Flashcards in The Cytoplasm Deck (76):
First zygotic cellular division produces cells called
Blastomeres of the inner cell mass that are transfered to tissue culture
Embryonic stem cells
Cells undergo a specialization process in which they differentially express sets of genes that mediate specific cytoplasmic activities becoming efficient in specialized functions
limiting membranes that envelop all eukaryotic cells
Plasma membrane Also called cell membrane/ plasmalemma
Function of cell membrane
1.Selective barrier regulating the passage of material into and out of the cell and facilitating transport of molecules
2.Keep constant ion content of cytoplasm
3.Carry no. Of specific recognition and signaling functions (role in interactions of the cells with its environment)
Are Plasma membrane protein linked to both the cytoskeleton and ECM components.
Under which microscope can the cell membrane can be seen and why
Since thickness is between 7.5-10 nm can only be seen under the electron microscope
What part of the cell can be seen under a light microscope
The line between adjacent cells consist of plasma membrane protein plus ECM materials
Are amphipathic consisting of 2 non polar (hydrophobic) long chain fatty acids linked to a charged polar (hydrophilic) head that bears a phosphate group. They are stable when in bilayer with fatty acids chains located in the middle away from the water
Sterollipids inserted at varying densities among the closely packed phospholipids fat acids. They are amphipathic
Phospholipids on the outer layer are mostly glycolipids which are lipids with attached oligosaccharide chains that extend outward from the cell surface
Cytoplasmic membrane under electron microscope
Exhibit Trilaminar appearance after fixation with osmium tetroxide, osmium binds to the polar head of phospholipid and the oligosaccharide chains producing two dark lines that enclose the light band of osmium free fatty acids.
Incorporated directly within the lipid layer
Bound to one of the two membrane surfaces
How can peripheral Proteins be extracted
With salt solution
Integral protein extraction
Only my using detergents to disrupt the lipids
The polypetide chains of many integral Proteins span the membrane from one side to the other several times
How are Proteins integrated into the bilayer
Due to hydrophobic interaction between the lipids and non polar amino acids of Proteins
Delicate cell surface coating formed by Carbohydrate moieties, oligosaccharide of glycolipids and glycoproteins.
Function of Carbohydrate moieties of the glycocalyx
1.Act as receptors
4.Response to protein hormones
Protein are able to move laterally. Membrane protein comprise a movable mosaic within the fluid lipid bilayer - fluid mosaic model
How is lateral diffusion restricted
1.by their cytoskeletal attachments
2.in epithelial cells tight junction between cells
3.Proteins that are components of large enzymes are less mobile
Involved in transduction of signals from outside the cell. Specialized membrane patches with high concentration of cholesterol and saturated fatty acids which reduce fluidity
Function of cholesterol
Affect the packing of fatty acids chains
Effect on membrane fluidity
Transport of small non polar molecules through the lipid layer lipophilic molecules
Multipass Proteins forming transmembrane pores through which ions or small molecules pass selectively
Transmembrane protein that binds small molecule and translocate then via confirmational change
Enzymes engaged in active transport utilizing energy from the hydrolysis of ATP against steep concentration gradient. Because the consume ATP pumps they are referred to as ATPase
Macromolecules enter the cell by being enclosed within folds of plasma membrane which due and pinch of internally to form vesicles
3 types of endocytosis
3. Receptor-mediated endocytosis
Ingestion of particles such as bacteria or dead cell remnants.
Cells specialized for Phagocytosis activity
Macrophages and neutrophils
Vacuole formed by Phagocytosis
Involves smaller invagination of cell membrane which fuse and entrap extra cellular fluid and is dissolved content the Pinocytotic vesicles pinch off inwardly. Either rise with lysosomes or move to opposite cell surface and fuse with the membrane and release their content outside the cell
Cytoplasmic cytoskeleton consist of
3. intermediate filaments
Microtubules organised into larger more stable arrays called axonemes in the cytoplasmic extensions called cilia and flagella. two more microtubules linked side-by-side by protein arms or bridges.
Protein subunits of microtubules
Heterodimer of alpha and beta tubulin each with the Molecular mass of 50kDa. Under appropriate conditions in the tubulin in heterodimers polymerize to form microtubules which have a slightly spiral organization
structure of Microtubules
Tubulin subunit align length wise to form protofilaments, with 13 parallel protofilaments forming the circumference of a microtubule wall. Each microtubule is hollow with the outer diameter 25 nm and wall thickness 5 nm, length varies.
What causes polymerization of tubulin
Directed by microtubule organizing center (MTOCs) which contain short assembly of tubulin that act as nucleating sites for further polymerization
Polarity of microtubules
microtubules have a positive and negative end therefore are polarized structures with growth occurring more rapidly at the positive end
Relative stability of microtubules
Microtubule show dynamic instability with continuous cycle so polymerization and depolarization at steady state conditions which depend on concentration of tubulin, calcium, magnesium and presence of various microtubule associated Proteins (MAPs). Stability varies greatly with cellular location
DOMINANT MTOC in most cells is
Centrosones, which is organized around two cylindrical centrioles about 0.2 micrometers in diameter and 0.3-0.5 micrometers in length
Composed of 9 high organized microtubule triplets.
Function of centrioles
1. organize nearby tubulin complexes and other protein as a Pericentriolar matrix found close to nucleus of non dividing cell
2. System of intracellular transport of membranous vesicles, Marco molecular complexes and organelles
Centrioles during mitosis
Before cell division during dna replication each centrosome duplicates itself so that it has two pairs of centrioles. during mitosis the centrosome divides into half which move to opposite poles of the cell and become organizing centers for the microtubules of the mitotic spindle
Examples of microtubules as in just cellular transport system
1. Axoplasmic transport in neurons
2. transport in pigment cells
3. chromosome movement by mitotic spindle
4. movement among different cell compartments
Mechanism of transport along microtubules
controlled by proteins call motor proteins, which use ATP in moving the large structures. Kinesins carry material away from the MTOC near the nucleus to the plus end of the microtubules ( anterograde transport), cytoplasmic dyneins carry material along microtubules in the opposite direction (retrograde transport) generally towards the nucleus.
At stable tubulin concentration some microtubules grow while others shrink each existing in a condition called dynamic stability
Mechanism of dynamic instability of Microtubules
Where tubulin conc. is high tubulin GTP is added at the microtubules faster than the incorporated GTP can be hydrolyzed. the resulting GTP cap stabilizes that end of the microtubule and promotes rapid growth. Free tubulin conc. decrease, rate of growth decreases allowing GTP hydrolysis to catch up the resulting GDP cap is unstable and favor rapid depolarization - termed catastrophe. This increases local conc of free monomeric tubulin that stop the microtubule from completely disappearing by producing another shirt period of Microtubule elongation
function of microfilaments
Motility and contractile activities of the cell
Structure of microfilaments
Thin, polarized polymers, shorter and more flexible. Composed of G-action monomers that assemble into double stranded helix of filamentous F-actin
Formation of microfilaments
G-actin assembled in the presence of K+and Mg2+ into filamentous F-actin.
1. G-actin generally added to preexisting filaments
2. New filaments formed from pool of G-actin by action of nucleating protein - formin
3. Complex of polypeptides - Arp2/3 bind to the side of preexisting actin filament and induce new F-actin branch leads the formation of a microfilament network
Plasma membrane consist of
proteins, and oligosaccharide chains covalently linked to phospholipid and protein molecules.
Function of integrin
Exchange of influences in both directions between the cytoplasm and the material in the ECM
Fiction of cholesterol
restricting the movement of the phospholipid fatty acids in the cell membrane and modulating their fluidity
General mechanisms that allow the movement of most small molecules cross the membrane
Process of Phagocytosis
When a bacterium bound to the surface of a cell it becomes surrounded by extension of plasmalemma and cytoplasm in a process dependent on cytoskeletal changes. Fusion if the membrane encloses the bacterium in an intracellular Phagosome which merges with lysosomes for degradation.
Process where pinocytotic vesicles may
move to the opposite cell surface where they fuse with the membrane and release their contents outside the cell.
Function of transcytosis
This accomplishes bulk transfer of material across the cell
Receptors are integral membrane proteins at the cell surface. High affinity binding of ligands such as low-density lipoproteins and protein hormones, to their receptors causes these proteins to aggregate in special membrane regions that then invaginate and pinch off internally as vesicles.
are regions of the cell membrane specialized in receptor-mediated endocytosis occupied by receptors associate with other proteins on the cytoplasmic membrane surface and begin invagination
electrondense coating on the cytoplasmic surface of coated pits contains several polypeptides, a major one being:
Function of clathrin molecules
interact like the struts in a geodesic dome, forming that region of cell membrane into a cage-like invagination that is pinched off into the
cytoplasm as a coated vesicle with receptor ligands inside.
Another type of receptor-mediated endocytosis very prominent in endothelial cells uses invaginations called caveolae that involve the membrane protein caveolin.
a dynamic system of membranous tubules and vacuoles of various sizes and shapes located in the cytoplasm near the cell surface (early endosomes) or deeper in the cytoplasm (late endosomes).
common path of the vesicles after endocytotic processes
1.vesicles produced quickly enter and fuse with the endosomal compartment,
2.The clathrin molecules separated from the coated vesicles recycle back to the cell membrane to participate in the formation of new coated pits.
3.vesicle trafficking through the endosomal compartment is directed through peripheral membrane G proteins called Rab protein.
Small GTPases that bind guanine nucleotides and associated Proteins.
Ligands may have different fates within the endosomal compartment:
1. Receptors and ligands may be carried to late endosomes and then to lysosomes for
2. Ligands may be released internally and the receptors recycled to the cell surface.
3. Vesicles may move to and fuse with another cell surface, where the ligands are released
again outside the cell (transcytosis).
How do endosomes activate lysosomes
The menace of many late endosomes have ATP driven H+ pumps that acidify the interior and thus activate the hydrolytic enzymes of lysosomes
In this process a membrane-limited cytoplasmic vesicle fuses with the plasma membrane, resulting in the release of its contents into the extracellular space without compromising the integrity of the plasma membrane.
Exocytosis is triggered in many
transient increase in cytosolic Ca2+
Protein secretion involving exocytosis may follow two pathways:
1.Constitutive secretion: for products that are released from cells continuously, as soon as
synthesis is complete, such as procollagen for the ECM.
2. Regulated secretion occurs in response to signals coming to the cells, such as the release of digestive enzymes from pancreatic cells in response to specific stimuli.
A process of membrane movement and recycling. Portions of the cell membrane become part of the endocytotic vesicles or vacuoles during endocytosis; during exocytosis, membrane is returned to the cell surface.
Importance of membrane trafficking
1. crucial for maintaining the cell
2.and for physiologically important processes such as reducing blood lipid levels.
Subpopulations of vacuoles among the early and late endosomes in many cells accumulate small
vesicles and tubules within their lumens by further invaginations of their limiting membranes becoming multivesicular bodies.