Chapter 18 Flashcards
What is the structure of the purines
double-ring
A and G
What is the structure of the pyrimidines
Single ring
T and C
What did Chargaff discover
DNA from different cells have the same percentage of each of the four bases
Percentages of bases do not vary with…
tissues age, within an individual, nutritional state, and environment
Where does the DNA vary
Species to species
closely related species have similar compositions
What was Chargaff’s most important discovery about DNA base amounts
A=T
G=C
A+G=C+T
What is Watson and Crick’s DNA model
Double-helix
polymer with a backbone of repeating sugars and phosphate groups
what is the diameter of the helix
2nm
What holds together the purine-pyrimidine pairs
Hydrogen bonds
What is significant about the Hydrogen bonds versus the covalent bonds holding the backbone together
The hydrogen bonds can easily be broken for things like replication while leaving the nucleotides intact
How many nucleotides per turn
10
DNA denaturation
The DNA splitting apart which can be induced experimentally with heat
DNA renaturation
the reverse of denaturation where you lower the temp and the DNA comes back together
What determines the melting temperature of DNA
Base composition (GC bases increase temp) and proper pairing (increases temp)
Why do GC base pairs take longer to melt
because they are held together by 3 H bonds rather than the 2 H bonds that hold AT together
Genome
the DNA that contains one complete copy of genetic information
What is B-DNA
Right hand helix
main form of DNA
What is Z-DNA
left hand helix
zig-zag pattern of backbone
What is the function of Z-DNA
process by which some genes are expressed
What is the major groove generally the site for
direct info readout
What is the minor groove important for
target for a few regulatory and structural proteins
What is the nucleoid
region where the bacterial chromosome resides
what is the deal with the bacterial nucleoid
they have super long DNA that is somehow packaged into a tiny space and scientists still aren’t sure how they do it
Histones
group of proteins with strong positive charge
What charge does DNA have
negative
what is chromatin
DNA packaged together with proteins
Nucleosome
proteins are clustered at 2 bp intervals along the DNA molecule in chromatin fibers
(beads on a string)
what is nuclease
enzyme that chops up nucleotides
what is nucleosome structure
8 histone molecules and the core with DNA wrapped around the histones (146 bp DNA makes 2 wraps around core)
What are the levels of chromatin packing from smallest to largest
nucleosomes, fibers, looped domains, hectochromatin, highly condensed (chromosomes)
what are fibers
30nm chromatin fibers made of coiled nucleosomes
what are looped domains attached to
attached to scaffolding proteins
what is the difference between hectochromatin and euchromatin
hecto is more tightly packed and usually not active. It shows up as dark spots in micrographs
What kind of DNA is not present in high amounts in mitochondrial DNA
Non-coding DNA
What are two ways mitochondrial and plastid DNA is more similar to bacterial DNA
Circular DNA and no histones
If every cell contains the genes for every protein in the body, how come we don’t make insulin in our elbows
the nucleus plays a role in controlling gene expression
What is the basic composition of the nuclear envelope
composed of two membranes and nuclear pores
outer membrane of nuclear envelope
continuous with rough ER
inner membrane of nuclear envelope
chromatin is stuck to it
perinuclear space
the space in between the membranes of the nuclear envelope
how are nuclear pores composed
elaborate structure of about 100 proteins
octagonal arrangement
what can pass through nuclear pores
small water soluble molecules pass unimpeded
larger molecules can pass with approval
What are transporters
help move molecules out of nuclear pores
what things can be moved out by transporters
completed mRNA, assembled ribosomal subunits
What things are required for import through nuclear pores
nuclear localization signal, importin, GTP hydrolysis
What things are required for a molecule to be exported through a pore
Nuclear export signal, exportin, GTP
What is the nuclear localization signal/nuclear export signal
structure on molecule that is binding site for importin/exportin
What are two primary functions of the nucleus
RNA synthesis and ribosomal subunit synthesis
What is the nucleolus organizer region
region where the nucleoli form
what is the NOR comprised of
stretch of DNA where multiple copies of the gene for rRNA are located
what is created at the site where all the ends of chromosomes with NOR cluster together
the nucleolus
