Weekly quizzes

Question 1

Living systems are incredibly diverse in size, shape, environment, and behavior. It is estimated that there are between 10 million and 100 million different species. Despite this wide variety of organisms, it remains difficult to define what it means to say something is alive. Which of the following can be described as the smallest living unit?

Answer 1

Cell

Question 2

Changes in DNA sequence from one generation to the next may result in offspring that are altered in fitness compared with their parents. The process of change and selection over the course of many generations is the basis of ___________________

Answer 2

evolution

Question 3

The __________ __________ is made up of two concentric membranes and is continuous with the membrane of the endoplasmic reticulum.

Answer 3

nuclear envelope

Question 4

Which of the following statements about mitochondria is NOT true?
Mitochondria are thought to have originated from bacteria
Mitochondria contain their own DNA
Mitochondria have an inner and outer membrane
Mitochondria are not present in plant cells
Mitochondria generate chemical energy for the cell

Answer 4

Mitochondria are not present in plant cells

Question 5

Which of the following statements about chloroplasts is NOT true?
Chloroplasts contain their own DNA
Chloroplasts have an internal stack of membranes that is enclosed by two other membranes
Chloroplasts are thought to have originated from mitochondria
Chloroplasts produce food molecules and generate oxygen
Chloroplasts are present in plant and algal cells

Answer 5

Chloroplasts are thought to have originated from mitochondria

Question 6

What structure in an interphase cell contains ribosomal rRNA and proteins for the formation of ribosomes?

Answer 6

Nucleolus

Question 7

Which of the following structures can be easily detected and resolved by fluorescence light microscopy?

Answer 7

Mitochondria and the nucleus

Question 8

Which of the following organelle provides a safe place in the cell to carry out biochemical reactions that generate and breakdown harmful, highly reactive oxygen species?

Answer 8

Peroxisomes

Question 9

Cell biologists employ targeted fluorescent dyes or modified fluorescent proteins in both standard fluorescence microscopy and confocal microscopy to observe specific details in the cell. Even though fluorescence permits better visualization, the resolving power is essentially the same as that of a standard light microscope because the resolving power of a fluorescent microscope is still limited by the __________________ of visible light.

Answer 9

wavelegnth

Question 10

Zebrafish (Danio rerio) are especially useful in the study of early development because their embryos ___________________ .

Answer 10

are transparent

Question 11

Which one of the following statements about the polypeptide backbone is FALSE?
a. It plays an important role in the formation of both the alpha helix and beta sheet, two common secondary structures.
b. It includes the amino acid side chains.
c. It includes the peptide bond formed between the amino group on one amino acid and the carboxyl group on another amino acid.
d. It contains a repeating sequence of the core atoms (N-C-C) in every amino acid

Answer 11

b

Question 12

Which one of the following statements about protein folding is FALSE?
a. The protein’s amino acid sequence ultimately determines the 3-D shape of a protein.
b. Two or more alpha-helices with hydrophobic stripes can interact to form a coiled coil.
c. The distribution of polar and nonpolar amino acids in a folded protein is largely determined by hydrophobic interactions, which favor clustering of nonpolar side chains in the interior.
d. The amino acid side chains are involved in forming the hydrogen bonds that stabilize the alpha helix and beta sheet secondary structures

Answer 12

d

Question 13

What is the best definition of a protein domain?
a. The location of a protein subunit within a multi-subunit enzyme
b. An alpha-helix
c. The region in a cell where a protein is located
d. A segment of a protein that can fold independently into its own compact, stable 3D structure

Answer 13

d

Question 14

Which one of the following statements about protein binding sites is FALSE?
a. Binding sites are often located in a cavity on the protein surface
b. Each antibody contains three antigen binding sites, which can bind many different antigens non-specifically
c. All proteins can bind themselves and/or other molecules called ligands
d Some proteins can bind to themselves to form higher order macromolecules, and the shape of the macromolecules is determined by the location of the binding sites.

Answer 14

b

Question 15

Protein folding can be studied using a solution of purified protein and a denaturant (urea), a solvent that interferes with noncovalent interactions. Which of the following is observed after the denaturant is removed from the protein solution?

The polypeptide returns to its original conformation.
The polypeptide adopts a new, stable conformation.
The polypeptide remains denatured.
The polypeptide forms solid aggregates and precipitates out of solution.

Answer 15

The polypeptide returns to its original conformation.

Question 16

The variations in the physical characteristics between different proteins are influenced by the overall amino acid compositions, but even more important is the unique amino acid ______________.

Answer 16

sequence

Question 17

Ras is a small protein that functions in many signaling pathways. In its active form, with GTP bound, Ras transmits a signal that leads to cell proliferation. In its inactive form, with GDP bound, the signal is not transmitted. Mutations in the gene for Ras are found in many cancers. Which type of mutation in Ras is MOST likely to contribute to uncontrolled cell growth?

A mutation that increases the binding of Ras to GTP
A mutation that decreases the binding of Ras to GTP
A mutation that prevents Ras from being made
A mutation that increases the binding of Ras to GDP

Answer 17

A mutation that increases the binding of Ras to GTP

Question 18

How does phosphorylation control protein activity?

a. The addition of a phosphate group can induce a conformational change in a protein
b. The phosphate group, with its two negative charges, prevents other negatively charged molecules from interacting with a protein
c. Phosphorylation always activates a protein
d. The addition of a high energy phosphate group adds energy to a protein

Answer 18

a

Question 19

Which one of the following methods is the BEST way to assess the number and sizes of proteins in complex mixture?

Answer 19

gel electrophoresis

Question 20

The attachment or removal of covalent modifications can control what aspects of a protein?
Its stability
Its behavior, activity, stability and/or location inside the cell
Its behavior or activity
Its location inside the cell

Answer 20

all

Question 21

Complete the sentence: In a DNA double helix, _____________

the two DNA strands run antiparallel.
the two DNA strands are identical.
adenosine pairs with guanine.
thymine pairs with cytosine.

Answer 21

the two DNA strands run antiparallel

Question 22

The process of sorting human chromosome pairs by size and morphology is called karyotyping. Which of the following questions would NOT be answered by using karyotyping?

Do any chromosomes contain mutations in their nucleotide sequences?
Is the individual genetically female or male?
Do any of the chromosomes contain pieces that belong to other chromosomes?
Does the individual have an extra chromosome?

Answer 22

a, any mutations

Question 23

The chromosomes we typically see in images are isolated from mitotic cells. These mitotic chromosomes are in the most highly condensed form. Interphase cells contain chromosomes that are less densely packed and ______________ .

Answer 23

occupy discrete territories in the nucleus

Question 24

Which of the following human cells contains a gene that specifies eye color?

Cells in the eye, the heart and the brain
Cells in the eye
Cells in the heart
Cells in the brain

Answer 24

all

Question 25

A eukaryotic interphase chromosome in G1 (before DNA replication) contains which of the following:

a. A single double-stranded DNA molecule, two telomeres, one centromere, and multiple origins of replication
b. A single double-stranded DNA molecule
c. Two telomeres and one centromere
d. Multiple origins of replication
e. A single double-stranded DNA molecule, two telomeres and one centromere

Answer 25

a

Question 26

Which of the following is NOT true of the N-terminal domain of histones?

a. It binds DNA in a sequence specific manner
b. It is subject to covalent modifications
c. It extends out of the nucleosome core
d. It helps DNA pack tightly

Answer 26

a

Question 27

The N-terminal tail of histone H3 can be extensively modified, and depending on the number, location, and combination of these modifications, these changes may promote the formation of heterochromatin. What is the result of heterochromatin formation?

Answer 27

gene silencing

Question 28

Which histone is considered the linker histone that pulls the nucleosomes together into a regular array, forming the 30-nm fiber?

Answer 28

histone H1

Question 29

How do chromatin remodeling complexes work?

a. They use the energy from ATP hydrolysis to alter packaging of DNA around the nucleosome core particle and make DNA more accessible to other proteins
b. They add methyl groups to amino acid side chains on histone tails
c. They bind nucleosomes in the 30-nm fiber and induce another layer of packaging
d. They condense interphase chromatin to mitotic chromatin

Answer 29

a.

Question 30

The inactivation of one X chromosome is established by the directed spreading of heterochromatin. The silent state of this chromosome is __________ in the subsequent cell divisions.

Answer 30

maintained

Question 31

What is the name of the subunit of bacterial RNA polymerase that recognizes the promoter of a gene?

Answer 31

sigma factor

Question 32

Which of the following statements about mRNA splicing is NOT true:

Introns increase the stability of mature mRNA.
Alternative splicing increases the coding potential of eukaryotic genomes.
Proteins that bind the 5’ cap, poly-A tail and splice junctions promote export of mRNA from the nucleus.
Splicing of introns from mRNA occurs in the nucleus.
Splicing of introns from mRNA is performed by the spliceosome.

Answer 32

introns increase the stability of mature mRNA

Question 33

Which of the following statements about transcription and translation is NOT true:

a. In both prokaryotes and eukaryotes, a single gene can be transcribed by multiple RNA polymerases at the same time.
b. In both prokaryotes and eukaryotes, a single mRNA can be transcribed and translated at the same time.
c. In eukaryotes, a single gene can encode multiple related proteins.
d. In prokaryotes, a single mRNA can encode multiple different proteins.
e. In both prokaryotes and eukaryotes, a single mRNA can be translated by multiple ribosomes at the same time.

Answer 33

b

Question 34

Which of the following statements about codons in mRNA molecules is NOT true?

a. Some codons code for more than one amino acid.
b. Codons in mRNAs bind to complementary anticodons in tRNAs.
c. Some codons do not code for amino acids.
d. In some cases, several different codons code for the same amino acid.

Answer 34

a

Question 35

Amino acids are attached to their tRNA molecules by:

Answer 35

aminoacyl-tRNA synthetase

Question 36

Within the ribosome, the formation of peptide bonds is catalyzed by:

Answer 36

an RNA molecule in the large ribosomal subunit

Question 37

In the bacterial cell, the tryptophan operon encodes the genes needed to synthesize tryptophan. When the concentration of tryptophan inside the cell is high, _____________________

A. the tryptophan repressor is activated, allowing transcription of the tryptophan operon.
B. the tryptophan repressor is inactivated, which shuts down the tryptophan operon.
C. expression of the tryptophan repressor is increased, which shuts down the tryptophan operon.
D. the tryptophan repressor is activated, which shuts down the tryptophan operon.
E. the tryptophan repressor is inactivated, allowing transcription of the tryptophan operon.

Answer 37

D

Question 38

Which of the following questions regarding gene expression in eukaryotes is TRUE?

a. All of the statements are correct.
b. Multicellular organisms use combinatorial control of gene expression to create different cell types.
c. In eukaryotes, a single gene is typically controlled by dozens of transcriptional regulators working together.
d. Multicellular organisms switch genes on and off in response to signals in their environments.
e. In eukaryotes, a single transcriptional regulator can switch several genes on or off together, as a unit.

Answer 38

all

Question 39

Which is NOT an example of epigenetic inheritance?

a. inheritance of a regulatory protein that activates its own transcription
b. inheritance of a single nucleotide mutation in a gene
c. inheritance of patterns of chromosome condensation
d. inheritance of methylation patterns in DNA
e. inheritance of a stable pattern of gene expression

Answer 39

inheritance of a single nucleotide mutation in a gene, b

Question 40

Which of the following is NOT involved in post-transcriptional control?

dicer
RISC
the spliceosome
mediator

Answer 40

mediator