Dunn M&C - Cytoskeleton & Cell Interactions

basement membrane / basal lamina

most abundant types of animal cell ECM; underlies epithelial tissue and interstitial matrix of connective tissue

extracellular matrix (ECM)

A complex network usually of proteins and carbohydrates that provides structural and biochemical support to surrounding cells; influences cell shape and gene expression

• experimentally what is left lover after you decellularize a tissue

• most ECM molecules have glycoproteins (protein and carb components)

interstitial matrix of connective tissue

makes up the bulk of connective tissue

epithelial tissue

solid cells; interacting w/ one another

connective tissue

cells are not interacting on all sides w/ each other; dispersed

characterized by sparse cells and substantial amounts of extracellular matrix (ECM)

collagen

abundant ECM protein

fibroblasts

the primary cells responsible for producing and maintaining the extracellular matrix (ECM) in connective tissues

skin layers

epidermis and dermis

epidermis

several cell layers thick and is an epithelial tissue — here mainly keratinocytes (IFs) but also melanocytes

dermis

mostly made up of connective tissue

• also contains the nerve endings and blood vessels

• strong and flexible

• the main cell type found here is fibroblasts, which synthesize the extracellular matrix and repair wounds

animal cell ECM

in animals; made up of proteins, glycoproteins, and carbohydrates that provide structural and biochemical support to surrounding cells.

integrins

transmembrane receptors that facilitate cell-ECM adhesion, allowing cells to bind to the extracellular matrix and communicate with their environment.

• used in adhesion junctions

cadherin

integral membrane protein that play a crucial role in cell adhesion, helping cells stick together and communicate

• attaches to the cytoskeletal proteins on the cells interior which couples a cell’s skeleton to its neighbor’s

• used in adhesion junctions

adhesion junctions

cells need to stick to one another and to ECM to form/maintain tissue

occluding junctions

prevent passage of hydrophilic solutes from one side of cell layer to the other (“ziploc”); prevents food in the gut form passing into the surrounding tissue; prevents apical PM proteins from diffusing to the basolateral membrane

• cells with junctions aresealed together, maintaining compartmentalization.

channel-forming junctions

sharing small molecules in the cytosol; makes cell-signaling faster so that cells in a tissue can coordinate their activity temporally

tight junction

occluding junction; seals cells together like ziplock to create a barrier

desmosomes

adhesive intercellular junctions that strengthen tissues by linking the intermediate filament cytoskeletons of adjacent cell

gap junctions

channel-forming junctions; acts as channels between cells allowing direct communication and exchange of small molecules.

plant cell wall

extracellular matrix of plant tissues; made up of different types of carbohydrate polymers (nitrogen (needed for proteins) is scarce)

cellulose

tensile strength (resistance to pulling) in plant cell walls, providing structure and support.

keratinocytes

primary cell type found in the epidermis, making up about 90% of its cellular content. They are responsible for forming the protective barrier of the skin by producing keratin, a fibrous protein that provides strength and water resistance

melanocytes

specialized skin cells located primarily in the basal layer of the epidermis. They are responsible for the production of melanin, the pigment that gives skin, hair, and eyes their color

only applies to actin microfilaments and microtubules

1. Structures can be quickly depolymerized and reassembled

2. Subunits are available in a pool to construct new polymers as needed by the cell

3. A large number of cellular proteins bind to cytoskeletal filaments to regulate their stability and organization

true for all three cytoskeletal structures

structures of variable size can be built.

microtubules

A hollow tubule formed from tubulin dimers (alpha-tubulin and beta-tubulin), subunits.

• emanate from the centrosome (stuck) near cell center (minus ends at the centrosome, + ends toward the plasma membrane)

• can act like roads for motor proteins to walk on

• dividing cells use these to move the duplicated chromosomes and the actin/myosin to pinch the cell in two

microfilaments

a double helix of actin monomers

• most concentrated underneath the PM (like the nuclear lamina to the PM)

intermediate filaments

A strong fiber composed of intermediate filament proteins. has fibrous subunits twist together, solid proteins with no holes (not hollow)

• not all cells have this

• stretch throughout the cell PM-to-PM

• provides resistance to mechanical stress

• all built in the same way; the exact sequence of the monomer differs from one type of IF to another

• NOT polar (therefore symmetrical), therefore has no (known) motor proteins

cytoskeletal functions

present in prokaryotes too

1. structure and support

2. intracellular transport

3. contractility and motility

4. spatial organization

motile cells

can use flagella (microtubule-based) to swim or actin-myosin to crawl

microtubules and microfilaments

have polarity — subunits are preferentially added to the plus ends and preferentially lost from the minus ends [not charge-based, just two opposite ends] (intermediate filaments do not have polarity).

plus end

the end where it is fast-growing of subunits

minus end

where subunits is slow-growing or typically lost

microtubules near centrosomes

minus ends at centrosomes, plus ends toward the plasma membrane. kinesins walk secretory vesicles to the plasma membrane.

• grow and shrink from the centrosome. the subunits are gained and lost from the plus end

kinesins

+ (plus) end directed microtubule motor proteins that usually carry secretory vesicles; carries cargo

dynamic instability

this spontaneous growing and shrinking behavior; where subunits are constantly gained and lost from the plus end

• grows, lost momentum, falls apart.

cytoskeletal motor proteins

bind and hydrolyze ATP (to ADP), to fuel a conformational rearrangement that causes the motor protein to move relative to the cytoskeletal fiber (microfilaments and microtubules only)

• these are directional

conformational rearrangements

significant shape change of proteins

myosin

the most famous for its role in muscle contraction; most ____ are + end directed; carries cargo

dynein

(-) minus end directed microtubule motor protein; found near the nucleus, will keep the Golgi in its place.

• induces sliding of microtubules doublets past one another, forcing the cilium/flagellum to bend (uses ATP hydrolysis)

cilia and flagella

specialized motile structures based on microtubules; most cells don’t use them for motility

actin

a protein that helps cells maintain their shape, with crawling and muscle contraction, membrane extensions and cytokinesis

• microfilaments allow eukaryotic cells to adopt a variety of shapes and perform a variety of functions. MF can connect to PM complexes.

microvilli

non motile actin structures which increase surface area of the plasma membrane in the gut lining to increase the efficiency of nutrient absorption

• take all nutrients from diets (stuffed actin microfilaments)

lamellipodia

actin can form these sheet-like structures that pushes a cell forward — “cell crawling”

• form near ends/edges

nuclear lamina

supports nuclear envelope; major cytoskeletal structure inside the nucleus constructed from lamin intermediate filaments

thick filaments

myosin assembles tail-to-tail, forming a symmetrical, overlapping structure

sarcomeres

symmetrical structures containing actin filaments and thick filaments. to contract a muscle, these shorten in length