White Cyto 1 Flashcards
Essay Question #1: Differentiate actin filaments, microtubules and intermediate filaments.
Actin filaments: “like mardi-gras beads.” Two-stranded, helical polymers consisting of globular ACTIN subunits. Flexible. Determine the shape of cell’s surface. Necessary for locomotion, secretion, and endocytosis.
Microtubules: “slinky of life.” Forms tube like structure, determining the positions of organelles, directs intracellular transport. Made of globular TUBULIN. Make up centrioles, mitotic spindle, cilia, flagella (sperm flagella, cilia moves eggs in Fallopian tubes). MORE RIGID than actin filaments.
Intermediate Filaments: “like girders in building.” Provide mechanical strength, strong filament, resists mechanical stress, allows formation of hair/fingernails. Staggered side to side binding of filaments forms rope like structure.
Essay Question #2: Define and differentiate nucleation, catastrophe and rescue.
Nucleation: The polymerization of an actin filament or microtubule. In order for large filament to form, subunits must aggregate. This is called nucleation.
Catastrophe: Change from growth to rapid shrinkage (caused by loss of GTP cap).
Rescue: change from rapid shrinkage to growth (caused by gain of GTP cap).
Essay Question #3: Describe treadmilling in actin filaments.
Treadmilling: When the polymer maintains a constant length as the plus end grows and the minus end shrinks.
In epithelial cells, intermediate filaments are attached to ___, connecting two cells together, and ___, giving the cell contact with the basal lamina.
desmosomes.
hemidesmosomes.
In epithelial cells, ___ form tracks to get newly synthesized proteins to proper locations.
microtubules.
Actin monomers contain a binding site for ___. They come together forming two protofilaments, arranged __-_-__. This generates a __ end and a __ end.
The ___ end is fast-growing/fast-shrinking. The ___ end is slow-growing/slow-shrinking.
ATP.
head-to-tail.
plus. minus.
Plus end. Minus End.
Tubulin consists of both ___ and ___ monomers. Therefore, they come together to form a ___-___.
Both have a binding site for one ___.
Microtubules contain this many protofilaments:
Like actin filaments, microtubules contain a __ end and a __ end.
alpha-tubulin.
beta-tubulin.
hetero-dimer.
GTP.
13.
plus. minus.
Tubulin consists of both ___ and ___ monomers. Therefore, they come together to form a ___-___.
Both have a binding site for one ___.
Microtubules contain this many protofilaments:
Like actin filaments, microtubules contain a __ end and a __ end.
alpha-tubulin.
beta-tubulin.
hetero-dimer.
GTP.
13.
plus. minus.
After filament nucleation, ___ phase occurs, causing filament elongation. Then, ___ phase occurs, which is considered a steady state because…?
Growth. (Subunits are added to the ends of nucleated filaments)
Equilibrium. Considered steady-state because the rate of monomer addition equals the rate of monomer loss.
After filament nucleation, ___ phase occurs, causing filament elongation. Then, ___ phase occurs, which is considered a steady state because…?
Growth. (Subunits are added to the ends of nucleated filaments)
Equilibrium. This phase is considered steady-state because the rate of monomer addition equals the rate of monomer loss.
Describe Nuceloside Hydrolysis:
What does the T and D form stand for? What form of actin (or tubulin) is found on the plus side? What form is found on the minus side?
Hydrolysis refers to a change from the ATP/GTP form, soon after it is assembled into the polymer, to the ADP/GDP form.
T = nucleoside triphosphate. D = nucleoside diphosphate. The T (ATP/GTP) form is found on the plus side. The D form (ADP/GDP) is found on the minus side.
What does nucleoside hydrolysis of filaments lead to and describe the process.
Treadmilling: When the polymer maintains a constant length as the plus end grows and the minus end shrinks.
(T/F) Treadmilling predominates in actin filaments.
True.
GDP-tubulin dimers can easily depolymerize. What other structural change occurs when tubulin-GTP hydrolyzes to tubulin-GDP?
When tubulin-GTP is added, it produces straight filaments. Hydrolysis of GTP to GDP, after assembly, produces CURVED protofilaments.
Describe Dynamic Instability:
What process is this important in?
T/F: Dynamic Instability predominates in microtubules.
A growing microtubule has a stable cap of GTP-subunits. Loss of the cap lets the GDP-filaments relax into curved structure, leading to shrinking of microtubule.
DI is important during separation of chromosomes during mitosis.
True.
