Cytoskleton Flashcards
3 - make up the cytoskeleton
Actin micro filaments
Intermediate filament
Microtubles
Microtubles (overview)
subunit: alpha, beta tubles
growth: + end
Enzyme activity: GTP
Motor protein: Kinesine/Dyneins
Associate proteins: MAPS
Structure: hallow tube
Function: chromosome movement, cytoplasmic streaming (cilia+flagella)
Intermediate filaments overview
sub-units; globular proteins growth: internal polarity: none Enzyme activity: none Motor proteins: none Associate proteins: plakins Structure: Rope like fibers. Function: structural support.
Actin filaments overview
subunits: actin monomers growth + ends polarity: yes Enzyme activity: ATP Motor protein: myosin Associated proteins: Actin proteins Structure: Thin solid flexible fibers Functions: Contractility motility
Structure of microtubles
- alpha and beta tubulin
- ATP GTP and Beta GTP = heterodimers
- 13 alpha micro filaments
- (-) end is stable , grows from the + end
Colchicine ?
binds to beta subunits and prevents the addition of elongation of microtubles
Function of microtubules
- chromosome movement: spindle fibers form during mitosis are made up of bundles of microtubules,
- cytoplasmic streaming
The cell cycle
- G0
- G1 phase
- S-phase
- G2 phase
- M phase
- back into G0 or G1 phase
- Cytokinesis
The G0 phase
cell resting not going through mitosis, functional stage of the cell.
G1 phase -
Growth phase, synthesize and prep enzymes and proteins to duplicate it’s chromosome.
G2 phase
cell preps and synthesize the enzymes and proteins to undergo mitosis.
M phase
mitosis cell separates the duplicated chromosomes and enclose them into two different nuclei.
What happens after the M phase?
the cell can go back to G0 phase or G1 phase.
Cytokineses
separation of the cytoplasm
Steps of Mitosis
PMAT
Prophase
a. Duplicated chromosomes condense
b. Nuclear membrane dissociates
c. Centriole duplicates
Structure of centrioles
a. Radial spoke proteins
b. B+C = have 10 microfilaments
c. B filaments are attached to the adjacent C microtubules by a nectin-like protein
Metaphase:
spindle fibers form (bundles of microtubules) from centrioles and grow out to center of cell where they join to duplicated chromosomes
a. Pericentiolar area - formation site of the spindle fibers via
i. 13 gamma tublin
Centrosome
found near the nucleus.
- Made up of 2 centrioles.
- Formation site for mitotic spindle and microtubles.
How do fibers attach to the chromosome?
a. Via the centromere – composed of satellite DNA, highly repetitive DNA , no protein coding regions
b. Duplicated chromosome joined at centromere
Centrome structure:
Chromosome Inner Protein plate - Interzone proteins Interplate proteins spindle fibers.
what does Kinesin do during mitosis?
motor proteins that carry alpha and beta sub-units to a spindle fiber to lengthen it.
Anaphase:
duplicated chromosomes separate , spindle fibers sorten and single chromosomes pull apart . Dynein motor proteins carries alpha and beta subunits to centrioles
Telophase:
a. Single chromosomes reach the centrioles
b. Spindle fibers have been broken down
c. Nuclear membrane reforms
d. One centriole at each nucleus is broken down.
Cytokinesis:
separating of cytoplasm after mitosis.
Cytokinesis (animal cells)
a. Animal cells – actin microfilaments in cytoplasm between 2 cells
i. Actin and its motor protein
Cytokinesis (plant cells)
cytokinesis is called cell plate formation
i. Golgli complexes in plant cells releases vesicles of membrance and cell wall
ii. Vesicles join to form membrane and cell wall fro separation.
How are 7. Microtubules responsible for Vesicle movement in the cytoplasm ?
a. Example: in a nerve cell, the movement of nuerotransmiters down the axon
i. Anterograde transport : from the body to the end of the axon “forward movement”
ii. Retrograde transport: from the end of axon back to the cell body
- MAPS: microtubules associated proteins
microtubules associated proteins
kinesin (family of proteins)
i. Kinesin moves molecules in a anterograde transport toward the + end of microtubule.
1. Orginally called CENP-E (centriole protein E)
Dymein family protein
Dymein family protein of motor protein moves vesicles in retrograde transport (back toward the (– ) end of microtubule.
Melanophores
pigment containing vesicles found in frogs to darken the skin = anterograde transport toward the cell membrane. To lighten the skin retrograde transport of vesicled toward the center the cell.
Experiment to demonstrate MAP’s #1
EXP #1: Giant squid axon Isolate cystoplam from squid axon spread on a microscope slide - add dye containing vesicles RESULTS: Vesicles moved along the microtubule in the squid cytoplasm.
Experiment to demonstrate MAP’s #2
i. Added isolated mictotuble added TAXOL chemical joined microtubule into bundle add ATP added vesicles containing dye –> Results: no movement of vesicles along the microtubule.
MAPS
d. MAPS are part of the kinesin family of motor protein. 380,000 molecular weight , 4 polypeptides 2 long and 2 short
i. Globular head function: ATP hydrolysis , ATP ADP, Pi + energy
ii. Carboxyterminal and short protein bind to vesicles .
Kinesin
ATP motor proteins that walk along microtubules anterograde + end.
Dynein
ATP motor proteins that walk along microtubules retrograde
- end.
Microtubules responsible Cilia and Flagella movement of whole cell
- Microtubules responsible Cilia and Flagella movement of whole cell
a. Sperm have flagella
b. Cells line respiratory system have cilia (to remove foreign materials)
c. Cilia – short , flagella – long
