DNA Structure And Replication Flashcards
Sequence of DNA that tells a cell how to assemble amino acids into a particular protein
Gene
Single building block of DNA
Nucleotide
Nucleotide consists of
Deoxyribose
Phosphate group
Nitrogenous bases
(2) are_____, which have a two-ring structure
Adenine (A) and guanine (G)
purines
(2) are_____, which have a single-ring structure.
Cytosine (C) and thymine (T)
pyrimidines
are the information-containing parts of DNA because they form sequences.
bases
Nucleotides join into long chains when chemical bonds form between the deoxyribose sugars and the phosphates. This creates a continuous__________
sugar-phosphate backbone
The opposing orientation of the two nucleotide chains in a DNA molecule is called_____. It derives from the structure of the sugar-phosphate backbone._______ becomes evident when the carbons of the sugars are assigned numbers to indicate their positions in the molecule
antiparallelism
are the informational parts of nucleotides.
DNA bases
________of a nucleic acid consists of a 5-carbon sugar, a phosphate group, and an organic, nitrogenous base (G, A, C, or T).
nucleotide
These specific purine-pyrimidine couples are called
complementary base pairs
Chemical attractions called__________ hold the base pairs together.
They are weak individually, but over the many bases of a DNA molecule impart great strength.
_____hydrogen bonds join A and T, and_____ hydrogen bonds join G and C
hydrogen bonds
Two
three
DNA consists of two chains of_______.
nucleotides
(a)_______ hold the nitrogenous bases of one strand to the nitrogenous bases of the second strand (dotted lines).
Note that the sugars point in opposite directions—that is, the strands are_____.
Hydrogen bonds
antiparallel
The_______ nature of the DNA double helix becomes apparent when the carbons in the sugar are numbered.
antiparallel
The double-stranded, helical structure of DNA gives it great strength—____times the strength of single-stranded DNA, C which would not form a helix.
50
the DNA coils around proteins called
Histones
The bead part is called a_________. It is a little like wrapping a very long, thin piece of thread around your fingers, to keep it from unraveling and tangling.
nucleosome
DNA wraps at several levels, until it is compacted into a______.
Specifically, a nucleosome forms around packets of____ histone proteins (a pair of each of four types).
chromosome
eight
Altogether, the chromosome substance is called_______, which means “colored material.”
chromatin
Chromatin is not just DNA; it is about 30 percent______,
30 percent_______,
30 percent_____, and
10 percent______
histone proteins
DNA binding proteins
DNA
RNA
The DNA double helix is______, its strands running in an opposite head-to-toe manner.
antiparallel
DNA winds tightly about______, forming______, which in turn wind tighter, forming_______.
histone proteins
nucleosomes
chromatin
DNA has _______ replication because each new DNA double helix conserves half of the original
semiconservative
some researchers suggested that DNA might replicate in any of three possible ways:
■
■with one double helix specifying creation of a second double helix, and
■with a double helix shattering into pieces that would join with newly synthesized DNA pieces to form two molecules.
semiconservative
conservative
dispersive
T or F
DNA is highly condensed
True!
DNA spools around_____ of four types of histone proteins, forming_____.
octets
nucleosomes
DNA replication occurs during _____ phase of the cell cycle
S phase
Enzymes called______ unwind and hold apart replicating DNA, enabling other enzymes to guide the assembly of a new DNA strand.
helicases
Human DNA replicates about___ bases per second
50
A site where DNA is locally opened, resembling a fork, is called a
replication fork
DNA replication begins when a_____ breaks the hydrogen bonds that connect a base pair
helicase
hold the two strands apart.
Binding proteins
______, then attracts complementary RNA nucleotides to build a short piece of RNA, called an_____, at the start of each segment of DNA to be replicated.
primase
RNA primer
The RNA primer is required because the major replication enzyme,______, can only add bases to an existing nucleic acid strand. (A______ is an enzyme that builds a polymer, which is a chain of chemical building blocks.)
DNA polymerase (DNAP)
polymerase
_________attracts DNAP, which brings in DNA nucleotides complementary to the exposed bases on the parental strand; this strand serves as a mold, or template.
New bases are added one at a time, starting at the______
RNA primer
unwinds parental double helix.
Helicase
stabilize separate strands.
Binding proteins
adds short primer to template strand.
Primase
binds nucleotides to form new strands.
DNA polymerase
joins Okazaki fragments and seals other nicks in sugarphosphate backbone.
Ligase
________ proofreading activity checks and replaces incorrect bases.
DNA polymerase
Continuous strand synthesis continues in a _____ direction.
5′ to 3′
Discontinuous synthesis produces Okazaki fragments on the _____template.
5′ to 3′
DNAP works directionally, adding new nucleotides to the exposed___′ end of the sugar in the growing strand.
Overall, replication proceeds in a ___________ direction, because this is the only chemical configuration in which DNAP can add bases.
3”
5′ to 3′
______then seals the sugar-phosphate backbones of the pieces, building the new strand.
These pieces, up to 150 nucleotides long, are called_______, after their discoverer
ligase
Okazaki fragments
also “proofreads” as it goes, excising mismatched bases and inserting correct ones.
It also removes the RNA primer and replaces it with the correct DNA bases.
DNA polymerase
________, rewinds any sections of the DNA molecule that remain unwound
annealing helicase
seal the entire sugar-phosphate backbone.
It comes from a Latin word meaning “______.”
ligases
to tie
T or F
DNA replication occurs simultaneously at several points on each chromosome, and the pieces join.
True!
At each initiation site,____ directs synthesis of a short RNA primer, which DNA eventually replaces.______ adds complementary bases to the RNA primer.____ joins the sugar-phosphate backbone.
primase
DNA polymerase
Ligase
DNA is highly coiled, and complexed with protein to form_____.
chromatin
_______form as hydrogen bonds break between base pairs.
____builds short RNA primers, which DNA sequences eventually replace.
Next _______ fills in DNA bases, and ligase seals the sugar-phosphate backbone.
Replication forks
Primase
DNA polymerase
