The Cytoskeleton I- Structure Flashcards
Dr. White
What is the significance of the cytoskeleton?
represents bones of the cell
important in organization fo the cell
maintains correctly shaped cells
insures cells are properly structured internally
What are functions of the cytoskeleton?
moves the cell
rearranges the cellular compartment
supports the plasma membrane
mechanical strength
pulls chromosomes apart during cell division
guides intracellular traffic
vesicles move using cytoskeleton as sidewalk
motor (for sperm) and crawling (WBC, fibroblasts)
muscle cell contraction
What happens if the cytoskeleton has defects?
disease can develop
What is RBC cytoskeleton is defective?
leads to anemia which can be severe and lethal
What disease can anemia lead to?
heredity spherocytosis
What is heredity spherocytosis?
RBS spherical not biconcave
fragile red blood cells burst
hemolytic anemia
cytoskeleton protein defects or deficiencies can lead to serious disease
Cytoskeleton filaments are consisted of multiple ______
protofilaments
What are protofilaments?
long linear strings of protein subunits joined end to end
Are protofilaments thermally unstable?
yes, easy to break one linear filament
When cytoskeleton filaments are created from multiple protofilaments bound side to side they _______ breakage by ______ ________ conditions
resist; ambient thermal
What are the three main types of filaments?
actin filaments
microtubules
intermediate filaments
What are actin filaments?
two stranded helical polymers of the protein actin
actin subunits are compact and globular
flexible structures 5-9 in diameter
What is the role of actin filaments?
determine the shape of cell’s surface and are necessary for whole cell locomotion, secretion, endocytosis
What are the properties of microtubules?
forms tube like structure
determine the positions of membrane enclosed organelles
directs intracellular transport
What do microtubules make up?
centrioles and mitotic spindles
cilia and flagella
What contributes to cystic fibrosis?
lack of function in cilia
Describe the structure of microtubules
long hollow cylinders made of tubulin subunits long and strait more rigid than actin have centrosomes
What are properties of intermediate filaments?
provide mechanical strength
strong filament
resists mechanical stress
allows formation of hair and fingernails
Describe the structure of intermediate filaments
rope like fibers, 10 nm diamter
large heterogenous family
made of smaller subunits that are elongated and fibrous
span from one cell-cell junction to another
Why are intermediate filaments in a staggered organization?
tolerates bending and stretching
forms rope like structure
What does the apical surface do?
absorbs nutrients
Are microvilli on the apical or basolateral surface?
apical
What happens at the basolateral surface?
cells transfer nutrients to bloodstream
How is polarity maintained for intestinal cells?
maintained by actin filaments, microtubules, and intermediate filaments
What forms stable cell surface protrusions?
actin
What type of filament is attached to desmosomes and hemidesmosomes?
intermediate filaments
What filament forms tracks to get newly synthesized proteins to proper locations?
microtubules
What builds a cytoskeleton filament?
protein subunit
Cytoskeleton filaments (or polymers) are held together by weak ________
noncovalent interactions
Assembly and disassembly of the cytoskeleton occurs_____
rapidly
____ subunits are used for assembly fo actin filaments
actin
What shape does actin subunits form?
helical
Actin monomers contains binding site for _____ or _____
ATP or ADP
Actin filaments are arranged ______ to generate structural polarity
head to tail
What are the two ends of an actin filament?
plus and minus end
What is the plus end of an actin filament?
fast growing or fast shrinking end
What is the minus end of an actin filament?
slow growing or slow shrinking end
ATP actin _______ and ADP actin ______
polymerizes (grows); disassembles (shrinks)
What subunits form microtubules?
tubulin subunits
Describe tubulin
hetero dimer of alpha tubulin and beta tubulin with non covalent bonds
both have binding site for one GTP
The top beta tubulin binds to bottom _____ subunit
alpha
Do microtubules have plus and minus ends?
yes
What is polymerization?
assembly of actin or tubulin subunits into a linear polymer
What is depolymerization?
removal of monomers at the ends of the polymer
What are the steps in formation of cytoskeletal filaments?
- filament nucleation
- filament elongation- growth phase
- steady state- equilibrium phase
What is filament nucleation?
process of rotation of initial aggregate, or nucleus
What is filament elongation?
subunits are quickly added onto the ends of nucleated filaments
What is the steady state?
rate of monomer addition equals the rate of monomer loss
What are actin and tubulin?
enzymes that catalyze ATP or GTP
What is the T form of subunit?
ATP/ GTP
What is the D form of subunit?
ADP/GDP
What formation does the plus end remain in?
T formation
What formation does the minus end remain in?
D formation
What is tread milling?
plus end growing while minus end is shrinking
Where does tread milling predominate?
actin filaments
What is catastrophe?
change from growth to rapid shrinkage
What is rescue?
change from rapid shrinkage to growth
Adding tubulin GTP produces ______ protofilaments
straight
Where does dynamic instability predominates?
microtubules
Is there a nucleotide binding site on intermediate filaments?
no
What are keratins?
the most diverse group of intermediate filaments
How many keratins are found in human epithelial cells?
20
How many keratins are specific to hair and nails?
10
How many distinct keratin goes are in the human genome?
50
True or false? Actin monomers are microtuble subunits?
False
