BIOS TEST 2 Answers

There is a mutation that is found in E. coli in the repressor that results in a molecule known as a super-repressor because it represses the lac operon permanently. Which of the following characteristics would you expect to observe in such a mutant?

It cannot bind to the inducer

Which of the following molecules helps to "turn off" genes in a cell?

corepressor

Which of the following processes would result from a mutation that deactivates a regulatory gene of a repressible operon in an E. coli cell?

continuous transcription of the structural gene controlled by that regulator

When taken up by a cell, which of the following molecules binds to a repressor so that the repressor no longer binds to the operator?

inducer

Which of the following molecules is a protein produced by a regulatory gene?

repressor

The reason for differences in the sets of proteins expressed in a nerve and a pancreatic cell of the same individual is that nerve and pancreatic cells contain different ________

sets of regulatory protein

According to the lac operon model proposed by Jacob and Monod, what is predicted to occur if the operator is removed from the operon?

The lac operon would be transcribed continuously.

How does the transcription of structural genes in an inducible operon occur?

It starts when the pathway's substrate is present.

Altering patterns of gene expression in prokaryotes would most likely serve an organism's survival by ________.

allowing an organism to adjust to changes in environmental conditions

For a repressible operon to be transcribed, which of the following conditions must occur?

RNA polymerase must bind to the promoter, and the repressor must be inactive.

Which of the following statements defines a genome?

the complete set of an organism's genes and other DNA sequences

Asexual reproduction occurs during which of the following processes?

mitosis

Which of the following statements is correct in comparing sexual and asexual reproduction?

In sexual reproduction, individuals transmit half of their nuclear genes to each of their offspring.

At which stage of mitosis are chromosomes usually photographed in the preparation of a karyotype?

metaphase

Which of the following statements is true of a species that has a chromosome number of 2n = 16?

Each diploid cell has eight homologous pairs of chromosomes

Which of the following statements describes an example of alternation of generations?

A diploid plant (sporophyte) produces a spore by meiosis that gives rise to a multicellular, haploid pollen grain (gametophyte).

A particular organism has 46 chromosomes in its karyotype. Which of the following statements is correct regarding this organism?

It must be an animal.

Which of the following processes might produce a human zygote with 45 chromosomes?

an error in meiotic anaphase occurring in either an egg or sperm

Which of the following characteristics do homologous chromosomes exhibit?

They carry information for the same traits.

Many organisms spend most of their life cycle in the diploid state. If meiosis produces haploid cells, how is the diploid number restored for these types of organisms?

by fertilization

Eukaryotic chromosomes are composed of which of the following macromolecules?

DNA and proteins

Scientists isolate cells in various phases of the cell cycle. They isolate a group of cells that have 1 1/2 times more DNA than G1 phase cells. What is the most likely part of the cell cycle from which these cells were isolated?

in the S phase of the cell cycle

G1 is associated with which of the following cellular events?

normal growth and cell function

What is the name of the microtubule-organizing center found in animal cells as an identifiable structure present during all phases of the cell cycle?

centrosome

In the cells of many eukaryotic species, the nuclear envelope has to disappear to permit which of the following events in the cell cycle?

attachment of microtubules to kinetochores

The mitotic spindle plays a critical role in which of the following processes?

separation of sister chromatids

Metaphase is characterized by ________.

alignment of chromosomes on the equator of the cell

In what way do kinetochore microtubules facilitate the process of splitting the centromeres?

They create tension by pulling toward opposite poles.

Certain cell types normally have several nuclei per cell. How could such multinucleated cells be explained?

The cell underwent repeated mitosis, but cytokinesis did not occur.

At which phase of the cell cycle do centrioles begin to move apart in animal cells?

prophase

Which of the following investigators was (were) responsible for the discovery that in DNA from any species, the amount of adenine equals the amount of thymine, and the amount of guanine equals the amount of cytosine?

Erwin Chargaff

Cytosine makes up 42% of the nucleotides in a sample of DNA from an organism. Approximately what percentage of the nucleotides in this sample will be thymine?

8%

Thymine makes up 28% of the nucleotides in a sample of DNA from an organism. Approximately what percentage of the nucleotides in this sample will be guanine?

22%

It became apparent to Watson and Crick after completion of their model that the DNA molecule could carry a vast amount of hereditary information. Which of the following characteristics of DNA is responsible for this?

sequence of bases

In an analysis of the nucleotide composition of a molecule of DNA, which of the following combinations of base pairs will be found?

A + C = G + T

Hershey and Chase set out to determine what molecule served as the unit of inheritance. They completed a series of experiments in which E. coli was infected by a T2 virus. Which molecular component of the T2 virus actually ended up inside the cell?

DNA

Which of the following statements accurately describes the differences between DNA replication in prokaryotes and DNA replication in eukaryotes?

Prokaryotic chromosomes have a single origin of replication, whereas eukaryotic chromosomes have many

What is meant by the description "antiparallel" regarding the two strands that make up the DNA double helix?

The 5' to 3' direction of one strand runs counter to the 5' to 3' direction of the other strand.

Which of the following statements correctly describes the difference between the leading and the lagging strands of DNA during DNA replication?

The leading strand is synthesized in the same direction as the movement of the replication fork, and the lagging strand is synthesized in the opposite direction.

Why does a new DNA strand elongate only in the 5' to 3' direction during DNA replication?

DNA polymerase can add nucleotides only to the free 3' end.