Cell Bio Exam 3

overall role of cytoskeleton

organize and position organelles within cell, structural support, intracellular transport

filaments are held together by ____ interactions between protein subunits

noncovalent

benefit of noncovalent interactions for holding together filaments

allows for dynamic assembly and disassembly

most stable and durable filaments

intermediate filaments

intermediate filaments are the (thinnest/middle/thickest) of the three major types of protein filaments

middle

intermediate filaments provide cells with

mechanical strength

intermediate cells are important to tissues that are constantly exposed to

stress and stretching

in animal tissues, proteins/protein filaments form this structure to connect neighboring cells

desmosomes

benefit of a continuous mechanical link across multiple cells (intermediate filaments)

forces are distributed rather than single cells being damaged

intermediate filaments are found in the

cytoplasm, nucleus

steps of building intermediate filaments (long, twisted, ropelike)

1) 2 monomers coil together to form a coiled-coil dimer
2) 2 dimers come together anti-parallel to form a tetramer

3) tetramers assemble laterally

4) ends of tetramer bundles join together to form growing filament

type of interactions involved in building of intermediate filaments

noncovalent

purpose of nuclear lamina

structural support to nucleus

lamins in mitosis

1) prophase - lamins are phosphorylated to trigger the disassembly of nuclear envelope

2) after mitosis - dephosphorylation for reassembly of nuclear lamina around daughter nuclei

1) cytoplasmic intermediate filaments (are/are not) regularly disassembled by phosphorylation during mitotic cycles

2) nuclear lamins (are/are not) regularly disassembled by phosphorylation during mitotic cycles

are not, are

nuclear lamins are _____ to actin filaments and microtubules by______

cross-linked, linker proteins

stiff, hollow tubes made from protofilaments, arranged side by side to form a hollow cylindrical structure

microtubules

dimer of microtubules

protofilaments

in protofilaments of micro-tubules, alpha-tubulin is at the (plus/minus) end, while beta-tubulin is at the (plus/minus) end

minus, plus

protofilaments align (head to tail/tail to head) for structural polarity

head to tail

tubulin dimers (microtubule subunits) are held together by ___ interactions

noncovalent

centrosome

major microtubule organizing center in animal cells

dynamic instability

ability for individual microtubules to rapidly switch between growth and shrinkage

energy source and signaling molecule for microtubule growth (and to end growth)

GTP - guanosine triphosphate

tubulin binds to ____ to promote microtubule growth

GTP

what can be done to GTP to weaken a microtubule lattice

hydrolyze to GDP

what creates dynamic instability in microtubule structures

switch between GTP and GDP bound states of tubulin

practical advantage of dynamic instability in microtubule formation

rapid remodeling during mitosis and intracellular transport

purpose of GTP cap

stabilizes end of microtubule at the plus end

result of loss of GTP cap

rapid shrinkage of microtubule

benefit of consistent polarity of microtubule filaments

supports directional transport of vesicles and organelles over long distances

motor proteins that move cargo towards the plus end (outwards)

kinesins

motor proteins that move cargo towards the minus end (inwards)

dyneins

what property of kinesins ensure efficient use of ATP for long distances

kinesins can take many consecutive steps without detaching from the microtubule

many hairlike (sometimes) motile organelles on the surface of many eukaryotic cells

cilia

motile cilia

many, beat around fluid to move cell

non-motile/primary cilia

one, sensory organelle to monitor properties of extracellular fluid

flagella

occur singly/in pairs, beating patterns (waveforms)

purpose of actin filaments

helps shape plasma membrane, supports cell structure

location of actin filaments

cell cortex - outer area within cell

the polymer of actin filaments _____ assemble into ______

G-actin, F-actin

F-actin filaments are organized into

ordered arrays, highly branched networks, or tightly anchored bundles

important role of actin filaments

major contractile muscle protein in eukaryotic cells

actin filaments have ____ within their monomoers, with a barbed (plus/minus) end and a pointed (plus/minus) end

consistent polarity, plus, minus

4 actin-binding proteins

formins, integrins, ARPs, myosins

Formins (actin-binding protein)

promote formation of unbranched, linear actin filaments (filopodia, stress fibers)

Integrins (actin-binding protein)

transmembrane proteins, connect ECM to actin cytoskeleton via intracellular adaptor proteins

ARP (actin-related protein) complexes (actin-binding protein)

nucleate and promote formation of branched actin networks (lamellipodia)

myosins (actin-binding protein)

motor proteins moving plasma membrane or vesicles against actin filaments

primary function of cellulose microfibrils in plant cell wall

tensile strength, resistance to stretching

glucose monomers are produced (internally/externally) and then transported across the membrane to the site of ______

internally, polymerization

allows a plant’s primary cell wall to expand during growth

flexibility of the primary wall

deposited inside the primary cell wall once cell growth stops for rigidity and strength

secondary cell wall

generates turgor pressure (outward force) in plant cells

osmosis into the vacuole

effect of lignin on properties of plant cell wall

increases rigidity and waterproofing in woody tissues

directs the orientation of cellulose deposition during wall formation

cortical microtubules (guide the orientation of cellulose fibers)

role of cellulose synthase complexes in plant cells

assemble cellulose microfibrils

microtubules (do/do not) physically attach to the outer cell membrane to guide cellulose deposition

do not

protein family responsible for linking adjacent cells together at adherens junctions

cadherins

Cadherins (are/are not) dependent on calcium

are

specialized cell to cell junctions composed of cadherins and other proteins

adherens junctions

type of actin network forms when Rac activates Arp2/3

branched actin network

small GTPase regulating actin cytoskeleton remodeling during adherens junction formation

Rac

meshwork of actin filaments and associated proteins just beneath cell membrane (structural support, cell shape changes)

cell cortex

makes cell cortex softer, more pliable, allows membranes of adjacent cells come into close contact

branched actin network

cell-cell contact is made possible when the cell cortex becomes (harder/softer)

softer

two main structural proteins in animal connective tissue

collagen and elastin

protein in animal connective tissue responsible for resistance to b

protein in animal connective tissue responsible for elasticity, allows tissue to stretch and recoil

elastin

what happens to tissue when elastin is digested

how is elastin digested

trypsin treatment

main cell type responsible for organizing collagen fibers in the ECM

fibroblasts

how do fibroblasts align collagen fibers after secretion?

use cytoskeletal contraction of fibroblasts to pull and align fibers

structure of collagen fibers formed by fibroblasts and benefit

organized sheets/bundles, structural integrity and strength of tissues to withstand mechanical strength

unique features of hyaluronic acid compared to other GAGs

synthesized at plasma membrane (other GAGs made in golgi apparatus), not sulfated or covalently attracted to a core protein (exists as free polysaccharide chain)

function of hyaluronic acid in tissues like cartilage and the eye

forms large, hydrated networks for lubrication and cushioning, fills space and absorbs shock

fibronectin’s role in the extracellular matrix

connects collagen/elastin in ECM to integrins in cells

which receptors does fibronectin bind to on the cell surface?

integrins

transmembrane receptor proteins that connect ECM components to cytoskeleton

integrins

integrins link ECM to actin filaments in cytoskeleton through

adaptor proteins

what does the beta subunit of integrins connect to inside the cell?

adaptor proteins

____ subunits can pair with multiple ____ subunits, while ____ subunits cannot do the same

beta, alpha, alpha

what type of tissues rely on alpha7 integrin subunits

muscle tissues (alpha7 subunits are muscle-specific

proteoglycans are composed of

core protein + GAG chains

property of proteoglycans due to GAG chains

attracts water to make the ECM gel-like

Which ECM component mainly resists compression?

Proteoglycans - core protein + GAG chains

Which ECM component mainly provides tensile strength?

Collagen

What are the main components of the basal lamina?

Type IV collagen

What distinguishes type I collagen from type IV collagen?

Type I forms fibrils; type IV forms a mesh.

What is the main function of the basal lamina?

Anchors and filters cells; supports tissues and mediates signaling.

What does TEER stand for?

Transepithelial Electrical Resistance.

What does a high TEER value indicate about an epithelium?

Tight barrier with low permeability; strong junctions.

Do kidney epithelia have high or low resistance?

High — kidneys and bladder require tight barriers.

Why do intestinal epithelia have lower TEER values?

To allow absorption and ion exchange; leaky epithelia aid transport.

What is the relationship between current (I), voltage (V) and resistance (R)

I = V/R

What proteins mediate cell–cell adhesion in adherens junctions?

Cadherins.

Which cytoskeletal filament connects to adherens junctions?

Actin filaments.

What motor protein generates tension at adherens junctions?

Myosin II.

What type of intermediate filament anchors desmosomes?

Keratin.

In what tissues are desmosomes especially important?

Heart and epidermis — tissues under mechanical stress.