Midterm Exam Answers Flashcards
(39 cards)
microRNAs (miRNAs) have been found to regulate gene expression during animal development. What
is a miRNA and how it is controlling gene expression. [2 marks]
-miRNAs are genes that do not code for proteins but code for molecules that are processed into short
double stranded RNA molecules. [1]
-miRNA work through the RISC complex to inhibit translation of
mRNAs by binding to their 3’UTRs. [1]
Whole cell movement and shape change is an important process during embryo development. Briefly
describe how a cell is able to move across a substratum, such as the extracellular matrix. Describe the
two major components of the cytoskeleton involved. Describe at least two proteins (there are more than
two but describe two) and explain their function during cytoskeleton rearrangement. [4 marks]
-For a cell to crawl, it must generate and maintain a structural polarity through the microtubule
(tubulin) [1] and microfilament (actin) cytoskeletons.
-Protrusion at the leading edge (by assembly of new actin filaments) [1]
-adhesion of the newly
protruded part of the cell to the substratum through focal adhesions [1]
-traction via molecular
motors (myosin) to bring the cell body forward [1]
-disassembly of old cell-substratum contacts
[0.5]
-Newly nucleated actin filaments are attached to the sides of preexisting filaments through the ARP
(actin related protein) complex. [1]
-Filaments become susceptible to depolymerization by cofilin [1].
-Microtubules emanate outward from the centrosome. [0.5]
-Vesicles with plus-end-directed kinesin attached move outward [1]
-vesicles with minus-end- directed dynein attached move inward [1].
3) In the canonical Wnt pathway, explain the function of the following three proteins. [3 marks]
a) APC/Axin/GSK-3B
b) β-catenin
c) Frizzled
a) APC/Axin/GSK-3B – in the absence of the Wnt ligand, this complex targets b-catenin for degradation
b) β-catenin – transcription co-factor, stabilized with Wnt signal, enters the nucleus and partners with
TCF/LEF to control gene expression
c) Frizzled – receptor for Wnt ligand, binds Dishevelled and prevents b-catenin degradation
In Lewis Wolpert’s French flag model of development, he defines three important features of how a
molecule can be used to pattern a field of cells such as an organ or an entire embryo. First, he predicted
the existence of a morphogen, second he described how this molecule can provide positional
information and finally he suggested how threshold concentrations of a morphogen can instruct cell
fate decisions. Use this model to answer the following questions.
Provide a specific example of how threshold concentrations are instructing cell fate within the
Drosphila embryo. In particular, explain how a stripe, such as one seen in the French flag, can be
generated in the Drosophila embryo. Provide specific genes and experiments to support your answer. [3 marks]
-Hunchback and Krupple
-hunchback in an anterior to posterior gradient with highest concentration in
the anterior
-Highest levels of hunchback repress Krupple expression, intermediate levels activate
expression, lowest levels are insufficient to activate expression. [2]
-Threshold levels mediating
repression or activation create a stripe of Krupple in the centre of the embryo.
-Experiments that reduce
the amount of Hunchback show a widening of the stripe to anterior of the embryo. [1]
In the late Drosophila embryo, the transcription factor ________, marks the posterior compartment of
each segment. [1 mark]
engrailed
__________ are specialized cell-cell junctions that can form between closely apposed plasma
membranes. These junctions directly connect the cytoplasms of the joined cells via narrow water-filled
channels. [1 mark]
Gap junctions
An important feature of cellular differentiation is the ability to control gene expression. Genes that
are important for cellular functions can have their expression repressed or activated. When, where and
how much of a gene is present is under tight regulation within the developing embryo. In the space
below, describe two major ways that gene transcription can be regulated in the cell. Discuss the
function of control regions and chromatin as a part of your answer. Give two examples of each to
explain your answer. [4 marks]
-Each gene can be transcribed with a different efficiency.
-A promoter region, which is responsible for the binding of RNA polymerase II and general
transcription factors for the subsequent initiation of transcription. [1]
-Enhancers are the major determinant of differential transcription in space (cell type) and time.
-There can be multiple signals to determine whether a given gene is transcribed. A given gene can have
several enhancer sites linked to it, and each enhancer can be bound by more than one transcription
factor. [1]
-The interaction between the proteins bound to the enhancer sites and the transcription initiation
complex assembled at the promoter is thought to regulate transcription.
-Transcription factors are proteins that bind to enhancer or promoter regions and interact to activate or
repress the transcription of a particular gene.
-Gene expression is controlled by reversibly changing local chromatin structures. ATP-driven
chromatin remodeling complexes [1], and an enzymatically catalyzed covalent modification of the N- terminal tails of the four core histones [1] are used to regulate chromatin conformations.
-It is likely that histone-modifying enzymes and chromatin remodeling complexes work in concert to
condense and decondense stretches of chromatin.
During Drosophila development, the formation of segment boundaries and segment polarity are
functionally linked. Name two signalling pathways that are regulating this process and briefly explain
how they might be regulating boundary formation and segment polarity at the same time. [Hint: you do
not need to explain the complex levels of control for each pathway but should be able to highlight major
features of each]. [3 marks]
-Wingless/Wnt
-Hedgehog /Hh
-Wingless and Hedgehog signalling forms a positive regulatory loop to maintain the parasegment
boundary and establish engrailed expression. Wingless protein is secreted and diffuses to the
surrounding cells. A wingless gradient provides anterior-posterior polarity
Stem cells are important in the maintenance and repair of tissues. Give the definition of a stem cell and
describe three properties of stem cells. [3 marks]
-Stem cells are undifferentiated cells that divide/replicate to replace themselves AND generate other cell
types.
-Self-renewing: one cell can differentiate into a variety of cells, while other remains a stem cell.
-Stem cells have a niche, an environment that maintains cells in an undifferentiated state.
-Multipotent: stem cells have the competence to develop into different cell types.
___________, is a process where a series of rapid mitotic divisions divide the egg cytoplasm into
numerous smaller, nucleated cells. These resulting cells are called ________. [2 marks]
Cleavage
blastomeres
Edward Lewis was awarded the Nobel Prize in Physiology or Medicine in 1995 for his foundational
work on anterior-posterior patterning of the Drosophila embryo. From this work he defined a class of
genes called the homeotic selector gene complex. Name the two major gene complexes found in this
larger complex. Describe the function of these complexes in more detail. As a part of your answer explain
how these genes display co-linearity and posterior dominance during anterior-posterior patterning of
the embryo. [4 marks]
-Antennapedia and bithorax [1]
-controls segment identity along anterior-posterior axis [1]
-master regulatory genes, set the future developmental fate of each segment, control activity of genes that
control differentiation of cells in each segment
-co-linearity - position of gene within the complex correlates to anterior-posterior position of expression
in the embryo [1]
-posterior dominance: Hox genes expressed in more anterior segments (i.e. Ubx) are repressed by more
posterior Hox genes [1]
-The combination of expression in each segment instructs segment identity along the anterior-posterior
axis.
Competence is described as the state of a cell being able to respond to an inductive signal. Give an
example of a condition that can influence a cell’s competence. [1mark]
Expression of signalling pathway components, chromatin state (opened vs. closed)
After fertilization of the Drosophila oocyte, a rapid series of nuclear divisions without cytokinesis
results in the formation of the __________. The resulting nuclei migrate to the periphery of the
embryo and share a common cytoplasm. [1 mark]
syncytial blastoderm
The Epidermal Growth Factor receptor is an example of a receptor for the receptor tyrosine kinase
(RTK) pathway. During vulva development in C. elegans, this pathway mediates an inductive event. Describe this inductive event including the cells involved, the genes required, and the cell fate choices
that are made in response to this signal. For each gene, explain their function in the RTK signalling
pathway. [4 marks]
-Anchor cell (inductive signal lin-3 EGF ligand) [1] and hypoderms (VPC or Pnps) competent to
receive signal (let-23 EGF receptor). [1]
-Activated let-23 uses let-60 Ras-GTPase as a molecular switch
to activate kinase cascade within the nearest cell [1].
-VPC takes on primary cell fate instead of the
default tertiary fate. [1]
During metamorphosis in Drosophila development, _________ are folded sacs of epithelial tissue
in larvae that are set aside will replace larval tissues with adult structures. [1 mark]
imaginal discs
During Drosophila embryo development, maternal factors control expression of ___________. These
genes divide the embryo into broad domains. [1 mark]
gap genes
Programmed cell death is important for maintaining the appropriate number of cells during
tissue development. Give an example of a C. elegans gene that is important for this process and briefly
explain its function. [2 marks]
- Egl-1 (BIM/BID) – associated with mitochondria, promoter of apoptosis
- Ced-9/bcl-2 inhibitor of apoptosis, inhibited by egl-1
- Ced-3/caspase – proteolytic cascade that initiates cell death program
\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ are small sacs of larval tissue that will give rise to adult tissues during metamorphosis of the Drosophila larvae. a. Pole cells b. Syncytium c. Imaginal discs d. Denticles
c. Imaginal discs
________________ were found to be important in controlling the timing of development in C. elegans. a. miRNAs
b. Heterochronic genes
c. Homeotic genes
d. siRNAs
e. a. and b.
e. a. and b.
During antero-posterior pattern of the Drosophila embryo, which of the following is a pair-rule gene?
a. hunchback
b. bicoid
c. fushi tarazu
d. Krüpple
e. a. and b.
c. fushi tarazu
Is the following statement True or False? Chordates and arthropods have undergone an inversion of the
embryonic dorsal-ventral axis. This is evident by the dorsal placement of the central nervous system in the fly
embryo.
a. True
b. False
b. False
5) Which of the following is an example of an homeotic transformation?
a. The absence of a vulva in the C. elegans hermaphrodite.
b. The premature timing of cell divisions during C. elegans larvae development.
c. Adult flies that have legs instead of antennae on their head.
d. A random direction of hair growth on a Drosophila wing.
c. Adult flies that have legs instead of antennae on their head.
When considering the germ layers of the vertebrate embryo, match the following tissue or organ (6-9) to the germ layer they develop from (a. to c.) 6) intestine 7) the central nervous system 8) muscles 9) lungs
a. endoderm
b. ectoderm
c. mesoderm
6) intestine a.
7) the central nervous system b.
8) muscles c.
9) lungs a.
\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ describes the polarity of cells within the plane of a tissue. Cells are able to sense their direction within a group of cells. a. Segmentation b. Inductive signalling c. Planar cell polarity d. Epithelial adhesion
c. Planar cell polarity
