Biology Genetics Grade 12

• Helicase unzips protein at the start of DNA Replication
• Single Stranded Binding Proteins bind to the separated DNA and prevent it from connecting back together
• Topoisomerase prevents DNA from supercoiling
• Primase makes RNA primers, which tell the DNA Polymerase where to start
• DNA Polymerase 3 builds new DNA in the 5' to 3' direction, starting at the RNA Primers
• The lagging strand will have pieces of unconnected DNA called Okazaki Fragments
• DNA Polymerase 1 will replace RNA primers with DNA bases when the primers are no longer needesd
• Ligase fills the gaps between Okazaki Fragments
• The replication of DNA is semi-conservative, meaning each new helix of DNA has one original copy and one new copy
• Chromatin is a double helix form of genetic information
• DNA wraps 8 histones 1.65 times to make a nucleosome.
• DNA is negative and histones is positive, that’s how they pack so tightly
• Adding a H1 Histone to a nucleosome makes a chromatosome
• Chromatosome/nucleosome folds up to make 30nm fiber. Each 6 of a nucleosome is a solenoid.
• If needed for meiosis/mitosis, the fiber will tightly coil to make chromatids
• If a segment of DNA needs to be accessed, the nucleosome alters to allow proteins/enzymes access for RNA replication
• Prokaryotes such as eubacteria typically have one circular chromosome and no nucleus. There are also small circular pieces of DNA called plasmids that can be exchanged between cells acting to increase diversity. This was called

  conjugation.

   
• RNA Polymerase creates a mRNA molecule that is complementary to a specific gene on DNA. Formed in 5’ to 3’ direction.
• pre-mRNA is modified into mRNA, then it exits the nucleus
• As the ribosome moves along the mRNA, a complementary tRNA comes and binds to 3 nucleotide bases, called a codon.
• The 3 bases on a tRNA that correspond to a codon on the mRNA are called the complementary anti-codon
• A specific tRNA has a certain amino acid, which will be added to the next tRNA, eventually making a chain of amino acids (PROTEIN) via peptide bonds.
• AUG specifies amino acid called methionine, which is the start codon
• UAA, UAG, and UGA don’t code for an amino acid, and they make the stop codons.