DNA, RNA, and Proteins By Liz LaRosa www.middleschoolscience.com 2011

DNA and Protein Synthesis DNA contains the genetic information to make amino acids Amino acids combine to make proteins These proteins determine the physical traits of an organism and control cellular functions. Proteins do everything, and DNA gets all the credit! Think of them as tiny minions who do all the work

DNA and Protein Synthesis

DNA and Protein Synthesis Codon: three bases code for a specific protein: ex: AAA = Lysine The codons code for 20 amino acids Just like the alphabet has 26 letters to make all the words we know, the 20 amino acids make all the different proteins found in living organisms The codons are the template for protein synthesis, which takes place on the ribosomes (rRNA) in the cytoplasm

Name the Amino Acid: UAU CCG AGU Tyrosine GCA Proline Serine Alanine DNA and Protein Synthesis – Codons and amino acids Name the Amino Acid: UAU CCG AGU GCA Tyrosine Proline Serine Alanine

But… How does the information get from the DNA to the cytoplasm? DNA and Protein Synthesis But… How does the information get from the DNA to the cytoplasm? mRNA

Messenger RNA (mRNA) carries the DNA message out into the cytoplasm where protein synthesis takes place.

DNA and Protein Synthesis - Transcription 1) DNA unzips 2) mRNA (messenger ribonucleic acid) copies info from DNA using base pairings RNA is different from DNA Single stranded, not double stranded Instead of deoxyribose, it has ribose instead of Thymine, it uses Uracil 3) Carries the genetic code from the nucleus to the ribosome in the cytoplasm

DNA and Protein Synthesis - Translation rRNA (ribosomal RNA) attaches to mRNA and starts reading the codons tRNA (transfer RNA) – carries amino acids and attaches them to the growing protein chain When protein production is complete, the ribosome releases the protein chain

DNA and Protein Synthesis - Summary

DNA G A T T A C A C U A A U G U mRNA DNA and Protein Synthesis Practice making mRNA using the DNA template DNA G A T T A C A C U A A U G U mRNA

mRNA CUA AUG UGC DNA and Protein Synthesis Amino acids are linked together in the same order as the codons , creating a protein chain Just like linking letters to make words, linking amino acids makes proteins mRNA CUA AUG UGC Leucine methionine Amino Acid Amino Acid Amino Acid

Translation Translation begins when a ribosome attaches to an mRNA molecule in the cytoplasm. As the ribosome reads each codon of mRNA, it directs tRNA to bring the specified amino acid into the ribosome. One at a time, the ribosome then attaches each amino acid to the growing chain.

Translation Each tRNA molecule carries just one kind of amino acid. In addition, each tRNA molecule has three unpaired bases, collectively called the anticodon—which is complementary to one mRNA codon. The tRNA molecule for methionine has the anticodon UAC, which pairs with the methionine codon, AUG.

Translation The ribosome has a second binding site for a tRNA molecule for the next codon. If that next codon is UUC, a tRNA molecule with an AAG anticodon brings the amino acid phenylalanine into the ribosome.

Translation The ribosome helps form a peptide bond between the first and second amino acids—methionine and phenylalanine. At the same time, the bond holding the first tRNA molecule to its amino acid is broken.

Translation That tRNA then moves into a third binding site, from which it exits the ribosome. The ribosome then moves to the third codon, where tRNA brings it the amino acid specified by the third codon.

Translation The polypeptide chain continues to grow until the ribosome reaches a “stop” codon on the mRNA molecule. When the ribosome reaches a stop codon, it releases both the newly formed polypeptide and the mRNA molecule, completing the process of translation.

Mutations are any changes that take place in DNA: DNA and Mutations Mutations are any changes that take place in DNA: Can be spontaneous or caused by mutagens ex: Chemicals, high temperatures, UV light, radiation Can change the genetic code, and be replicated when forming new body cells. In sex cells, can be passed on to offspring. Mutations can be neutral, beneficial, or harmful ex: Blue eyes – a mutation that occurred 6-10,000 years ago, can be traced back to one ancestor what kind of mutation is that?

DNA and Mutations – Lets looks at different mutations THE DOG BIT THE CAT

Substitution - Replace just one letter: THE DOG BIT THE CAR DNA and Mutations - Substitution THE DOG BIT THE CAT Substitution - Replace just one letter: THE DOG BIT THE CAR

Deletion: Delete just one letter (T): THE DOG BIT HEC AT DNA and Mutations - Deletion THE DOG BIT THE CAT Deletion: Delete just one letter (T): THE DOG BIT HEC AT

Insertion - Add just one letter (E): THE DOE GBI TTH ECA T DNA and Mutations-Insertions THE DOG BIT THE CAT Insertion - Add just one letter (E): THE DOE GBI TTH ECA T Cells have “proof reading” proteins that constantly check the DNA and fix errors, so most are corrected