Chapter 6 Rundown

T/F: the leading strand is synthesized in the 5' to 3' direction, but the lagging strand is synthesized in the reverse

FALSE

T/F: because the phosphodiester bond is between the 5' carbons of two deoxyribose molecules, there is no directionality to the DNA molecule

FASE

T/F: The area of DNA that is unwound by DNA helicase is called a replication bubble, and it contains a single replication fork

FASLE

One of the tails invades the nearby double strand of the _______ __________

Nonsister chromatid

Topoisomerase

Prevents supercoiling of the DNA strands ahead of the replication bubble

Eventually junction must be resolved by _________ so that the chromatids can separate and _______ can continue

Revolvase, meiosis

deoxyribonucleotides (dNTPs)

DNA polymerase adds dNTPs onto the 3′ end of the primer, using the template to add complementary base pairs one-by-one.

recombination

the generation of new combinations of alleles by crossing-over and/or independent assortment. (In this chapter, we focus specifically on the generation of new allelic combinations through crossing-over.)

ribonucleic acid (RNA)

a polymer of ribonucleotides that is similar in structure to DNA with the following exceptions: (i) in RNA, the sugar molecule is ribose instead of deoxyribose in DNA; (ii) uracil is present instead of thymine; and (iii) RNA is usually single-stranded.

deoxyribonucleic acid (DNA)

a polymer that contains genetic information made of four different types of subunits called nucleotides. Each nucleotide contains a sugar (deoxyribose), a phosphate group, and one of four nitrogenous bases: either a double-ring purine [adenine (A) or guanine (G)], or a single-ring pyrimidine [cytosine (C) or thymine (T)].

phosphodiester bonds

covalent linkages between adjacent nucleotides in DNA. The phosphate on the 5′ carbon on the sugar ring of an incoming nucleotide is linked to the hydroxyl group on the 3′ carbon of the sugar of the last nucleotide in the growing polymer.

site-specific recombination

crossing-over that occurs between two specific short DNA sequences, due to the action of specific enzymes called recombinases.

antiparallel

describes the opposing orientations of the two strands of double-stranded DNA. DNA polymers have direction - polarity - because at one end (the 5′ end), the 5′ carbon of the sugar on the first nucleotide is not connected to any other nucleotide; while at the other end (the 3′ end), the 3′ carbon of the sugar on the final nucleotide is not connected to any other nucleotide

replication fork

during DNA replication, a Y-shaped area where the top of the Y consists of two unwound DNA strands that are both used as templates for semiconservative DNA replication. The replication fork moves continually in the direction of the stem of the Y as the double-stranded DNA that constitutes the stem continually unwinds. leading strand and lagging

RNA primer

during DNA replication, a short stretch of RNA synthesized by primase enzyme that initiates (primes) DNA synthesis.

DNA ligase

during DNA replication, the enzyme that stitches Okazaki fragments together by forming phosphodiester bonds between adjacent nucleotides

semiconservative DNA replication

each strand of a double-stranded DNA molecule is used as a template for synthesis of a complementary antiparallel DNA strand. Thus, after DNA replication, every double-stranded DNA molecule consists of one old strand (the template) and one newly synthesized strand.

complementary base pairing

formation of hydrogen bonds between specific bases (A−T and G−C) on antiparallel DNA strands. The two DNA strands in double-stranded DNA are complementary; the base sequence of one strand predicts the base sequence of the other strand.

gene conversion

in a heterozygote, change in the base sequence of one allele to that of the other allele due to heteroduplex formation and mismatch repair during recombination.

Holliday junctions

interlocked regions of two nonsister chromatids in recombination intermediates. During recombination, resolvase enzyme separates the two chromatids by breaking one DNA strand of each nonsister chromatid at each of two Holliday junctions.

T/F: a DNA nucleotide is a nitrogenous bases attached to the sugar deoxyribose

FALSE

T/F: a phosphodiester bond connects each nitrogenous base to a deoxyribose

FALSE

T/F: an RNA primer is necessary tho terminate DNA replication at the telomere

FALSE

In resection, the 5' ends at the break are degraded., leaving two ___ ______-_______ _____

3' single-stranded tails

The heteroduplex region is enlarged by ________ ______ as the junctions move outward in a zipper like fashion

Branch migration

The invading strand base pairs with one of the two strands, and the displaced strand forms a __-_______

D-loop

T/F: deoxyribose is derived from ribose by addition of a phosphate group

FALSE

During meiotic prohpase, a ________-________ ______ is made in one of the chromatids on one homolog

Double-stranded break

leading strand and lagging strand

During DNA replication, the leading strand is synthesized continuously in the 5′-to-3′ direction toward the unwinding replication fork. The lagging strand has a polarity opposite to that of the leading strand, and so it must be synthesized discontinuously as small Okazaki fragments that are ultimately joined into a continuous strand.

T/F: DNA contains four nitrogenous bases of which only one is a pyrimidine

FALSE

T/F: Okazaki fragments must be joined together by DNA polymerase II (Pol III)

FALSE

The region between Holliday junctions is termed the _________ region

Heteroduplex

The D loop then base pairs with non-invading 3' Trial, and new DNA synthesis fills in the gaps, forming two X shaped ______ _______

Holliday junctions

DNA polymerase

Synthesizes the daughter strands during DNA replication

T/F: A new DNA strand is always synthesized in the 5' to 3' direction

TRUE

T/F: Okazaki fragments must be joined together by DNA ligase

TRUE

T/F: Pol III can copy only unwound DNA; it can add nucleotides only to the end of an existing chain, and it can move in only one direction

TRUE

T/F: a DNA nucleoside is a nitrogenous base attached to the sugar deoxyribose

TRUE

T/F: a DNA nucleotide is a nitrogenous base attached to the sugar deoxyribose, plus a phosphate group attached at the 5' carbon of deoxyribose

TRUE

T/F: a phosphodiester bond connects nucleotides into a DNA strand or polymer

TRUE

T/F: an RNA primer is necessary to imitates DNA replication by Pol III

TRUE

T/F: because the phosphodiester bond is between the 5' carbon of one deoxyribose and the 3' carbon of the next deoxyribose, DNA has directionality

TRUE

T/F: each replication bubble contains two replication forks, each of which is the point at which the two DNA strands are unwinding from each other

TRUE

T/F: removing O from a ribose produces deoxyribose

TRUE

T/F: the four nitrogenous bases of DNA consist of two purine and two pyrimidines

TRUE

T/F: the lagging strand is synthesized in the 5' to 3' direction, but this direction results in. Okazaki fragments

TRUE

primer

The primer is a segment of RNA (or DNA) that hybridizes to the template and that provides a free 3′ end. DNA polymerase adds nucleotides to this 3′ end in succession; DNA polymerase thus synthesizes new DNA in the 5′-to-3′ direction as the enzyme moves in the 3′-to-5′ direction along the template.

template

The template is stretch of single-stranded DNA to be copied by DNA polymerase through base complementarity.

crossover pathway and noncrossover pathway

after initiation of recombination, crossing-over may occur through Holliday junction formation and resolution (crossover pathway), resulting in two heteroduplex regions, one on each chromatid. Alternatively, formation of Holliday junctions can be aborted by anticrossover helicase enzyme (noncrossover pathway), resulting only in the formation of one heteroduplex region.

DNA polymerase

an enzyme complex that polymerizes DNA in the 5′-to-3′ direction by extending a primer bound to a DNA template. DNA polymerase III extends the RNA primers, and DNA polymerase I fills in the gaps after the RNA primers are removed

heteroduplex

region of DNA where the the two strands originate from different nonsister chromatids. Heteroduplexes form during the process of recombination.