Chapter 16 Flashcards
What is transformation?
a change in genotype and phenotype due to the assimilation of external DNA by a cell
What is a virus, and how does it infect?
DNA enclosed by a protective coat
In order to infect, it must take over a cell’s metabolic machinery
What is the heriditary material?
Nucleic acid
How do nitrogenous base amounts differ? (2)
Different species have different concentrations of specific nitrogenous bases
example- human nucleotide has 30.4% adenine, while sea urchins have 32.8%
What is Chargaff’s rule? (3)
The base composition of DNA varies between species
For each species, the percentage of A and T bases are roughly equal, and the percentages of G and C
bases are roughly equal
What is a double helix?
Presence of two strands
What is antiparallel? (2)
subunits run in opposite directions
The sugar-phosphate backbones of DNA run antiparallel
Why don’t bases pair like-like? (2)
because purines (adenine and guanine) are twice is wide as pyrimidines
The opposite pairs can also bond due to hydrogen bond placement
What is the basic model of DNA replication? (3)
The parental model has two complementary strands of DNA
The two strands separate. Each parental strand serves as a template for a new, complementary strand
Nucleotides complementary to the parental strands connect to form the sugar phosphate backbones of the new daughter strands
What is the semiconservative model? (2)
DNA replication model where the parent strand is used to make a new strand
Correct model
What is the conservative model of replication?
DNA replication where the parent strands somehow come back together after the process
What is the dispersive model?
all four strands of DNA following replication have a mixture of old and new DNA
What is the origins of replication? (2)
a site where the replication of chromosomes begin
Contain a specific sequence of nucleotides
How do bacteria replicate chromosomes? (2)
A bubble separates the circular DNA strands
Replication of DNA proceeds in both directions until the molecule is copied
How do eukaryotic chromosomes replicate? (2)
Multiple origins of replication
Proceeds from the 5’ to 3’ direction
What is the replication fork? (2)
end of a replication bubble
Y-shaped region where the parental strands of DNA are being unwound
What is a helicase?
enzymes that untwist the double helix at the replication forks
What is a single-strand binding proteins?
bind to unpaired DNA strands to keep them from repairing
What is topoisomerase?
relieves strain of double helix by breaking, swiveling, and rejoining DNA strands
What is a primer? (2)
Initial nucleotide chain produced during DNA synthesis
Made of RNA
What is primase?
Synthesizes a primer by starting a complementary RNA chain from a single RNA nucleotide
What is DNA polymerase? (2)
catalyze synthesis of new DNA by adding nucleotides to a preexisting chain
Requires a primer and a DNA template strand
What is dATP? (3)
Nucleotide added consists of a sugar attached to three phosphate groups
Two phosphate groups are lost as each monomer joins the growing end
Releases pyrophosphate
What direction does DNA polymerase add nucleotides?
On the free 3’ end of a primer
What is a leading strand?
end where nucleotides are continuously added
What is a lagging strand? (2)
end where nucleotide are continuously added away from the replication fork
Synthesized discontinuously, in a series of fragments (Okazaki fragments)
How are lagging strands synthesized? (4)
Each fragment is primed separately
DNA pol 3 forms an okazaki fragment
DNA pol 1 replaces the RNA nucleotides of the adjacent primer with DNA nulceotides
DNA ligase form s a bond between the new DNA and the DNA of adjacent Okazaki fragment
How is DNA Replicated? (3)
Helicase unwinds the parental double helix
Molecules of single-strand binding protein stabilize the unwound template strand
Leading strand is synthesized continuously in the 5’ to 3’ direction by DNA pol 3
What is the DNA replication complex?
various proteins that participate in DNA replication
What happens after nucleotides bond with its template? (2)
DNA polymerase proofread each nucleotide
if an incorrect pairing occurs, polymerase removes the nucleotide
What is mismatch repair? (2)
other enzymes remove and replace incorrectly paired nucleotides
When mismatched nucleotides evade proofreading by a DNA polymerase
What is a mutation?
permanent changes to DNA
What is nuclease? (2)
enzymes that cuts out damaged DNA sections
Aka nucleotide excision repair
Why does eukaryotic DNA become shorter? (2)
it cannot add onto 5’ ends
Results with replications of shorter DNA molecules
What are telomeres? (4)
nucleotide sequences that prevent genes from eroding away
Consists of multiple repetitions of one short nucleotide sequence
Prevents the staggered end of the daughter molecule from activating the cell’s system for monitoring DNA damage
Acts as a buffer zone against gene shortening
What is telomerase? (3)
catalyzes the lengthening of telomeres
Not active in human somatic cells
Active in cancerous cells, preventing cell division from shortening telomeres, prolonging cell division
What are histones? (2)
responsible for the first level of DNA packing in chromatin
⅕ of this is positively charged, binding to the negative phosphate backbone of DNA
What are 10 nm fibers made up of? (2)
Nucleosome- beadlike structures making up unfolded chromatin
DNA wound twice around a protein core of 8 histones
Two of H2A, H2B, H3, H4
Linker DNA- the “string” between nucleosome
What are 30 nm fibers? (2)
Interaction between histone tails of one nucleosome and the linker DNA and nucleosomes on either side
H1 histone interacts, causing the 10 nm fiber to coil and fold to form a chromatin fiber
What are 300 nm fibers? (2)
looped domains
30 nm fibers forms loops
What are metaphase chromosomes? (2)
Looped domains coil and fold
700 nm
What are heterochromatin?
visible as irregular clumps under a microscope
What are euchromatin? (2)
less compact chromatin
Used in transcription
