RNA and Protein Synthesis

1. RNA and Protein Synthesis Mrs. McNamara Chapter 10-2 and 10-3 (pgs 190-197)

2. Click here to read the case study about protein synthesis.

3. Making Proteins Big Question: How do cells use the genetic information stored in DNA to make millions of different proteins the body needs?

4. Key Concept: • Genetics shows that genes code for proteins.

5. Making Proteins Remember: each gene consists of a linear sequence of nucleotides arranged in a specific order according to our genetic ancestry. The order of these nucleotides makes up the genetic information or “code” which determines the sequence of amino acids that will be assembled.

6. Making Proteins Proteins are made up of a linear sequence of amino acids that get twisted up. And, in all cells, except for bacteria, DNA is stored in the nucleus and protein synthesis takes place in the ribosome (located in the cytoplasm)… Ribosome

7. If a gene is used to make a protein, we say that gene is “expressed”.

8. Be able to answer the following questions. You will have to answer a question at the start of class tomorrow: • What is a gene? • What is a protein made of? • What do we mean when we say a gene is expressed?

9. Key Concept: • The genetic code carried by RNA is translated into amino acid sequences of proteins.

10. Problem: • DNA cannot leave the nucleus (it is TOO BIG!) How can we get DNA’s information from the nucleus to the ribosomes (site of protein synthesis)?

11. We use RNA to move DNA’s code from the nucleus to the ribosome!3 Types of RNA: 1. mRNA 2. tRNA 3. rRNA RNA: ribonucleic acid. Takes DNA information to the ribosome and uses information from DNA to make proteins.

12. Comparison of DNA and RNA:

13. FYI - RNA Hey kids…RNA differs from DNA in several ways. • An RNA molecule has only one side of the ladder shape. • RNA has the bases A, G, and C. However, it has a base U or Uracil, instead of base T or thyamine. • So when forming base pairs, base A pairs with base U.

14. 1. mRNA (Messenger RNA) Structure-single, uncoiled strand of RNA nucleotides. Function-takes information from DNA (in nucleus) to ribosome to use during protein synthesis. Used as a template for the assembly of amino acids during protein synthesis. mRNA is made from DNA in the nucleus.

15. mRNA is “read” in order in 3 base “groups”. • Each called a CODON- a 3-base sequence of mRNA that codes for a specific amino acid. • 3 mRNA bases=1 codon= code for 1 amino acid • 64 different codons exist…several will code for the SAME amino acid.

17. Two Important Types of Codons: • START CODON-tells the ribosome to begin reading the mRNA and to bring and assemble a chain of amino acids (begin translation). • This codon and amino acid is the same in EVERY PROTEIN. • STOP CODON-tells the ribosome to stop reading the mRNA. No more amino acids are brought and assembled (stop translation-ends the assembly of the protein).

18. Stop and Think: 3 mRNA bases = code for 1 amino acid If you have 450 mRNA bases, how many amino acids would you code for? How many codons would you have?

19. 2. tRNA (Transfer RNA) Structure-single strand of RNA nucleotides folded into a hairpin shape. Function-pairs with mRNA to transfer amino acids into the growing polypeptide chain in the correct sequence.

20. How does the tRNA know where to bring the amino acids (what order)? • One end of the tRNA is an ANTICODON-3-base sequence of tRNA that complements (fits into) an mRNA codon. • The tRNA brings the amino acid to the codon that it fits into.

21. Be able to answer the following questions. You will have to answer a question at the start of class tomorrow: • How is RNA able to move DNA’s information out of the nucleus? • If a strand of mRNA has 1500 bases, how many codons is that? How many amino acids does it call for?

22. Key Concept(s): • DNA Expression begins with its transcription to RNA. • Translation of the genetic code is mediated by tRNA and ribosomes.

23. Making Proteins Protein Synthesis takes place in two steps: • Transcription • Translation Like copying a cookie recipe from a cookbook, then baking the cookies.

24. Making Proteins Part 1- Transcription

25. 1. TRANSCRIPTION-mRNA is made from DNA in the nucleus.

26. Making Proteins

27. How does mRNA get made? 1. RNA polymerase (enzyme) unzips section of DNA. • This section is a GENE-piece of DNA that codes for a protein. 2. RNA polymerase moves along one side of the DNA causing complementary mRNA nucleotides floating in the nucleus to be assembled. 3. RNA polymerase reaches the termination sequence of the gene and releases mRNA and DNA. 4. DNA zips back up; mRNA leaves the nucleus.

28. How does the mRNA only assemble for one section of DNA (one gene)? PROMOTER-beginning of the gene being transcribed. Tells transcription to begin. TERMINATION SEQUENCE-end of the gene being transcribed. Tells the RNA polymerase “let go”.

29. Making Proteins Part 2- Translation

30. Making Proteins Now, how does the template of bases found in the mRNA get used to assemble the protein? This requires “translating” the nucleotide-base language of mRNA to the new, amino acid language of protein synthesis.

31. Making Proteins - Translation TRANSLATION: the second step of protein synthesis; (enzyme assisted!!) the ribosomes ‘read’ the mRNA base sequence in groups of three bases (called a codon).Amino acids are transferred to growing chain by tRNA.

32. Making Proteins - Translation Remember: the tRNA anticodon (sequence of 3 bases) fits into an mRNA codon; when they fit together, that is the spot in the chain the amino acid will occupy.

33. How does the amino acid chain get assembled? 1. mRNA goes to ribosome (proteins made here). 2. Ribosome reads mRNA from start codon to stop codon. 3. As the ribosome reads each codon, the corresponding tRNA will come and match its anticodon to the correct codon. 4. The amino acid carried by the tRNA will be linked to the prior amino acid in the chain. 5. Ribosome repeats 2-4 until itreadsthe stop codon and the process stops.

34. mRNA codon and corresponding amino acids.

35. Making Proteins The diagram below shows a ribosome attach to mRNA, and then move along the mRNA adding amino acids to the growing polypeptide chain.

36. Part 2: Translation

37. Let’s Review: DNA makes RNA makes PROTEIN. It is a 2 - step process Transcription - when DNA makes a copy of the protein recipe. The copy is called mRNA. Translation - when the ribosome makes the protein. Has helper molecules called tRNAthat carry the amino acids. Except for bones, fat, and water, the rest of your body is made of protein.

38. Making Proteins

39. Summary: Let’s watch protein synthesis in ACTION!

40. Be able to answer the following questions. You will have to answer a question at the start of class tomorrow: • Why is protein synthesis important to your life? • What are the two parts of protein synthesis – summarize them VERY BRIEFLY. • What is tRNA’s role in protein synthesis?