Protein Synthesis Protein Synthesis DNA acts like an
- Slides: 37
Protein Synthesis
Protein Synthesis • DNA acts like an "instruction manual“ – it provides all the information needed to function • the actual work of translating the information into a medium that can be used directly by the cell is done by RNA – RNA= Ribonucleic acid
RNA • Similar molecule to DNA – Made up of a long chain of nucleotides • 3 main differences between DNA and RNA 1. Single stranded 2. Sugar= ribose 3. Contains Uracil instead of Thymine
Types of RNA (1) • m. RNA- messenger RNA – carry instructions for making proteins – Made during transcription
Types of RNA (2) • r. RNA- ribosomal RNA – Along with proteins make up Ribosomes
Types of RNA (3) • t. RNA- transfer RNA – Bring amino acids to the ribosome to construct proteins
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 • RNA a disposable copy of a part of DNA – A working copy of a single gene • Main job used in Protein synthesis Why can’t we just send DNA out into the cytoplasm ? It could get damaged, information could be lost
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
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
animation
Step 1 • Initiation- RNA polymerase binds to DNA promoter region – Promoter region- specific base sequence that RNA polymerase binds to – The promoter contains an initiation site where transcription of the gene begins.
Step 2 • Elongation- nucleotides are bound together based on the DNA template – Assembles RNA strand based on template (3’ 5’ strand)
Step 2 • RNA polymerase arranges nucleotides that are complimentary to the DNA strand being copied. – RNA contains uracil instead of thymine. • A gene can be transcribed many times by multiple RNA polymerase molecules
Step 3 • Termination- RNA polymerase stops transcription • RNA polymerase continues to elongate until it reaches the terminator – Termination= a specific sequence of nucleotides that signals the end of transcription.
Transcription video • Transcription on hemoglobin
RNA editing • Where on the DNA strand 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 • m. RNA leaves the nucleus and is used to create a protein needed by the cell • RNA Proteins – Change the language
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 10 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
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.
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