Lecture 3

Question 0

Mreb

Answer 0

• prokaryotic ancestor of actin

- give rod-shaped bacteria structure

Question 1

Microfilaments

Answer 1

• made up of actin (alpha muscle, beta/gamma non)
• abundant in all tpyes of eukaryotic cells
• 4 muscle, 2 non
• actin is highly conserved

Question 2

Cytochalasins

Answer 2

• bind to barbed end
• block elongation
• can inhibit mitosis

Question 3

Phalloidin

Answer 3

• prevents dissociation

- can be labeled with fluorescent dyes

Question 4

Spectrin

Answer 4

• found in RBCs
• binds cortical cytoskeleton to plasma membrane
• ghost RBCs after bursting

Question 5

Dstrophin

Answer 5

• binds cortical cytoskeleton to plasma membrane

- muscular dystrophy gets name from this

Question 6

Villin and Fimbrin

Answer 6

-cross-links in microvilli

Question 7

Caalmodulin and Myosin 1

Answer 7

-cross-links actin to plasma membrane in microvilli

Question 8

alpha-actinin

Answer 8

• cross-links stress fibers and connects actin to protein-plasma membrane copes
• adaptor for integrins to interact with F-actin

Question 9

Filamin

Answer 9

• cross-links actin at wide angles to form screen-like gels

Question 10

Thymosin

Answer 10

• controls treadmilling

- captures actin monomers and prevents from being polyerized

Question 11

Profilin

Answer 11

• binds to actin monomers, prevents polymerization
• controls treadmilling
• facilitates exchange of bound ADP for ATP
• *only ATP-actin monomers can assemble into F-actin

Question 12

Gelsolin

Answer 12

• controls treadmilling
• destabilizes F-actin and caps filaments, prevents loss and addition of G-actin
• in presence of Ca, fragments actin filament and remains bound to plus end

Question 13

Cofilin

Answer 13

• controls tread

- triggers depolymerization of ADP-bound actin at minus end

Question 14

Arp 2/3

Answer 14

• initiates growth of F-actin fro sides of existing filament
• causes branching
• nucleation (3 actin monomers coming together) is rate-limiting

Question 15

Formin

Answer 15

• and Arp 2/3 complex determine where filament are formed
• large dimers that bind initial monomer, and move along the growing filament
• nucleate long unbranched actin filaments, many stabilized by tropomyosin

Question 16

Laatrunculins

Answer 16

• bind to G-actin and induce F-actin depolymerization

- non native proteins, used in research to break down filaments

Question 17

Parallel Bundles

Answer 17

• closely spaced actin filaments aligned in parallel

- barbed ends adjacent to plasma membrane

Question 18

Contractile Bundles

Answer 18

• more widely-spaced filaments, cross-linked by alpha-actinin
• allows motor protein myosin to interact with actin

Question 19

Intermediate Filaments

Answer 19

• abundant in cells subject to mechanical stress
• provide tensile strength to cells such as neurons and muscle
• strengthen epithelial cells such as desmo and hemi
• common monomer consisting of central a-helix rod flanked by head and tail domains

Question 20

Intermediate Assembly

Answer 20

• 2 antiparallel dimers form staggered tetramer
• form spontaneously, doesn’t require ATP
• formed by poly of long, rodlike proteins
• repeated AA segents (heptads)

Question 21

Intermediate Filament Associated Proteins (IFAPs)

Answer 21

• stabilize filament
• may cap to prevent further elongation
• filaggrin, epinemin, paranemin, plectin, synemin

Question 22

Intermediate Filament Types

Answer 22

• Type I: acidic keratins, associaed with plaques of desmo and hemi
• Type II: neutral to basic keratins
• Type IV: neurofilaments, axons and dendrites
• Type V: nuclear lamins, mechanical support for nuclear envelope
• Type VI: nestin, associated with CNS stem cells

Question 23

Microtulues

Answer 23

• thick, composed of tubulin dimers
• consist of 13 protofilaments
• plus end grows more rapidly in presence of low Ca

Question 24

Factors Inhibiting Microtubule Polymerization

Answer 24

- colchicines, used to create karyotype - colcemid - vincristine and vinblastin, anti-cancer - taxol stabilize

Question 25

Cilium Structure

Answer 25

- 9 peripheral doublets + central pair of microtubules | - each doublet has alpha tubule (13 protofilaments) and beta (10-11)

Question 26

Fatty Acid Characteristics

Answer 26

- long-chain pack well together and limit movment - short are more limited but create spaces which other chains can move - saturated has no double bonds, max H+

Question 27

Outer Leaflet of Phospholipid bilayer

Answer 27

- Cholesterol - phosphatidylcholine - sphingomyelin

Question 28

Inner Leaflet of Phospholipid bilayer

Answer 28

- cholesterol, phosphatidylethanolamine, phosphatidylserine (- charge) - phosphatidylinositol, - charge, important in cell signaling, only in inner

Question 29

Glycolipids

Answer 29

-outer leaflet with carbohydrate portion facing extracellular, forms glycocalyx

Question 30

Cholesterol

Answer 30

- High temps, interfers with FA chain movement, makes membrane less fluid, reduced permeability to small molecules - low temps, prevents membranes form freezing

Question 31

Glycocalyx

Answer 31

- not integral part of membrane | - carb coat composed of carb portions of glycolipids and glycoproteins

Question 32

Lipid Rafts

Answer 32

- small patches of cholesterol and sphingolipids | - no proteins, smooth surface

Question 33

Peripheral Proteins

Answer 33

-can be removed by altering pH or ionic content of environment

Question 34

Integral Proteins

Answer 34

- Embedded, extracellular portion typically glycolsylated | - can only be removed by detergents

Question 35

Transmembrane Proteins

Answer 35

- integral that pass completely through both layers - channel or transporter proteins - 1 hydrophobic and 2 philic domains - membrane-spanning portions usually a helix with 20-25 hydrophobic AA (glycophorin, band 3 anion tranporter for Cl ions)

Question 36

Single Pass Transmembrane Proteins

Answer 36

- single hydrophobic domain passes through layer only once - enzyme-like receptrors (receptor tyrosine kinases) - glycophorin (RBC membranes)

Question 37

Multiple-pass Transmembrane Proteins

Answer 37

- use two or more hydrophobic domains - activated by add of phosphate - G-protein-linked receptors (7 trans domains) - Large transporter and channel proteins (porin has 12 trans domains as does glucose)