Protein Synthesis

Learning Objectives By the end of this class you should understand: The purpose and mechanism of codons The two steps of protein synthesis (transcription and translation) The purpose and process of removing introns The major components of transcription and translation and their functions The terminology and function of amino acid chains The process of protein folding and what disorders are caused by folding errors Major pathways of gene expression and regulation

Genetic Information So now we know how DNA bases work  So far, this is just like knowing what a book is made of and what ink it uses  Now we learn to read! Each active coding segment of DNA (a gene) contains info for a protein  But how??

The Composition of Protein Proteins are made of many amino acids strung together like beads Different amino acids have different properties  Some bond with each other  Some repel each other  Some are hydrophobic like oil Our body uses 20 different types

Peptide Bond Each amino acid has a C end and an N end The C and N can make a peptide bond  This links them into a chain  An H 2 O is removed The side chain is what makes the amino acid special

Sample Amino Acids

The Full Set

How To Code For Amino Acids? If your DNA alphabet is only four letters, how many different things can you code for?  1 letter: 4 possibilities  2 letters: 4*4=16 possibilities  3 letters: 4*4*4=64 possibilities One codon is 3 DNA/RNA bases and codes for one amino acid

Complete Codon Chart

Gene Expression Each cell has the entire genome so why only express certain proteins?  Most genes are inactivated Protein in the chromosome can be modified to deactivate the gene  Chromatin remodeling DNA can also be directly methylated block its activity  Gene silencing

DNA to RNA to Protein Permanent information is stored in DNA DNA information is copied using RNA The information is for protein sequences  Alterations to the DNA are faithfully copied and result in different protein sequences  This is mutation!

DNA to RNA The DNA sequence is copied onto a strand of RNA in a process called transcription Referred to as messenger RNA or mRNA  Technically must be processed first to be mRNA Achieved with RNA Polymerase

Promoter Region The DNA sequence “upstream” of the coding sequence is very specific and allows a promoter to attach to the DNA  The promoter is a protein that facilitates the transcription process

RNA Polymerase Remember RNA polymerase causes RNA bases to attach that match their complement RNA sequence must still be processed

mRNA Formation

mRNA Processing To be considered mRNA three things must occur:  The 5' (head) has a methylated cap to prevent it being damaged  The 3' (tail) has a lot of extra As attached to also prevent damage  The introns must be removed

Introns & Exons Some portions of the RNA are removed  Introns stay in the nucleus  Exons form the mRNA that ultimately leaves By removing different introns, the sequence may code for more than one protein!

Outside the Nucleus Once the mRNA is fully prepared it exits the nucleus Ribosomes rapidly attach to it  Ribosomes are made of protein and rRNA  Actually two parts that attach around the mRNA

Translation The ribosome performs translation of the nucleic acid language to the amino acid language Initiation is the attachment of the ribosome, followed by elongation Key player: tRNA watch?v=NJxobgkPEAo

TL;DR The ribosome has spaces to let each tRNA match its anticodon to the mRNA one by one It then catalyzes the chain to move forward, using energy in the process Many ribosomes may attach to a single mRNA and all produce proteins at once!

Protein Folding Once the chain is complete it must still fold into the correct organization The forces between the various amino acids are complex  Includes hydrogen bonds and covalent bonds, as well as repulsion forces

Four Levels of Structure

Protein Folding Note the proteins below, one has more helix forms but the other has more sheets The second protein is called a prion and it is an infectious particle  Smallest infectious particle known to man!  Can force existing regular proteins to switch shape to prion shape

Infectious Protein?? Was only discovered recently (Nobel prize in 1997 for the discovery) A major outbreak in England of Mad Cow's Disease caused by these proteins

Prion Diseases Bovine Spongiform Encephalopathy (Mad-cow disease) is caused by a misfolded protein  Transmissible to humans  Some humans are also genetically at risk to develop natural prion diseases in the same protein Most proteins fold without lethal complications!

Transcription & Translation mRNA can also be blocked at the translational level to control gene expression  Controls level rather than presence/abs ence

RNA Interference Through a complex chemical pathway, RNA can be used to block translation of mRNA  These molecules are called RNAi  Very recent discovery that may provide new pathways for medicine

Have an excellent 4 th of July!