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The Molecular Basis of Inheritance - Coggle Diagram
The Molecular Basis of Inheritance
DNA is the genetic material
Evidence That Viral DNA Can Program Cells
bacteriophages
A virus that infects bacteria; also called a phage. (
Phages
for short)
Virus
is little more than DNA (or sometimes RNA) enclosed by a protective coat, which is often simply protein.
Experiments with bacteria and with phages provided the first strong evidence that the genetic material is DNA
Watson and Crick deduced that DNA is a double helix and built a structural model. Two antiparallel sugar-phosphate chains wind around the outside of the molecule; the nitrogenous bases project into the interior, where they hydrogen-bond in specific pairs, A with T, G with C.
Many proteins work together in DNA replication and repair
DNA replication
, the copying of DNA
The Basic Principle: Base Pairing to a Template Strand
When a cell copies a DNA molecule, each strand serves as a template for ordering nucleotides into a new, complementary strand
semiconservative model
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.
DNA Replication: A Closer Look
Getting Started
The replication of chromosomal DNA begins at particular sites called origins of replication
Multiple replication bubbles form and eventually fuse, thus speeding up the copying of the very long DNA molecules
replication fork
A Y-shaped region on a replicating DNA molecule where the parental strands are being unwound and new strands are being synthesized.
Helicases
An enzyme that untwists the double helix of DNA at replication forks, separating the two strands and making them available as template strands.
single-strand binding proteins
A protein that binds to the unpaired DNA strands during DNA replication, stabilizing them and holding them apart while they serve as templates for the synthesis of complementary strands of DNA.
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Synthesizing a New DNA Strand
enzymes that synthesize DNA cannot initiate the synthesis of a polynucleotide; they can only add DNA nucleotides to the end of an already existing chain that is base-paired with the template strand.
primer
A short polynucleotide with a free 3′ end, bound by complementary base pairing to the template strand and elongated with DNA nucleotides during DNA replication
primase
An enzyme that joins RNA nucleotides to make a primer during DNA replication, using the parental DNA strand as a template.
DNA polymerases
An enzyme that catalyzes the elongation of new DNA (for example, at a replication fork) by the addition of nucleotides to the 3′ end of an existing chain. There are several different DNA polymerases
Antiparallel Elongation
leading strand
The new complementary DNA strand synthesized continuously along the template strand toward the replication fork in the mandatory 5' to 3' direction.
lagging strand
A discontinuously synthesized DNA strand that elongates by means of Okazaki fragments, each synthesized in a 5' to 3' direction away from the replication fork.
Okazaki fragments
A short segment of DNA synthesized away from the replication fork on a template strand during DNA replication. Many such segments are joined together to make up the lagging strand of newly synthesized DNA.
steps 1-6
1) Primer is added (starting point for DNA copying)
2) DNA pol III adds DNA to start a fragment
3) DNA keeps building the Okazaki fragment
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mismatch repair
The cellular process that uses specific enzymes to remove and replace incorrectly paired nucleotides.
nuclease
An enzyme that cuts DNA or RNA, either removing one or a few bases or hydrolyzing the DNA or RNA completely into its component nucleotides.
nucleotide excision repair
A repair system that removes and then correctly replaces a damaged segment of DNA using the undamaged strand as a guide.
euchromatin
The less condensed form of eukaryotic chromatin that is available for transcription.
heterochromatin
Eukaryotic chromatin that remains highly compacted during interphase and is generally not transcribed.
Chromosomes occupy restricted areas in the interphase nucleus. In interphase cells, most fiber chromatin is loosely arranged (euchromatin), but some is more densely arranged (heterochromatin). Euchromatin, but not heterochromatin, is generally accessible for gene transcription.