RNA & Protein Synthesis

1. RNA & Protein Synthesis Chapter 12-3

2. What is DNA used for? • DNA molecules are the coded instructions used by cells to build proteins (Protein Synthesis) • Proteins are the keys to everything about a cell (looks, functions, growth, passing of genetic information) • Proteins are integral pieces of many cell structures (ex. Cell membrane) and perform many cell functions (regulating reactions, transport, motion, protection, support, communication) • It is the presence of specific proteins that determines how an organism develops & what characteristics an organism will have

3. What is DNA used for? • Proteins are polymers made out of monomers called amino acids • There are 20 different amino acids • Polypeptide – a chain of amino acids • Each protein contains a combination of any or all of the 20 different amino acids • The properties of proteins are determined by the order in which the different amino acids are joined • In order to build a protein, cells must “know” which amino acids to use & what order to put them in • A DNA gene indicates which amino acids to use, and what order to put them in, to build a specific protein

4. What is DNA used for? • DNA molecules contain many individual genes – each gene is the instructions to build one specific protein • DNA only holds the instructions, it does not actually do the building of protein • RNA molecules carry out the process of making proteins

5. Analogy - A dictionary is to words as DNA is to proteins • In order to spell a word, you must know which of the 26 letters to use and what order to put them in • A dictionary holds this information • In order to build a protein, a cell must know which of the 20 amino acids to use and what order to put them in • DNA holds this information

6. The Structure of RNA • RNA (ribonucleic acid) is a long chain of nucleotides • There are 3 main differences between DNA and RNA: • The sugar in RNA nucleotides is ribose • RNA molecules are single-stranded • RNA contains the base uracil(U), but not thymine (T)

7. Types of RNA • There are 3 main types of RNA: • Messenger (mRNA) – an RNA copy of a single gene that “carries” instructions from DNA to ribosome • Ribosomal (rRNA) – makes up ribosome and assembles amino acids making a protein chain • Transfer (tRNA) – transfers amino acids from the cytoplasm to the ribosome for assembly

8. Protein Synthesis – How do cells make protein? • Protein synthesis is a 2-step process: • Transcription – an mRNA copy of a specific gene is made • mRNA is a copy of a single gene, NOT an entire DNA molecule • Translation – information from mRNA is used to build a protein

9. Building a protein is like building a house… You need a master set of instructions for the house in the construction office – this is like the DNA in the nucleus You need a work site to build the house – this is like the ribosome You need a copy of the master plan (blueprint) that can travel to the work site – this is like the mRNA You need workers to deliver the materials to build the house to the job site – this is like the tRNA You need builders to put all the materials together and make the house – this is like the rRNA

10. Building a protein is like building a house… The blueprint is copied and the copy is brought to the work site. Workers bring the correct materials to the work site and set them up according to the information in the blueprint. Builders put everything together building the house. An mRNA copy is made of DNA and the mRNA travels to the ribosome. The tRNA brings the correct amino acids to the ribosome and lines them up according to the information in the mRNA. The rRNA puts the amino acids together forming the protein.

11. The Genetic Code – How does an mRNA molecule “tell” a cell what amino acids to use and where to put them? • The mRNA instructions are called the genetic code • The genetic code is read 3 bases at a time • Each 3-base sequence is equivalent to 1 amino acid • Codon – A 3-base sequence of mRNA that specifies a single amino acid in the protein chain

12. A Triplet Code

13. The Genetic Code - Example • mRNA sequence UCGCACGGU has 3 codons and is read like this: • UCG – CAC – GGU • Each codon stands for a specific amino acid • UCG = serine • CAC = histidine • GGU = glycine • The polypeptide created from that mRNA sequence would look like this: • serine – histidine – glycine

14. Transcription – A closer look • In eukaryotic cells, transcription takes place in the nucleus, in two steps: • RNA polymerase “unzips” DNA at the correct location • RNA polymerase uses one strand of DNA to form a complementary mRNA molecule • DNA: A G C G T G C C A • mRNA: U C G C A C G G U • mRNA can travel to a ribosome where the protein can be assembled • Transcription is like finding the recipe you want in a cookbook and copying it down onto a single sheet of paper – the copied recipe can then be brought to the kitchen

15. Transcription – Animated Movie

16. Transcription – 3D Animation

17. Translation – A closer look • Translation takes place on ribosomes and involves mRNA, rRNA, and tRNA molecules • tRNA is responsible for bringing the correct amino acids to the ribosome • tRNA molecules have amino acids bonded at one end, and three unpaired bases (anticodons) at the other • tRNA anticodons match up with complementary mRNA codons • Different tRNA molecules carry different amino acids

18. Translation – 5 Steps • mRNA attaches to ribosome – translation begins at AUG, the “start” codon • Two complementary tRNA molecules carrying amino acids bond with the first two mRNA codons • The ribosome bonds the amino acids together, and breaks the bonds between the tRNA molecules an amino acids • The first tRNA is released and the ribosome moves down the mRNA to the 3rd codon, where another complementary tRNA brings in a 3rd amino acid which is bonded to the first two • The ribosome continues down the mRNA in this way until a “stop” codon is reached and the finished protein is released

19. Translation – Animated Movie

20. Translation – 3D Animation

21. Transcription – DNA “unzips”

22. Transcription – mRNA is made

23. Transcription – mRNA is made

24. Transcription – mRNA is made

25. Transcription – mRNA is made

26. Transcription – mRNA is made

27. Transcription – mRNA is made

28. Transcription – mRNA is made

29. Transcription – mRNA is made

30. Transcription – mRNA is made

31. Transcription – mRNA is made

32. Transcription – 3D Animation

33. Translation – ribosome attaches to mRNA molecule

34. Translation – translation begins at AUG, the “start” codon

35. Translation – tRNA anticodons bond with complementary mRNA codons

36. Translation - 2 complementary tRNA molecules carrying amino acids bond with the first 2 mRNA codons

37. Translation – the ribosome bonds the 2 amino acids together, breaks the bond between the first tRNA and its amino acid, and brings in a 3rd tRNA

38. Translation – the first tRNA is released, ribosome bonds the 2nd and 3rd amino acids together and breaks bond between 2nd tRNA and its amino acid

39. Translation – ribosome moves down the mRNA one codon

40. Translation – a 4th tRNA bonds with the 4th mRNA codon, bringing in another amino acid to add to the growing polypeptide chain

41. Translation – the 2nd tRNA is released, the3rd and 4th amino acids are bonded together

42. Translation – ribosome moves down the mRNA one codon

43. Translation – ribosome continues down the mRNA in this way until a “stop” codon is reached and the finished protein is released

44. Translation – 3D Animation

45. Why is it important to eat protein? Your body needs 20 different amino acids to make all the necessary proteins Your body is only able to produce 12 of these amino acids on its own The other 8 amino acids come from foods you eat that contain protein (meat, nuts, dairy products, beans, etc.) – These are called essential amino acids because you cannot survive without eating them

46. The bottom line about DNA… No DNA = No Protein = No Cells = No Life Reproduction is all about passing DNA from one cell to another and from one generation of organisms to the next

47. DNA: A T C G mRNA: U A G C How To Transcribe

48. How To Transcribe – Example 1 • DNA: TAC TCA CGC ATC • mRNA: AUG AGU GCG UAG

49. How to Translate • Every 3 mRNA bases together stand for 1 amino acid in the protein chain – these pieces of mRNA are called codons • Use the amino acid chart to figure out which amino acid each codon stands for

50. How to Translate – Example 1 • mRNA: AUG AGU GCG UAG • AUG = Met (start codon) • AGU = Ser • GCG = Ala • UAG = STOP • Protein: Met-Ser-Ala-STOP