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*CHAPTER 16 - Coggle Diagram
*CHAPTER 16
DNA Is the Genetic Material
Stores hereditary information
Passed parent → offspring
Found in chromosomes
Holds instructions for proteins
Early experiments showed DNA, not protein, is genetic material
Stable molecule for long-term information
Structure of DNA (Double Helix)
double helix - twisted ladder
sugar-phosphate backbone
nitrogen bases inside:
A = T
G = C
Hydrogen bonds hold base pairs
A - T = 2 H-BONDS
G - C = 3 H-BONDS
strands are antiparallel (5' - 3- opposite directions)
sequences of bases = genetic code
replication emzymes
Helicase
unwinds DNA
breaks hydrogen bonds
opens replication fork
SSBPs
hold strands apart
prevent re-pairing
Topoisomerase
prevents supercoiling
cuts & rejoins DNA ahead of fork
Primase
builds RNA primer
provides 3' end for DNA polymerase
DNA polymerase I
removes RNA primers
replaces with DNA
Ligase
seals gaps
joins fragments
creates continous strand
Leading vs. Lagging strands
leading strand
built toward fork
continous
needs one primer
follows helices smoothly
lagging strand
built away from work
discontinuous
creates Okazaki fragments
requires many primers
primers removed by DNA pol I
ligase seals fragments
Proofreading and Repair
DNA polymerase checks bases
fixes mismatched
repair enzymes correct errors
keeps mutation rate low
Telomeres & Telomerase
Telomeres
repetitive DNA at chromosome bases
protect coding genes
shorten each division
associated with cellular aging
Telomerase
extends telomeres
active in germ cells, stem cells
overactive in cancer cells