RNA 2 Translation

Big Picture DNA Gene Protein Trait 4 bases Base paring Double helix Observed physical Characteristics Segment of DNA @ specific location. Instructions for making Proteins

So Far... DNA contains genes (segments of DNA at a specific location) Genes have the instructions to make specific proteins On the gene, an RNA copy of the DNA is made (Transcription)

Quick Review What does a protein do? “Machinery” of the cell: pumps, enzymes, contraction, cytoskeleton... Sure...but what are they?

Proteins are... ...polymers of amino acids A “string of beads” Amino acids have Central carbon atom Amino group Acid Group “Side Group” There are 20 amino acids used in proteins, all with different “side groups.”

Proteins

Protein Chains The order and the properties of the amino acids of the 20 different types give proteins their unique characteristics and abilities.

how do we get from a gene to a protein? It’s all about the code... We need a code that can tell us which amino acids to put where to get the results we want.

Genetic Code It takes 3 DNA nucleotides to “code for” the 20 possible amino acids 1 molecule would give us how many options? 4 different bases in one location: A or T... 4 options or 41 (not enough) 2 molecules would give us...? AA or AT or AG or... 16 options or 42 (not enough) 3 molecules gives us...? 64 options or 43 (plenty)

Using the 64 combinations One combination “starts” the sequence DNA sequence: TAC mRNA sequence: AUG 3 combinations “stop” the sequence DNA sequences: ATT, ACT, ATC mRNA sequences: UAA, UGA, UAG Each 3-letter mRNA sequence is called a codon.

Codons More than one codon can code for an amino acid Alanine = GCU, GCC, GCA, GCG Each codon only codes for one amino acid. GCU is always alanine The redundancy, or back-up duplicates, in the code offer some protection from errors

Amino Acids Asparagine (Asn) Lysine (Lys) Glutamic Acid (Glu) Phenylalanine (Phe) Leucine (Leu) Isoleucine (Ile) Valine (Val) Serine (Ser) Proline (Pro) Threonine (Thr) Alanine (Ala) Tryosine (Tyr) Histidine (His) Glutamine (Gln) Asparagine (Asn) Lysine (Lys) Glutamic Acid (Glu) Aspartic Acid (Asp) Cystenine (Cys) Tryptophan (Trp) Argenine (Arg) Glycine (Gly) Methionine (Met) Start codon

Codons Codons are like words The letters tell you what the word means Which amino acid to use The words for a sentence The combination of amino acids that produces the working protein.

How can we tell what Amino Acid is used?

We read the Amino Acid Chart

How to we Read the Amino Acid (AA) Chart? The chart is read by looking at the codon on the mRNA strand Steps: Read the mRNA codon and then look to chart to find the corresponding amino acid Left, Up, Right “Clockwise starting from the left”

Let’s Practice

DNA Strand: TAC mRNA Strand: AUG Amino Acid: Met (Methionine) DNA Strand: TACGTAAAT mRNA Strand: AUGCAUUUA Amino Acid: [Met][Tyr][Leu]

How do we actually make proteins? Translation

Steps of Making Proteins √ Transcription: mRNA Copy Translation: Protein Synthesis Proteins

Making Proteins We already have: Protein making instructions (mRNA) Translation: Protein Synthesis We already have: Protein making instructions (mRNA) We still need: A Workbench Amino Acids

mRNA to Proteins To start the process, the mRNA is transported to a ribosome (workbench) In the ribosome, the mRNA will provide directions for how to make proteins This process is called translation Translation = the creation of proteins by linking chains of amino acids together (polymers) Occurs in cytoplasm or attached to RER.

mRNA: messenger RNA tRNA: transfer RNA rRNA: ribosomal RNA The Players

Types of RNA mRNA: messenger RNA tRNA: transfer RNA rRNA: ribosomal RNA Types of RNA

Types of RNA mRNA: messenger RNA tRNA: transfer RNA rRNA: ribosomal RNA Types of RNA

Types of RNA mRNA: messenger RNA tRNA: transfer RNA rRNA: ribosomal RNA Types of RNA

The Players mRNA: messenger RNA tRNA: transfer RNA Ribosomes:* rRNA + Proteins

Transfer RNA: (tRNA) It’s job is to transfer amino acids from cytoplasm to ribosome Anticodon is located on the bottom (base pairs to mRNA codon) Must match the mRNA codon exactly in order to pair Amino acid attaches to the top The specific amino acid that the tRNA carries is determined by its anticodon

Ribosome The ribosome has two major parts (called subunits) The large and small subunits Both are made from proteins and ribosomal RNA (rRNA) mRNA is pulled through and read only when the subunits join together Ribosome

Ribosome Reads the mRNA between the subunits Also has space for 3 tRNA Called the P site, A site, E site

Disclaimer: You are not expected to know the exact details of Translation, but it sometimes is helpful to see how the process works to better understand it. I will tell you what you should and should not know.

Translation Three parts Initiation Elongation Termination

Initiation Ribosome locks around the mRNA tRNA pairs with start codon AUG, tRNA amino acid is Met (methionine)

Elongation Codon Recognition, an incoming tRNA binds to the codon in right site Bond formation, the ribosome forms a bond between the new amino acid and the growing protein chain

Elongation Continued the tRNA in the right site is moved to the middle site, taking the mRNA along with it, middle site open to next tRNA The tRNA in the right site moves to the left site and is released from the ribosome, the ribosome shifts the mRNA by one codon

Termination When the ribosome reaches the termination codon (UAG,UAA,UGA) on the mRNA The protein chain in released Subunits separate

Practice Turn to your neighbor... Describe the summary of translation in your own words Switch and have the other neighbor try it Be Prepared to share your summary with the class

Translation Summary mRNA is sent from nucleus to cytoplasm Ribosome attaches to the mRNA in the cytoplasm tRNA’s bring the amino acids to the ribosome It is the anticodon of the tRNA that determines which AA the tRNA carries The first tRNA brings the AA Met to the start codon

Translation Summary The mRNA is read by the ribosome (pulled like a tape) The mRNA codon is matched to the tRNA anticodon If the codon & anticodon match, the AA is added to the protein chain When the stop codon is reached on the mRNA, the ribosome separates and the protein is released

Put it all together Take out a half sheet of paper Explain how a protein is made beginning from DNA Be sure to include Transcription & Translation This is a great level 3 question

Practice Protein Synthesis Snorks