Chapter 16 Flashcards
who introduced the double helical model for DNA in 1953?
James Watson and Francis Crick
what is encoded in DNA?
hereditary information
DNA directs the development of what?
biochemical, anatomical, physiological, and behavioral traits
how was DNA’s role in heredity first discovered?
by studying bacteria and the viruses that infect them
Frederick Griffith did what to discover the genetic role of DNA
worked with two strains of bacterium, one pathogenic and one harmless
-he mixed heat killed remains of the pathogenic strain with living cells of the harmless strain, some living cells became pathogenic
transformation
a change in genotype and phenotype due to assimilation of foreign DNA
bacteriophages (or phages)
viruses that infect bacteria
DNA is a _____ of nucleotides each consisting of a _____ base, a _____, and a ______ group
- polymer
- nitrogenous
- sugar
- phosphate
what are Chargraff’s rules
- The base composition of DNA varies between species
2. In many species the number of A and T bases are equal and the number of G and C bases are equal
nitrogenous base
a nitrogen containing molecule
What does the 5’ end mean and what does the 3’ end mean?
5’ and 3’ refer to the number of carbon in the sugar (deoxyribose) molecule in the DNA
5’ end attaches to a phosphate and if it is an end than it is still attached to a phosphate and it is the 5th carbon in the molecule
3’ end can also attach to a phosphate but if it is an end it is not attached to anything and this is the 3rd carbon in the molecule
a bunch of nucleotides make what?
A DNA molecule:
Structure of DNA back bone…
(nucleotide 1) - (nucleotide 2)
(nucleotide 3) - (nucleotide 4)
what makes up a nucleotide? (3)
a phosphate group, a sugar molecule, and a nitrogenous base (either Thymine, Adenine, Cytosine, and Guanine)
What did Franklin’s X-ray crystallographic images of DNA enable Watson to deduce?
That DNA was helical
- as well as the width of the helix and the spacing of the nitrogenous bases
- the pattern in the photo suggested that the DNA molecule was made up of two strands, forming a double helix
- concluded that there were two outer sugar-phosphate backbones, with the nitrogenous bases paired in the molecules interior
what brings together the two nitrogen bases?
a hydrogen bond
antiparallel
their subunits run in opposite directions
Adenine pairs with….
Thymine
Guanine pairs with….
Cytosine
semiconservative model
when a double helix replicates, each daughter molecule will have one old strand (derived or “conserved” from the parent molecule) and one newly made strand
origins of replication
where the two DNA strands are separated, opening up a replication “bubble”
true or false:
a eukaryotic chromosome may have hundreds or even thousands of origins or replication
TRUE
replication fork
The point at which the two strands of DNA are separated to allow replication of each strand.
Helicases
enzymes that untwist the double helix at the replication forks
Single strand binding proteins
bind to and stabilize single stranded DNA
-prevent helix from reforming during replication
Topoisomerase
corrects “overwinding” ahead of replication forks by breaking, swiveling, and rejoining DNA strands
A DNA replication can only start from
_’ to _’
3’ to 5’
primase
Primase functions by synthesizing short RNA sequences that are complementary to a single-stranded piece of DNA, which serves as its template. It is critical that primers are synthesized by primase before DNA replication can occur.
RNA primer
A primer is a strand of short nucleic acid sequences (generally about 10 base pairs) that serves as a starting point for DNA synthesis. It is required for DNA replication because the enzymes that catalyze this process, DNA polymerases, can only add new nucleotides to an existing strand of DNA.
each nucleotide that is added to a growing DNA strand is a ______ _______
-then dATP supplies _____ to DNA (similar to ATP) in order to lose two ______ groups (as a molecule of pyrophosphate)
- nucleoside triphosphate
- adenine
- phosphate
leading strand
the DNA polymerase synthesizes this continuously
the DNA polymerase adds on nucleotides in what direction?
creating the strand 5’ to 3’ towards the fork!!
lagging strand
this requires more work. DNA polymerase must work in the direction away from the replication fork
Okazaki fragments
a series of segments on the lagging strand
DNA ligase
join together the okazaki fragments
mismatch repair
repair enzymes correct errors in base pairing
how can DNA undergo spontaneous changes
cigarette smoke and X-rays
nucleotide excision repair is when a _____
nuclease cuts out and replaces damaged stretches of DNA
The usual replication machinery provides no way to complete the 5’ ends, so…
repeated rounds of replication produce shorter DNA molecules with uneven ends
*only a problem for eukaryotic cells
telomeres
special nucleotide sequences… they postpone erosion of genes near the ends of DNA molecules….like the blank pages in a book
telomerase
causes the lengthing of telomeres in germ cells
true or false:
shortening of telomeres might protect cells from cancerous growth by limiting the number of cell divisions
True
a bacterial chromosome is a double stranded, circular DNA molecule associated with a small amount of ______
protein
eukaryotic chromosomes have linear DNA molecules assoicated with a large amount of ____
proteins
in bacterium, the DNA is “supercoiled” and found in a region of the cell called the ____
nucleoid
Chromatin
a complex of DNA and protein, is found in the nucleus of eukaryotic cells
is the RNA primer always present in the DNA?
no it is eventually turned into DNA nucleotides with polymerase I
