Protein Synthesis Athena, Jen, Natalie

DNA versus RNA DNARNA Contains a 5-C sugar 5-C sugar is deoxyribose5-C sugar is ribose Each nucleotide has 1 of 4 nitrogenous bases The bases are adenine, thymine, cytosine and guanine The bases are adenine, uracil, cytosine and guanine Double stranded moleculeSingle stranded molecule

Transcription When a cell needs to make specific polypeptides Transcription factors tell a special enzyme where to bind Upstream from a gene, template strand of DNA, This enzyme is called RNA polymerase It binds to a site packed with adenine and thymine It’s not transcribed but unwinding is very easy Between these bases are only 2 hydrogen bonds; This promoter region’s bonds are not as strong RNA polymerase unwinds the Helix And so the template strand gets complimented Into a single strand of mRNA, There’s no thymine in it But uracil takes its place Polymerase then adds nucleotides In the direction of mRNA’s 5 to 3 prime Just like DNA replication It’s the direction of all genetic creation The DNA strand that is read is called the template Its bases compliment those bases in the RNA A template strand of TACTG Will code for AUGAC But what about the other strand of DNA? It isn’t read at the same time as the polymerase Its coding strand and RNA are identical Except thymine contains the base uracil

Protein synthesis Protein Synthesis Begins in the nucleus mRNA is synthesized Then to the cytoplasm where it binds To a ribosome tRNA finds Amino acids to form a polypeptide Gene to polypeptide

Transcription happens ‘til a terminator sequence Where there’s RNA and DNA dissociation The polymerase then is free to bind With another promoter that it can find Before primary transcript leaves the nucleus It’s been modified because outside of it It would be destroyed by digestive enzymes We wouldn’t want that cause the cell would probably die The 5 prime cap, 7- methylguanosine Is added to the 5 prime end of our primary Transcript, and then a poly-A tail Is added to the 3 prime end so it won’t fail There are parts of our molecule that do not code For a polypeptide, and so... For our protein not to be dysfunctional Introns are cut out by spliceosomes

Introns versus exons Introns: DNA or RNA segments that interrupt the sequence of genes Exons: DNA or RNA segments with important info coding for a protein or peptide sequence

Prokaryotes versus Eukaryotes Eukaryotes have many more genes, spread across multiple chromosomes Prokaryotes have fewer genes all located on one chromosome

Where do we go next? Then out to the cytoplasm mRNA goes Where it meets up with its friend ribosome 60 and 40S subunits then clamp on to the mRNA...

Next up: Translation! In the ribosome there are 2 special sites A is for acceptor P is for peptide Once the subunits have clamped on mRNA reading frame is read in codons Codon: a sequence of 3 nucleotides AUG: the first codon recognized The start codon codes for methionine Whose tRNA enters the P-site tRNA: single stranded nucleic acid It’s shaped like a clover and here’s what happens

Aminoacyl tRNA synthetase Binds one amino acid to the tRNA tRNA also has an anticodon This complements the mRNA codon If the codon transcribed was AUG The anticodon would be UAC Methionine tRNA is in the P site A second tRNA enters the A site The 2 amino acids then peptide bind To begin the formation of a polypeptide The first transfer RNA leaves the ribosome The second one moves over for elongation To the A site another one comes along And it goes on and on and on and on Until comes the end of translation When the A site hits a stop codon For these codons no tRNA exist Elongation is almost finished A release factor protein dismantles the complex The ribosome can bind to more mRNA next Sugars or phosphates may be added at this time And these polypeptides make up proteins and enzymes

Roles of proteins in life 1. Proteins in the cell have a duty as enzymes, which catalyze chemical reactions 2. Proteins are necessary in animals' diets, since proteins are crucial in the formation of amino acids. Without proteins they would not have the nutrients they need to survive. They obtain essential amino acids from food.

Primary Protein Structure The amino acid sequence, determined by the base sequence of the gene that codes for the protein

Secondary Protein Structure Secondary structures have cylindrical alpha helices and planar beta pleated sheets, which form due to H-bonds between the peptide groups of the main chain

Tertiary Protein Structure 3D conformation occurs because of protein folding, which is stabilized by H- bonds, hydrophobic interactions, ionic bonds & disulphide bridges. The bonds are intramolecular, and form between the R groups of different amino acids.

Quaternary Protein Structure 2 or more polypeptide chains associate to form a single protein Ex. Haemoglobin consists of 4 polypeptide chains. Haem group is a prosthetic group Conjugated proteins have a non-polypeptide structure called a prosthetic group

Gene Mutations & their impact Addition/deletion of nucleotides  a shift in the reading frame of the codons in the mRNA. This may alter the amino acid sequence during translation. This can alter the function of the protein. Base Pair substitution: replacement or substitution of a single nucleotide base with another in a DNA/RNA molecule.

Impact of gene mutations A condition caused by mutations in one or more genes is called a genetic disorder. What are some examples of genetic disorders?

Credits Kathleen June, singer songwriter who wrote the protein synthesis song IB Biology textbook Biology 12 textbook