Motor proteins are able to generate force by ___________.

undergoing a series of conformational changes

Why does an actin thin filament manage to move continuously during a contraction cycle?

All of the myosin heads beat out of synchrony with one another.

In what form are proteins and neurotransmitters usually transported down the axon of a nerve cell?

inside transport vesicles

A(n) ________ motor, like muscle myosin (myosin II) and unlike myosin V, remains in contact with its track, in this case the thin filament, for only a small portion, less than 5 percent, of the overall cycle.

nonprocessive

Nucleation of microtubules takes place rapidly inside a cell, where it occurs in association with a variety of specialized structures called _____________.

All of the provided answers

The central, rod-shaped domain of an intermediate filament is flanked on each side by globular domains of variable size and sequence. What structure forms the core of the central, rod-shaped domain?

alpha-helix

EDTA is a chemical that binds to and removes (chelates) divalent cations from solution. Treatment of isolated axonemes with EDTA leads to the removal of the inner and outer arms extending from the A microtubules of the axoneme. Which of the following statements wouls appear to be true based on this information?

Magnesium ions are required for dynein to bind to the A tubules of the axoneme.

Which of the following appears to be the most extensible?

intermediate filaments

What would happen if you cultured a frog embryo just after gastrulation in the presence of cytochalasin?

The cells of the neural plate elongate normally but do not become constricted as usually happens.

The cross-bridges that hold intermediate filaments together are composed of _______.

plectin

Which of the following molecules is a non-diffusible, integral protein of the plasma membrane that binds specifically to its receptor on the surface of the growth cone? This protein acts as a neuronal guidance factor.

ephrin

Toward the end of gastrulation in vertebrates, the ectodermal cells situated along the embryo's dorsal surface elongate and form a tall epithelial layer that is called the _________

neural plate

Which Microtubule-Organizing Center (MTOC) gives rise to cilia and flagella?

basal bodies

The focal complexes that form near the leading edge of a motile cell exert traction force through their associated __________ and then typically disassemble as the cell moves forward or mature into larger, more contractile focal adhesions.

actin filaments

Which of the following appears to be the most extensible?

intermediate filaments

Treatment of isolated sperm axonemes with 0.6 M NaCl has been shown to remove selectively the outer arms from the A microtubules of the axoneme, leaving the inner arms in place. What would be the most likely effect on the NaCl-treated axoneme when ATP was added to the medium?

The axonemes would beat at about half the rate of the intact axoneme

Structures that move from the cell body of a neuron down the axon toward the neuron terminals are said to move in a(n) _________ direction. radial

anterograde

Which type of cytoskeletal element is described as tough, ropelike fibers composed of a variety of related proteins like keratin?

intermediate filaments

One of the WASP/WAVE family of proteins, specifically WASP, the founding member of the family, is associated with what disease below

Wiskott-Aldrich syndrome

Along which structure do membranous vesicles and organelles typically engage in local movement in the cell periphery of an animal cell?

microfilaments

What is the direct source of energy that powers molecular motors?

hydrolysis of ATP

What motor is associated with microfilaments?

myosin

The first direct measurement of a motor taking single steps was an analysis of ________ stepping using ________.

kinesin, optical trap technology

What happens to the Z lines after contraction of the sarcomere?

The distance between the Z lines decreases

Kinesin movement along a microtubule is said to be highly ________ meaning that it can move considerable distances along an individual microtubule without falling off.

processive

From what structure do cillia and flagella emerge?

basal bodies

What is the minimum number of kinesin heads in contact with a microtubule at all times?

1

If you were to fix a fish keratocyte and stain it with fluorescent antibodies for myosin II, where would you see the myosin II?

in a band where the rear of the lamellipodium joins the rest of the cell

What protein is responsible for intraflagellar transport of IFT trains back toward the cell body?

cytoplasmic dynein

Which of the following is a plausible explanation for the fact that the chemical EGTA [ethylene glycol-bis(β-aminoethyl ether)-N,N,N',N'-tetraacetic acid; also known as egtazic acid] blocks microtubule disassembly?

EGTA binds to Ca²⁺ ions, which are known to induce microtubule depolymerization

A single gene can encode a number of related proteins as a result of a process called _______.

alternative splicing

Which polyploidization mechanism is thought to occur most often in plants?

Two related species mate, forming an organism with the combined chromosomes from both parents.

Alcaptonuria is a genetic disease that is characterized by _________.

urine turning dark upon exposure to the air

How might a transposase be responsible for our ability to ward off infectious disease?

Enzymes involved in antibody gene rearrangement may be derived from a transposase encoded by an ancient DNA transposon.

Where is the RNA polymerase II phosphorylated during its activation?

in the carboxyl-terminal domain (CTD) of the largest RNA polymerase II subunit

What causes unequal crossing over?

A pair of homologous chromosomes aligns imperfectly during meiosis followed by genetic exchange.

What is the supposed function of the loops in tRNAs?

They serve as potential recognition sites for various proteins.

Most of the cellular RNA is in what form?

rRNAs

When a gene has been duplicated one or more times, what are the possible things that can happen to the duplicated gene?

All of these are correct.

The enzyme in eukaryotes that is responsible for the synthesis of RNA from a DNA template is called _______.

DNA-dependent RNA polymerase

With what protein does the double-stranded miRNA become associated? The RNA duplex then is disassembled and one of the single strands is incorporated into a RISC complex.

an Argonaute protein

When a gene has been duplicated one or more times, what are the possible things that can happen to the duplicated gene?

All of these are correct.

You incubate eukaryotic cells for 30 minutes in 3H-uridine and then immediately kill the cells and extract the RNA. Where does the radiolabel appear after this experiment?

in larger RNAs in the cytoplasm

The Law of Independent Assortment states that ____________.

segregation of an allelic pair for one trait has no effect on segregation of alleles for another trait

Why does it make sense that cells would be able to recognize dsRNAs as undesirable using a mechanism such as RNAi?

dsRNAs are not produced by the cell's normal genetic activities.

The nucleotide at which transcription is initiated is called _____.

+1

Which of the following is an RNA nucleoside?

cytosine and ribose

Different versions of a gene are called _________.

alleles

In mammalian cells, radiolabeled methyl groups appear first in what size RNA molecule that is a precursor to rRNA?

45S RNA

The genetic code has 64 codons, while there are only 20 amino acids. Thus, some amino acids are coded for by more than one codon. As a result, the genetic code is said to be ________.

degenerate

The surfaces of the two ribosomal subunits that face one another contain the binding sites for the mRNA and incoming tRNAs and are thus of key importance for the function of the ribosomes. The fact that these surfaces consist largely of RNA supports what proposal?

the proposal that primordial ribosomes were composed exclusively of RNA

What chemical group is attached to the first methionine in a polypeptide chain in prokaryotes?

a formyl group

In a right-handed double helix, if one looks down the central axis of the molecule, _________.

each strand follows a clockwise path as it moves away from the observer

What is the supposed function of the loops in tRNAs?

They serve as potential recognition sites for various proteins.

The reverse reaction of nucleic acid synthesis almost never happens. What prevents it?

Nucleic acid synthesis is coupled to the highly exergonic pyrophosphate hydrolysis.

What provides the energy that drives the polymerization of RNA from a DNA template?

ribonucleoside triphosphates (NTPs)

Mammalian oocytes have recently been shown to produce siRNAs. What are they called?

endo-siRNAs

Which type of enzyme is essential for processes like DNA replication and transcription to prevent excessive supercoiling from developing as the complementary strands of the DNA duplex separate and unwind?

topoisomerase

which of the following is normally associated w the cilia of organisms from protists to mammals?

a 9+2 pattern

a shift in concentration or activity of which type of proteins can cause a shift in the equilibrium between actin monomers and ploymers?

monomer-sequestering proteins

The _______ link is an elastic protein-based linkage that connects tubulin doublets in cilia and flagellae. The resultant bridges play an important role in ciliary and flagellar movement by limiting the extent that adjacent doublets can slide over one another. The resistance to sliding provided by these bridges causes the axoneme to bend.

nexin

What is a major influence in determining the organization and behavior of actin filaments inside cells?

actin-binding proteins

What is the name of the largest protein yet discovered? It extends from the M line in the center of the sarcomere along the myosin filament and past the A band to terminate at the Z line.

Titin

What provides the energy that drives sarcomere contraction?

ATP

In cell biology and with respect to microtubules, intermediate filaments, and microfilaments, the word "dynamic" means ________.

ever-changing

Expression of the Actin assembly-inducing protein (ActA) in previously non-motile strains of bacteria allowed for the _______________ and ___________ characteristic of pathogenic strains.

formation of actin comet tails, motility

How are microtubules thought to affect cell shape in plants?

Microtubules of the plant cell cortex are thought to affect the movement of cellulose-synthesizing enzymes in the cell membrane, which, in turn, affect cell wall growth and shape.

The protein FtsZ acts in the bacterial cell analogously to the ______ cytoskeleton during eukaryotic cytokinesis and is a(n) _________ homolog that is found in nearly all prokaryotic cells.

actin, tubulin

Which of the following does not describe the types of microfilament organization normally seen in cells?

cylindrical conglomerations

Which of the following molecular motors is associated with microfilaments?

myosins

Which of the following molecules is diffusible and serves as an attractant for axons growing within the early embryo?

netrin

For a long time, it was thought that cilia were unimportant or _________, despite their presence on almost all cells. This idea arose because the cilia on most cells are non‐motile, and it was assumed that motility was the key function of cilia.

vestigial

The protein _________ has been implicated in regulating the shape of some bacterial cells; it is expressed in rod-shaped and helical bacteria. It resembles __________in structure.

MreB, actin

Which protein below is often a component of intermediate filaments?

keratin

What chemical below is known to bind to free actin monomers and block their incorporation into the polymer?

latrunculin

Along which structure do membranous vesicles and organelles typically move long distances in an animal cell?

microtubules

The deletion of the creS gene in Caulobacter crescentus results in __________.

cells that look like straight rods

Which of the following words best describes the structure of an actin filament?

double helix

The sperm basal body becomes ______________.

a centriole during the first mitotic division of the fertilized egg

What kind of cells seems to rely mostly on microfilaments for long-distance transport of cytoplasmic vesicles and organelles, probably due to the restricted microtubule distribution in these cells?

plant cells

The protein ParM has been shown to play a role in plasmid segregation during bacterial cell division analogous to the action of ___________ during mitosis and is structurally similar to __________.

microtubules, actin

Which element of the cytoskeleton is found in the cytoplasm and the nucleus?

intermediate filaments

As life was first evolving, what molecule is thought to have performed double duty as the genetic material and performing catalysis of chemical reactions?

RNA

Which of the following is a DNA nucleotide?

a phosphate group, guanine and deoxyribose

What is the significance of the variability of the third nucleotide in a codon?

The same tRNA can recognize more than one codon.

What features set pre-rRNAs apart from other RNA transcripts?

pseudouridine residues and methylated nucleotides

What was the new name of Beadle and Tatum's hypothesis after it was discovered that some enzymes were composed of more than one polypeptide chain?

the One Gene – One Polypeptide hypothesis

While RNA polymerase is a processive enzyme that remains attached to the DNA over long stretches of template, it must be associated _______ enough so that it can move from nucleotide to nucleotide along the template.

loosely

The information encoded in DNA resides in ________.

the DNA base sequence

What word below refers to a pair of homologous chromosomes?

bivalent

Which of the following is not required for protein synthesis?

anions

Transposase is an enzyme that __________.

catalyzes transposon excision from a donor DNA site and its subsequent insertion at a target DNA site

Which of the following is not required for protein synthesis?

anions

The surfaces of the two ribosomal subunits that face one another contain the binding sites for the mRNA and incoming tRNAs and are thus of key importance for the function of the ribosomes. The fact that these surfaces consist largely of RNA supports what proposal?

the proposal that primordial ribosomes were composed exclusively of RNA

DNA sequences in bacteria that on rare occasions moved from one place in the genome to another are called ________.

transposons

You are looking at an electron micrograph of several transcriptional units for rRNA. How can you tell where the transcription initiation site is?

It is near the shortest nascent transcripts.

The greatest variability among codons that specify the same amino acid occurs _________.

in the third nucleotide of the triplet

What molecule is TFIIH known to phosphorylate?

RNA polymerase II

How would you describe the half-lives of rRNAs and tRNAs?

days or weeks long

What kind of DNA is the DNA that codes for rRNA?

moderately repetitive DNA

The building blocks of a nucleotide are ___________.

a pentose sugar, a phosphate group and a nitrogenous base

What is the significance of the variability of the third nucleotide in a codon?

The same tRNA can recognize more than one codon.