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Chp 16 DNA: Molecular basis of inheritence - Coggle Diagram
Chp 16 DNA: Molecular basis of inheritence
Bacteriophages
a virus that affects bacteria
DNA
Double helix
2 strands
Antiparallel
Chargaffs rules
The base composition of DNA varies between species
In any species the number of A and T bases is equal and the number of G and C bases is equal
A=T
G=C
The basis for these rules was not understood until the discovery of the double helix
DNA vs RNA
DNA
2 strands
A-T, C-G
RNA
1 strand
A-U, C-G
X ray evidence
• Maurice Wilkins and Rosalind Franklin used a technique called X-ray crystallography to study molecular structure
• Watson and Crick’s semiconservative model
of replication predicts that when a double helix replicates, each daughter molecule will have one old strand (derived or “conserved” from the parent molecule) and one newly made strand
Replication begins at particular sites called origins of replication
DNA rplication
Anytime an organism is hurt or developing, DNA replicates
Enzymes
DNA polymerase
adds DNA bases to exposed DNA strands
DNA ligase
connects the Okazaki fragments together
Helicase
Unzips DNA
Primase
enzyme that tells the RNA primer where to start,
the RNA Primer tells DNA polymerase where to begin adding bases
Topoisomerase
relaxes and unwinds DNA
DNA repair
nucleotide excision repair
a nuclease cuts out and replaces damaged stretches of DNA
proofreading
The error rate after proofreading and repair is low but not zero
Sequence changes may become permanent and can be passed on to the next generation
mismatch repair
of DNA, repair enzymes replace incorrectly paired nucleotides that have evaded the proofreading process
Chromosome Structure & Telomeres
Eukaryotic chromosomal DNA molecules have special nucleotide sequences at their ends called telomeres (like caps in the chromosomes)
Telomeres do not prevent the shortening of DNA molecules, but they do postpone the erosion of genes near the ends of DNA molecules
It has been proposed that the shortening of telomeres is connected to aging 9the reason we get older)
There is evidence of telomerase activity in cancer cells, which may allow cancer cells to persist.
• The shortening of telomeres might protect cells from cancerous growth by limiting the number of cell divisions
There is evidence of telomerase activity in cancer cells, which may allow cancer cells to persist.
Chromatin Types
Euchromatin
loosely package DNA
Heterochromatin
promptly packed DNA
