Protein Synthesis Honors Biology 1 RNA Structure The

Protein Synthesis Honors Biology 1

RNA Structure

The Central Dogma

What are Genes? • A segment of DNA that codes for a specific protein (enzymes are subclass of proteins) – The Beadle and Tatum experiment showed that one gene codes for one protein. • A polypeptide is a chain of covalently bonded amino acids. Covalent bond is also known as a peptide bond in a polypeptide. 5

Sample Protein Functions • Enzymes catalyze chemical reactions • Transport proteins carry small molecules or ions across the plasma membrane • Signaling proteins carry signals from cell to cell • Structural proteins give cells their different shapes • There are many more… 6

What are the similarities & differences between DNA & RNA Characteristic DNA RNA Subunit Sugar Bases # Strands Function Process formed in Location in Eukaryotic Cells 7

The Sugar Ribose

Four RNA Bases Adenine Guanine Uracil Cytosine

The Subunit - Nucleotides A C G U

3 Main Types of RNA 1. Messenger RNA (m. RNA) – takes genetic message from DNA in nucleus to ribosome in cytoplasm 2. Ribosomal RNA (r. RNA) – makes up ribosomes which read the message in m. RNA 3. Transfer RNA (t. RNA) – transfers appropriate amino acid to ribosome when “instructed” 11

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Think-Pair-Share 1. What is the difference between genes and DNA? 2. What are differences between RNA and DNA? 13

Transcription From DNA to m. RNA

Transcription • What is it? Transcription is the process by which RNA is built from a template of DNA • Where does it take place? Transcription takes place in the nucleus of the cell (eukaryotic cells) and in the cytoplasm (prokaryotic cells) **Why does transcription take place in the cytoplasm of prokaryotic cells and not the nucleus?

Transcription

What is Initiation in Transcription? • RNA polymerase binds to a “promoter” gene on the DNA - RNA Polymerase

What is Elongation in Transcription? • RNA polymerase unwinds DNA exposing the nucleotides • RNA polymerase places complementary RNA nucleotides. NOTE: In RNA, uracil, rather than thymine, pairs with adenine. • This elongation forms a single stranded RNA molecule and assembles 5’ to 3’

What is Termination in Transcription? • RNA polymerase releases from the DNA when a “stop” signal is reached in the DNA sequence.

Review…Let’s Whiteboard • Diagram the steps of transcription with both words and a diagram. • You have 2 minutes to review with your group. • Be prepared to present for your group. 22

Let’s build our m. RNA • Where does the DNA molecule separate for transcription? • Keep in mind which direction m. RNA is assembled. • Create your m. RNA using the black licorice. 23

Need to Know… Show me when you are done. Nitrogen Bases: Adenine = green Thymine = pink Cytosine = yellow Guanine = orange Uracil = pink with “U” 24

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Translation is the process by which protein is made from a RNA template. • The m. RNA below is made in nucleus by transcription and edited for translation. codon AUGGGCUUAAAG CAGUGCACGU U m. RNA molecule 26

Why Editing RNA?

Where does m. RNA go? • m. RNA leaves the nucleus through pores and enters the ER. • the m. RNA molecule attaches to a ribosome on the rough ER. Ribosome (composed of r. RNA) AUGGGCUUAAAG CAGUGCACGUU

How to read m. RNA Codon – 3 nucleotide sequence that codes for a specific amino acid. 29

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Deciphering Diagrams For each of the following diagrams you will be given 1 minute to talk with your group to describe what is being shown in the diagram. Use your notes and diagram sheet. Each person in the group must have a number 1 -4. Where are my 1 s? ARE YOU READY? ? ? 33

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What is Initiation in Translation? • The start codon of m. RNA (AUG) signals a t. RNA to bring an amino acid (Methionine) to the ribosome. • The anticodon (three nitrogen base sequence) of the t. RNA (UAC) matches up with the m. RNA codon (AUG). • The large ribosomal subunit attaches to the m. RNA and small ribosomal subunit creating a complex for protein synthesis to proceed. 35

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What is Elongation in Translation? • Another t. RNA molecule comes into the ribosome’s A site bringing another amino acid. • The anticodon of the t. RNA pairs up with the codon from the m. RNA. • A peptide bond (specific type of covalent bond) forms between the amino acids creating a longer polypeptide. • The ribosome moves down the m. RNA to read the next codon and the process continues. • The previous t. RNA separates from the m. RNA and moves back into the cytoplasm. 37

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Translation: Termination • Elongation continues until a stop codon is reached on the m. RNA. • The polypeptide is released into the cytoplasm to become a protein. Interesting Fact… Multiple ribosomes move along the m. RNA to make polypeptide strands, making protein synthesis a more efficient process 39

Translation (Figure from Krogh, Biology, a Guide to the Natural World, 2005)

Think-Pair-Share 1. In transcription, how come the whole DNA molecule is not copied into m. RNA? 2. How does one gene differ structurally from another? 3. Because one gene differs from another, what molecules in the cell will also be different? 41

Let’s Revisit Characteristic DNA RNA Subunit Sugar Bases # Strands Function Process formed in Location in Eukaryotic Cells 42

What are the similarities & differences between DNA & RNA Characteristic DNA RNA Subunit Nucleotide Sugar Deoxyribose Ribose Bases A, T, G, C A, U, G, C # Strands 2 1 Function Process formed in Location in Eukaryotic Cells Codes for all components of organism DNA replication Nucleus Codes for proteins & enzymes Transcription & Translation Nucleus & Cytoplasm 43

Processing & Communicating Translation • Create a flow map representing the steps in translation. • Let’s whiteboard and share them. • Compose a 7 -9 sentence paragraph explaining the steps of translation. 44