Molecular Genetics Part 1
Describe the structure of DNA (including structure of sugar and phosphate, recognize bases, purines vs. pyrimidines, what pairs together, what attaches to each carbon: 5’, 3’, 1’)
DNA is made up of a series of units called nucleotides, a nucleotide has three parts sugar (deoxyribose), phosphate group, nitrogenous base, the nitrogenous bases includes pyrimidines and purines, pyrimidines include cytosine and thymine they are single rings, purines include adenine and guanine they are double ring, For numbering the 5 carbons are labeled clockwise from oxygen, the nitrogenous base is on carbon 1, the phophate is on carbon 5, the hydroxyl group is on carbon 3, nucleotides are joined together to form long chains, in nucleotide pairing adenine binds to thymine and guanine to cytosine, hydrogen bonding between nitrogenous base pairs
Explain the antiparallel nature of DNA
Antiparallel structure of the dna is that one end ends in 5 and the other end is 5 which gives direction to the strands, the dna double helix has one strand 5 to 3 and other 3 to 5
Outline the process of DNA replication
The first step of DNA replication is strand separation, proteins bind at replication origin sites on the DNA, DNA helicase breaks hydrogen bonds between base paurs to expose a template strand, topoisomerases relieve tension produced by unwinding the double helix, single strand binding protiens bind to the DNA to stabilize the molecule and prevent strands from annealing at the bases, replication origin is a specific nucleotide sequence that acts as a starting point, a replication fork is a y shaped structure that forms as DNA separates and the replication bubble is the space between the replication fork that is filled with new DNA, During replication new nucleotides are added by a group of enzymes called DNA polymerases, DNA polymerase 3 uses energy of the bonds between the first and second phosphates to drive the dehydration synthesis and add a complementary nucleotide to the new strand, DNA is always synthesized in the 5 to 3 direction because they are anti parallel, RNA primase must lay down RNA primers at he origin so that DNA polymerase knows where to start and goes 5 to 3, Only one stand can build continuously toward the replication fork (leading strand), the other strand goes in short fragments (lagging strand), polymerase 3 synthesizes the short segment of DNA between primers, DNA polymerase 1 replaces the RNA primers with DNA, DNA ligase joins the fragments of the lagging strand, DNA polymerase 2 proofreads newly formed strands and when a mistake occurs it cuts out the nucleotide,At the end 2 identical copies of DNA is present as sister chromatids, the 5’ to 3’ is the leading strand and the 3’ to 5’ is the lagging strand.
Explain how DNA is packaged in eukaryotes and in prokaryotes
In Eukaryotes: DNA is wound around special proteins called histones, histones are positively charged proteins and the negatively charged DNA molecules are attracted to them reducing the space, 8 histone proteins and the wrapped DNA is called nucleosome, further packaging involves coiling strings of nucleosomes into fibers called solenoids and they contain six nucleosomes and these can be supercoiled to form x shaped chromosomes. Prokaryotes: smaller circular pieces of DNA float throughout the cell called conjugation, these small pieces plasmids are able to exit and enter cells when one bacteria is close to another, when this happens the plasmid can pass and the bacterium incorporates it into its genome. Prokaryotes use coiling technique to store DNA, it twists to form tiny coils can keeps going until it forms a tight ball. This is called supercoiling
State the purpose of telomeres and why some DNA is lost with each replication
The RNA primers are normally filled in with DNA by DNA polymerase 1 at the 3’ end of the okazaki fragment, at the very ends of DNA there is no neighboring fragment to fill the gaps because no enzyme works 3’ to 5’ direction, the unpaired nucleotides eventually break off, a lot of basses are lost, to prevent the loss of important information the ends of the chromosomes have stretches of repetitive nucleotide sequences that do not code for anything, these are called telomeres
Explain what is meant by the central dogma? Why doesn’t DNA code for proteins directly?
The central dogma is a fundamental principal of molecular genetics which says that genetic info flows from DNA to RNA to proteins, it says that genetic information is stored as DNA and it is read into the RNA by transcription and the formation of the protien is translation, the dna doesn’t code directly because too much energy is needed, it can damage the DNA and the DNA can be copied many times which can speed protein synthesis
Describe how RNA differs from DNA (3 ways)
RNA contains the sugar ribose and DNA doesn’t, RNA doesn’t contain a nitrogen base thymine but instead contains uracil, RNA is single stranded only half a ladder, at times it can fold into itself and produce regions of complementary base pairs
State the 3 types of RNA and their roles
The first tyoe of RNA is the messenger RNA, the length of the mRNA depends on the gene that is being transcribes, the longer the gene the longer the RNA, Transfer RNA transfers the appropriate amino acid to the ribosome to build a protein as dictated by the mRNA template, the bottom contains an anti codon, the top has corresponding amino acid attached, the ribosomal RNA is a structural component of the ribosome, along with proteins it forms ribosome and assembles polypeptides
Explain how the genetic code is considered universal, redundant and continuous
The genetic code has important characteristics, continuity is the code reads as a long series of 3 letter codons that have no spaces or punctuation and never overlap, redundancy is that there are 64 possible codons but only 20 amino acids, each amino acid has 3 possible codons this allows for the occasional mutation without damage to the protein, universality is that the genetic code is the same in almost all living organisms from bacteria to mammals, this means the same RNA codons correspond to the same amino acids in almost all organisms