Cell Bio week 8 quiz Flashcards
How many amino acids does CRH have?
41
What animals share homology with human CRH?
Fish and frogs
What is CRH involved in?
Stress response and pregnancy
What assay was used to confirm CRH activity?
Injection into rats and measurement of ACTH levels
Why was isolating CRH difficult?
It was very hydrophobic and stuck to lab glassware
What protein does CRH stimulate the release of?
ACTH (Adrenocorticotropic Hormone)
Where else is CRH secreted aside from the hypothalamus?
Placenta
What are two theories explaining placental CRH effects?
- Binding protein inactivation
(This theory suggests that placental CRH may influence the levels of corticosteroid-binding globulin (CBG), a protein that binds cortisol and regulates its activity. CRH could lead to the inactivation or decreased production of CBG, resulting in higher levels of free, bioactive cortisol. This could have significant effects on both the maternal and fetal stress response during pregnancy) and - pituitary desensitization
(Another theory posits that placental CRH contributes to the desensitization of the maternal pituitary gland. When CRH is released from the placenta, it can stimulate the maternal pituitary to release ACTH (Adrenocorticotropic hormone), which in turn stimulates cortisol production. Over time, however, continued exposure to CRH could lead to a decrease in the pituitary’s responsiveness, reducing ACTH secretion and preventing an excessive increase in cortisol levels.)
What hormone interacts with opioids in the brain?
Beta-endorphin
What might be linked Postpartum depression/blues?
opioid withdrawal post-birth
What test is used to study HPA axis feedback?
Dexamethasone suppression test( used to evaluate how the body regulates cortisol production via the hypothalamic-pituitary-adrenal (HPA))
The specific graph in class:
* Dexamethasone is a synthetic glucocorticoid that normally suppresses cortisol production via negative feedback on the HPA axis.
* In non-pregnant controls, this suppression works as expected: cortisol drops sharply.
* In pregnant women, however, cortisol remains elevated even after dexamethasone is administered, suggesting resistance to suppression, which is typical during pregnancy due to increased production of corticotropin-releasing hormone (CRH) from the placenta
What happens to CRH and related peptides during pregnancy?
They increase in blood levels
What cells are affected by CRH and related peptides during pregnancy?
Myometrial cells
What pathway do CRH and Urocortin activate?
MAPK (Mitogen-Activated Protein Kinase)
study on how different peptides impact MAPK activation in myometrial cells
The researchers stimulated myometrial cells with CRH, urocortin, and sauvagine. They then lysed the cells and separated proteins using SDS-PAGE. These proteins were transferred to membranes via Western blotting, and specific proteins were detected using antibodies and chemiluminescence
Which peptide had a stronger effect on MAPK activation?
Urocortin
What technique was used to detect MAPK activation?
Western blotting and chemiluminescence
What is gene expression?
The process by which information encoded in a gene is used to synthesize a functional protein or RNA molecule.
Why is gene expression important?
It allows cells to respond to environmental changes and differentiate into specialized cell types.
What is cell differentiation?
The process where cells become specialized in structure and function, driven by changes in gene expression.
What is cell dedifferentiation?
A process where specialized cells revert to a less specialized state, also known as ‘reprogramming’.
What are the main levels of gene expression control?
Transcriptional, post-transcriptional, translational, and post-translational.
What role do transcription regulators play?
They bind specific DNA sequences to activate or repress gene expression.
What is combinatorial control in gene expression?
Gene expression regulated by combinations of proteins working together. stead of one transcription factor controlling one gene, multiple factors work together in various combinations to regulate gene expression
How do steroid hormones regulate gene expression?
They are extracellular signal molecules that bind to intracellular receptors that act as transcription factors and regulate target gene expression.
What is the function of nuclear receptors?
They regulate gene expression by binding to specific DNA sequences when activated by ligands or other mechanisms.
Describe the Notch signaling pathway.
Ligand binding leads to proteolytic cleavage ( breaking down proteins by cleaving peptide bond) of Notch receptor, releasing Nicd (notch intracellular domian) which enters the nucleus and activates gene transcription.
What is the Wnt/β-catenin pathway?
A canonical pathway where Wnt proteins bind receptors, stabilize β-catenin, which enters nucleus to regulate genes.
What are non-canonical Wnt pathways?
Pathways regulating cell polarity and Ca2+ levels, affecting transcription through different intermediates like JNK and NFAT.
What is the Hedgehog signaling pathway?
Hedgehog protein is synthesized and
secreted by cells and then binds to specific
receptors on the surfaces of target cells,
triggering a cascade of signalling events
that ultimately control gene expression
and cell fate determination.
It is a key regulatory pathway in animals, but absent in plants
What activates the NF-κB signaling pathway?
Stimuli like cytokines, pathogens, and stress, leading tolead to the activation of the NF-κB transcription factors(can trigger
the expression of a variety of genes
involved in immune function, cell growth,
and survival).
What regulates the circadian rhythm in gene expression?
A protein oscillator system influenced by daily cycles, involving genes like Per (Period) and Tim (Timeless)
Process:
* The Tim and Per genes are transcribed into mRNAs.
* they then move from the nucleus to the cytosol.
* these mRNAs are translated into Tim and Per proteins.
* Tim and Per proteins form a heterodimer in the cytosol.
* The heterodimer enters the nucleus and inhibits further transcription of Tim and Per genes — a negative feedback loop.
* Per protein undergoes regulated phosphorylation and degradation.
* Tim protein is degraded in response to light, which also disrupts the heterodimer.
* Once Tim and Per proteins are degraded, transcription resumes, restarting the ~24-hour cycle.
Name 6 major signaling pathways involved in gene regulation.
RTK pathway, GPCR pathway,
Wnt pathway, Hedgehog pathway, Notch pathway, NFκB signaling pathway.
What is the main function of the plant cell wall in signaling?
It provides structural support, protection, and acts as a barrier affecting the movement of signaling molecules.
Name four key signalling pathways in plants.
- Hormonal signalling:vital roles in regulating plant growth, development, and responses to environmental stimuli. These hormones act by binding to specific receptors and activating signaling cascades that affect gene expression and cellular processes
- calcium signalling: Calcium ions (Ca²⁺) act as secondary messengers in many signaling pathways in plants. can regulate many processes
- protein kinase signalling: Protein kinases, particularly mitogen-activated protein kinases (MAPKs), are crucial in transmitting signals from cell surface receptors to the nucleus. They phosphorylate specific target proteins, which helps regulate processes like cell division, stress responses, and developmental pathways.
- reactive oxygen species (ROS) signalling: reactive molecules that play a central role in plant stress responses, including responses to biotic and abiotic stressors. ROS also regulate plant growth and development by modulating various signaling pathways and gene expression
What do plant and animal signaling have in common?
They both use NO (nitric oxide), cGMP, Ca2+, and small GTP binding proteins of the Rho family.
Which signaling pathways are absent in plants but present in animals?
STAT, TGFb, Notch, Wnt, and Hedgehog pathways.
What is the role of calcium signalling in plants?
Calcium is universal second messenger. It involves transient changes in Ca²⁺ concentration and is crucial for growth, stress responses, and signal transduction.
How does G-protein signaling differ in plants compared to animals?
Plant G proteins can spontaneously exchange GTP/GDP, and their 7TM-RGS can sustain signaling from endocytosed proteins. animals need a ligand to attach
What type of kinases are predominant in plant cell surface receptors? (and how does it work)
Serine/Threonine kinases, especially with leucine-rich repeat (LRR) structures.
- Ligand Binding (Outside the Cell)
A ligand (such as a hormone, peptide, or pathogen-associated molecule) binds to the extracellular domain of the RLK.
This domain usually contains Leucine-Rich Repeats (LRRs) that help recognize specific ligands. - Receptor Activation (Across the Membrane)
Ligand binding causes a conformational change in the receptor.
This often leads to dimerization or oligomerization (two or more RLKs coming together). - Signal Transmission (Inside the Cell)
The cytoplasmic kinase domain becomes activated.
It phosphorylates specific serine or threonine residues—either on itself (autophosphorylation) or on downstream signaling proteins. - Downstream Signaling Cascade
The phosphorylation event activates signaling pathways, such as:- MAP kinase cascades (e.g., MPK3/6)
- Calcium signaling
- Transcription factor activation
- Biological Response
Depending on the RLK and the context, this leads to:
- Immune response (e.g., WRKY activation after flagellin binding to FLS2)- Growth regulation (e.g., BR signaling via BRI1)
- Developmental processes (e.g., meristem maintenance via CLV1)
- Symbiosis with microbes (e.g., nodulation via NFR1/NFR5)
What happens when brassinosteroid signaling is disrupted in plants?
Loss-of-function leads to dwarfism, while gain-of-function leads to overgrowth.
What is the CLV3 pathway responsible for?
Regulating stem cell maintenance and differentiation
- CLV3 is a small peptide hormone produced in the outer layer of the SAM.
- It binds to a receptor complex composed of CLV1 and CLV2 on adjacent cells.
- This activates a downstream signalling cascade that represses the WUSCHEL (WUS) transcription factor.
- WUS, in turn, promotes CLV3 expression, creating a self-regulating feedback loop.
- This balance ensures the right number of stem cells is maintained — not too many (overproliferation) or too few (differentiation without renewal).
WUS is normally expressed in the organizing center and promotes stem cell fate by inducing CLV3 expression in overlying cells.
So WUS promotes CLV3, and CLV3 represses WUS. This creates a negative feedback loop that balances:
Too much WUS → too many stem cells (overgrowth)
Too much CLV3 → WUS shut down → no new stem cells (differentiation)
What is the role of auxin in plants?
mportant regulatory role for leaf initiation and
formation of leaf pattern.
What triggers gravitropism in plant roots?
The statoliths (or amyloplasts)
are redistributed in the cell in
response to gravity, which
cause the Aux/IAA redistributed as
well.
What is the role of ABA in leaf senescence(death of tissue)?
High ABA concentration induces growth stop and formation of the abscission layer.
What is the function of ethylene in plants?
It controls fruit ripening, leaf senescence, and response to mechanical stress.
What plant photoreceptors respond to red and blue light?
Phytochromes respond to red light; cryptochromes (CRY) respond to blue light.
chloroplasts in signaling.
- anterograde signaling:
import of nucleus gene encoded
proteins into the chloroplast; In
turn, several chloroplast
products act as retrograde
signals to regulate expression of
nucleus-encoded genes. - Chloroplasts are coupled to
the ER so that signals may move
from the chloroplast to the ER. - Chloroplast products
supports peroxisomal pathways
in peroxisomes (metabolic functions)
What are the three types of protein filaments in the cytoskeleton?
Intermediate filaments, Microtubules, Microfilaments (actin filaments)
What are the main functions of actin?
Cell movement, intracellular motile processes like vesicle transport, phagocytosis, and cytokinesis
What is actin composed of?
A single polypeptide chain folded into a compact structure with four subdomains
What is the dynamic process of actin polymerization?
Monomers are added at the barbed end and released from the pointed end at the same rate (treadmilling)
What is the function of Profilin?
Binds to actin monomers and PROMOTES their assembly into filaments
(Profilin binds to actin monomers and holds them in a way that favors their addition to the barbed (+) end of growing actin filaments. This accelerates filament elongation.
Profilin also prevents actin monomers from binding to other proteins that might sequester them or prevent polymerization)
What is the function of Thymosin?
Binds to actin monomers and PREVENTS their assembly into filaments
What does the Arp2/3 complex do?
Initiates growth of actin filaments by binding to existing filaments and forming new branches at a 70-degree angle to the old
(plays a critical role in the dynamics of the actin cytoskeleton by initiating the growth of new actin filaments)
What is the role of NPFs(Nucleating Promoting Factors)?
Bind to Arp2/3 and stimulate its nucleation activity
(the Arp2/3 complex by itself requires activation to nucleate new actin filaments. NPFs bind to the Arp2/3 complex and activate )
What protein promotes disassembly of actin filaments?
Cofilin
What does Spire do?
promotes formation of actin filaments by binding multiple monomers through WH2 domains
How do Formins promote actin filament formation?
FH2 domain binds actin monomers; FH1 domain delivers profilin-actin to the barbed end (these are the little rings that help formation)
Name four actin cross-linking proteins.
α-actinin, Filamin, Spectrin, Dystrophin
What is the function of α-actinin?
Cross-links actin filaments to stabilize and organize the cytoskeleton
What does Spectrin do?
Forms a tetramer with two α and two β subunits; provides mechanical strength
What is the role of Myosin in actin dynamics?
Acts as a motor protein moving along actin filaments for muscle contraction and organelle transport
What is Myosin-V responsible for?
Organelle transport
What is the function of end-blocking proteins?
Stop filament elongation or prevent disassembly
What cellular processes involve actin?
Membrane trafficking, cell migration, cell division
What was the first successful attempt at tissue culture?
Wilhelm Roux maintained a portion of a chicken embryo’s medullary plate in saline solution in 1885.
What method did Ross Granville Harrison develop?
He established a method for tissue culture in the early 1900s.
What was Jonas Salk’s contribution to cell culture?
He and his team advanced virology and cell culture methods, leading to the development of the polio vaccine.
What are key factors in maintaining cell cultures?
- Fetal bovine serum (FBS) (often used in cell culture media because it provides essential growth factors, hormones, and nutrients required for the cells to thrive. It helps to support cell growth, proliferation, and viability)
- sterile technique
- regular feeding and subculturing
- proper environmental conditions.
What are Class I, II, and III biological safety cabinets?
Class I: protects user; Class II: protects user and culture; Class III: provides the highest level of protection for both.
What methods are used to sterilize equipment and surfaces in cell culture?
Physical tools (scissors, scalpel), surface sterilization with bleach or alcohol.
Why is collagen or ECM used in culture vessels?
To encourage cell adhesion and growth, especially for adherent cultures.
What are protoplasts?
Plant cells without cell walls
What is the purpose of plant cell cultures?
Production of secondary metabolites, genetic engineering, research, propagation, and conservation.
What is included in cell culture media?
Nutrients, electrolytes, growth factors, vitamins, typically pH-indicated and red in color.
What are immortalized cell lines?
Cells modified to divide indefinitely via oncogenes or suppression of tumor suppressor genes.
What colors represent microtubules and actin in immunohistological staining?
Green represents microtubules and red represents actin microfilaments.
What does red staining indicate in a divided cell?
Red staining indicates intermediate filaments.
What are lamellipodia and filopodia?
They are cellular projections involved in movement, formed by actin filaments.
lamellipodia is the dip whereas filopedia is the part that reaches out
What changes occur in the cytoskeleton during cell division?
There are reorganizations, especially around microtubule organizing centers with motor proteins aiding chromosomal movement.
What is shown in the image of a neutrophil chasing bacteria?
The leading edge of the neutrophil, involved in movement, is stained red.
What features characterize polarized epithelial cells?
They exhibit structural polarity with features like microvilli at the apical surface and hemidesmosomes at the basal surface. (one of the drawings)
What structural characteristics do intermediate filaments have?
They have a rope-like construction providing flexibility and elasticity.
What role do intermediate filaments play in the nucleus?
They support and strengthen the nuclear envelope.
From where do microtubules typically grow?
Microtubules grow from a microtubule organizing center (MTOC).
What protein makes up microtubules?
Microtubules are made of αβ tubulin dimers.
What is the polarity of microtubule growth?
Microtubules grow typically from the minus end towards the plus end.
What is the thermal stability of cytoskeletal filaments with dynamic ends?
Microtubules exhibit thermal instability due to their dynamic ends. breakge can occur in the middle, or the end.
What was discovered by Kalam et al. (2018) regarding β-tubulin?
β-tubulin is reorganized and fragmented for uterine receptivity, with increased levels at day 6 of rat pregnancy.
What cellular structure forms to facilitate embryo implantation?
Uterodomes form on epithelial cells to aid in uterine receptivity.
How was β-tubulin analyzed during uterine receptivity?
Using Western blot analysis to observe β-tubulin levels during rat pregnancy.
What are the two main models of cell migration?
Mesenchymal mode (thin actin based protusion) and amoeboid cell migration (thick actin based protrusion)
How does ActA protein on bacterial surface function?
Activates Arp2/3 complex to nucleate new actin filaments
What controls the arrangement of actin filaments?
Extracellular signals and activation of GTP-binding proteins
What motor protein is associated with actin filaments?
Myosin
How can the force of a single myosin molecule be measured?
Using an optical trap
What is the function of Myosin V?
Transports cargo and organelles along actin cables
How is mechanical strength achieved in non-muscle cells?
Through contractile structures formed by actin and myosin
What is cytoplasmic streaming?
Flow of cytoplasm inside the cell driven by the cytoskeleton
main plant myosins
Myosin VIII (in the cortex. may create tension in actin network) and Myosin XI (interact with binding proteins)
What are myofibrils made of?
Myofibril is a cylindrical structure found inside muscle cells (muscle fibers). it is made up of Repeating chains of sarcomeres (basic structural and functional unit of a muscle fiber)
Describe the steps in the actin-myosin contractile model.
- Attached: Attached (rigor state)
Myosin head is tightly bound to actin. No ATP is bound. - Released: ATP binds to the myosin head. Myosin’s affinity for actin decreases.Myosin releases from the actin filament.
- Cocked:ATP is hydrolyzed to ADP and Pi.
Myosin head cocks (changes conformation), storing potential energy.It moves into a high-energy state but is not yet bound to actin. - Force-generating: Pi is released, which triggers the power stroke.The myosin head pivots, pulling actin along
- Attached: .ADP is released near the end of the stroke. Myosin is again tightly bound to actin.The cycle is ready to repeat when another ATP binds.
What triggers muscle contraction?
Sudden rise in Ca++
What are the regulatory proteins in muscle contraction?
Troponin and tropomyosin
What distinguishes smooth muscle from skeletal muscle?
Lack of regular striations
How does myosin convert chemical energy into movement?
Via ATP hydrolysis into mechanical work
What is the building block of microtubules?
Tubulin
What influences the dynamic instability of microtubules?
GTP
What is dynamic instability?
The process where microtubules grow and shrink rapidly
What is ‘catastrophe’ in microtubules?
The rapid shrinkage of microtubules
What is ‘rescue’ in microtubules?
The switch from shrinkage to growth
Where does microtubule elongation mainly occur?
At the plus ends
What structure organizes microtubules in the cell?
The microtubule organizing centre (MTOC), including the centrosome
What is the role of γ-tubulin?
It nucleates microtubules at the centrosome
What are centrioles?
Paired structures in the centrosome that help organize microtubules
How can microtubule stabilization affect a cell?
It can polarize the cell
What proteins help in organizing microtubule bundles?
MAPs (microtubule-associated proteins)
What protein sequesters tubulin to regulate microtubule assembly?
Stathmin
What are the two main motor proteins on microtubules?
Kinesins and dyneins
How do kinesins and dyneins move?
Using their globular heads to ‘walk’ along microtubules
What does dynactin do?
It helps dynein attach to vesicles for transport
What determines the type of cargo transported on microtubules?
The specific motor proteins and adaptors involved
(Motor proteins like kinesin and dynein move along microtubules in opposite directions:
- Kinesins generally move cargo toward the plus end (usually toward the cell periphery).
- Dyneins move cargo toward the minus end (usually toward the cell center or MTOC).
- These motors attach to cargo via adaptor proteins, which help recognize and bind specific cargo types like vesicles, organelles, mRNA, or protein complexes.
The combination of motor protein and adaptor essentially acts as a molecular “address label,” ensuring the right cargo goes to the right place.)
What is the typical microtubule arrangement in a cilium or flagellum?
A 9+2 arrangement in the axoneme (2 “paper towel tubes” in each instead of 3)
What causes the bending of an axoneme?
The sliding of microtubules driven by motor proteins like dynein
How can microtubules help locate the cell center?
Through an unknown mechanism involving microtubule array dynamics
What is the seam of a microtubule?
A line where the protofilaments of the microtubule are misaligned
G Protein Signaling animals vs plants
In animals: GPCRs activate G proteins via ligand binding and phosphorylation by GRKs.
In plants (e.g. Arabidopsis): G protein signaling can occur independently of ligands, with spontaneous GDP/GTP exchange.
What controls transcription of the Lac operon?
A repressor and an activator, which are both transcription regulators.
What happens to the Lac operon when both glucose and lactose are present?
Operon is OFF
- CAP is not bound (glucose present)
- Repressor is not bound (lactose present)
- Low transcription
What happens to the Lac operon when glucose is present but lactose is absent?
Operon is OFF
- CAP is not bound (glucose present)
- Repressor is bound (no lactose to remove it)
- Transcription is blocked
What happens to the Lac operon when both glucose and lactose are absent?
Operon is OFF
- CAP is bound (glucose absent → ↑cAMP)
- Repressor is bound (no lactose to remove it)
- Transcription is blocked
What happens to the Lac operon when glucose is absent and lactose is present?
Operon is ON
- CAP is bound (glucose absent → ↑cAMP)
- Repressor is not bound (lactose inactivates it)
- RNA polymerase can bind and transcribe
What is the role of the CAP (cAMP Activator Protein) in Lac operon regulation?
Binds upstream of the promoter in low glucose conditions to enhance RNA polymerase binding and increase transcription.
What is the role of the Lac repressor?
Binds the operator and blocks RNA polymerase unless lactose is present to inactivate it.
