Grade 12 Biology

• Helicase helps to unwind the parent DNA.
• Primase synthesizes RNA primer used to generate Okazaki fragments.
• SSB proteins help stabilize single-stranded regions of DNA when it unwinds.
• Topoisomerase II helps relieve strain on double-stranded regions of DNA while it unwinds.
• DNA polymerase I,II,III adds nucleotides to the 3’ end of a growing polynucleotide strand, removes RNA primer and fills gaps between Okazaki fragments, and proofreads newly synthesized DNA.
• DNA ligase joins the ends of Okazaki fragments in the lagging strand.
• Initiation phase begins when several inhibitor proteins bind to the DNA at the origin of replication, and begin to unwind a portion of the helix.
• Elongation phase: DNA polymerase III catalyzes the addition of 1 nucleotide at a time to the 3’ end of each new growing strand.
• DNA polymerase III moved in the 5’ to 3’ direction on the NEW STRAND.
• 3’  5’ strand of og is the leading.
• 5’  3’ strand of og is the lagging.
• Gene expression is the synthesis of a protein based on the DNA sequence of a gene.
• Transcription involves unwinding of the DNA, addition of nucleotides to the growing mRNA strand, and termination caused by a special DNA sequence in the template (antisense) strand.
• In eukaryotes, before transferred across nuclear membrane, a 3’ poly-A tail and 5’ cap are added to the mRNA.
• Regulation of Gene Expression controls whether a gene is active or inactive and the level of activity and amount of protein that is available in the cell.
• Constitutive genes coded by the gene are needed for the survival of the cell.
• Regulation in prokaryotes can occur at 3 different levels: transcription, translation and after protein is synthesized.
• Most common form of regulation is during transcription during initiation.
• In bacteria, many genes are clustered together in a region under control.
• The Polymerase Chain Reaction (PCR) is used to increase the number of copies of DNA from one biological sample in just a few hours.
• The Polymerase Chain Reaction (PCR) was invented by Kary Mullis.
• The Polymerase Chain Reaction (PCR) involves three steps: Denaturation, Annealing, and Elongation.
• During Denaturation, the temperature is cranked to 94-96 degrees Celsius for 20-40 seconds, causing hydrogen bonds to break and the DNA strands to separate.
• During Annealing, the temperature goes down to 50-65 degrees for 20-40 seconds, allowing DNA primers to attach near the 3’ end of the target sequence and the other at the 3’ end of the other strand, both primers are oriented in the 5’ to 3’ direction.
• During Elongation, DNA polymerase binds to the primer-template hybrids and adds complementary nucleotides until it reaches the 5’ end of the template.
• A very special DNA polymerase (Taq polymerase) is used due to its ability to withstand high temperatures.
• After cycle 3, 2/8 molecules exactly match the target molecules.
• Each cycle of the Polymerase Chain Reaction (PCR) takes about 5 min.
• Mieschner - first person to observe DNA, discovered 'nuclein'
• Levene - discovered nucleotides and what they were composed of
• Chargaff - discovered chargaff's rule that # of purines = # of pyrimidines
• Franklin - discovered the double helix through x-ray diffraction
• Watson & Crick - published Franklin's discovery
• Purines are double-ringed
• Pyrimidines are single-ringed