Transcription and Translation Reading the DNA code What

Transcription and Translation

Reading the DNA code • What is DNA used for? – To make proteins that control growth and repair in a living organism • Steps to making a protein (Protein Synthesis) – DNA RNA Protein • DNA RNA= Transcription - change writing • RNA Protein= Translation - change language

RNA • Similar molecule to DNA – Made up of a long chain of nucleotides • 3 main differences between DNA and RNA 1. Sugar= ribose 2. Single stranded 3. Contains Uracil instead of Thymine

DNA vs. RNA

Why RNA? • What is RNA used for? – Sent outside of the nucleus to be use to make a protein • Why can’t we just send DNA out into the cytoplasm ? – It could get damaged, information could be lost

RNA • RNA a disposable copy of a part of DNA – A working copy of a single gene • Main job used in Protein synthesis

Types of RNA (1) • m. RNA- messenger RNA – carry instructions for making proteins

Types of RNA (2) • t. RNA- transfer RNA – Bring amino acids to the ribosome to construct proteins

Types of RNA (3) • r. RNA- ribosomal RNA – Along with proteins make up Ribosomes

Transcription • Part of a DNA molecule is copied into a single strand of RNA (changing the writing) • Where does transcription take place? – the nucleus animation

Transcription • How does RNA polymerase know what part of the DNA to transcribe? • Promoter region- specific base sequence that RNA polymerase binds to

Key “players” • Transcription factors– Proteins that bind to promoter regions of a gene – “show” RNA polymerase where to bind • RNA polymerase– Binds to DNA – Separates the strands – Uses one strand of DNA as a template to make RNA

RNA polymerase • RNA polymerase binds to promoter regions of DNA indicated by transcription factors • Assembles RNA strand based on template (3’ 5’ strand)

3 main steps 1. RNA polymerase binds to DNA promoter region 2. Elongation- nucleotides are bound together based on the DNA template 3. Termination- RNA polymerase stops transcription

animation

Transcription video • Transcription on hemoglobin

RNA editing • Where does transcription begin? – At the promoter • Extra DNA is transcribed into RNA – DNA contains nucleotides that are not involved in making proteins (introns) • Before RNA leaves the nucleus introns are cut out leaving just exons (sequences that code for proteins)

Translation Protein synthesis

Translation

Proteins • Made of a long chain of amino acids called a polypeptide • 20 different amino acids in the human body – Your body makes about half of them, the other 9 come from your food • The code for making proteins is found on the m. RNA strand

Genetic Code • The m. RNA strand is “read” 3 letters at a time – Each 3 letter sequence is called a codon • Some amino acids are made by more then 1 codon • START codon- indicates the start of the protein • STOP codon- ends translation, does not code of an amino acid

Amino Acid Chart

Translation • Takes place in the Ribosomes 4 steps 1. As the m. RNA strand is read by the ribosome t. RNA brings the correct amino acid – Each t. RNA carries only 1 amino acid – t. RNA has 3 unpaired bases (anticodon) that are complimentary to the m. RNA strand

Translation (cont. ) 2. Amino acid is transferred to the growing polypeptide chain • Each ribosome has 2 binding sites

Translation (cont. ) 3. Ribosome adds a polypeptide bond between the amino acids and breaks the bond between the t. RNA and the m. RNA

Translation (cont. ) 4. Translation continues until a STOP codon is reached – 3 STOP codons • UAA • UAG • UGA animation

Practice

Putting it all together 1. A short length of DNA is copied into m. RNA 2. m. RNA leaves the nucleus and enters the cytoplasm 3. A ribosome reads the strand of m. RNA in sets of 3 and matches the t. RNA with its amino acid 4. Amino acids are released from t. RNA and bond together in order making a polypeptide 5. The polypeptide folds into a functional protein to be used by the organism.