Lecture 40: Cell Adhesion And Movement

Front 1

Describe homophilic interactions

Back 1

homophilic interactions are when cells interact with identical molecules on the surface of the cell they interact to

Front 2

Describe heterophilic interactions

Back 2

A cell adhesion receptor on one cell interacts with a different molecule on the surface of the cell to which it attaches

Front 3

Describe CAMs

Back 3

members of the immunoglobulin superfamily, well organized loops, interact homophilically with CAMs on adjacent cells

Front 4

Describe cadherins

Back 4

group of adhesive glycoproteins, important for cell-cell recognition and adhesion, require calcium to function, zip together

Front 5

Describe lectins

Back 5

carbohydrate binding proteins which promote cell cell adhesion by binding to a specific sugar or sequence of sugars on the cell surface

Front 6

What role do selectins play in leukocyte adhesion

Back 6

selectins are cell surface glycoproteins that mediate leukocyte adhesions to the endothelium

Front 7

Describe the actin and myosin motors in a stationary cell

Back 7

The plus ends of actin are found near the leading edge where G actin monomers are added. Myosin motors pull the actin rearward to create retrograde flow, when the cell is stationary these processes are balanced

Front 8

Describe the actin and myosin motors when a cell is moving forward

Back 8

Retrograde flow is resisted by attachment to the underlying substrate, reward movement of actin does not occur, polymerization drives the leading edge forward

Front 9

In order to crawl, what must a cell produce?

Back 9

extensions or protrusions at their front or leading edge two examples of such protrusions are lamellipodium and filopodium

Front 10

Describe the steps of cell crawling (3 steps)

Back 10

1. the leading edge extends via polymerization of actin at its tip
2. new adhesions, anchored by actin, form on the undersurface of the lamellipodium
3. the trailing edge of the cell detaches and is drawn foward by contraction of the cell body

Front 11

Explain how actin polymerization is involved in cell movement.

Back 11

Actin polymerization driven by Arp2/3 dependent dendritic branching . As actin polymerizes at the tip of a protrusion, the protrusion pushes forward. At the same time that extension of the tip of a protrusion is occurring , the polymeized actin is drawn toward the base of the protrusion where is is disassembled.

Front 12

Explain how integrins mediate cell-substrate attachment which is necessary for cell movement

Back 12

On the outside of the cell, integrins attach to extracelluar matrix proteins. Inside the cell, integrins are connected to actin filaments through linker proteins.

Front 13

What are focal contacts

Back 13

Indtegrin dependent attachments that are crucial for cell migration

Front 14

Describe leukocyte rolling adhesion (3 steps)

Back 14

1. rolling of leukocytes is mediated by selectins
2. prior to invading a blood vessel, integrins are activated and "snatch" the leukocyte
3. firm attachment to ICAM allows invasion

Front 15

What is the purpose of adhesive junctions

Back 15

adhesive junctions link cells together into tissues thereby enablling cells to function as a unit

Front 16

What are the two main types of cell cell adhesive unctions

Back 16

Adheren junctions and desmosomes

Front 17

What two proteins do adhesive junctions all contain

Back 17

intracellular attachment proteins (link the uction to cytoskeletal filaments) and cadherins (protrude on the outer surface of the membrane and bind cells to each other)

Front 18

Describe adherens junctions

Back 18

cadherin mediated adhesive junctions that interact with actin

Front 19

What are desmosomes

Back 19

strong adhesion between adjacent cells in a tissue, give the tissue structural integrity enabling cells to function as a unit and resist stress. It consists of two core proteins desmocollin and desmoglein

Front 20

Describe tight junctions

Back 20

leave no space between cells, connected along sharply defined ridges, claudins are the major trnasmembrane protein

Front 21

What are claudins

Back 21

Claudins in the plasma membrane of adjacent cells interlock to form a tight seal. they are the major transmembrane protein of the tight junction.

Front 22

Explain how tight junctions help to keep the plasma membrane of an epithelial cell polarized

Back 22

They acts as gates are prevent the movement of fluids and ions between cells. they also act like fences and block the lateral movement of of lipids and proteins within the membrane

Front 23

Describe gap junctions

Back 23

a region where the plasma membranes of two cells are aligned and brought into intimate contact. The gap junction provides a point of cytoplasmic contact between two adjacent cells through which ions and small molecules can pass. It allows cells to be in direct electrical and chemical contact with each other.

Front 24

How are the plasma membranes joined at a gap junction between two cells

Back 24

connexons

Front 25

What are hemidesmosomes involved in

Back 25

cell-basal lamina adhesion, localized points of attachment ,associated with intermediate filaments

Front 26

what proteins are responsible for the strength of the extracellular matrix

Back 26

collagens- they form fibers with high tensile strength, they form rigid triple helices and have unusual amino acids

Front 27

How is collagen formed?

Back 27

In the lumen of the ER, three alpha chains assemble to form a triple helix called procollage. Once procollagen is secreted from the cell into the intercellular space, it is converted to collagen by procollagen peptidase

Front 28

What role do elastins play in the extracellular matrix

Back 28

Elastins impart flexibility and elasticity to the ECM

Front 29

What role do proteoglycans play in the extracelluar matrix?

Back 29

Proteoglycans form the matrix in which elastins and collagen are embedded

Front 30

What is hyaluronate

Back 30

Hyaluronate molecules have lubricating properties and are most abundant in places where friction must be reduced

Front 31

What role do fibronectins play in the extracellular matrix

Back 31

Fibronectins bind cells to the extracellular matrix and guide celluar movement

Front 32

Explain the relationship betweeen fibronectin and cell shape/ movement

Back 32

fibornectin binds to cell surface receptors and to ECM components such as collagen and heparin. It functions as a bridging molecule that attaches cells to the ECM. Migrating cells are guided by binding to fibronecting moecule along the way

Front 33

What are laminins

Back 33

Laminins are a type of adhesive glycoprotein that are found on the basal lamina.

Front 34

Give some properties of the basal lamina

Back 34

serves as a structural suppor that maintains tissue organization and as a permeability barrier that regulates the movement of molecules and cells, prevents the passage of underlying connective tissue cells into the epithelium but permits the mirgration of white blood cells

Front 35

What are integrins

Back 35

cell surface receptors that bind ECM constituents, they are the primary means by which cells bind to ECM protiens like collagen, fibronectin, and laminin

Front 36

Do integrins link the extracellular matrix to the cytoskeleton directly?

Back 36

no, the tails of integrins interact with proteins in the cytosol that link integrins to cytoskeletal proteins

Front 37

What are focal adhesions

Back 37

focal adhesions mediate the attachment of migratory and non-epithelial cells to the extracellular matrix, focal adhesions contain clustered integrins that interact with bundles of actin microfilaments via linker proteins

Front 38

How do epithelial cells attach to laminin in the basal lamina

Back 38

they attach via hemidesmosomes

Front 39

describe the linker proteins in hemidesmosomes

Back 39

the linker proteins in hemidesmosomes form a dense plaque that connects clustered integrins to the cytoskeleton. Among the linker proteins, members of teh plakin family are prominent.