module 2 Flashcards
What structures does the cytoskeleton consists of?
- network of microtubules
- microfilaments
- intermediate filaments within the cytoplasm.
What is the role of the cytoskeleton?
- Mechanical support (resists pressure)
- Structural maintenance
- Cellular transport
- Cell motility
- Signaling support
What are the functions of the cytoskeleton?
- Organizes cell structure and anchors organelles, facilitating cellular activities.
- Allows organelles and enzymes to attach and move within the cell.
- Maintains and modifies cell shape (especially in animal cells without cell walls).
- Participates in cell division by separating and pulling apart chromosomes.
What is the structure of microtubules?
- Thick, hollow rod composed of tubulin proteins.
- Tubulin is a dimer consisting of two subunits: alpha tubulin and beta tubulin.
(yhe term “dimer” refers to the combination of two subunits, specifically alpha tubulin and beta tubulin, ) - Microtubules have polarity with a “plus end” and a “minus end.”
Where can a microtubule grow and shrink from?
microtubule can grow and shrink in length from its “plus end” through the processes of polymerization (growth) and disassembly (shrinkage) of the tubulin dimers.
The minus end of the microtubule is attached to:
the centrosome
Functions of Microtubules:
- Maintenance of cell shape (acting as compression-resisting girders).
- Facilitating cell motility (e.g., in cilia and flagella).
- Assisting in chromosome movements during cell division.
- Enabling organelle movements within the cell.
Microtubules are involved in the movement of what?
movement of organelles, vesicles and enzymes across the cell
What is the movement of microtubules is caused by?
aused by motor proteins powered by ATP (converts chemical energy to mechanical energy).
What are the two types of motor proteins?
kinesin and dynein
Kinesin moves cargo in what direction
towards the plus end of the microtubules
Dynein moves cargo in what direction
owards the minus end of microtubules
Describe polymerzation of microtubule
The process by which microtubules grow in length.
- It involves the addition of tubulin dimers to the “plus end” of the microtubule.
- This elongation is critical for various cellular functions, including cell motility and intracellular transport.
What role do microtubules play during mitosis?
- Microtubules play a crucial role in separating chromosomes during mitosis.
- they radiate from the centrosome, helping to organize and segregate genetic material into daughter cells during cell division.
What is the centrosome?
A structure present in the cytoplasm of animal cells, typically located near the nucleus.
- It functions as a microtubule-organizing center (MTOC) and plays a crucial role during cell division.
How many centrioles are in a centrosome?
2 centrioles that are perpendicular to one another
what’s a centriole
- A cylindrical structure found in the centrosome of animal cells
- composed of 9 microtubule triplets arranged in a “9+0” pattern
= indicating that there are 9 microtubule triplets together but none at the center. - Centrioles play a role in cell division.
What happens to centrioles after mitosis?
the two centrioles separate, and each is replicated for the next cell cycle.
What is the hierarchal order for microtubule structure? (from low-high)
- Tubulin
- Tubulin dimer
- microtubule
- centriole
- centrosome
Microtubules are involved in the beating of:
flagella and cilia
What is the function of cilia/flagella?
- Both cilia (short and numerous)
- flagella (long and few) are cell appendages containing microtubules.
- They are used in locomotion (flagella and cilia)
- for moving fluids and facilitating feeding (cilia).
What is the core of Cilia and flagella called + what is composed of?
- The core of both cilia and flagella is called the axoneme.
- The axoneme is composed of nine outer doublet microtubules and two inner single microtubules, arranged in a “9+2” pattern
= meaning there are 9 pairs of microtubules surrounding 2 central microtubules.
= These microtubules are covered by the plasma membrane.
What does the sliding of microtubules depend on?
depends on a motor protein (dynein)
-> this creates the beating of flagella
How does SARS-Cov-2 affect cilia in the respiratory system?
- loss or shortening of cilia (axoneme) in tracheal epithelial cells.
- Misorientation of the basal body
= disrupting the proper alignment and function of cilia in the respiratory tract.
How does SARS-Cov-2 affect mucociliary clearance?
- Decreased percentage of ciliated area in the respiratory tract.
- Reduction in the mean clearance speed of viral particles.
- These effects can hinder the effective clearance of mucus and viral particles from the airways.
What are microfilaments (actin filaments)
- Thin filaments composed of actin proteins.
- They function alone or in conjunction with myosin to cause cell contraction
= enabling various cellular processes such as muscle contraction and cell movement.
What is the function of microfilaments?
- Maintenance of cell shape.
- Facilitating changes in cell shape.
- Playing a crucial role in muscle contraction.
- Promoting cytoplasmic streaming in plant cells.
- Enabling cell motility, such as in amoeboid movement.
- Assisting in the division of animal cells.
What are microfilaments composed of?
- double chain of actin subunits
What are key features of microfilaments?
- form a network and can branch within the cell.
- Provide resistance to compression, maintaining the cell’s shape, especially in the cortex (thin region directly beneath the plasma membrane).
- Can interact with the protein myosin to facilitate muscle cell contraction.
What is the sliding of microfilaments powered by?
myosin
what is myosin
a motor protein that powers movement in cells, particularly muscle cells, by converting chemical energy from ATP into mechanical work.
what are the steps in muscle contraction
- Nerve Signal: A nerve signal stimulates the muscle, leading to the release of calcium ions (Ca2+) from the sarcoplasmic reticulum.
- Actin and Myosin Interaction: Calcium ions bind to troponin, allowing myosin heads to bind to actin filaments.
- Cross-Bridge Formation: Myosin heads attach to actin, forming cross-bridges.
- Power Stroke: ATP is hydrolyzed, causing myosin heads to pivot and slide actin filaments, contracting the muscle.
- Relaxation: When nerve signals stop and calcium ions are pumped back into the sarcoplasmic reticulum, the muscle relaxes.
What are intermediate filaments?
- Strong and flexible filaments of intermediate size
- They provide mechanical support to the cell
= helping it withstand physical stress and maintain its structural integrity.
What are the main functions of intermediate filaments?
- Maintenance of cell shape, serving as tension-bearing elements.
- makes sure nucleus and certain other organelles within the cell.
- Formation of the nuclear lamina, a supportive network that surrounds the nucleus.
Intermediate filaments are only found where?
mainly in the cytoplasm of animal cells.
What differentiates intermediate filaments from microtubules/microfilaments?
Intermediate filaments are more permanent structures and do not undergo disassembly and reassembly to the same extent as microtubules and microfilaments.
What is plasmodesmata?
plasmodesmata are tiny channels connecting plant cells, enabling communication and nutrient exchange.
What are neighbouring cells in plants connected by?
Cytoplasmic channels called plasmodesmata
What is the function of plasmodesmata?
facilitate the easier transport and communication of molecules and substances between plant cells.
They are tiny channels that connect cells, allowing things to move between them.
What are the 3 different types of cell junctions in animals?
- tight junctions;
2: desmosomes; - gap junctions
What are tight junctions?
protein-based structures that tightly bind the plasma membranes of adjacent animal cells, forming a strong barrier.
What is the function of tight junctions?
- act as barriers
= preventing the leakage of fluid + selective passage of substances between cells in animal tissues.
What is an example of tight junction?
- Blood-brain barrier
- Epithelial cells like skin cells (keratinocytes)
- enterocytes in the intestine
- Endothelial cells in blood vessel walls
What are desmosomes?
cellular structures that firmly attach neighboring cells together using transmembrane proteins linked to intermediate filaments, promoting cell adhesion and tissue stability.
What is the function of desmosomes?
Keeping neighboring cells tightly connected, particularly in stretchable tissues.
What is an example of desmosomes
Muscle cells (myocytes) are held together by desmosomes, ensuring strong connections in contractile tissues.
Cadherins
the proteins that link cells in desmosomes
What are gap junctions?
- specialized cellular junctions similar to plasmodesmata in plants.
- They consist of channels formed by six proteins known as connexins, allowing for direct communication between neighboring cells.
What is the function of gap junctions?
facilitating cell-to-cell communication by:
- allowing the passage of ions and small molecules
= (including amino acids and sugars ) between neighboring cells.
What is an example of gap junctions?
heart muscle cells
