Chapter 16 - Molecular Basis of Inheritance Flashcards
where is DNA found in bacteria?
it’s supercoiled and found in the nucleoid
how often does DNA make a full turn?
every 3.4 nm
every 10 layers of bases
what are purines? what are pyrimidines?
purine: A/G (large)
pyrimidine: C/T (small)
types of bonds in DNA
covalent bonds between sugar phosphate backbone
hydrogen bonds between bases in the center
what’s the conservative model?
black DNA strand splits, makes white replicates, and then original strands come back together
N15/N15 –> N14/N14 and N15/N15 –> 3N14/N14 and N15/N15
what’s the semiconservative model?
when the double helix replicated, each of the two daughter molecules will have one old strand from the parent and one newly made strand
N15/N15 –> 2N14/N15 –> 2N14/N15 and 2N14/N14
this model was correct!
what’s the dispersive model?
all four strands of DNA following replication have a mixture of old and new DNA (the one with the weird fractions)
how many DNA molecules are in a cell?
46 DNA molecules in a nucleus - one DNA molecules per chromosome
6 billion nucleotide pairs
where does replication start?
particular sites called origins of replication, short stretches of DNA having a specific sequence of nucleotides
what unwinds DNA?
helicases are enzymes that untwist the parent helix at the replication forks
what stabilizes single stranded DNA after it’s been split apart?
after parental strands separate, single-strand binding proteins bind proteins bind to the unpaired DNA strands, keeping them from re-pairing until they’re used as templates
what relieves stress from the untwisting of the double helix?
topoisomerase helps relieve strain by breaking, swirling, and rejoining the parental DNA ahead of the replication fork
where is the primer located?
on the 5’ of the leading strand and at the end of each okazaki fragment
primase synthesizes primer: RNA chain
where does the replication start?
at the 3’ end of the template strand
which DNA polymerase adds nucleotides to the RNA primer?
II
what drives the polymerization reaction?
as each monomer joins the DNA strand, two phosphatee groups are lost as a molecule of pyrophasphate which is then hydrolyzed into two molecules of inorganic phosphate (exergonic reactions)
which functional groups are at the ends of DNA?
3’ is hydroxyl
5’ is phosphate
characteristics of leading strand?
continuously being elongated in the 5’–>3’
only one primer is needed to synthesize the entire strand
what is the lagging strand?
it’s elongated in the direction away from the replication fork
synthesized discontinuously as a series of okazaki fragments
okazaki fragments
DNA pol II forms okazaki fragments but then DNA pol I replaces the RNA nucleotides of the adjacent primer from the 5’ end with DNA nucleotides –> DNA ligase has to actually join the Okazaki fragments into a continuous strand
what molecule proofreads transcription?
DNA polymerases proofread each nucleotide against its template
what happens when there’s damage to a complementary DNA strand during transcription?
the segment containing the damage is cut out by an enzyme called a nuclease –> the gap is filled with nucleotides using the undamaged strand as a template
what is caused by UV radiation?
thymine dimers
what is the name of a DNA repair system?
nucleotide excision repair
shape of eukaryotic vs. prokaryotes DNA?
linear DNA (eukaryotes) circular DNA (prokaryotes)
what keeps eukaryotic DNA from shortening due to primers being located at the 5’ end?
eukaryotic DNA have special nucleotide sequences called telomeres at the ends which don’t contain genes - it’s just a repetition of TTAGGG
what are the protective functions of telomeres?
1) prevents cell from activating cell destruction since staggered ends are usually signs of double breaks
2) act as buffer against genes shortening
what is telomerase?
catalyzes the lengthening of telomeres to restore their original length and compensate for the shortening that occurs during replication
what happens if you have too much telomerase?
telomerase activity is abnormally high in cancerous somatic cells
what’s responsible for the first level of DNA packing
histones
lots of histone’s amino acids are positively charged so they bind tightly to negative phosphate group of DNA
what are the levels of chromatin packing?
10 nm –> 30 nm –> 300nm –> 700 nm
what is a 10 nm fiber?
unfolded chromatin that resembles beads on a string
each bead is a nucleosome (DNA would twice around protein core of 8 histones)
what’s 30 nm fiber?
interaction between histone tails of one nucleosome and the linker DNA and nucleosomes on either side which cause fiber to fold and twist into thicker fibers
interphase!
what is 300 nm fiber?
30 nm fibers form loops called looped domains attached to a chromosome scaffold
what is 700 nm fibers?
metaphase chromosome: looped domains themselves fold and further compact to produce characteristic metaphase chromosome
what is euchromatin?
loosely packed chromatin –> DNA is accessible go the genes in euchromatin can be transcribed
what is heterochromatin?
during interphase a few regions of chromatin are highly condensed –> inaccessible to the machinery
