Chapter 17 Flashcards
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
3 main types of protein filaments that make up the cytoskeleton
- actin/microfilaments (MF)
- intermediate filaments (IF)
- microtubules (MT)
size of protein filaments largest to smallest
microtubules
intermediate filaments
actin/microfilaments
what are the subunits of each cytoskeleton protein filament
MF = globular actin subunits
IF = family of fibrous IF proteins
MT = globular tubulin subunits
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)
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
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
what are the main types of intermediate filaments
CYTOPLASMIC
-keratin filaments MAIN WE LOOK AT
-vimentin filaments
-neurofilaments
NUCLEAR
-nuclear lamins
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
describe nuclear IFs
-nuclear lamins
~in all animal cells
describe IF keratin
-help distribute stress to neighboring cells!
-anchored to the plasma membrane by desmosomes
-in epithelial tissue
epithelial cells undergo a lot of _____ and _____ ______ so cells are indirectly connected to other cells thru ______
stretching and mechanical stress
cells thru desmosomes
describe IF nuclear lamina
-structure and support to nucleus
-in between nuclear envelope and nucleus
-important in recruiting DNA mechanisms
what are plectins
green accessory pigments that crosslink intermediate filaments into bundles as well as IFs to MTs, MFs and desmosomes
-stabilizes the IF
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
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
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
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
which end do dimers in MT grow from
dimers grow/added to (+) end / beta-tubulin
where do microtubules arise from in the cell and the 3 types
-microtubule organizing centers (MTOC)
1.centrosomes
2.basal body
3.mitotic spindle
what is the major MTOC in animal cells
centrosomes
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
- kinesins - move to + end of MT
- 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)
- cell pushes out protrusions of cell membrane at leading edge
- this forms new regions of actin
- protrusions adhere to the crawling surface thru new points of anchorage (Integrins=allow for attachment)
- 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
- 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
