Flashcards in Molecular Basis of Inheritance Deck (67):
What technique was used to study molecular structure?
Franklin's X-Ray Crystallographic images of DNA enabled Watson to deduce that DNA was
X-Ray images also enabled Watson to deduce the
width of the helix and the spacing of the nitrogenous bases
Pattern in the photo suggested that the DNA molecule was made up of _____ , forming a ______
Watson and Crick built models of a double helix to conform to the _____ and _____ of DNA
Franklin had concluded that there were two outer ______, with the Nitrogenous ______
Nitrogenous bases paired in the molecule's interior
Watson built a model in which the backbones were ____
antiparallel (their subunits run in opposite directions)
Pairing a ___ with a ____ resulted in a uniform width consistent with the X-Ray Data
Purine + Purine =
Pyrimidine + Pyrimidine =
DNA Base Parings
Adenine - Thymine
Guanine - Cytosine
Watson - Crick Model explains
In any organism, the amount of A=T will be equal to the amount of G=C
Since the two strands of DNA are complementary, ____
each strand acts as a template for building a new strand in replication
In DNA replication, the parent molecule unwinds, and two new daughter strands are built based on ____
Predicts that when a double helix replicates, each daughter molecule will have one old strand (derived or "conserved" from the parent molecular) and one newly made strand
Two parent strands rejoin
Each strand is a mix of old and new
Replication begins at particular sites called _____
Origins of Replication
What happens at the origin of Replication?
Two DNA strands are separated, opening up a replication "bubble"
A eukaryotic chromosome may have _____ origins of replications
hundreds or even thousands
Replication proceeds in ____ , until the entire molecule is copied
both directions from each origin
At the end of each replication bubble is a ____
replication fork, a Y-shaped region where new DNA strands are elongating
____ are enzymes that untwist the double helix at the replication forks
_____ bind to and stabilize single-stranded DNA
Single-strand binding proteins
______ corrects "overwinding" ahead of replication forks by braking, swiveling, and rejoining DNA strands
DNA polymerases cannot initiate synthesis of a polynucleotide; they can only ____
add nucleotides to an existing 3' end
The initial nucleotide strand is a short ____
what does Primase do?
Can start a RNA chain from scratch and adds RNA nucleotides one at a time using the parental DNA as a template
The primer is _______ and the _ end serves as te starting point for the new DNA strand
short (5-10 nucleotides long)
What do DNA Polymerase do?
Catalyze the elongation of new DNA at replication fork
Most DNa polymerases require a ____ and a ____
DNA Template Strand
The rate of elongation is what in bacteria and humans?
500 nucleotides per second in bacteria and 50 per second in human cells
A ____ structure of a double helix affects replication
DNa polymerases add nucleotides only to the ____ of a growing strand
Free 3' End
New DNA strand can elongate only in the ____ direction
5' to 3'
Along one template strand of DNA, the DNA polymerase synthesizes a ____
leading strand continuously, moving toward the replication fork
To elongate the other new strand, called the ____, DNA polymerase must work in the direction ___ from the replication fork
Lagging strand is synthesized as a series of segments called ____ , which are joied together by _____
Okazaki Fragmet size in Eukaryotes and Prokaryotes
100-200 n in Eukaryotes and 1000-2000 in prokaryotes
Unwinds parental double helix at replication forks
Single-Strand Binding Protein
Binds to and stabilizes single-stranded DNA until it is used as a template
Relieves overwinding strain ahead of replication forks by breaking, swiveling, and rejoining DNA strands
Synthesizes an RNA primer at 5' end of leading strand, and at 5' end of each Okazaki fragment of lagging strand
DNA Poll III
Using parental DNA as a template, synthesizes new DNA strand by adding nucleotides to an RNA primer or a pre-existing DNA strand
DNA Pol I
Removes RNA nucleotides of primer from 5' end and replaces them with DNA nucleotides
Joins Okazaki fragments of lagging strand; On leading strand, joins 3' end of DNA that replaces primer to rest of leading strand DNA
DNA Polymerases job is to
proofread newly made DNA, replacing any incorrect nucleotide
In mismatch repair of DNA, repair enzymes
correct errors in base pairing
DNA ca be damged by
exposure to harmful chemical or physical agents such as cigarette smoke and X-Rays; it can also undergo spontaneous changes
In Nucleotide excision repair, a nuclease _____
cuts out and replaces damaged stretches of DNA
Can sequence changes become permanent?
Yes, and they can be passed on to the next genertion
Mutations due to sequence changes are the source of ____ upon which natural selection operates
The unusual replication machinery provides no way to complete the ___ , so repeated rounds of replication produce __ DNA molecules
Telomeres are located where?
At the ends of eukaryotic chromosomes
What do Telomeres do?
They are like a protective cap, to ensure all genetic information is passed from one generation to next after replication. Prevents damage to end and joining with adjacent chromosomes
How many times does TTAGGG repeat in Vertebrates?
Average cell divides ____ , losing ____ of telomere with each division.
Aging driven by
What happens when the telomere is too short?
Chromosome reaches "critial length" and can no loger replicate and cell dies (apoptosis)
RNP - Reverse TRabscriptase, carries its own RNA
Telomerase; what is the strand name that is carried in Vertebrates?
Telomerase; Adds telomere repeat _ to 3" end of chromosomes
Why is telomerase activated?
To treat aging and age related diseases
Using Telomerase _____ to treat cancer
Cancer cells cause then to be 10-20 more active. Shorting protect cells from cancerous growth by limiting number of cell divisions
What would happen if chromosomes of germ cells became shorter in every cell cycle?
Essential genes would eventually be missing from the gametes they produce