GRU5 LECTURE POST-TRANSCRIPTIONAL MODIFICATION AND TRANSCRIPTION

Transcription

1 GRU5 LECTURE POST-TRANSCRIPTIONAL MODIFICATION AND TRANSCRIPTION

2 Do Now 1. What was the DNA template for this mrna: 5 -A-A-C-G-U-3? (Write it 5 to 3 ) 2. State the Central Dogma of biology. 3. Name 3 differences between DNA and RNA. 4. What happens during the termination phase of transcription?

3 We have Learned the structure of DNA Talked about DNA replication and all of the complicated vocabulary that goes with it Discussed the Central Dogma and transcription

4 Now today we will learn how mrna is turned into protein through TRANSLATION.

5 Agenda 1. Do-now review 2. Post-transcriptional Processing 3. Translation

6 Objectives 1. SWBAT describe 3 modifications that occur to RNA before it leaves the nucleus. 2. SWBAT explain what alternative splicing is and how it enables one gene to make many proteins. 3. SWBAT convert from DNA to mrna to amino acids and back again. 4. SWBAT accurately describe the 3 stages of translation

7 Post-translational Processing Key Point #1: Once mrna is transcribed, it is called premrna Pre-mRNA must be processed in 3 ways before it can leave the nucleus 1. Addition of the 5 cap 2. Addition of the poly-a tail 3. RNA splicing

8 Fig. 17-3b-3 Nuclear envelope TRANSCRIPTION DNA RNA PROCESSING Pre-mRNA mrna TRANSLATION Ribosome Polypeptide (b) Eukaryotic cell

9 5 Cap and poly-a Tail Key Point #2: The 5 end gets capped off and the 3 end receives a tail of many As, called a poly-a tail. These both 1. Help move mrna out of the nucleus 2. Protect mrna from harmful enzymes 3. Help the ribosomes attach to the 5 end 5ʹ (we ll see this in a second!) Protein-coding segment Polyadenylation signal G P P P AAUAAA AAA AAA 5ʹ Cap 5ʹ UTR Start codon Stop codon 3ʹ UTR Poly-A tail 3ʹ

10 Introns and Exons Key Point #3: Most genes have long noncoding sequences (sections of DNA that do not make it into mrna and protein). Noncoding sequences are called intervening sequences or introns The coding sequences, which will be expressed, are called exons RNA splicing removes introns and joins exons, making an mrna with a continuous coding sequence

11 Fig Pre-mRNA 5ʹ Cap 5ʹ Exon Intron Exon Intron Exon 146 3ʹ Poly-A tail Coding segment Introns cut out and exons spliced together mrna 5ʹ Cap ʹ UTR 3ʹ UTR Poly-A tail

12 Objectives 1. SWBAT describe 3 modifications that occur to RNA before it leaves the nucleus. 2. SWBAT explain what alternative splicing is and how it enables one gene to make many proteins. 3. SWBAT convert from DNA to mrna to amino acids and back again. 4. SWBAT accurately describe the 3 stages of translation

13 n Alternative splicing means that one gene can make many different proteins Alternative Splicing Key Point #4: The same gene can make more than one polypeptide, depending on which segments are treated as exons during RNA splicing The creation of these variations is called alternative splicing

14 Fig DNA Gene Exon 1 Intron Exon 2 Intron Exon 3 Transcription RNA processing Translation Domain 3 Domain 2 Domain 1 Polypeptide

15 Objectives 1. SWBAT describe 3 modifications that occur to RNA before it leaves the nucleus. 2. SWBAT explain what alternative splicing is and how it enables one gene to make many proteins. 3. SWBAT convert from DNA to mrna to amino acids and back again. 4. SWBAT accurately describe the 3 stages of translation

16 Translation Key Point #5: In TRANSLATION, the information in the mrna is read. Then the RIBOSOME uses the info to make a protein. Protein mrna

17 Proteins Key Point #6 Proteins are made of building blocks called amino acids. The number and type of amino acids determine what the protein does.

18 In English, you read words The letters B, I, and O do not mean anything by themselves. BIO together means something. One mrna nucleotide (A, G, C, or U) does not mean anything by itself...

19 The mrna code Key Point #7: Every 3 nucleotides of mrna codes for 1 amino acid. Many amino acids make up a protein. Key Point #8 A codon is a set of 3 nucleotides. A codon table is used to translate mrna sequences.

20 Table of CODONS From your three letter codon, you can use this table to figure out what amino acid it is. Third Letter

21 Let s Practice Codon: UAC What is the amino acid? Tyrosine!

22 STOP! All polypeptides begin with a (AUG)/methionine and end with a STOP codon (UGA, UAA, UAG). After a protein is done being made- it needs to have a signal to stop adding on more amino acids. All mrna chains will end in a STOP codon. This is the end of the protein.

23 Codon Tables Could look a couple of different ways All read the same though

24 Putting it all together Change this DNA sequence into mrna CCATCGGGAACT à DNA GGUAGCCCUUGA à RNA Now split the mrna into codons GGU-AGC-CCU-UGA Finally, make an amino acid sequence Glycine-Serine-Proline-Stop

25 ! What is translation?

26 What is going on in this picture?

27 NOTES NOTES NOTES What is a codon?

28 How many nucleotides make up a codon?

29 Make this DNA into a protein Change this DNA sequence into mrna CACTGAGTGATC GUGACUCACUAG Now split the mrna into codons GUG-ACU-CAC-UAG Finally, make an amino acid sequence Valine-Threonine-Histidine-Stop

30 Objectives 1. SWBAT describe 3 modifications that occur to RNA before it leaves the nucleus. 2. SWBAT explain what alternative splicing is and how it enables one gene to make many proteins. 3. SWBAT convert from DNA to mrna to amino acids and back again. 4. SWBAT accurately describe the 3 stages of translation

31 Translation Key Point #9: Translation has 3 stages, involving some new key molecules: 1. Initiation: The 2 ribosomal subunits, an mrna, and a trna attached to an amino acid come together 2. Elongation: Amino acids are added one at a time to a growing polypeptide chain 3. Termination: The stop codon reaches the A site of the ribosome and a release factor separates all molecules

32 Translation Key Point #10: Two new key players: 1. Transfer RNA (trna): cloverleafshaped molecule that brings amino acids to the mrna at the ribosome 2. Ribosomal RNA (rrna): a structural molecule that binds with proteins to make up the ribosome, which is made in the nucleolus

33 Translation Key Point #10: Two new key players: 1. Transfer RNA (trna): cloverleafshaped molecule that brings amino acids to the mrna at the ribosome 2. Ribosomal RNA (rrna): a structural molecule that binds with proteins to make up the ribosome, which is made in the nucleolus trna molecules Growing polypeptide 5ʹ E P A mrna 3ʹ Exit tunnel Large subunit Small subunit (a) Computer model of functioning ribosome P site (Peptidyl-tRNA binding site) E site (Exit site) mrna binding site E P A A site (AminoacyltRNA binding site) Large subunit Small subunit (b) Schematic model showing binding sites Amino end mrna 5ʹ E Codons Growing polypeptide Next amino acid to be added to polypeptide chain trna 3ʹ (c) Schematic model with mrna and trna

34 EXTRA READING STUDENTS PLEASE REMEMBER TO GO THROUGH THE EXTRA READING PPTS UPLOADED ON THE WEBSITE.