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Molecular Basis of Inheritance - Coggle Diagram
Molecular Basis of Inheritance
What DNA Is
DNA structure
DNA is built from nucleotides
A nucleotide has three parts
Nucleotide parts
Sugar called deoxyribose
Phosphate group
Base A T G or C
DNA strands have direction five prime and three prime
Strand ends
Five prime end has free phosphate
Three prime end has free OH group
DNA has negative charge
Reason for negative charge
Phosphate groups carry negative charges
Base pairing and antiparallel
A pairs with T using two hydrogen bonds
G pairs with C using three hydrogen bonds
Two strands run in opposite directions called antiparallel
Examples for DNA structure
A T G C pairs with T A C G
Chromosomes are long DNA molecules
Hydrogen bonds make strands easy to unzip
Enzymes That Build New DNA
Proteins that help copy DNA
Helicase
Unzips DNA by breaking hydrogen bonds at the fork
Single strand binding proteins
Hold single strands apart so they do not rezip
Primase
Makes short RNA primers so DNA polymerase can start
DNA polymerase three
Builds most of the new DNA strand in the five prime to three prime direction
DNA polymerase one
Removes RNA primers and replaces them with DNA
Ligase
Seals gaps in the sugar phosphate backbone
Topoisomerase
Cuts swivels and rejoins DNA to relieve twisting
Important building rule
New DNA can only be added to the three prime end
All DNA synthesis goes from five prime to three prime
Okazaki fragments
Short DNA pieces made on the lagging strand
Each fragment starts with an RNA primer
Ligase joins these pieces into one strand
Examples for enzyme actions
Helicase is like unzipping a jacket
Ligase acts like glue that seals cracks
Topoisomerase prevents DNA from becoming too tightly coiled
How DNA Replication Starts
Beginning of copying DNA
Replication starts at an origin of replication
Prokaryotes have one origin
Prokaryote example
E coli has one circular chromosome
Eukaryotes have many origins
Eukaryote example
Human chromosomes are linear and very long
DNA opens into replication bubbles
Replication bubble details
Each bubble has two replication forks
Forks move in opposite directions
Each strand is used as a template
Why replication works
Hydrogen bonds between bases are weak and can be unzipped
Base pairing rules let each old strand guide building of new strand
Number of bases copied
E coli has about six million bases
Humans have about three point five billion bases
Many origins help copy large DNA faster
Leading and Lagging Strands
Two ways new DNA is built
Leading strand
Features of leading strand
Builds toward the replication fork
Needs only one RNA primer
Made in one smooth continuous piece
Examples for leading strand
Like drawing one long line
DNA polymerase keeps going as helicase unzips more DNA
Lagging strand
Features of lagging strand
Builds away from the replication fork
Needs many RNA primers
Made as short fragments
Examples for lagging strand
Like drawing many short dashes then connecting them
Every time DNA opens more a new fragment must start
Both strands follow five prime to three prime rule