Ch 16 Flashcards
DNA replication
the process by which a DNA molecule is copied
Frederick’s Griffith’s experiment
When he mixed the remains of heat-killed pathogenic bacteria with living nonpathogenic bacteria, some of the living cells became pathogenic. Demonstrated transformation
transformation
change in genotype and phenotype due to assimilation of external DNA
bacteriophages/phages
viruses that infect bacteria
virus
DNA enclosed in protective protein coat
How does a virus reproduce?
reproduce by infecting cell and taking over metabolic machinery
When was Griffith’s experiment?
1928
How did Hershey and Chase demonstrate that nucleic acids were the genetic material?
Used radioactive sulfur to tag the protein and radioactive phosphorus to tag the DNA of T2 phages. Only the phosphorus tagged DNA entered the host cells, so nucleic acids transmitted the genetic information
Chargaff’s rules
- Base composition varies between species
2. The number of A and T bases are equal and the number of G and C bases are equal
double helix
presence of two strands
antiparallel
the strands, specifically the backbones, run in opposite directions
What is a nucleotide made of?
a nitrogenous base, a five carbon ring, and a phosphate group
What is a nucleoside?
just the base and carbon ring
What did Watson and Crick discover?
the double helix
Purines
2 rings, A and G
Pyrimidines
1 ring, T and C
According the complementary base pairing property, which bases pair with each other
A and T
G and C
What holds the sugar-phosphate backbone together?
phosphodiester linkage
What holds base pairs together?
Hydrogen bonds
How many bonds hold A and T together?
2
How many bonds hold G and C together?
3
Why does the twisted helix form?
- negative oxygens in the backbone repel each other
- bond angles
- Van der Waals interactions
A ____ always pairs with a _____
purine and pyrimidine
Name of the five carbon ring
deoxyribose
What is meant by 3’ and 5’?
Refer to the direction of the strand. Named for carbon #3 and carbon #5 on the ring.
What were the two main potential models for DNA replication?
conservative and semiconservative
conservative model
original strands ultimately stay together and the new strands form a separate helix
semiconservative model
each daughter molecule will have one old strand and one new strand
The original parental strand acts as a ______ for replication
template
Meselson and Stahl
Proved the semiconservative model. DNA with light 14N was provided with heavy 15N for replication. When the replicated DNA was centrifuged, it only showed a band of 14N/15N.
origin of replications
short stretches of DNA with a specific nucleotide sequence where replication starts
replication bubble
opening created by the separation of strands from which replication proceeds in both directions
replication fork
Y-shaped region where parental strands are unwound
primer
initial RNA chain synthesized by primase in DNA replication and produced as a starting point for base insertion
DNA polymerases
enzymes that catalyze DNA synthesis by adding nucleotides to a preexisting chain
DNA polymerases only move…
forward from 5’ to 3’ of the synthesized strand
leading strand
continuously adds bases, only one primer needed
lagging strand
synthesized discontinuously and requires multiple primers
How did Chargaff’s rules contribute to the understanding of the DNA double helix
The equal numbers of bases created the idea that each had a complement on a complementary strand.
Why do we use the terms “leading” and “lagging” strands in DNA replication?
Leading continues as the strands unwind, but the lagging strand is delayed because it must wait for enough template to show; therefore it is the same speed but starts later and only works in segments.
What are Okazaki fragments?
the segments of the lagging strand, separated by gaps left by primers
Proofreading
check for base pairing errors as polymerase places them, removes wrong ones and continues
mismatch repair
when polymerase doesn’t catch the error, other enzymes will remove and replace an incorrect pairing
Why might uncorrected “typos” actually be beneficial?
Mutations cause variation that have the potential to makes organisms better fit to live
What are telomeres or telomerase necessary
The gap from the primer at the 5’ end of the DNA cannot be filled in by DNA polymerase because there is nowhere to start insertion. The cell will chop off the single strand left over.
telomeres
buffer nucleotide sequences at the end of eukaryotic chromosomal DNA that postpone erosion.
telomerase
enzymes that catalyzes the lengthening of telomeres, have built-in primers to fill in the gap
chromosome packing
chromosome condenses with protein to fit in the nucleus
chromatin
complex of DNA and protein
histone
positive protein that binds tightly to the negative DNA
nucleosome
basic unit of DNA packing, DNA wound twice around a protein core, unfolded, like beads on a string
Process of packing
DNA Histones Nucleosomes 30 nm fiber Looped domains Metaphase chromosome
Heterochromatin
condensed during interphase
Euchromatin
more dispersed during interphase
