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) mRNA- messenger RNA – carry instructions for making proteins – Made during transcription

Types of RNA (2) rRNA- ribosomal RNA – Along with proteins make up Ribosomes

Types of RNA (3) tRNA- 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 mRNA 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 mRNA strand

Genetic Code The mRNA 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 mRNA strand is read by the ribosome tRNA brings the correct amino acid – Each tRNA carries only 1 amino acid – tRNA has 3 unpaired bases (anticodon) that are complimentary to the mRNA 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 mRNA 2.mRNA leaves the nucleus and enters the cytoplasm 3.A ribosome reads the strand of mRNA in sets of 3 and matches the tRNA with its amino acid 4.Amino acids are released from tRNA and bond together in order making a polypeptide 5.The polypeptide folds into a functional protein to be used by the organism.