University:
Virtual High School
Course:
SBI4U | Biology
Academic year:

2023
Views:

17

Pages:

2
Author:

anon

SBI4U – Grade 12 AP Biology – DNA Test DNA replication – Conservative – parental helix remains intact and a second all new copy is made – Semi Conservative – two strands of the parental helix separates and each functions as a template for synthesis of a new complementary strand – Dispersive – mixture of old and new synthesized parts – DNA replicates Semi conservatively – In prokaryotes since they have circular DNA there is only one origin of replication – In eukaryotes they have linear DNA which allows there to be many origins of replication – There are 5 steps to replicate DNA 1. Helicase (an enzyme) unwinds the helix 2. Single stranded binding proteins (S.S.B.P.) help keep DNA open and unwound 3. The leading strand is synthesized continuously; made 5’ è 3’ but is read as 3’ è 5’ by DNA Pol. III 4. The lagging strand is synthesized in fragments called Okazaki fragments which are made in a process similar to 2 steps forward, 1 step back. RNA primes made by RNA primase flag the DNA Pol. III 5. The DNA Pol I replaces the RNA primers with DNA 6. DNA ligase joins Okazaki fragments 7. Gyrase relieves the stress brought on by the uncoiling (in bacteria). Topoisomerase makes tiny cuts in the DNA to lessen some of the stress caused by over-wound DNA ( in people) Telomeres – Each daughter cell will have a relatively shorter telomere – Human telomeres lose 100 base pairs from telomeric DNA at each mitosis – At this rate after 125 mitotic divisions the telomeres would be completely gone and the cell would therefore die – Exceptions are stem cells, unicellular eukaryotes and cancer cells Protein Synthesis – Proteins are the links between genotype and phenotype – One gene – one protein hypothesis : that each gene dictates production of a specific enzyme – Gene expression – process by which DNA directs protein synthesis, includes two stages – Transcription (at the nucleus) : the synthesis of RNA under the direction of DNA, produces mRNA. Initiation: copying of RNA Elongation : removal of introns and some segments are added Termination : adding the poly A tail – Translation ( at the ribosome) : the synthesis of a polypeptide which occurs under the direction of mRNA DNA -> RNA -> Protein Lac Operon (E-Coli & Lactose) Insulin