PROTEIN SYNTHESIS. Higher Level

Transcription

1 PROTEIN SYNTHESIS Higher Level

2 Lesson Objectives At the end of this lesson you should be able to 1. Outline the steps in protein synthesis 2. Understand DNA contains the code for protein 3. Understand that enzymes unwind the DNA 4. Understand this code is transcribed to mrna 5. Know the role of RNA polymerase 6. Know the role of a codon

3 Lesson Objectives (cont.) At the end of this lesson you should be able to 7.Know the code is translated on the ribosome 8.Know the ribosome is composed of subunits 9. Understand the amino acids are assembled in the correct order determined by the codons on mrna to synthesise the protein 10. Understand a stop codon on mrna signals the release of the protein

4 Lesson Objectives (cont.) At the end of this lesson you should be able to 11. Know that the protein folds into its functional shape 12. Give the location of protein synthesis 13. Understand the molecular involvement of DNA, mrna, trna, rrna and amino acids in the process of protein synthesis

5 You need: For Protein Synthesis 1. A supply of amino acids cytoplasm 2. Instructions as how to join the amino acids together genetic code 3. An assembly line ribosomes 4. A messenger to carry information from DNA to ribosomes

6 Protein Synthesis - Steps 3 stages: 1. Transcription 2. Translation Remember: DNA RNA Protein

7 RNA is composed of 3 parts 1. Ribose: smaller sugar than deoxyribose of DNA 2. Phosphate 3. 4 Nitrogenous Bases A,G,U,C RNA is single stranded and thus smaller & able to leave the nucleus of the cell

8 Transcription Translation DNA RNA Protein DNA Nuclear membrane Eukaryotic Cell Transcription RNA Processing mrna Translation Ribosome Protein

9 DNA RNA Protein DNA Transcription Translation mrna Ribosome Protein Prokaryotic Cell No nucleus

10 Learning Check What is RNA composed of? How does RNA (ribonucleic acid) differ from DNA (deoxyribonucleic acid)? What are the three stages in Protein synthesis?

11 1. Transcription DNA Nuclear membrane Eukaryotic Cell Transcription RNA Processing mrna Translation Ribosome Protein

12 1. Transcription The transfer of information in the nucleus from a DNA molecule to an RNA molecule. Only 1 DNA strand serves as the template When complete, mrna molecule is released into the cytoplasm

13 Video Clip available in extra material folder

14 Transcription Takes places in the nucleus of the cell The process by which the information from DNA is transferred to RNA. DNA uncoils and unzips. The exposed DNA bases are matched up with RNA bases in the nucleus to form mrna.

15 1. Transcription DNA RNA Polymerase mrna Enzyme

16 This is a molecule of messenger RNA. It was made in the nucleus by transcription from a DNA molecule. codon A U G G G C U U A A A G C A G U G C A C G U U mrna molecule

17 Learning Check What type of RNA molecule is responsible for taking the DNA copy from the nucleus into the cytoplasm What parts of the cell do you find RNA in? Can you outline the stages in transcription?

18 mrna Takes place in the nucleus of the cell The process by which the information from DNA is transferred to RNA. DNA uncoils and unzips. The exposed DNA bases are matched up with RNA bases in the nucleus to form mrna.

19 Types of RNA Three types of RNA: A. messenger RNA (mrna) B. transfer RNA (trna) C. ribosomal RNA (rrna) Remember: all produced in the nucleus!

20 A. Messenger RNA (mrna) Carries the information for a specific protein. Made up of 500 to 1000 nucleotides long. Made up of codons (sequence of three bases) Each codon is specific for one amino acid.

21 A. Messenger RNA (mrna) mrna start codon A U G G G C U C C A U C G G C G C A U A A codon 1 codon 2 codon 3 codon 4 codon 5 codon 6 codon 7 protein methionine glycine serine isoleucine glycine alanine stop codon Primary structure of a protein aa1 aa2 aa3 aa4 aa5 aa6 peptide bonds

22 B. Transfer RNA (trna) Made up of 75 to 80 nucleotides long. Picks up the appropriate amino acid floating in the cytoplasm Transports amino acids to the mrna. Has anticodons that are complementary to mrna codons. Recognizes the appropriate codons on the mrna and bonds to them with H-bonds.

23 C. Ribosomal RNA (rrna) Made up of rrna is 100 to 3000 nucleotides long. Important structural component of a ribosome. Associates with proteins to form ribosomes.

24 Ribosomes Large and small subunits. Composed of rrna (40%) and proteins (60%). Both units come together and help bind the mrna and trna.

25 Ribosomes Large subunit A U G mrna C U A C U U C G Small subunit

26 Learning Check What are the three types of RNA? Where is each type produced? What is the function of each type of RNA?

27 3. Translation DNA Nuclear membrane Eukaryotic Cell Transcription RNA Processing Pre-mRNA mrna Translation Ribosome Protein

28 Video Clip available in extra material folder

29 3. Translation Synthesis of proteins in the cytoplasm Involves the following: 1. mrna (codons) 2. trna (anticodons) 3. rrna 4. ribosomes 5. amino acids

30 Translation In the cytoplasm, translation occurs. The mrna binds to a ribosome. The strand of mrna is pulled through the ribosome three bases at a time, in triplets. Each of these triplets on the mrna strand is called a codon.

31 This is a molecule of messenger RNA. It was made in the nucleus by transcription from a DNA molecule. codon A U G G G C U U A A A G C A G U G C A C G U U mrna molecule

32 A ribosome on the rough endoplasmic reticulum attaches to the mrna molecule. ribosome A U G G G C U U A A A G C A G U G C A C G U U

33 Amino acid trna molecule A transfer RNA molecule arrives. It brings an amino acid to the first three bases (codon) on the mrna. anticodon The three unpaired bases (anticodon) on the trna link up U A C with the codon. A U G G G C U U A A A G C A G U G C A C G U U

34 Another trna molecule comes into place, bringing a second amino acid. Its anticodon links up with the second codon on the mrna. U A C A U G G G C U U A A A G C A G U G C A C G U U

35 Another trna molecule brings the next amino acid into place. A U G G G C U U A A A G C A G U G C A C G U U

36 A peptide bond joins the second and third amino acids to form a polypeptide chain. A U G G G C U U A A A G C A G U G C A C G U U

37 The process continues. The polypeptide chain gets longer. This continues until a termination (stop) codon is reached. The polypeptide is then complete. A U G G G C U U A A A G C A G U G C A C G U U

38 trna Transfer RNA (trna), reads the strand of mrna and translates it into a strand of amino acids. A molecule of trna has at one end a set of three bases that will complement the mrna strand; this is called the anticodon.

39 trna If the 3 base anticodon of the trna complements the 3 base codon of the mrna, they briefly combine. The amino acid is left behind when the trna leaves. As each codon is read, the next trna brings in a new amino acid and the polypeptide (protein) chain grows. This requires enzymes and ATP.

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41 End Product The end products of protein synthesis is a primary structure of a protein. A sequence of amino acid bonded together by peptide bonds. aa2 aa3 aa4 aa5 aa199 aa1 aa200

42 Functional Protein The protein now has to undergo folding and the addition of bonds Folding allows the Protein to reach its 3D (Tertiary Shape) which influences its Function.

43 Learning Check The anticodon UAC belongs to a trna that recognizes and binds to a particular amino acid. What would be the DNA base code for this amino acid?

44 Answer: trna mrna DNA - UAC (anticodon) - AUG (codon) - TAC

45 What have you learned? Can you 1. Outline the steps in protein synthesis 2. Understand that a strand of DNA is copied by transcription 3. Understand the role of mrna 4. Know the function of a ribosome in protein synthesis 5. Understand the process of translation that leads to the formation of a new protein 6. Know that the shape of a protein determines its function

46 End