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
Mitosis and the Human Genome Every human cell was produced by mitosis from the original zygote created during fertilization This means every cell has the complete human genome in its nucleus Genome: the complete set of a human’s DNA contained in 46 chromosomes The human genome contains many genes (active segment of DNA), most of which code for proteins
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! Most genes contains info for a particular protein Referred to as coding DNA 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
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
Gene Expression Each cell has the entire genome so why only express certain proteins? Most genes are inactivated Chromatin remodeling and gene silencing are two ways genes are inactivated This is why your eye produces rods and cones while your pancreas produces insulin, not the other way around
Transcription & Translation mRNA can be blocked at the translational level to control gene expression Controls level rather than presence/abs ence
See you in a week! No school on President’s day (Monday after Valentine’s day weekend! Coincidence? You be the judge…) Next week: histology! Chapter 4