Chapter 11 genetics

Chromosome length remains the same throughout the life of eukaryotic organisms.

False While telomerase has been found in all eukaryotes studied, this enzyme is not often active in the somatic cells of adult organisms. Therefore, telomeres of each chromosome do shorten after each cell division.

Why is an RNA primer considered essential for DNA synthesis by DNA polymerase III?

The enzyme requires a free 3′-OH group. Polymerase III requires a free 3′-OH group to begin synthesis of DNA. An RNA primer provides a 3′ hydroxyl group, from which the DNA polymerase can initiate synthesis.

Which of the following enzymes is a reverse transcriptase?

telomerase Telomerase synthesizes DNA repeats from an RNA template. The RNA that serves as a template for this synthesis is part of the telomerase enzyme.

telomerase function

the enzyme responsible for maintenance of the length of telomeres by addition of guanine-rich repetitive sequences. Telomerase activity is exhibited in gametes and stem and tumor cells. ... Besides catalytic telomere elongation, independent telomerase functions can be also involved in cell cycle regulation

A mutation in the rep gene would affect which process in DNA replication?

unwinding the double helix Helicases unwind the double helix, allowing synthesis to proceed along each strand. rep is a gene that codes for DNA helicase.

DNA polymerase

The main function of DNA polymerase is to make DNA from nucleotides, the building blocks of DNA.

What is the role of the Rad51 protein in eukaryotes?

The protein binds single-stranded DNA ends and searches for a homologous sequence.

The overall rate of eukaryotic replication is essentially the same as it is in prokaryotes, even though eukaryotic genomes are hundreds to thousands of times bigger than their prokaryotic counterparts. Which of the following statements could account for this observation?

There are more replication origins in eukaryotes. There are many more origins of replication, which define a replicon, allowing more DNA to be synthesized at any one time.

DNA ligase function

an enzyme that facilitates the joining of DNA strands together by catalyzing the formation of a phosphodiester bond

Which structures can be involved in recombination?

chromatids of homologous chromosomes Chromatids of homologous chromosomes can recombine during meiosis.

The discovery of Okazaki fragments suggested that DNA synthesis is __________.

discontinuous DNA is replicated in a semiconservative manner; however, this was not suggested by the discovery of Okazaki fragments.

In an organism heterozygous for Dd, the four gametes from a single meiosis are usually in a 2:2 ratio. What would explain a 1:3 or 3:1 ratio?

gene conversion Reciprocal recombination would change the linkage arrangements but not the ratio of alleles.

Which event is the consequence of a mismatch in the heteroduplex that forms during general recombination?

gene conversion The Holliday structure is a stable, covalent intermediate formed between homologous DNA duplexes.

Crossing over in prophase I is an example of __________.

homologous recombination Homologous recombination is genetic exchange at the equivalent point of two chromosomes with considerable sequence homology, such as two homologous chromosomes.

DNA Poly III

is the enzyme that performs the 5'-3' polymerase function. Primase - The requirement for a free 3' hydroxyl group is fulfilled by the RNA primers that are synthesized at the initiation sites by these enzymes. (In prokaryotes, like E. coli, DNA Pol III is the major polymerase involved with DNA replication)

If the dispersive model of DNA replication were correct, how many bands would have been observed by Meselson and Stahl after two rounds of replication?

one

In eukaryotes, ARSs serve a function similar to that of __________ in prokaryotes.

oriC Both sequences are origins of replication.

All of the following are required for the synthesis of DNA in vitro by DNA polymerase EXCEPT __________.

ATP DNA polymerase requires a ready supply of substrates to synthesize a growing DNA chain.

Which enzyme catalyzes the addition of nucleotides to a growing DNA chain?

DNA polymerase DNA polymerase catalyzes the addition of nucleotides to a growing DNA chain.

Which DNA polymerase is responsible for the removal of the RNA primers at the origin and at the 5′ ends of the Okazaki fragments in E. coli?

DNA polymerase I RNase H degrades RNA, but not the particular RNA at the end of a DNA chain, during primer removal and replacement.

DNA poly I

During replication, RNase H removes the RNA primer (created by primase) from the lagging strand and then polymerase I fills in the necessary nucleotides between the Okazaki fragments in a 5'→3' direction, proofreading for mistakes as it goes.

All of the following proteins and enzymes function at the origin of replication in E. coli EXCEPT __________.

DNA ligase These proteins are essential for recognition, initial binding, and initial unwinding of the DNA helix at the origin of replication.

Which of the following statements describes the results found by Herbert Taylor, Philip Woods, and Walter Hughes?

Both sister chromatids were labeled after one round of replication. The cells were incubated in 3H-labeled medium during the first round of replication and in nonradioactive medium during the second round.

DNA Poly II

DNA Pol II is the major polymerase for the repairing of inter-strand cross-links.

DNA helicase function

DNA helicase continues to unwind the DNA forming a structure called the replication fork, which is named for the forked appearance of the two strands of DNA as they are unzipped apart. The process of breaking the hydrogen bonds between the nucleotide base pairs in double-stranded DNA requires energy.

Primase function

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.

All of the following are involved in resolution of the Okazaki fragments in E. coli EXCEPT __________.

RNA ligase This activity is essential for the removal of the RNA primer from the 5′ end of the succeeding Okazaki fragment.

Which of the following statements best describes Okazaki fragments?

They are formed in the lagging strand. Okazaki fragments are short sequences synthesized in the lagging strand because DNA polymerase can synthesize only from 5′ to 3′, and the DNA strands are antiparallel.