Cytoskeleton & Cell Division Flashcards
1
Q
Functions of cytoskeleton
A
- Provide structural support for plasma membrane & cell organelles
- Intracellular movement/transport of substances
- Cell locomotion (amoeboid movement, embryonic development, cilia, flagella)
- Muscle contraction
2
Q
What are the 3 main elements of cytoskeleton
A
- microfilaments
- intermediate filaments
- microtubules
3
Q
Microfilament structure and function
A
distributed in 3-D network throughout cytoplasm
•Important in maintaining cell shape; facilitate shape changes during movement, wound contraction during healing & Mm contraction
4
Q
what makes up microfilament
A
actin and myosin
5
Q
actin structure
A
- Thin filament
- made of smaller G-actinsubunits
- 2 protofilaments twist together to form a double helix (F-actin). These combine to form larger actin filaments
6
Q
G actin
A
G-actinis a small, globular protein monomer; polymerizes to form protofilaments
7
Q
actin location
A
In microvilli& stereocilia, and beneath plasma membrane, actin links with another protein, filamin.
8
Q
filamin
A
- Forms support meshwork called cell cortex(= terminal web)
- Prevents cell from deformation
9
Q
myosin structure
A
- Thick
- Myosin molecules are long & rod-shaped, with globular heads
- Form thick, ropy “cables” with myosin heads sticking out sides
- Myosin heads form cross-bridges between adjacent filaments
- Ca & ATP required for movement of filaments for Mm contraction
10
Q
what can myosin be classified as?
A
“motor protein” along with dynein and kinesin
11
Q
intermediate filament structure
A
- Intermediate in size between microfilaments & microtubules
- Generally form large filaments that bind with intracellular structures
- Heterogenous group; molecular make-up varies between cells
12
Q
intermediate filament function
A
- 1’ structural function
- Several different classes, each expressed in different cell types—1 cell may produce more than 1 type of filament
- Useful in immunohistochemistry & tumor ID
13
Q
types of intermediate filaments (6)
A
- Cytokeratin
- vimentin
- desmin
- neurofilament proteins
- GFAP
- Lamin
14
Q
Cytokeratin
A
characteristic of all epithelial cells; In epidermis of skin forms tonofibrils
(part of intermediate filament)
15
Q
vimentin
A
found in mesodermal cells of mesenchymal origin (includes endothelial cells, muscle & neuroectodermalcells)
(part of intermediate filament)
16
Q
desmin
A
unique to muscle cells; mesodermal origin
part of intermediate filament
17
Q
neurofilament proteins
A
resent in nerve cells (neurons)
part of intermediate filament
18
Q
GFAP
A
Glial Fibrillaryacidic Protein. Found in glial (support) cells of nervous system(astrocytes)
(part of intermediate filament)
19
Q
Lamin
A
forms layer on inside of nuclear membrane.
part of intermediate filament
20
Q
Microtubules Structure
A
- Larger than microfilaments or intermediate filaments
- Composed of 2 types of globular protein subunits—a& b tubulin—arranged in coiled, spiral pattern
- Polymerize to form hollow tubes—readily assemble & disassemble
21
Q
Microtubles Function
A
- cell movement, maintenance of cell shape, & intracellular transport of substances
- Movement occurs via addition or subtraction of tubulin subunits from microtubules
- Stabilize microtubules along with capping proteins
22
Q
Microtubule- associated proteins (MAP’s)
A
provide energy as ATPase
23
Q
how do motor proteins interact with microtubules?
A
Motor proteins dynein& kynesinattach microtubules to organelles; allow movement in cytoplasm
24
Q
Classic example of microtubules
A
cell spindle during cell division
25
what drugs inhibit polymerization of microtubules and cell division?
vincristine & vinblastin
26
Where can microtubules be found in?
* cilia & flagella
* centrioles
* basal bodies of cilia
* mitotic spindles
27
Axoneme Structure
•9 pairs of microtubules (peripheral doublets) containing dynein arms arranged in circle with central doublet in middle
(9 + 2 structure)
•Central doublet connects to peripheral doublets by radial spokes& peripheral doublets connect to each other by protein nexin
28
what is the structure of axoneme in cilia?
In cilia, axoneme grows from basal body, derived from modified centriole
29
Centrioles location
in region of cell called centrosome, or “cell center” near nucleus
30
Centrioles Function
cell divison. A pair of centrioles oriented at right angles to each other within centrosome
31
what is a pair of centrioles called?
diplosome
32
Centrioles Structure
Each centriole consists of 9 triplets of microtubules arranged in a cylinder
Acts as a nucleation center for microtubules
33
Mitotic spindle
Occurs during mitosis, centrioles divide.
| Role: controls distribution of chromosomes in daughter cells
34
Cell division
Movement of chromosomes occurs via tubulin subunits & attachment proteins to chromatids at kinetochore(= centromere)
35
Mitosis
growth & replication of cell
36
What is interphase and its subphases?
"resting phase”, or time between divisions—occupies most of life of cell
subphases: (G1, S, G2)
37
G1
Longest of cell phases (hrs to days); during which cell growth, maturation, & differentiation occur
38
what specifically occurs during G1
hypertrophy—↑in cell size
39
what specifically occurs during mitosis?
hyperplasia—↑in cell #
40
Synthesis
Replication of DNA prior to division
41
what happens at the beginning of S phase?
chromosome # is 2n;at end = 4n
42
what happens prior to replication, in S phase?
each chromosome has a single chromatid with attached centromere
43
what is the result of replication of centrioles during synthesis?
2 diplosomes
44
G2
* Preparation for mitosis
| * Synthesis of ATP & tubulin for mitotic spindle
45
during cell division, what is Mitosis characterized by?
karyokinesis (nuclear division) followed by cytokinesis (cytoplasmic division)=> 2 daughter cells
46
what happens to chromosomes during S & M phase?
chromosomes condense, become visible, look like coiled snakes
47
what happens to chromosomes during G1 & Go phase?
chromosomes exist in an unraveled mass
48
Go
-extended phase where some cells end up when they lose capacity for cell divison.
-may be permanent or reversible
("o" outside cell cycle)
49
Facultative dividers
retain capacity for division with proper stimulus (e.g., reserve stem cells)
50
Terminally differentiated
cells lose the capacity to divide (e.g., neurons, cardiac myocytes)
51
Prophase
* Chromosomes visibly condensed
* Microfilaments & microtubules of cytoskeleton disaggregate
* Centrioles migrate to poles of cell, form spindle apparatus with interpolarmicrotubules between them
52
Prometaphase
* late prophase
* Nuclear membrane & nucleoli disappear at end of prophase
* Mitotic spindle attaches to chromosomes at kinetochore
53
Metaphase
chromosomes line up along equator (“metaphase plate”)
54
Anaphase
* centromeres split apart, chromosomes migrate to opposite ends of cell
* Pulled by microtubules connecting centriole & kinetochore
55
Telophase
* Nuclear envelope reassembles, nucleoli reappear
* Mitotic spindle disaggregates
* Plasma membrane forms cleavage furrow, cytokinesisbegins => 2 genetically identical daughter cells
56
Mitotic index
* Used to describe proportion of cells in a tissue in mitosis at any given time
* Important in tumors—estimated by counting # of mitotic figures / HPF (normally <1)
57
Meiosis
- Reduction division
| - Sexual reproduction requires production of haploid gametes(eggs & sperm) via gametogenesis
58
Where does meiosis occur?
only in germ cells of gonads; in male = spermatogenesis; in female = oögenesis
59
what does meiosis involve?
* Involves chromosomal duplication followed by two consecutive cell divisions (=> haploid gametes)
* Fusion of gametes (fertilization) produces diploid zygote(fertilized egg)
60
Result of meiosis
2 daughter cells
61
what 2 ways do mitosis and meiosis differ?
1. During prophase I, homologous pairs of chromosomes form tetrads, with exchange of chromatin via cx (chiasmataformation)
Results in hybrid chromatids different from parents.
Each chromosome pair has potential for cx during prophase I (23 pairs total in humans)
2. Centromeres do not split during anaphase I
62
Second meiotic division
* Brief interphase II (interkinesis) with no replication of DNA
* Nocrossing over during prophase II
* Anaphase II—centromeres split
* Telophase II—cytokinesis yields four haploid gametes, each genetically unique
63
Gametogensis in male and female
* In male 3 or 4 viable gametes (sperm) produced
| * In female, cytoplasmic division unequal =>1 functional gamete (ovum) & 2 or 3 non-functional polar bodies
64
when does spermatogenesis occur in males
at puberty
65
when does oogenesis begin in females
during fetal development
66
what occurs during oogenesis
* Female germ cells enter prophase I ~ 5th month of gestation during fetal development & stop
* Remain in prophase Iuntil ovulation (12-50 years later)
67
what triggers apoptosis?
* Timing in fetal development; referred to as programmed cell death
* Some cells have finite, predetermined life spans (e.g., epithelial cells of skin or GI tract)
* Growth & regression of ovarian follicles
* Destruction of virus/tumor infected cells
* Clonal deletion in thymus; removal of t-cells that react to “self” molecules
Failure of clonal deletion may => autoimmune diseases
68
how does apoptosis happen?
* Begins with nuclear chromatin condensation & shrinkage of nucleus (pyknosis)
* Cell swells (as result of influx of water due to loss of ATP to maintain pumps in cell membrane)
* Lysosomes release catalytic enzymes into cytoplasm => autolysis
69
caspace cascade
final pathway initiated. caspaces are normally inactive enzymes
70
karyolysis
chromatin in nucleus begins to degenerate
71
Karyorhexis
nuclear material begins to fragment & nuclear membrane disintegrates
72
what is apoptotic bodies, and what does it lead to?
Fragmented nuclear debris.
| Leads to dead, necroticcells, later phagocytosed by macrophages & neutrophils
73
Necrosis
refers to death of cells as a result of inflammation, traumatic injury, or pathology
