The cytoskeleton

Question 1

the biological importance of the cytoskeleton?

Answer 1

—It organizes the cell structure, anchor the organelles and facilitate cellular activities
—Organelles and enzymes can attach to the cytoskeleton and move across the cell
— maintenance and modifications of the cell’s shape (animal cells lack cell wal

Question 2

the characteristics of microfilaments?

Answer 2

—thin filament composed of actin proteins acting alone or with myosin to cause cell contraction
—Microfilaments form a network and can be branched
—Double chain of actin subunit

Question 3

the functions of microfilaments?

Answer 3

—Resist compression and maintains the shape of the cell
—Can interact with a protein myosin to cause muscle cells contraction

Question 4

the characteristics of microtubes?

Answer 4

—thick hollow rod composed of tubulin protein
—The tubulin is a dimer (two subunits): -tubulinɑ and β-tubulin.
— The microtubule has an orientation (polarity) “plus end”
and “minus end”.
—A microtubule can grow and shrink in length from the “plus end” through polymerisation and disassembly of the tubulin dimers.
—The minus end is attached to the centrosome

Question 5

the functions of microbtubes?

Answer 5

—are involved in the movement of organelles, vesicles and enzymes across the cell.
— involved in the separation of chromosomes
during mitosis.
— involved in the beating of flagella and cilia

Question 6

the characteristics of intermediate filaments?

Answer 6

—strong and flexible filaments of intermediate size (between microtubules and microfilaments)
—Intermediate filaments are only found in the cells of some animals
—Intermediate filaments are more permanent as much as microtubules and microfilaments

Question 7

the function of intermediate filaments?

Answer 7

—provide mechanical support of the cell against physical stress
—Can bear tension (like microfilaments), maintain the shape of a cell and the nucleus (nuclear lamina) and fix the position of organelles.

Question 8

Explain how motor proteins use energy to move along cytoskeletal tracks?

Answer 8

—Kinesin move cargo towards the plus end of the microtubules
Dynein moves cargo towards the minus end of microtubules

Question 9

Predict the orientation of microtubules based on its structure and polymerization dynamics?

Answer 9

—Growing microtube
—metastable intermediate microbe
—shrinking microtube
—depolymerization
—GTP>GDP
—polymerization
—Growing microtube

Question 10

Describe how microtubules are involved with mitosis?

Answer 10

—Centrosome: structure present in the cytoplasm of animal cells
near the nucleus that functions as a microtubule-organizing center (MTOC) and is important during cell division
—A centrosome has two centrioles that are perpendicular to one another, Centriole is a cylindrical structure in the centrosome of an animal cell composed of 9 microtubule triplets (“9+0 arrangement”)
—After mitosis, the two centrioles separate, and each is replicated for the next cell cycle

Question 11

Describe how microtubules are involved with the beating of both cilia and flagella?

Answer 11

— Both cilia (short and numerous) and flagella (long and few) are appendages in eukaryotic cells that contain microtubules and are used in locomotion (flagella and cilia) or used to move fluid around and feed (cilia)
—The sliding of microtubules onto each other depends on a motor protein (dynein)
—core of axoneme 9+2

Question 12

Predict whether a muscle fiber is contracted or not based on its configuration (cross bridge, level of enery)

Answer 12

1—ATP/low energy/no bridge
2—ADP Pi/high energy/start to bridge
3—ADP Pi/high energy/bridge
4—low energy/thin filament moves toward the centre (contracted)

Question 13

the structure and function of Plasmodesmata?

Answer 13

—In plants, neighbouring cells are connected by cytoplasmic channels called plasmodesmata that go through the cell walls, making the membrane continuous between cells
—Many substances can pass from one cell to another.

Question 14

the structure and function of tight junctions?

Answer 14

—plasma membranes of adjacent cells are
bound together by proteins
—Prevents leakage of fluid through the epithelium layers (impermeability)

Question 15

the structure and function of Desmosomes?

Answer 15

—anchors adjacent cells together through
transmembrane proteins (that belong to the cadherins family) that are linked to the intermediate filaments
—keep adjacent cells tight together, especially in tissues that can stretch

Question 16

the structure and function of gap junctions?

Answer 16

— similar to plasmodesmata in plant cells. 6 proteins (connexins) form a channel and allow the communication of adjacent cells
— letting through ions and small molecules such as amino acids, sugars..

Question 17

the importance of a given cell junction in various cellular mechanisms

Answer 17

—Neighbouring cells of multicellular organisms adhere and communicate to one another.

Question 18

Analyze a fluorescent microscopy image from an experiment and determine the type of cell junction it highlights

Answer 18

—microtubes 中间有两瓣
—actin filaments 多边形
—intermediate filament拉撑的形状

Question 19

the size of all filaments

Answer 19

—biggest Actin filament
—intermediate filaments
—microtubes