Cell Biology Flashcards
Metaplasia
A switch that occurs in tissue differentiation that converts one cell type to another, altering functional ability of a particular cell type in an organ. It is often seen in lung disease (pulmonary fibrosis) and intestinal disorders (E.g Inflammatory bowel disease and Crohn disease)
What intracellular protein complex links microtubules of the spindle apparatus to sister chromatids during mitosis and meiosis?
Kinetochore
You are investigating maternal factors that regulate the cell cycle during early development. A mouse embryo is flushed from the uterine tube, treated with acid Tyrode solution to remove its zona pellucida, and examined by phase microscopy. The embryo exhibits a cleavage furrow and appears to be undergoing cytokinesis. These events take place during what phase of mitosis?
Telophase
As part of your research, you examine integral membrane proteins in cleavage-stage mouse embryos using fluorescence microscopy (shown in the image). A pulse of high-intensity UV light is directed at a small patch on the surface of one blastomere, therebycausing an immediate loss of fluorescence emission (photobleaching). Over the next 10 minutes, fluorescence emission from this patch of membrane recovers.
Membrane fluidity
You are studying cell migration during embryonic development. Neural tubes are harvested from post-implantation mouse embryos and placed in culture on plastic dishes coated with fibronectin. Time-lapse imaging reveals neural crest cells migrating away from the explanted tissue. The cells are observed to undergo continuous changes in cell shape, including the formation and retraction of lamellipodia. What protein is the principal mediator of membrane ruffling and locomotion in these cultured cells?
Actin
A sample of adrenal cortex obtained at autopsy is fixed with formalin, embedded in paraffin, sectioned at 6 micro-meter. Stained with H & E, and examined by light microscopy. Cells of the zona fasciculata appear washed out and “spongy” due to an accumulation of cholesterol and other precursors for steroid hormone biosynthesis. Electron microscopic examination of these “ steroid factory” cells would be expected to show an abundance of which of the following organelles?
Smooth endoplasmic reticulum.
A portion of the small intestine is collected at autopsy, and sections are stained with periodic acid-Schiff (PAS) and counterstained with hematoxylin. The mucosa of the intestine is examined by light microscopy (shown in the image). PAS is particularly useful for identifying which of the following biological materials?
Sugars.
You are asked to lead a seminar on intracellular protein trafficking. What organelle provides a microenvironment for the posttranslational modification and sorting of membrane and secretory proteins?
Golgi apparatus
Hematopoietic stem cells are cultured in vitro at 37 C in the presence of recombinant erythropoietin. A photomicrograph of a typical “burst-forming unit” committed to the erythrocyte pathway of differentiation is shown in the image. Which of the following histochemical stains can be used as a “vital dye” to distinguish viable from nonviable cells in your cell culture?
Trypan Blue
Hepatocytes in a liver biopsy are examined by electron microscopy. The parallel lines with knob-like features (arrows, shown in the image) represent which of the following intracellular organelles?
Endoplasmic Reticulum
A soft tissue biopsy is examined in the pathology department. Normal adipocytes are examined at high magnification. The clear space that has pushed the cytoplasm and nucleus to the periphery of these cells is best described by which of the following terms?
Inclusion
You are studying the role of mitochondrial dysfunction in alcoholic liver disease. Genes for an inner mitochondrial membrane protein is expressed in mouse embryo fibroblasts. The distribution of mitochondria in the transfected cells is visualized by confocal fluorescence microscopy. Inhibition of the electron transport chain in this organelle leads to which of the following reversible changes in cell behavior?
Hydropic Swelling
Release of cytochrome c from the organelle mitochondria activates which of the following cellular processes?
Apoptosis
The motor neurons described in Question 13 are labeled by immunocytochemistry using antibodies directed against a neuron-specific protein that helps maintain the shape of dendrites and axons. This structural protein forms which of the following intracellular organelles?
Intermediate filaments
Which of the following cell adhesion proteins forms anchoring junctions that link actin microfilaments to adhesive glycoproteins on the surface of the culture dish?
Integrins
Which of the following cellular processes describes the uptake of extracellular fluids and small particles by the cell described in Question 18?
Pinocytosis
The genes for green fluorescent protein and tubulin are spliced, and the fusion protein is expressed in a myoblast cell line. The distribution of microtubules is monitored by confocal fluorescence microscopy. During mitosis, these cytoskeleton proteins are reorganized to coordinate chromosome separation. Which of the following organelles is the principal microtubule-organizing center in these myoblasts?
Centrosomes
What are centrosomes?
Cellular structure involved in the process of cell division.
You attend a national meeting on regenerative medicine. One of the talks focuses on cellular senescence and cancer. Reactivation of the gene for which of the following nuclear proteins may enable some cancer cells to escape cellular senescence, continue to proliferate, and maintain genomic stability?
Telomerase
The gene for green fluorescent protein is modified by the addition of a signal sequence that targets the translation product to the lumen of the endoplasmic reticulum (ER). The distribution of the rough ER in a transfected myoblast cell line is monitored by confocal fluorescence microscopy. Which of the following families of proteins facilitates proper protein folding in the ER, cytoplasm, and nucleus of the muscle stem cell?
Chaperones
Hepatocytes from a liver biopsy are examined by electron microscopy. Identify the elongated organelles shown in the image.
Mitochondria
A 42 year old woman presents with increasing abdominal girth and yellow discoloration of her skin and sclera. Physical examination reveals hepatomegaly and evidence of liver failure (jaundice). A Prussian blue stain of a liver biopsy is shown in the image. This stain identifies which of the following elements?
Iron
Which of the following proteins contributes to the structural matrix that anchors chromatin to the nuclear membrane during interphase of the cell cycle?
Lamin
An 85 year old woman with Alzheimer disease dies in her sleep. At autopsy, hepatocytes are noted to contain golden cytoplasmic granules that do not stain with Prussian blue. This “wear-and-tear” pigment of aging (lipofuscin) accumulates primarily within which of the following cellular organelles?
Lysosomes
You are involved in a translational research project to develop small-molecule inhibitors of pepsin secretion by chief cells in the stomach muscosa. Chief cells store precursor enzymes within zymogen granules. By electron microscopy, these “protein factory” cells would most likely show an abundance of which of the following intracellular organelles?
Rough endoplasmic reticulum.
Which of the following structural proteins mediates LDL receptor internalization by organizing small buds of plasma membrane into endosomes?
Clathrin
Patient with Gaucher disease carriers mutations in the genes for glucocerebrosidase. Without this hydrolytic enzyme, glucocerebroside accumulates within which of the following cellular organelles?
Lysosomes
You are studying the differentiation of epithelial cells lining the intestinal mucosa and identify a common stem cell for the secretory lineage that gives rise to Paneth cells, enterocytes, and globet cells. Which of the following terms describes the developmental potential of these gastrointestinal stem cells?
Multipotent
A cervical biopsy is obtained from a 42 year old woman with a history of abnormal Pap smears. The tissue is tested for human papillomavirus (HPV) by in situ hybridization using cDNA probes. Evidence of HPV viral genome is detected in cells in the cervical biopsy (dark blue spots). The patient is told that she is at increased risk for the development of cervical cancer. She asks you to elaborate. You explain that HPV encodes an early gene (E6) that activates a cellular protein that, in turn, accelerates the degradation of the tumor suppressor protein. Name the protein that is activated by HPV E6.
Ubiquitin ligase.
A cervical biopsy is obtained from a 42 year old woman with a history of abnormal Pap smears. The tissue is tested for Human papillomavirus (HPV) by in situ hybridization using cDNA probes. Evidence of HPV viral genome is detected in cells in the cervical biopsy (dark blue spots). The patient is told that she is at increased risk for the development of cervical cancer. HPV encodes an early gene (E6) that activates a cellular protein that, in turn, accelerates the degradation of the protein tumor suppressor protein. Name the protein that is activated by HPV E6.
Ubiquitin ligase.
You join a research laboratory to investigate the growth and differentiation of human embryonic stem (ES) cells. These remarkable cells have been shown to differentiate into a wide variety of somatic cell types including (1) dopamine-producing neurons, (2) cardiac myocytes, and (3) insulin-producing pancreatic islet cells. ES cells are similar or equivalent to which of the following populations of cells/tissues in the early embryo?
Epiblast
As part of your research, you investigate the role of cyclins and cyclin-dependent kinases in regulating ES cell growth in vitro. These rapidly dividing cells spend most of their time in which phase of the mitotic cell cycle?
G1
You are invited to give a seminar on the molecular mechanisms of lineage formation and cell differentiation. During the seminar, you are asked to list the primary germ layers of the embryo and discuss their derivatives. Blood vessels and hematopoietic stem cells originate from which of the following tissues/ structures during embryogenesis?
Mesoderm.
The principal investigator of your laboratory asks you whether pluripotent ES cells can differentiate into neural crest cells or primordial germ cells. You suggest that cellular and molecular markers would help you answer that question. Markers for which of the following cells could be used to monitor neural crest cell differentiation in vitro?
Melanocytes
Endocytosis
Involves the formation of vesicles at the plasma membrane by a process of vesicle budding.
1) Pinocytosis (constitutive uptake of fluid and small particles)
2) Phagocytosis (uptake of large particles by macrophages and other phagocytic cells)
3) Receptor-mediated endocytosis (clathrin-dependent uptake of specific ligands).
Epithelial cells line the gastrointestinal tract, respiratory tree, cardiovascular system, and genitourinary system and cover the skin. Which of the following cellular properties best distinguishes lining/coating epithelial cells from other cells/tissues in the body?
A. Apical and basal membrane domains
Your instructor reminds you that epithelial cells have membrane channels that permit ions and small signaling molecules to pass between adjacent cells. Which of the following proteins forms these intercellular (gap) junctions?
Connexins
Further examination of the embryo described in Question 7 reveals fluid-filled cavities above and below the amnion. Which of the following proteins plays an important role in regulating fluid transport and cavity formation in this embryo?
Na/K ATPase
A 10 year old girl scrapes her elbow on the sidewalk while skateboarding. Physical examination reveals a 5 cm superficial skin abrasion. Which of the following cellular processes regulates regeneration of the epidermis in this patient’s superficial abrasion?
Loss of cell contact inhibition of growth and motility.
A 58 year old woman presents with painless hematuria (blood in her urine). Urine cultures are negative for E. coli. A biopsy of the urinary bladder is examined in the pathology department. Identify the type of epithelium.
Transitional.
You attend a lecture on the physiology of lactation and breast-feeding. Under the influence of pregnancy associated hormones, epithelial cells of the mammary gland secrete lipids, carbohydrates, and proteins. The lipid components of breast milk are released from the apical surface of the glandular epithelial cells as a lipid droplet within an envelop of the plasma membrane. Which of the following terms best describes this mechanism of secretion?
Apocrine
2 Key classes of proteins that control the progress of a cell through the cell cycle are the:
1) Cyclins
2) Cyclin-dependent kinases (Cdk)
Anticancer agents, such as camptothecins target:
Human Type I topoisomerases
Etoposide targets:
Human type II topoisomerases
Bacterial DNA gyrase
A unique target of a group of antimicrobial agents called fluoroquinolones (Ex. ciprofloxacin)
Bacterial Translation Inhibitors:
1) Chloramphenicol
2) Streptomycin
3) Tetracycline
4) Erythromycin
Bacterial Transcription Inhibitor
Rifamycin (inhibits prokaryotic RNA polymerase)
Bacterial DNA gyrase and inhibitors of replication
Fluoroquinolones and ciprofloxacin
Eukaryotic inhibitors of translation
Cycloheximide (inhibits peptidyl transferase activity) and diphtheria toxin
Eukaryotic transcription inhibitors
Alpha-amanitin (inhibits eukaryotic RNA polymerase-II) and actinomycin D (also inhibits replication)
Inhibitors of DNA replication are:
The nucleoside analogs (cytarabine, azidothymidine), actinomycin-D (intercalating agent and disrupts the template)
Which of the following karyotypes would most likely be present among mature, normal, human sperm?
A. 24, Y
B. 22, X
C. 46, XY
D. 23, Y
E. 46, XX
23, Y
Sperm formation and maturation from precursor cells is studied in a model system. When these cells complete meiosis:
A. the daughter cells are diploid
B. the daughter cells are genetically different
C. Each sperm cell will contain a Y-chromosome
D. they did so without forming a chiasmata
E. The X and a Y chromosomes are paired
The daughter cells are genetically different (recombination)
Which of the following is true with respect to meiosis?
The products of meiosis are haploid.
Lamina Propria
A thin layer of loose connective tissue found beneath the epithelial cells or epithelium
The 3 main categories of extracellular macromolecules that make up the ECM:
1) Glycosaminoglycans (GAGs), proteoglycans
2) Fibrous proteins, including collagen and elastin
3) Adhesive proteins, including fibronectin and laminin
GAGs are also called:
Mucopolysaccharides with repeating disaccharide chains where one of the sugars is an N-acetylated amino sugar, either N-acetylglucosamine or N-acetylgalactosamine
Ground substance
Extracellular gel-like materials deposited between cells and is composed mainly of water and proteoglycans, but not fibrous proteins
Most prevalent GAG
Chondroitin sulfate
Other GAGs
Hyaluronic acid
Keratin sulfate
Dermatan sulfate
Heparin
Heparan sulfate
Types of Cell Junctions
Tight
Adherens
Desmosome
Gap
Hemidesmosome
Tight Junctions
Seals adjacent epithelial cells together; prevents leakage between cells
Adherens
Joins actin bundles between cells
Desmosome
Anchors intermediate filaments between cells
Gap junctions
Allows passages of small water-soluble molecules between cells
Hemidesmosome
Anchors intermediate filaments to basal lamina
Scurvy
Impaired collagen production caused by lack of dietary vitamin C
Osteogenesis imperfecta
Inherited disorders of collagen characterized by weak bones.
Ehlers-Danlos syndrome
Characterized by hyperextendible joints and stretchy skin
Marfan Syndrome
Defective fibrillin-1 impairs the maintenance of elastin and results in defects in the aorta, eye, and skeleton
-Autosomal Dominant Inheritance Pattern
Function of Glycosaminoglycans
Form a hydrated gel to help resist compressive forces
A 78 year old man is diagnosed with scurvy. His defective collagen results from
Impaired ability to hydroxylate Pro and Lys residues
Feature of collagen as a component of the extracellular matrix
Forms tough protein fibers that are resistant to shearing forces
A 32 year old woman with systemic lupus erythematosus (SLE) experiences joint pain and swelling that is accompanied by impaired joint pain and swelling that is accompanied by impaired compression/deformation abilities of her cartilage. Which of the following best describes the impaired extracellular matrix component and the impact it has on cartilage in this patient with SLE?
A. Collagen of SLE cartilage lacks hydroxylysine and is less stable.
B. Elastin of SLE cartilage is unable to stretch so cartilage cannot expand
C. Excess collagen in SLE cartilage causes joint stiffening
D. Laminin-mediated adhesion is interrupted, making SLE cartilage more diffuse
E. Reduced proteoglycan leads to impaired resilience of SLE cartilage.
E. Reduced proteoglycan leads to impaired resilience of SLE cartilage.
A peripheral membrane protein is best described as a protein:
Loosely attached to the inner membrane leaflet.
Mechanism of action of phalloidin
Toxin from the poisonous mushrooms Amanita phalloides.
-Can also be used in the laboratory as an imaging tool to identify actin
-Functions by disrupting the normal function of actin. It binds to F-actin polymers more tightly than to G-actin monomers and promotes excessive polymerization while preventing filament depolymerization
Cilia
Important in movement of fluids, such as mucus, across epithelial cells of the respiratory tract. They move in a cyclic manner, taking strokes through the fluid (9+2 arrangement of microtubules)
Flagella
Generally longer than cilia and are important in moving an entire cell, such as sperm, through fluids (9+2 arrangement of microtubules)
3 Major categories of extracellular macromolecules that make up the ECM:
1) Glycosaminoglycans (GAGs) and proteoglycans
2) Fibrous proteins, including collagen and elastin
3) Adhesive proteins, including fibronectin and laminin
Ground substance
Extracellular gel-like materials deposited between cells and is composed mainly of water and proteoglycans, but not fibrous proteins
GAGs
organized in long, unbranched chains and adopt extended structures in solution. Most GAGs are sulfated, and all contain multiple negative charges.
-Condroitin sulfate, hyaluronic acid, keratin sulfate, dermatan sulfate, heparin, and heparan sulfate
A 78 year old man is diagnosed with scurvy. His defective collagen results from:
Impaired ability to hydroxylate Pro and Lys residues (Copper is needed as a cofactor)
Rough ER
-Due to attached ribosomes
-Synthesize and modify proteins
Smooth ER
-No ribosomes
-Lipid and steroid synthesis
Golgi Apparatus
Modifying sorting and packaging proteins and lipids for intra- and extracellular transport
Lysosomes
Small organelles containing digestive enzymes
Mitochondria
Provide energy for the cell by producing ATP
-Contains mitochondrial DNA from the mother
Microtubules
Forms part of the cytoskeleton
Filaments
Forms part of the cytoskeleton
Centrioles
Microtubule organizing center
Ribosomes
Essential for protein synthesis
Glycocalyx
Carbohydrate rich zone on the cell surface:
-Glycolipids
-Glycoproteins
-Proteoglycans
*Help establish microenvironment at the cell surface
-Protection from: Mechanical damage, chemical damage
Hydrophobic Molecules
O2, CO2, N2, benzene
Small uncharged polar molecules
H2O, urea, glycerol
Large Uncharged polar molecules
Glucose
Sucrose
3 Types of Endocytosis
- Receptor-mediated:
-Cargo-specific
-Clathrin-dependent - Pinocytosis:
-Non-specific
-Clathrin-independent - Phagocytosis:
-Clathrin-independent
-Actin-dependent
Regulated
-Secretory cells:
1) Endocrine
2) Exocrine
3) Neurons
-Stimulus
-Fusion of secretory vesicles with plasma membrane
Constitutive
Substance for export continuously delivered to plasma membrane
Receptor-Mediated Endocytosis
-Selected uptake of large molecules and particles:
1) Clathrin-dependent
2) Clathrin-Coated pits
-Requires energy in the form of GTPase
a) Low-density lipoprotein (LDL) receptor
-Insulin-glucose transporter receptor
-Other peptide hormones and their receptors
b)Receptor and ligand recycled
-Iron, transferrin & transferrin receptor
-Major histocompatibility complex I & II
c) Receptor and ligand degraded
-Epidermal growth factor (EGF) & receptor
d) Receptor and ligand transcytosis
-Secretion of immunoglobulins (secretory IgA) into saliva
-Secretion of maternal IgG into milk
Endosomes
-Membrane-enclosed structure associated with the endocytotic pathway
-Early endosome: functions to sort and recycle proteins
-Late endosome: receives proteins for degradation
-Receives newly synthesized lysosomal enzymes from the Golgi
-Matures into a lysosome
Endocytosis
-Pinocytosis
-“Cell Drinking”
-Non-specific ingestion by small vesicles
-Constitutive
-Invagination of the plasma membrane
-No receptor proteins
-Clathrin-independent
-Vesicle pinches-off
-Fusion with lysosome
Phagocytosis
Ingestion of large particles
-Microorganisms
-Apoptotic cells
-Non-biological materials
Usually performed by specialized phagocytes: Macrophage, Neutrophil
-Particles binds to plasma membrane receptor
Filopodia
Finger-Like projections
-Core of long, bundled actin filaments
Lamellipodia-fibroblasts
-Sheet like structures
Pseudopodia-white blood cells
3 dimensional projections
Extravasation
- Rolling
- Activation
- Adhesion
- Transendothelial migration
Intermediate Filaments
-Rope like filaments
-Structure: formed from non-polar & highly variable subunits
-Structural: stabilize cell structure, mechanical strength & maintain the position of the nucleus and other organelles
-Resist shearing forces: extend across cytoplasm
-Connecting with desmosomes & hemidesmosomes
Classes of Intermediate Filaments
1 & 2: Keratins (in epithelial cells)
3: Vimentin & Vimentin-like (mesoderm-derived cells)
-Desmin: Muscle cells
-Glial fibrillary acid protein (GFAP): glial cells & astrocytes
4: Neurofilaments: extend from cell body into the ends of axons & dendrites
5: Lamins: Found in nucleus of all nucleated cells
6: Beaded Filaments: eye lens-specific group
Inclusions
Cytoplasmic or nuclear structures formed from metabolic products of the cell
Lipofuscin
-Brownish-gold pigment
-Generally seen in non-dividing cells
“Wear & tear pigment”
Melanin
Dark brown/brown/reddish pigment produced by the oxidation of tyrosine
-Produced by melanocytes in the skin & responsible for color of skin/hair pigmentation
*Also produced by certain neurons of the brain
Hemosiderin
Brown Pigment
-Iron-storage complex found in the cytoplasm
-Commonly found in macrophages
-Likely formed by indigestible residues of hemoglobin following phagocytosis of RBCs
-Demonstrated in the spleen, liver, lung
-Deposits may be also be linked to disease of iron overload
Physical barriers between individual cells
Tight or occluding junctions (zonulae occludentes)
Functions of desmosomes or anchoring junctions (maculae adherentes)
Function to couple neighboring cells to each other by interacting with components of the cytoskeleton (intermediate filaments and actin), the inner framework, or scaffolding within cells.
Function of adherens junctions (zonulae adherentes)
Function to couple neighboring cells to each other by interacting with components of the cytoskeleton (intermediate filaments and actin)
Functions of hemidesmosomes
Link cytoskeletal intermediate filaments to the basal lamina.
[ ] is required for cadherin binding to another cadherin
Calcium
Extravasation meaning
Cell migration from circulation to tissue (Ex. when a leukocyte from the immune system responds to an infectious agent in a tissue, its adhesion molecules must encounter their ligands and facilitate the cell’s movement from blood into the tissue)
Steps in extravasation
1) Rolling
2) Activation
3) Arrest/firm binding
4) Diapedesis
Fatty streak formation
One of the first pathological changes in cardiovascular disease: beings with injury to the inner lining of the blood vessel (endothelium, atherosclerotic process)
Alpha1-Antitrypsin deficiency
An autosomal dominant disorder caused by deficiency of the protease inhibitor that normally regulates actions of elastase, an enzyme that degrades elastin. In the lungs of all individuals, the alveoli are chronically exposed to low levels of neutrophil elastase, released from activated neutrophils.
Cadherins
Binds cells together, connects to the cytoskeletal actin of the cell. Additionally, requires Ca2+ and forms long lasting bonds.
Selectins
Transient cell to cell junctions. Important in migration of immune cells.
Immunoglobulin superfamily
Share structural characteristics with antibodies. Fine tune and regulate cell-to-cell adhesions. Some facilitate adhesion between endothelial cells and leukocytes.
Integrins
Cell-to-cell and cell-to-ECM, weak adhesive interactions.
