All GRE Subject Test: Biochemistry, Cell, and Molecular Biology Resources
Example Questions
Example Question #1 : Differentiation
The mesodermal germ layer can give rise to each of the following cell types except __________.
fibroblasts
the notocord
alveoli
myoblasts
alveoli
The mesoderm gives rise to the "middle" cells that line the body, such as the muscle. The notocord is a critical embryonic structure that forms from the mesoderm, and myoblasts and fibroblasts are cells that line the body. The alveoli are part of the lung, which originates from the endodermal germ layer.
Example Question #2 : Differentiation
Which of the listed processes are part of gastrulation?
The formation of ectoderm and endoderm germ layers in radially symmetric organisms
The ingression of cells from the epiblast to form a circular blastocyst
The invagination of the notochord to induce the formation of the neural plate
The formation of the primitive streak that undergoes epithelial to mesenchymal transition
The formation of the primitive streak that undergoes epithelial to mesenchymal transition
Gastrulation is the process of cells from the epiblast ingressing into the embryo to form the three germ layers of bilaterally symetrical animals. When gastrulation is complete, the embryo is referred to as a gastrula. The group of cells that lead the migration of cells into the embryo are called the primitive streak, and they undergo epithelial to mesenchymal transition to be able to migrate. You can image the epithelium as many tightly packed squares. Becomimg mesenchymal turns these cells into more malleable stage, like a soft cushion. They can then "drop" into the inner layer of the blastocyst and lead the process of gastrulation.
Example Question #3 : Differentiation
Which of the following statements about determination is true?
Determination follows differentiation
Once determined, a cell changes its appearance
Determination occurs after two cell divisions in most organisms
No matter where its placed in an embryo, a determined cell will keep its determination
The pattern of transcription is the same in a differentiated cell as it is in a determined cell
No matter where its placed in an embryo, a determined cell will keep its determination
Determination is the process of a cell committing to a particular fate and is influenced by the cell's environment as well as its own genome. It's not possible to tell the difference between an undetermined and a determined cell since determined cells do not change in appearance. After determination comes differentiation. Differentiation results from differential gene expression (transcription, mRNA splicing, and translation).
Example Question #4 : Differentiation
Which of the following terms describes when the single germ layered blastula reorganizes into a structure with mesoderm, endoderm, and ectoderm germ layers?
Gastrulation
Blastulation
Morphogenesis
Myogenesis
Somiteogenesis
Gastrulation
The correct answer is gastrulation. Gastrulation occurs through five stages (1. invagination 2. involution 3. ingression 4. delamination 5. epiboly) and results in the formation of a gastrula with the mesoderm, endoderm, and ectoderm germ layers. Blastulation is the formation of the single germ layered blastula, which is a process that precedes gastrulation. Somiteogenesis forms somites in developing embryos to give rise to the future spine. Myogenesis is the formation of muscle tissue. Morphogenesis is the process of an organism forming its shape, driven by cell cycle progression, differentiation, and subsequent development of organs and appendages.
Example Question #2 : Differentiation
Which embryonic structure is created by the process of gastrulation?
The mesoderm
The notochord
The neural tube
The epiblast
The mesoderm
Gastrulation is a process occurring in week three of development. At this time, the epiblast will further differentiate into three germ layers: the ectoderm, the mesoderm, and the endoderm. As a result, we can say that gastrulation allows for the creation of the mesoderm.
Example Question #5 : Differentiation
How do master regulators, which are transcription factors, establish cell subtypes and cell subtype-specific gene expression?
Master regulators bind promoters by not enhancers to initiate specific gene expression
None of the other answers
Master regulators promote the deposition of methyl or acetyl groups to mark inactive or active enhancers
Master regulators promote active promoter formation by deposition of methyl groups
Master regulators always promote formation of euchromatin in nucleosome dense regions
Master regulators promote the deposition of methyl or acetyl groups to mark inactive or active enhancers
The correct answer is master regulators promote the deposition of methyl or acetyl groups to mark inactive or active enhancers. Master regulators bind enhancer regions that have been created by pioneer factors to establish the chromatin state of the cell by deposition of methyl or acetyl groups on chromatin. Methylation correlates with inactive enhancers, whereas acetylation correlates with active enhancers. The fingerprint of active/inactive enhancers and its effect on gene expression establishes cell subtypes. Some, but not all master regulators function as pioneer factors to bind nucleosome rich DNA to promote euchromatin formation.
Example Question #1 : Help With Developmental Genes
RNA of Gene X was injected into the posterior of a fruit fly embryo, and the resulting embryo had two heads instead of a head and a tail. What type of protein does gene X most likely code for?
Morphogen
Enzyme
Receptor
Growth factor
Lipid
Morphogen
Morphogens are proteins that can regulate the patterning of embryos over a multi-cell distance. Classic morphogens were discovered by injecting cytoplasm of embryos from the anteiror to the posterior, which would give rise to an animal with two heads. Injecting cytoplasm from the posterior to the anterior would give rise to animals with two posteriors. If injecting the RNA of a particular gene changes the patterning of the animal dramatically, it is likely a morphogen.
Example Question #2 : Help With Developmental Genes
Homeobox (Hox) genes are essential regulators of development of an organism, as they define region specific development of an embryo along its anterior-posterioir axis. A mutation in the gene Antennapedia, for example, causes Drosophila melanogaster to grow legs from its head instead of antennae.
Given that hox genes regulate segmental identity of an organism, which of the following phenotypes would possibly be present in a fruit fly with a mutation in a Hox gene required for formation of very anterior structures?
Extra wing appendages
Head missing or malformed
Extra legs extending from thorax
Genital structures missing
Missing wing appendages
Head missing or malformed
The only 'very anterior' structure listed among the answers is the head. If this particular hox gene is required to create the proper anterior appendage, we can predict that of the structures listed the head is most likely to be affected.
Example Question #3 : Help With Developmental Genes
HOX genes are a group of genes that have been well characterized to control body plan development along the anterior to posterior axis in developing embryos. What do HOX genes encode?
Structural proteins
Transcription factors
Golgi-endoplasmic reticulum trafficking proteins
Transmembrane receptors
Mitochondrial proteins
Transcription factors
The correct answer is transcription factors. HOX transcription factors turn on genes during embryonic development to determine the type of segment structure (examples are legs or antennae) at different spatial regions of the embryo. Absence or mis-expression of HOX genes in early development renders misinformed or non-viable organisms.
Example Question #1 : Help With Stem Cells
Which of the following is an example of a multipotent stem cell differentiation into a terminal cell type?
Endoderm cells giving rise to enterocytes
iPS cells giving rise to cardiomyocytes
Bone marrow cells giving rise to lymphosites
A zygote giving rise to germ layers
Bone marrow cells giving rise to lymphosites
Multipotent cell types can give rise to a small number of cell types but have a restricted fate. This is in contrast to totipotent (zygote) or pluripotent cells (germ layers, iPS (induced pluripotent cells)) which can give rise to many different cell types, some that may make up very different parts of the body.
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