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Ch 16: The Molecular Basis of Inheritance - Coggle Diagram
Ch 16: The Molecular Basis of Inheritance
Proteins in DNA
DNA models
dispersive model is when all four strands of DNA following replication have a mixture of old and new DNA
semiconservative model is a type of DNA replication in which the replicated double helix consists of one old strand, derived from the parental molecule, and one newly made strand
conservative model is in which the two parental strands somehow come back together after the process (that is, the parental molecule is conserved)
DNA Replication
DNA replication is the process by which a DNA molecule is copied, also called DNA synthesis
topoisomerase is an enzyme that unwinds and relaxes DNA
helicase is an enzyme that unzips the DNA, making them available as template stands
primase is an enzyme that places a primer to indicate the starting point for polymerase
DNA polymerase is an enzyme that adds DNA bases to the exposed strand and adds 5' to 3' direction
Okazaki fragments are short segments of DNA synthesized away from the replication fork on a template strand during DNA replication
ligase is an enzyme that connects the Okazaki fragments
Proofreading DNA
mismatch repair is the cellular process that uses specific enzymes to remove and replace incorrectly paired nucleotides
other enzymes remove and replace incorrectly paired nucleotides that have resulted from replication errors
nucleotide excision repair is a system that removes and then correctly replaces a damaged segment of DNA using the undamaged strand as a guide
nuclease is an enzyme that that cuts DNA or RNA, either removing one or a few bases or hydrolyzing the DNA or RNA completely into its component nucleotides
DNA is Genetic Material
Viral DNA
bacteriophages are viruses that infect bacteria and are also called phages
also known as bacteria eaters
virus is an infectious particle incapable of replicating outside of a cell, consisting of an RNA or DNA genome surrounded by a protein coat (capsid) and, for some viruses, a membranous envelope
to produce more viruses, a virus must infect a cell and take over the cell’s metabolic machinery
DNA injected by the phage must be the molecule carrying the genetic information that makes the cells produce new viral DNA and proteins
Structure of DNA
covalent sugar phosphate bonds link nucleotides together
hydrogen bonds between bases hold the strands together
Van der Waals interactions between stacked base pairs help hold the molecule together
DNA is antiparallel so the strands are oriented in opposite directions
Possible Base Pairings
purines are nitrogenous bases with two organic rings
examples of purines are adenine and guanine
pyrimidines are nitrogenous bases with a single ring
examples of pyrimidines are thymine and cytosine
purine with a pyrimidine width is consistent with the X-ray data
Chromatin Packing
Nucleosomes
nucleosome is the basic unit of DNA packing, the string between beads is the linker DNA
the histone tail extends outward from the nucleosome and is involved in regulation of gene expression
a nucleosome consists of DNA wound twice around a protein core of eight histones
in the cell cycle and in transcription is where histones leave the DNA only briefly during DNA replication
Histones
histones are proteins that are responsible for the main level of DNA packing in interphase chromatin
positively charged histones bind tightly together to negatively charged DNA
there are 4 types of histones that are found in chromatin and they are H2A, H2B, H3, and H4
Chromatin
chromatin is a complex of DNA and proteins found in eukaryotic cells
euchromatin is the less condensed from of eukaryotic chromatin that is available for transcription
heterochromatin is eukaryotic chromatin that remains highly compacted during interphase and is generally not transcribed