Protein Synthesis Lecture Notes

Protein Synthesis DNA Structure • Deoxyribonucleic Acid (DNA): a biological macromolecule that encodes the genetic information for living organisms. o It is capable of self-replication o It is used to make ribonucleic acid (RNA) o The monomers of DNA are nucleotides ▪ Sugar, phosphates, and nitrogenous bases • • The sugar and phosphate make up the backbone of a DNA molecule. Each sugar is bonded to a nitrogenous base. o Adenine (A) o Thymine (T) o Cytosine (C) o Guanine (G) • Each nitrogenous base has a complementary pair that is held together with a hydrogen bond: o A -- T o G–C DNA Replication • In order for genetic information to be passed on to the next cell, generation, or offspring, the DNA has to replicate. o DNA Replication: the process in which DNA makes a duplicate copy of itself. Original Strand of DNA: ATACCG Complimentary Strand of DNA: T ATGGC • Semi-conservative Replication: the process in which each original strand of DNA becomes a template on which a new strand of DNA is constructed resulting in two DNA molecules identical to the original DNA molecule. Transcription • Both prokaryotes and eukaryotes use DNA to store the information to make protein, which performs a variety of structural and regulatory functions for cells. o Proteins are composed of amino acids. • The first process in protein synthesis is transcription. o Transcription: the process in which a strand of messenger RNA (mRNA) is made using the genetic information found in DNA as a template. ▪ mRNA: a type of ribonucleic acid that copies the information found in the DNA and transports that message to ribosomes in the cytoplasm. • RNA is a macromolecule that is similar to DNA, but has a few key differences: o The sugar in the backbone contains an extra oxygen. o RNA is only a single strand o RNA uses Uracil instead of Thymine • Complementary bases are used to produce the mRNA transcript: o DNA: A TCGGCAT o mRNA: UAGCCGUA • Once the mRNA transcript is complete, it will move to a ribosome so it can start translating the DNA’s instructions. o Translation: the process in which the messenger RNA molecule on a ribosome is decoded to produce a sequence of amino acids for protein synthesis. • Codon: a series of three nucleotides that codes for a particular amino acid. • Transfer RNA (tRNA): RNA that transfers specific amino acids to ribosomes for protein synthesis. • A codon table helps us determine which amino acid is used to put together a polypeptide. mRNA Editing • During transcription, the first mRNA transcript might include portions that do not code for a protein. o The mRNA is edited to only include the important parts. o The mRNA can then be put back together in different ways. ▪ One gene can code for multiple proteins! Epigenetics • Although almost all of our cells have the same DNA, different types of cells will turn certain genes on or off depending on the proteins they need to produce. o This process is called epigenetics o Explains why identical twins have differences over time. Organelles • Once the polypeptide has been produced, it must be folded into the correct shape in order to be functional. o The endoplasmic reticulum will help produce, process, and transport protein within the cell. o The golgi apparatus is responsible for the final stages of processing protein for release by the cell. Mutations • Gene Mutation: a permanent alteration that changes a segment of DNA within a gene. o Point Mutation: a single-base substitution causing the replacement of a single-base nucleotide with another nucleotide. ▪ Original: A T C G T T A ▪ Mutation: A T G G T T A • A point mutation can change the final protein being produced. o Missense Mutation: a change in a single nucleotide causes a change in one amino acid, which results in a nonfunctional protein. o Nonsense Mutation: a change in a single nucleotide codes for a premature stop codon, which results in a shortened, often nonfunctional protein. o Silent Mutation: a change in a single nucleotide does not change the amino acid sequence or codes for a different amino acid that does not cause any functional change in the protein. • Deletion Mutation: one or more nucleotides are removed from a section of DNA ▪ Original: A T C G T T A ▪ Mutation: A T G T T A • Insertion Mutation: one or more nucleotides are inserted into a section of DNA ▪ ▪ Original: A T C G T T A Mutation: A T C C G T T A • A deletion or insertion mutation can result in a frame-shift mutation in the final protein. o Frame-shift Mutation: the addition or removal of one or more nucleotides that is not divisible by three, which results in a completely different amino acid sequence than would be normal. ▪ This would cause every amino acid after the insertion or deletion to be different.