Chapter 17 Flashcards by Kennedy Chrest

what is the cytoskeleton

=intricate network of protein filaments that extends throughout the cytoplasm

 ~provides cellular support to the cytoplasm and allows organization of internal cell parts
 ~functions in movement of cell and movement within the cell (transport)
 ~important in animal cell since there's no cell wall
 ~mainly a feature of eukaryotic cells

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3 main types of protein filaments that make up the cytoskeleton

actin/microfilaments (MF)
intermediate filaments (IF)
microtubules (MT)

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size of protein filaments largest to smallest

microtubules
intermediate filaments
actin/microfilaments

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what are the subunits of each cytoskeleton protein filament

MF = globular actin subunits
IF = family of fibrous IF proteins
MT = globular tubulin subunits

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describe intermediate filaments (5) and their purpose

=strong, ropelike fibers made up of intermediate filament proteins
=toughest and most durable
~10 nm
~thoughout the cell
~very flexible / deform under stress but do not rupture

purpose:
to give cells tensile strength which enables cells to withstand mechanical stress (withstand stretch)

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describe intermediate filament structure

-2 monomer alpha helices wrap to form a coiled-coil dimer
-2 coiled-coil dimers form a tetramer with NO POLARITY
-lateral association of 8 tetramers
*groups of these 8 tetramers join along their lengths to grow a filament

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are all IF filaments the same in structure

all IF proteins will have similar diameter and internal structure but the terminal domains can vary in each

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what are the main types of intermediate filaments

CYTOPLASMIC
-keratin filaments MAIN WE LOOK AT
-vimentin filaments
-neurofilaments

NUCLEAR
-nuclear lamins

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describe the types of cytoplasmic IFs

-keratin filaments MAIN WE LOOK AT
~in epithelial cells
-vimentin filaments
~in connective tissue cells, muscle cells
-neurofilaments
~in nerve cells

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describe nuclear IFs

-nuclear lamins
~in all animal cells

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describe IF keratin

-help distribute stress to neighboring cells!
-anchored to the plasma membrane by desmosomes
-in epithelial tissue

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epithelial cells undergo a lot of _____ and _____ ______ so cells are indirectly connected to other cells thru ______

stretching and mechanical stress

cells thru desmosomes

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describe IF nuclear lamina

-structure and support to nucleus
-in between nuclear envelope and nucleus
-important in recruiting DNA mechanisms

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what are plectins

green accessory pigments that crosslink intermediate filaments into bundles as well as IFs to MTs, MFs and desmosomes

-stabilizes the IF

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what are desmosomes

hold epithelial cells together in sheets and allow keratin filaments of all adjoining cells to be indirectly connected = lots of tensile strength

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what was the first case study we did in class and what model could be used to study it

EB - epidermolysis bullosa
-keratin gene mutations that affect cell junctions and their attachments in the skin

-knockout mice

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describe microtubules (5) and its key role

=hollow cylinder made up of globular alpha and beta tubulin proteins
~25nm
~dynamic
~very rigid, rupture when stretched
~one end attached to MTOC

key role in cell organization / provide tracks within the cell

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describe MT structure (4)

-MT monomers are tubulin heterodimers bound by noncovalent bonds
~alpha-tubulin = (-) end
~beta-tubulin = (+) end
-has polarity for cells to conduct directional transport (not charged!)
-rings of 13
-includes GDP and GTP

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which end do dimers in MT grow from

dimers grow/added to (+) end / beta-tubulin

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where do microtubules arise from in the cell and the 3 types

-microtubule organizing centers (MTOC)

1.centrosomes
2.basal body
3.mitotic spindle

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what is the major MTOC in animal cells

centrosomes

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microtubules grow out from an ____ _____

organizing center

describe centrosomes (3)

in animal cells
-close to nucleus
-pair of perpendicular centrioles

which end of MT is anchored to the centrosome and by what

(-) end is anchored to centrosome by nucleation sites which are made up of gamma tubulin

how are centrioles arranged

9+0 arrangement

the MTOC for cilia and flagella is called ___

basal body

what is dynamic instability in MTs

=constant shift between polymerization and depolymerization aka MTs are constantly growing and shrinking

how are microtubules stabilized

capping proteins on cortex

dynamic instability is driven by ___ _____ and what happens if it happens too early

GTP hydrolysis too early = lose GTP "glue" / starts peeling and and so shrinks

in dynamic instability describe GTP vs GDP

GTP - like glue / GTP cap added to grow at (+) end GDP - less stable / shrink at (+) end

what are MAPS with example

microtubule associated proteins accessory proteins like motor proteins, plectin, EB1

describe motor proteins in MTs and the two types

-used to transport / movement -have ATPase activity to power movement 1. kinesins - move to + end of MT 2. dyneins - move to - end of MT

what do motor proteins bind to (2) and which do they not

microtubules and microfilaments NOT IFs!!!

in a motor protein describe the head vs tail

heads = attach to microtubule and do the end over end walking via ATPase tails = carry cargo

describe cilia and flagella (6)

=motile hair-like projections from plasma membrane -both contain bundles of microtubules and dynein -flagella are longer -grow from cytoplasmic basal body -MTs are stable not dynamic -cilia move fluid across cell (hairs) while flagella move entire cell (tails)

what MT arrangement do cilia and flagella have

9+2 arrangement

what does dynein allow for in cilia and flagella

dynein proteins allow for MT movement ex. MT sliding and bending

describe microfilaments (actin) (5)

=thin, flexible, twisted chains of identical actin monomers -monomers are globular actin -has polarity -7nm in diameter -highly concentrated in the cortex (just beneath plasma membrane)

what are microfilaments important in (4)

-microvilli -bundles in cytoplasm -filopodia/lamellipodia -contractile ring

describe microfilaments polymerization

-polymerization mainly at (+) end ~ Actin-ATP -depolymerization mainly at (-) end ~ Actin-ADP

compare polymerization/depolymerization mechanisms in microfilaments vs microtubules size / end of growth or shrinking/ energy use/ subunits

Mechanisms: MT-dynamic instability MF-treadmilling -microtubules are larger -MT growth/shrinking from only 1 end (+) where MF grow from (+) and shrink from (-) -MT use GTP/GDP where MF use ATP/ADP -MT subunits = alpha & beta heterodimers where MF subunits = globular actin

what is thymosin

monomer sequestering protein / prevents polymerization (growing of actin)

what are ARP2/3 and Formins

nucleating protein / promote polymerization (growing of actin) ARP2/3 = branching Formins = linear growth

what is profilin

monomer sequestering protein / mostly prevents polymerization

what is cofilin

severing protein / accelerates de-polymerization

what is spectrin

cross linking protein in cell cortex

what is chemotaxis

movement of cells in the direction of specific chemical signals

describe filipodia

thin, stiff protrusions at leading edge etc, contain loose bundle of 10-20 actin filaments

describe lamellipodia

dense meshwork of actin filaments in thin, sheet-like extensions at leading edge

which end of actin will be close to the leading edge of plasma membrane in cell crawling

(+) ends

describe cell crawling (5 steps)

1. cell pushes out protrusions of cell membrane at leading edge 2. this forms new regions of actin 3. protrusions adhere to the crawling surface thru new points of anchorage (Integrins=allow for attachment) 4. contraction at the rear of the cell (via myosin motor proteins) draws body of the cell forward in the direction of new attachment points/ old anchorage points are released 5. cell pushes further protrusions and cycle repeats

what pushes the leading edge of the lamellipodium and what assists

polymerizing actin filaments and ARP2/3 assists by branching

what are the actin motor proteins

myosin = bind and hydrolyze ATP, providing energy for movement

2 types of myosin and describe

-myosin-I ~utilize ATP hydrolysis ~move towards (+) end ~can bind to specific cargo (vesicles) or anchor on plasma membrane to reshape cell -myosin-II ~two myosin wrapped together