRNA arrives from the nucleus and attaches itself to a ribosome • the first mRNA codon is in the first slot on the ribosome awaiting tRNA • a tRNA molecule in the cytoplasm picks up an amino acid that corresponds to its anti-codon • the tRNA and its attached amino acid then travels to the ribosome and the anticodon on tRNA bonds with the codon on mRNA following the complementary base pairing rule. This ensures that the correct amino acid is in place

  13. STEPS(cont’d) • the second mRNA codon is available in the second slot on the ribosome (A site) • a second tRNA with its attached amino acid arrives and its anticodon bonds to the mRNA codon • now the two amino acids are bonded together forming a peptide bond, with the help of an enzyme • the first tRNA leaves, and the ribosome shifts down the mRNA, exposing the third codon

  14. STEPS(cont’d) • this process continues until all the amino acids have been bonded together into a long chain • when the ribosome reaches a stop codon, no more amino acids are added and the building of a polypeptide, which is a small portion of what will become the large protein molecule, is complete • the protein is released and folds up into its final functional form

  15. Diagram • http://www.youtube.com/watch?v=NJxobgkPEAo • http://www.youtube.com/watch?v=983lhh20rGY&feature=related

  16. Questions 1. Compare DNA and RNA. What is the function of each? Where is each located in a cell? • Why is genetic material crucial to the well-being of a cell • State the function of rRNA, mRNA and tRNA • Draw a diagram illustrating the process of protein synthesis. Make sure to label your diagram.

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