MOD 1 UNIT 2: THE CELL (PART 2) Flashcards
These irregular vesicles near the cell periphery form part of the pathway for receptor-mediated endocytosis and contain receptor–ligand complexes.
early endosomes
PAPASA BA TAYO DITO?
YES IS THE ONLY OPTION BITCH
A- FIRST TRUE
B- SECOND TRUE
C- BOTH TRUE
D- BOTH FALSE
early endosomes are also known as the Compartment for Uncoupling of Receptors and
Ligands (CURL).
Their acidic interiors (pH _ 4) are maintained by ATP-driven proton pumps.
“A”
second statement, “pH 6”
TRUE OR FALSE
Lysosomes are formed when sequestered material fuses with a late endosome,
and enzymatic degradation begins.
TRUE
TRUE OR FALSE
In early endosomes, the acidity aids in the uncoupling of receptors and ligands; receptors return to the plasma membrane and ligands move to a late endosome.
TRUE
These irregular vesicles (pH _ 5.5) deep within the cell receive ligands via microtubular transport of vesicles from early endosomes.
Late endosomes
A- FIRST TRUE
B- SECOND TRUE
C- BOTH TRUE
D- BOTH FALSE
Late endosomes play a key role in various lysosomal pathways and therefore are
sometimes known as the intermediate compartment.
Late endosomes contain both lysosomal hydrolases and lysosomal
membrane proteins, these are formed in the RER, transported to the Golgi complex
for processing, and delivered in separate vesicles to late endosomes.
“C”
TRUE OR FALSE
Once late endosomes have received a full complement of lysosomal enzymes,
they begin to degrade their ligands and are classified as chromosomes.
FALSE
“classified as lysosomes”
are formed by fusion of an early endosome containing endocytic vesicles with a late endosome.
Multivesicular bodies
are formed by fusion of a phagocytic vacuole with a late endosome
or a lysosome.
Phagolysosomes
are formed by fusion of an autophagic vacuole with a late endosome or lysosome.
Autophagolysosomes
are formed when cell components targeted
for destruction become enveloped by smooth areas of membranes derived from the RER.
Autophagic vacuole
are lysosomes of any type that have expended their capacity to degrade material. They contain undegraded material (e.g., lipofuscin and hemosiderin) and eventually may be excreted from the cell.
Residual bodies
are characterized by a visible cytoplasmic surface coat
Coated vesicles
are formed during receptor-mediated uptake (endocytosis) of specific molecules by the cell, this also function in the signal-directed (regulated) transport of proteins from the TGN either to the secretory granule pathway or to the late endosome–lysosome pathway.
Clathrin-coated vesicles
A- FIRST TRUE
B- SECOND TRUE
C- BOTH TRUE
D- BOTH FALSE
clathrin-coated vesicles consists of ten large and three small polypeptide chains that form a triskelion (three-legged structure).
Proteins called adaptins are also part of clathrin-coated vesicles.
“B”
first statement, “three large”
forms a ring around the neck of a budding vesicle or pit and aids in pinching it off the parent membrane to form a free clathrin-coated vesicle.
Dynamin (guanosine triphosphate (GTP)–
binding protein)
mediate the continuous constitutive protein transport (default pathway; bulk flow) within the cell. This also transport proteins from the RER to the VTC to the Golgi
apparatus, from one Golgi cisterna to another, and from the TGN to the plasma
membrane.
Coatomer-coated vesicles
ensure that the vesicle docks and fuses only with its correct target membrane.
SNARES protein
recognize and bind to complementary target SNARES (t-SNARES) to deliver not only cargo molecules but also membrane to the target compartment.
Coated vesicle SNARES (v-SNARES)
A- FIRST TRUE
B- SECOND TRUE
C- BOTH TRUE
D- BOTH FALSE
COP-II transports molecules backward from the RER to the VTC to the cis Golgi and
across the cisternae to the TGN (anterograde transport).
COP-I facilitates retrograde transport (from the VTC or any Golgi cisternal
compartment or from the TGN) to the RER.
“B”
first statement, “transport molecules forward”
TRUE OR FALSE
Caveolin-coated vesicles are less common and less well understood
TRUE
They have been associated with cell signaling and a variety of transport
processes, such as transcytosis and endocytosis, they also are invaginations of the plasma membrane in endothelial and smooth muscle cells.
Caveolin-coated vesicles
is an irregular network of membrane-bounded channels that lacks
ribosomes on its surface, which makes it appear smooth. It usually appears as branching, anastomosing tubules, or vesicles, whose membranes do not contain ribophorins.
Smooth endoplasmic reticulum (SER)
This is a double-membrane organelle (like the nucleus) that generates adenosine
triphosphate (ATP) to fuel energy-requiring activities of the cell. It also functions in some
specialized synthetic pathways such as that for steroid hormones.
Mitochondrion
A- FIRST TRUE
B- SECOND TRUE
C- BOTH TRUE
D- BOTH FALSE
Mitochondria possess an inner membrane, which surrounds the organelle, and an inner
membrane, which invaginates to form cristae.
Mitochondria are subdivided into an intermembrane compartment between the two membranes and an inner matrix
compartment.
“B”
first statement, “outer membrane”
A- FIRST TRUE
B- SECOND TRUE
C- BOTH TRUE
D- BOTH FALSE
Elementary particles (visible on negatively stained cristae) represent adenosine
triphosphate (ATP) synthase, a special enzyme embedded in the inner mitochondrial
membrane.
It consists of a head portion and a transmembrane H_ carrier and is involved in
coupling oxidation to phosphorylation of adenosine diphosphate (ADP) to form ATP.
“C”
are found in rapidly growing cells (e.g., germ cells, embryonic cells, and tumor cells), but their function and significance remain unknown.
Annulate lamellae
A- FIRST TRUE
B- SECOND TRUE
C- BOTH TRUE
D- BOTH FALSE
Mitochondria may have originated as symbionts (intracellular parasites).
Mitochondria proliferate by division (fission) of preexisting mitochondria and typically
have a 6-day life span.
“A”
second statement, “10-day life span”
A- FIRST TRUE
B- SECOND TRUE
C- BOTH TRUE
D- BOTH FALSE
In condensed mitochondria, the size of the inner compartment is decreased and the matrix density is increased.
Condensed mitochondria are present in brown fat cells, which produce heat, rather
than ATP because they have a special transport protein in their inner membrane that
uncouples respiration from ATP synthesis.
“C”
A- FIRST TRUE
B- SECOND TRUE
C- BOTH TRUE
D- BOTH FALSE
Mitochondria does not synthesize ATP via the Krebs cycle, which traps chemical energy and
produces ATP by oxidation of fatty acids, amino acids, and glucose.
ATP is also synthesized via a chemiosmotic coupling mechanism involving enzyme
complexes of the electron transport chain and ATP synthase present in elementary
particles of cristae.
“B”
first statement, “Mitochondria synthesize ATP”
A- FIRST TRUE
B- SECOND TRUE
C- BOTH TRUE
D- BOTH FALSE
Annulate lamellae are parallel stacks of membranes (usually 6 to 10) that
resemble the nuclear envelope, including its pore complexes.
They are often arranged
with their annuli (pores) in register and are frequently continuous with the RER.
“C”
(also known as microbodies) are membrane-bound, spherical, or ovoid
organelles that may be identified in cells by a cytochemical reaction for catalase.
Peroxisomes
A- FIRST TRUE
B- SECOND TRUE
C- BOTH TRUE
D- BOTH FALSE
Peroxisomes may contain a nucleoid, a crystalline core consisting of urate oxidase (uricase)
The human peroxisome is abundant in nucleoid.
“A”
second statement, “lacks a nucleoid”
A- FIRST TRUE
B- SECOND TRUE
C- BOTH TRUE
D- BOTH FALSE
They originate from preexisting peroxisomes, which grow by importing specific
cytosolic proteins that are recognized by receptor proteins (called peroxins) in the
peroxisomal membrane.
Then the peroxisome divides by fission; it has a life span of approximately 5 to 6 months.
“A”
second statement, “5 to 6 days”
contain various enzymes whose functions vary from the oxidation of long-chain fatty acids to the synthesis of cholesterol to the detoxification of substances such as ethanol.
peroxisomes
A- FIRST TRUE
B- SECOND TRUE
C- BOTH TRUE
D- BOTH FALSE
Inclusions are accumulations of material that is not metabolically active.
They usually are present in the cytosol only temporarily.
“C”
TRUE OR FALSE
Glycogen appears as small clusters (or in hepatocytes as larger aggregates, known as
rosettes) of electron-dense 20- to 30-nm _-particles, which are similar in appearance to but
smaller than ribosomes.
FALSE
“larger than ribosomes”
serves as a stored energy source that can be degraded to glucose, which enters the bloodstream to elevate blood sugar levels.
Glycogen
are storage forms of
triglycerides (an energy source) and cholesterol (used in the synthesis of steroids and
membranes).
Lipid droplets
A- FIRST TRUE
B- SECOND TRUE
C- BOTH TRUE
D- BOTH FALSE
Lipid droplets vary markedly in size and appearance depending on the method of
fixation, and they are not bound by a membrane.
Lipofuscin appears as membrane-bound, electron-dense granular material varying
greatly in size and often containing lipid droplets.
“C”
represents a residue of
undigested material present in residual bodies. Because the amount of this material
increases with age, it is called age pigment.
Lipofuscin
TRUE OR FALSE
Lipofuscin is most common in nondividing cells (e.g., cardiac muscle cells, neurons) but also is found in hepatocytes.
TRUE
it is the major microtubule-organizing center in the cell, this is composed of a pair of centrioles embedded in amorphous material.
centrosome
TRUE OR FALSE
The centrosome functions in organizing the array of microtubules in the cell’s cytoplasm and in developing the spindle apparatus during cell division.
TRUE
A- FIRST TRUE
B- SECOND TRUE
C- BOTH TRUE
D- BOTH FALSE
centrosome contains two centrioles and a
cloud of pericentriolar material.
Each member of the pair is
composed of five triplets of microtubules (5 _ 0 axoneme pattern) arranged radially in the
shape of a pinwheel.
second statement, “nine triplets”
A- FIRST TRUE
B- SECOND TRUE
C- BOTH TRUE
D- BOTH FALSE
The centrioles self-duplicate in the S phase of the cell cycle, as each parent centriole a
procentriole at right angles to itself.
Centrioles also form basal bodies, which appear identical to unpaired centrioles and
which give rise to the axonemes of cilia and flagella.
“C”
TRUE OR FALSE
Centrioles play big role in nucleating microtubules, and they help to maintain the
organization of the centrosome.
FALSE
“centrioles play no role in nucleating microtubules”
is the structural framework within the cytosol. It functions in maintaining cell shape, stabilizing cell attachments, facilitating endocytosis and
exocytosis, and promoting cell movement.
cytoskeleton
maintain cell shape; aid in the transport of macromolecules within the cytosol; assemble into the mitotic spindle during mitosis and ensure the correct distribution of chromosomes to daughter cells; and assist in the formation of cell appendages called cilia and flagella, which beat rhythmically and precisely.
MICROTUBULES
A- FIRST TRUE
B- SECOND TRUE
C- BOTH TRUE
D- BOTH FALSE
microtubules have a rigid wall composed of 20 protofilaments, each of which consists of a
linear arrangement of tubulin dimers; each dimer consists of nonidentical and tubulin
subunits.
Microtubules are polar, with polymerization (assembly) and depolymerization
(disassembly) occurring preferentially at the plus end when GTP is bound to tubulin dimers.
“B”
first statement, “13 protofilaments”
TRUE OR FALSE
Kinesin moves cargo toward the plus end of the
microtubule (outward), whereas cytoplasmic dynein moves it toward the minus end
(inward).
TRUE
play a role in many cellular processes, such as establishing focal contacts between the cell and the extracellular matrix, locomotion of nonmuscle cells, formation of the contractile ring (in dividing cells), and the folding of epithelia into tubes during development.
ACTIN FILAMENTS
TRUE OR FALSE
Actin filaments measure 7 nm in diameter and are composed of globular
actin monomers (G actin) linked into a double helix (F actin). They are thin, flexible, and
abundant in cells.
TRUE
A- FIRST TRUE
B- SECOND TRUE
C- BOTH TRUE
D- BOTH FALSE
Actin filaments display non-polarity similar to that of microtubules; that is, their polymerization and depolymerization occur preferentially at the plus end when ATP is bound by G actin.
Actin filaments are abundant at the periphery of the cell, where they are anchored to
the plasma membrane via one or more intermediary proteins (e.g., actinin, vinculin, and
talin).
“B”
first statement, “display polarity”
They constitute a population of
heterogeneous filaments that includes keratin, vimentin, desmin, glial fibrillary acidic
protein (GFAP), lamins, and neurofilaments.
intermediate filaments
TRUE OR FALSE
intermediate filaments provide mechanical strength to cells. They lack polarity and do not require GTP or ATP for assembly, which occurs along the entire length of the filament.
TRUE
TRUE OR FALSE
Cell membranes are composed primarily of phospholipids and proteins
TRUE
have a glycerol backbone, which is the hydrophilic (water soluble) head,
and two fatty acid tails, which are hydrophobic (water insoluble).
Phospholipids
TRUE OR FALSE
The hydrophobic tails face each other and form a bilayer.
TRUE
cross cell membranes because they can dissolve in the hydrophobic lipid bilayer. (e.g., O2, CO2, steroid hormones)
Lipid-soluble substances
cannot dissolve in the lipid of
the membrane, but may cross through water-filled channels, or pores, or may be
transported by carriers. (e.g., Na , Cl−, glucose, H2O)
Water-soluble substances
are anchored to, and imbedded in, the cell membrane through hydrophobic
interactions.
integral proteins
A- FIRST TRUE
B- SECOND TRUE
C- BOTH TRUE
D- BOTH FALSE
Integral proteins may span the cell membrane.
This include ion channels, transport proteins, receptors, and guanosine 5′-triphosphate
(GTP)–binding proteins (G proteins).
“C”
are not imbedded in the cell membrane.
Peripheral proteins
A- FIRST TRUE
B- SECOND TRUE
C- BOTH TRUE
D- BOTH FALSE
Peripheral proteins are covalently bound to membrane components.
They are loosely attached to the cell membrane by electrostatic interactions.
“B”
first statement, “are not covalently bound”
They are usually motile, with a whipping motion that consists of a power stroke and a recovery
stroke.
Cilia
These are cylindrical, nonmotile extensions, typically about 80 nm in diameter and 1
μm long.
Microvilli
TRUE OR FALSE
In some cells, microvillis are several micrometers long, in which case, they are called
stereocilia.
TRUE
Also called tight junctions, these are sites of fusion between plasmalemmas of adjacent epithelial cells that separate the lumen from the underlying connective tissue.
ZONULA OCCLUDENS
prevent materials from passing from one compartment to another by
diffusing through the space between adjacent epithelial cells.
Tight junctions
TRUE OR FALSE
tight junction may be “tight” (impermeable), as in the renal distal tubule, or “leaky” (permeable),
as in the renal proximal tubule and gallbladder.
TRUE
These are sites of mechanical adhesion between adjacent epithelial cells. They are
generally associated with and parallel to tight junctions.
ZONULA ADHERENS
Also called desmosomes, these, like zonula adherens, are sites of mechanical
adhesion between cells, but they are configured as spots rather than bands.
Macula adherens
Also called nexus junctions, the small space between the membranes is bridged by
connexons, each of which is a cylindrical complex of proteins forming a pore.
gap junctions
A- FIRST TRUE
B- SECOND TRUE
C- BOTH TRUE
D- BOTH FALSE
gap junctions do not allow free flow of small ions between cells, so that the cells are electrically
coupled.
are the attachments between cells that permit intercellular communication.
“B”
first statement, “allow free flow”
Infoldings of the plasmalemma at the basal surface of an epithelial cell provide
greatly increased surface area in support of extensive traffic of substances between the
cytosol and the underlying interstitial compartment.
Basolateral folds
This is an extracellular layer at the interface of a cell and the adjacent connective
tissue. These are characteristic of the basal surfaces of epithelia, but they are not
restricted to epithelia.
Basal lamina
TRUE OR FALSE
Lateral folds can
have an additional function of contributing mechanical strength to a layer of cells by
interlacing with complementary folds of an adjacent cell.
TRUE
is the uptake (internalization) of material by cells, this includes pinocytosis, receptor-mediated endocytosis, and phagocytosis.
Endocytosis
is the nonspecific (random) uptake of extracellular fluid and material in solution into pinocytic vesicles.
Pinocytosis (“cell drinking”)
is the specific uptake of a substance (e.g., low-density lipoproteins [LDLs] and protein hormones) by a cell that has a plasma membrane receptor
for that substance (which is termed a ligand).
Receptor-mediated endocytosis
[SEQUENCING]
Receptor-mediated endocytosis sequence of events:
A ligand binds specifically to its receptors on the cell surface.
The cytoplasmic clathrin coat is rapidly lost, leaving an uncoated endocytic vesicle
containing the ligand.
Ligand–receptor complexes cluster into a clathrin-coated pit, which invaginates and
gives rise to a clathrin-coated vesicle containing the ligand.
1,3,2
also known as “cell eating”, is the uptake of microorganisms, other cells, and particulate matter (frequently of foreign origin) by a cell.
Phagocytosis
[SEQUENCING]
Phagocytosis degrade proteins
and cellular debris and involves the following sequence of events:
A macrophage binds via its Fc receptors to a bacterium coated with the antibody
immunoglobulin G (IgG) or via its C3b receptors to a complement-coated bacterium.
Binding progresses until the plasma membrane completely envelops the bacterium,
forming a phagocytic vacuole.
1,2
is the release of material from the cell via fusion of a secretory granule
membrane and the plasma membrane. It requires interaction of receptors in both the
secretory granule membrane and the plasma membrane as well as the coalescence
(adherence and joining) of the two phospholipid membrane bilayers.
Exocytosis
TRUE OR FALSE
Exocytosis takes place in both regulated and constitutive secretion.
TRUE
is the release, in response to an extracellular
signal, of proteins and other materials stored in the cell.
Regulated secretion (signal directed)
is the more or less continuous release of
material (e.g., collagen and plasma proteins) without any intermediate storage step.
Constitutive secretion (default pathway)
TRUE OR FALSE
An extracellular signal is required for constitutive secretion.
FALSE
“it is not required”
maintains a relatively constant plasma membrane surface area following exocytosis. In this process, the secretory granule membrane added to the plasma membrane surface during exocytosis is retrieved through endocytosis via clathrin coated vesicles
Membrane recycling
A- FIRST TRUE
B- SECOND TRUE
C- BOTH TRUE
D- BOTH FALSE
Synthesis of membrane-packaged proteins involves translation of mRNAs encoding the
protein on polyribosomes at the surface of the RER, transport of the growing polypeptide
chain across the RER membrane and into the cisterna (lumen)
These water-soluble proteins will bud from the RER and be transported in vesicles
either for transfer into the lumen (or interior) of another organelle or for secretion from the
cell.
“C”
[SEQUENCING]
A three-step process translates mRNA as follows:
The mRNA moves a distance of one codon (three nucleotides) through the small subunit, and the “spent” initiator tRNA moves to the E site and is ejected, leaving the A site empty so that a new aminoacyl tRNA can bind
Methionine at the P site forms the first peptide bond with the incoming amino acid forming
a dipeptide
mRNA binds to the small subunit
of a ribosome that has three binding sites (A, P, and E) for tRNA molecules. The next codon is recognized by an aminoacyl tRNA bearing the proper amino acid, which then binds to the A site
3,2,1
[SEQUENCING]
Transport of the newly formed peptide into the RER cisterna is thought to occur by
a mechanism described by the signal hypothesis as follows:
mRNAs for secretory, membrane, and lysosomal proteins contain codons that encode a
signal sequence.
Synthesis of the growing chain stops until the SRP facilitates the relocation of the
polysome to SRP receptors in the RER membrane.
The large subunits of the ribosomes interact with ribosome receptor proteins, which bind
them to the RER membrane. The SRP detaches, and multisubunit protein translocators form a pore across the RER membrane. Synthesis resumes, and the newly formed polypeptide is threaded through the pore and into the RER cistern (lumen).
When the signal sequence is formed on the ribosome, a signal recognition particle (SRP)
in the cytosol binds to it.
1342
TRUE OR FALSE
not only one particular type of the many tRNAs in a cell can base-pair with each codon
FALSE
“only one type”
[SEQUENCING]
Posttranslational modification in the RER
The polypeptide is glycosylated.
After the newly formed polypeptide enters the cisterna, a signal peptidase cleaves the
signal sequence from it.
Disulfide bonds form, converting the linear polypeptide into a globular form.
2,1,3
TRUE OR FALSE
The ribosome moves along the mRNA in the 5_ to 3_ direction using acylated tRNAs as adapters to add each amino acid to the end of the
growing peptide chain, which is always located at the P site of the large subunit of the ribosome.
TRUE
[SEQUENCING]
Protein transport from the RER to the cis Golgi
Transitional elements of the RER give rise to COP-II coatomer–coated vesicles
containing newly synthesized protein.
These vesicles move to the VTC where they deliver the protein.
The VTC appears to be the first way station for the segregation of anterograde versus
retrograde transport in the secretory pathway. Either proteins move forward toward the cis
Golgi, or if they are RER-resident proteins that escaped from the RER, they are captured by
a specific membrane receptor protein and returned in COP-I coatomer-coated vesicles to
the RER along a microtubule guided pathway.
1,2,3
[SEQUENCING]
Synthesis of membrane-packaged proteins:
Transport of the newly formed peptide into the RER cisterna
Posttranslational modification in the RER
Protein transport from the RER to the cis Golgi
Anterograde transport from the VTC to the cis Golgi
Movement of material anterograde among the Golgi subcompartments
Protein processing in the Golgi complex
Sorting of proteins in TGN
1,2,3,4,5,6,7
[SEQUENCING]
Protein synthesis:
Synthesis of cytosolic proteins
Synthesis of membrane-packaged proteins
Synthesis of transmembrane proteins
3,1,2
[SEQUENCING]
Movement of material anterograde among the Golgi subcompartments may occur by
cisternal maturation and/or by vesicular transport, as follows:
Cisternae containing proteins may change in biochemical composition as they move
intact across the stack.
COP-II–coated vesicles may bud off one cisterna and fuse with the dilated rim of
another cisterna.
Retrograde vesicular transport occurs between Golgi cisternae and between the Golgi
and the VTC or RER via COP-I–coated vesicles.
Although both mechanisms have been observed, the precise way that anterograde
transport occurs across the Golgi stack of cisternae is unresolved.
1,2,4,3
TRUE OR FALSE
Anterograde transport from the VTC to the cis Golgi is via COP-I coatomer–coated
vesicles.
FALSE
“COP-II”
TRUE OR FALSE
Protein processing in the Golgi complex occurs as proteins move from the cis to the trans
face of the Golgi complex through distinct cisternal subcompartments.
TRUE
are sorted into clathrin-coated regions of the TGN that have receptors for mannose 6-phosphate and are delivered to late endosomes via clathrin-
coated vesicles.
Lysosomal proteins
are sorted from membrane and lysosomal proteins and delivered via clathrin-coated vesicles to condensing vacuoles, in which removal of water via ionic exchanges yields secretory granules.
Regulated secretory proteins
are sorted into coatomer-coated regions of the TGN and delivered to the plasma membrane in COP-II coatomer–coated vesicles.
Plasma membrane proteins
[SEQUENCING]
Protein processing may include the following events, each of which occurs in a different
cisternal subcompartment:
Proteins targeted for lysosomes are tagged with mannose 6-phosphate in the cis
cisterna.
A membrane similar in composition and thickness to the plasma membrane is acquired.
Mannose residues are removed in cis and medial cisternae.
Some proteins undergo terminal glycosylation with sialic acid residues and galactose.
Sulfation and phosphorylation of amino acid residues take place.
1,5,2,3,4
also takes place on polyribosomes at the surface of the RER, but rather than entering the lumen, the transfer process is halted (by a stoptransfer
sequence), and the transmembrane protein becomes anchored in the RER membrane.
Synthesis of transmembrane proteins
takes place on polyribosomes lying free in the cytosol and is directed by mRNAs that lack signal codons.
Synthesis of cytosolic proteins
Give the 2 types of Intracellular digestion
Nonlysosomal digestion and Lysosomal digestion
is the degradation of cytosolic constituents by mechanisms outside of the vacuolar lysosomal pathway.
Nonlysosomal digestion
is the degradation of material within various types of lysosomes by lysosomal enzymes.
Lysosomal digestion
A- FIRST TRUE
B- SECOND TRUE
C- BOTH TRUE
D- BOTH FALSE
The major site for the degradation of
unwanted proteins is the proteosome, a cylindrical complex of nonlysosomal proteases.
Proteins marked for destruction are enzymatically tagged with ubiquitin, which delivers them to the proteosome, where they are broken down to small peptides.
“C”
is the ingestion and degradation of foreign material taken into the cell by
receptor-mediated endocytosis or phagocytosis.
Heterophagy
is the segregation of an organelle or other cell constituents within
membranes from the RER to form an autophagic vacuole, which is subsequently digested
in an autophagolysosome.
Autophagy
is the fusion of hormone secretory granules and lysosomes and their subsequent digestion.
Crinophagy
TRUE OR FALSE
Crinophagy is used to remove excess numbers of secretory granules from the cell.
TRUE
A- FIRST TRUE
B- SECOND TRUE
C- BOTH TRUE
D- BOTH FALSE
Digestion of phagocytosed microorganisms occurs in multivesicular bodies
Digestion of endocytosed ligands and foreign particles begins and may be
completed in phagolysosomes.
“D”
first statement, “endocytosed ligands”
second statement, “phagocytosed microorganisms”
This constitutes the extracellular environment. It is an organized meshwork of macromolecules
surrounding and underlying cells.
Extracellular matrix
A- FIRST TRUE
B- SECOND TRUE
C- BOTH TRUE
D- BOTH FALSE
By affecting the metabolic
activities of cells in contact with it, the extracellular matrix may not alter the cells and influence their shape, migration, division, and differentiation.
Although it varies in composition, in general it consists of an amorphous ground substance (containing primarily glycosaminoglycans [GAGs],
proteoglycans, and glycoproteins) and fibers.
“B”
first statement, “may alter the cells”
are long, unbranched polysaccharides composed of repeating identical
disaccharide units.
GAGs (Glycosaminoglycan)
A- FIRST TRUE
B- SECOND TRUE
C- BOTH TRUE
D- BOTH FALSE
An amino sugar, either N-acetylglucosamine or N-acetylgalactosamine, is always one of
the repeating disaccharides.
Because GAGs are commonly sulfated and usually possess a uronic acid sugar, which
has a carboxyl group in the repeating disaccharide unit, they have a strong positive
charge.
“A”
second statement, “strong negative charge”
A- FIRST TRUE
B- SECOND TRUE
C- BOTH TRUE
D- BOTH FALSE
The attraction of osmotically active cations (e.g., Na_) to GAGs results in a heavily
hydrated matrix that strongly resists compression.
Their extended random coils occupy large volumes of space because they do not fold
compactly.
“C”
GAGs may be classified into four main groups
Hyaluronic acid, chondroitin sulfate, dermatan sulfate, heparin and heparan sulfate, and keratan sulfate.
is a very large unsulfated molecule up to 20 _m in length that is not attached to a core protein.
Hyaluronic acid
consist of a core protein from which many GAGs extend. These large molecules are shaped like a bottlebrush.
Proteoglycans
A- FIRST TRUE
B- SECOND TRUE
C- BOTH TRUE
D- BOTH FALSE
Proteoglycans act as binding sites for growth factors and other signaling molecules.
They confer unique attributes to the extracellular matrix in certain locations
“C”
are multifunctional molecules whose domains bind to components of the extracellular matrix and to receptors on the cell surface, thereby promoting adhesion between the cell and the matrix.
Glycoproteins
an adhesive glycoprotein, forms fibrils in the extracellular matrix.
matrix fibronectin
circulating plasma protein that functions in blood clotting, wound healing, and phagocytosis.
plasma fibronectin
A- FIRST TRUE
B- SECOND TRUE
C- BOTH TRUE
D- BOTH FALSE
Fibronectin has domains for binding collagen, heparin, various cell-surface receptors,
and cell adhesion molecules (CAMs).
It mediates cell adhesion to the extracellular matrix by binding to fibronectin receptors
on the cell surface.
“C”
is located in basal laminae, where it is synthesized by adjacent epithelial cells,
and in external laminae surrounding muscle cells and Schwann cells.
Laminin
A- FIRST TRUE
B- SECOND TRUE
C- BOTH TRUE
D- BOTH FALSE
The arms of this large cross-shaped glycoprotein have binding sites for cell surface
receptors (integrins), heparan sulfate, type IV collagen, and entactin.
Laminin mediates interaction between epithelial cells and the extracellular
matrix by anchoring the cell surface to the basal lamina.
“C”
is a component of all basal (and external) laminae. This sulfated adhesive glycoprotein binds laminin.
Entactin
TRUE OR FALSE
Entactin links laminin with type IV collagen in the lamina densa.
TRUE
is an adhesive glycoprotein most abundant in embryonic tissues.
Tenascin
A- FIRST TRUE
B- SECOND TRUE
C- BOTH TRUE
D- BOTH FALSE
Tenascin is secreted by glial cells in the developing nervous system.
Tenascin promotes cell–matrix adhesion and thus plays a role in cell migration.
“C”
a glycoprotein in cartilage, attaches chondrocytes to type II collagen.
Chondronectin
TRUE OR FALSE
By influencing the composition of its extracellular matrix, chondronectin plays a
role in the development and maintenance of cartilage.
TRUE
This extracellular-matrix calcium-binding glycoprotein found in bone is synthesized by
osteoblasts.
Osteonectin
A- FIRST TRUE
B- SECOND TRUE
C- BOTH TRUE
D- BOTH FALSE
Osteonectin has binding sites for type IV collagen and for integrins of osteoblasts and osteocytes.
Osteonectin plays a role in bone formation and remodeling and in maintaining bone mass by influencing calcification.
“Type I collagen”
They link fibronectin outside the cell to cytoskeletal components
inside the cell and may activate cell-signaling pathways which determine the
cell’s behavior
Fibronectin receptors
A- FIRST TRUE
B- SECOND TRUE
C- BOTH TRUE
D- BOTH FALSE
Fibronectin receptors, which belong to the integrin family of receptors, are
transmembrane proteins consisting of one polypeptide chains.
Because they enable cells to adhere to the extracellular matrix, they are known as
CAMs.
“B”
first statement, “two polypeptide chains”
is the most abundant structural protein of the extracellular matrix.
Collagen
[SEQUENCING]
Intracellular events in collagen synthesis occur in the following sequence:
Preprocollagen synthesis occurs at the rough endoplasmic reticulum (RER) and is directed by messenger ribonucleic acid (mRNAs) that encode the different types of chains to be synthesized.
Hydroxylation of specific proline and lysine residues of the forming polypeptide chain
occurs within the RER. The reaction is catalyzed by specific hydroxylases that require
vitamin C as a cofactor.
Attachment of sugars (glycosylation) to specific hydroxylysine residues also occurs
within the RER.
Procollagen triple-helix formation takes place in the RER and is precisely regulated by
propeptides (extra nonhelical amino acid sequences) at both ends of each chain. The
three chains align and coil into a triple helix.
Addition of carbohydrates occurs in the Golgi complex, to which procollagen is
transported via transfer vesicles. With the addition of carbohydrates, the oligosaccharide
side chains are completed.
Secretion of procollagen occurs by exocytosis after secretory vesicles from the trans-
Golgi network are guided to the cell surface along microtubules.
1,2,3,4,5,6
[SEQUENCING]
Extracellular events in collagen synthesis occur in the following sequence:
Cleavage of procollagen is catalyzed by procollagen peptidases, which remove most
of the propeptide sequences at the ends of each chain, yielding tropocollagen or simply
collagen.
Self-assembly of tropocollagen occurs as insoluble tropocollagen molecules aggregate
near the cell surface.
1,2
A- FIRST TRUE
B- SECOND TRUE
C- BOTH TRUE
D- BOTH FALSE
Synthesis of type IV collagen is unique in that it assembles into a meshwork rather than
fibrils.
Type IV collagen constitutes most of the lamina densa of basal laminae and external
laminae.
“C”
[ODD ONE OUT]
(1)The propeptide sequences are not removed from the ends of its procollagen
molecules.
(2) Its triple-stranded helical structure is interrupted in many regions.
(3) It forms head-to-toe dimers that interact to form lateral associations, creating
a sheetlike meshwork.
(3)
“head-to-head dimers”
an amorphous structural protein, imparts remarkable elasticity to the extracellular
matrix; 90% of elastic fibers or elastic sheets are composed of elastin.
elastin
A- FIRST TRUE
B- SECOND TRUE
C- BOTH TRUE
D- BOTH FALSE
Like a rubber band, after being stretched, the elastin returns to its original
shape once the tensile force is released.
Lysine residues of four different chains form covalent bonds called desmosine
cross-links to create an extensive elastic network.
“C”
a glycoprotein, organizes elastin into fibers and is the main component of the
peripheral microfibrils of elastic fibers.
fibrillin
A- FIRST TRUE
B- SECOND TRUE
C- BOTH TRUE
D- BOTH FALSE
Synthesis of elastic fibers is carried out by fibroblasts in elastic ligaments, smooth muscle
cells in large arteries, and chondrocytes and chondroblasts in elastic cartilage.
Synthesis begins with the elaboration of fibrillin microfibrils that appear near the surface
of the cell.
“C”
