Connects the actin microfilaments of one cell to another
Connects the intermediate filaments of one cell to another. Main function is to provide mechanical strength.
Anchors a cell via its intermediate filament to the Extra cellualr matrix.
Actin-linked cell matrix junctions
Anchors a cell via its Actin microfilaments to the ECM
Family of proteins that mediate attachments of cells to cells. Take their name from reliance on Ca++
Family of proteins that mediate attachment of cells to ECM
Interactions between two of the same extracellular molecules.
Interactions between two different extracellular molecules
Principal of cadherins that multiple linkages of homphilic cadherins make a stronger than individual attachment that can still be dissasembled by suquestialy seperating them.
Formed from a continuous loop of adhesion junctions that close beneath the apical face of the epithelial layer encircling each of the interacting cells in the epithelial sheet.
Two functions of occluding juctions
1. Forms a junction called a tight junction that seals the gap between two cells. 2. Function as 'fences' helping to separate areas of the plasma membrane to stop certain proteins and lipids from getting into the basil Lamina, keeps the polarity of epithelial cells.
Claudins and Occludins
Proteins in occluding tight junctions that are arranged in strands along the line of the junction to create the seal. Caludins are the main protein.
Protein complexes that form in gap junctions where small inorganic ions and water soluble molecules may pass. They pass through both cells membranes to form a single pathway.
Sub protein of Connexons, 4-pass transmembrane proteins six of these make a connexon.
Functions of Gap junctions
1.In tissues containing electrically excitable cells, cell-cell coupling via gap junctions allow action potentials to spread rapidly from cell to cell. 2. Allows neighboring cells to share signaling information.
Basic organization protein of the Basal Lamina, formed from three long polypeptide chains linked together via disulfide bonds, that can self assemble in vitro. (Also active in ECM)
Type IV collagen
Second protein of basal lamina which gives the BL its tensile (resistance to stretch) strength. Made up of triple helix of proteins. Proteins have every third amino acid as glycine and than any other two proteins.
nidogen + perlecan
Proteins that links t4 collagen to laminin proteins together when forming the basal lamina.
Role of ECM in cell behavior
Cell survival, division, mirgration, shape and function
specific cells that secrete an abundance of the proteins that make up the ECM of connective tissues.
Cells of the fibroblast family that secrete proteins and protoglycans (gags)that make up cartalige
Cells of the fibroblast family that secrete proteins and protoglycans (gags) that make up bone.
contain 1-60% carbohydrates by weight in the form of numerous relatively short, branched oligosaccharide chains.
Fibrous proteins in matrix of connective tissue
Collagens, fibronectin, elastin +
are distinguished fr om glycoproteins by the nature, quantity and arrangement of their sugar side chains. They have a small protein part and can contain as much as 95% carbohydrates by weight in the form of long, unbranched chains (~80 sugars long).
They are called GAGs because one of the two sugars in the repeating disaccharide is always an amino sugar (N-acetylglucosamine or N-acetylgalactosamine), which in most cases is sulfated. Because there are sulfate or carboxyl groups on most of their sugars, GAGs are highly negatively charged. They are the most anionic molecules produced by animal cells.
Main function of GAGs
is to resist compression and serve as a space filler. They do this by creating swelling pressure by creating large areas that attract mollecules like Na+ that bring in water to the area.
Only GAG that does not have a protein attached, made from 25000 of the same polysacharide. DOES NOT CONTAIN sulfated sugars. Facilitates cell migration.
Except for hyluronan all GAGS are
covalently asttached to proteins to form proeoglycans
Major protein of the ECM of which Colalgen I is the most common and principal molecule of bone and skin. Bone with Ca crystals.
Provide tensile strength to connective tissues, or resist strechting forces. Mesh work in skin to resist stretching in multiple directions.
Elastin + Elastin function
Gives tissues ability to stretch and bounce back like a rubber band. Collagen fibers are usually 'woven' in to limit extent of stretching.
Helps cells connect to the ECM, also acts as tracks in developing tissues.
General characteristics of actin microfiliaments
Helical polymers of actin protein, (2 chains) Structually polar, shorter more flexible than microtubulals.
Mechanisms of Polymerization and Depolymerization is similar to micro tubulars except for
ATP cap instead of GTP cap
Nucleation can be catalyzed by a complex of proteins that includes
two ARPS ARP 2/3 compex
Primary protein is Myosin II, F-actin in tight bundles with oppisite polarities. Function: Contraction, motility, cytokenisis, adhesion to surfaces.
Primary protein is Arp 2/3. Polar, f-actin in bundles Filopida, microvilli, lamelillopedia.
gel-like network (actin)
f-actin in a cross linked pattern making a viscous 3d array. Makes up cell cortex.
Responsible for a large amount of cellular movements.
membrane trafficking, cell motility, cytokinesis, organelle transport
skeletal muscle, smooth muscle, and non muscle. Conventional myosin, Crucial for the movement of opposite oriented F-actin: generates tension in stress fibers, contractile ring, adhesion belts, and muscle contraction
Cells reproduce by duplicating their contents and dividing in two, a process called
The Cell Cycle
Longest phase of cell cycle
Interphase 90% of time.
1. The first ‘gap’ stage after the M phase. What happens? i.Cell growth ii.Gene transcription iii.Protein synthesis iv.DNA repair v.Monitors/responds to external (nutrients, signaling molecules) vi.Organelles divide•
Replication, but not seperation of DNA
Growth continues, final preperation for M phase.
M phase (general) two major sections of M phase
1. Mitosis phase 2. Cytokenesis
Prolonged resting phase of cells where no activity is taking place replication wise.
Mitosis overview and phases.
Phase where division of cell into two identical daughter cell occurs. 1.Prophase 2.Prometaphase. 3.Metaphase 4.Anaphase 5.Telophase.
Cytoplasm is divided in two by a contractile ring, which pinches in the cell to create two daughters, each with one nucleus II. Tightening of contractile ring belt produces cleavage furrow. This belt is a bundle of actin microfilaments, myosin II, and other associated proteins III. Reformation of the interphase cytoplasmic microtubules IV. M phase ends, cells enters G1 phase
What happens in prophase?
I.Replicated chromosomes (each consisting of two closely associated sister chromatids) condense, which is aided by DNA binding protein condensin II.Sister chromatids held together by cohesin III.Mitotic spindle starts to assemble IV.Centrosomes separate V.Kinetochores form on centromere region
What happens in prometaphase?
Abrupt breakdown of the nuclear envelope allowing the chromosomes to attach to spindle microtubules via their kinetochores
What happens in Metaphase
Paired kinetochore microtubules on each chromosome attach to opposite poles of the spindle. There are three populations of spindle microtubules that make up the mitotic spindle: kinetochore, interpolar, astral II Chromosomes are aligned at the equator of the spindle, midway between the spindle poles forming the metaphase plate
What happens in Anaphase
Sister chromatids synchronously separate, and each is pulled slowly toward the spindle pole it is attached to. Kinetochore microtubules get shorter, and the spindle poles also move apart, both contributing to chromosome segregation
What happens in Telophase
I. Kinetochore microtubules depolymerize II. Interpolar microtubules elongate further and continue to push spindle poles apart III. Nuclear envelope reforms IV. Condensed chromatin expands V. Contractile ring forms, identifying the plane of division
form ring like structures and help to coil the mitotic chromatids into smaller, more compact structures that can be more easily segregated during mitosis
Sister chromatids are held together by protein complexes called cohesins, which assemble along the length of each sister chromatid as the DNA is replicated in S phase • Cohesins form protein rings that surround the sister chromatids keeping them united•
Kinetochore assemble on the condensed chromosomes during late prophase• Kinetochores attach chromosomes to the mitotic spindleV
Three microtubulas that make up the mitotic spindle
astel, interpolar, kenetochore
Plate formed in metaphase from chomotid that is lining up in the center of the cell in preperation for seperation.
Anaphase promoting complex (APC)
triggers the separation of sister chromatids by promoting the destruction of cohesins• Activated APC indirectly triggers the cleavage of the cohesins that hold sister chromatids together
Phase in which chromtid are pulled apart by kenetochore that are getting smaller or retracting.
Phase in which chromtid come apart becuase the interpolar microtubles are elongating or pushing apart.
Cell cycle control system
triggers the major processes of the cell cycle
Two key families of proteins control cell cycle
Cyclins and Cdks
Regulatory subunits of Cdks
Kinsaes that initialize and sustain events within the cell cycle
_________levels in the cell rise and fall with the stages of the cell cycle but the ________ levels remain stable
Induced by the higher concentration of cyclins in the cell that activate g1-cdk, pressing the cell twoards s phase. It relies on extracellular signaling for initiation
Triggers the cell to enter S phase, leading to replication of DNA
In early G1, the regulatory protein _______ associates with the ORC
When DNA is damaged, specific protein kinases respond by activating the ___ protein and halting its normal rapid degradation
Activated p53 protein then accumulates and binds to DNA There it stimulates the transcription of the gene that encodes the Cdk inhibitor protein ____ which then binds to G1/S-Cdk and S-Cdk and inactivates them, so that the cell cycle arrests in G1
Cdk that drives cell into M phase, requires phosphoralation at one spot and dephosporalation at two others. This is catalysed by Cak which phophoralizes one side and Wee1 which phosphorlizes at the two other spots. Than Cdc 25 dephops two spots activating the M-cdk
enzyme that phosporaltes M-Cdk
enzyme that phosphoralizes M-cdk at two spots
M-Cdk positive feedback loop
As M-Cdk is activated it phosphoralates more Cdc25 which in turn activates more M-Cdk
Degrades cycline at the end of mitosis.
Controlled mass death of cells.
Benefit of Apoptosis over cell death
Controlled, does not release contents causing swelling in other cells and tissues around dead cell.
Characteristics of apoptosis
Cell shrinks chromotomes condense , cytoskeleton colapses, nuclear envelope and other membranes disasemble, DNA breaks into fragments, Phag cells come and clean.
are activated by proteolytic cleavage in response to both extracellular (hormones, growth factors, nitric oxide) and intracellular (cell's response to stress) signals that induce apoptosis
is released from mitochondria due to the formation of large channel • Cytochrome c binds to an adaptor and ATP which then cleaves procaspase resulting in caspase
Classes of cell junctions in animals.
1.anchoring 2.occluding 3.channel forming or gap junctions
accessory anchor proteins
assemble at the tail of Cadherins to indirectly link cadherin to the ECM
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