Bk 2 Ch 5 Cell Movement Flashcards
Cyclosis
Flow of cytosol and organelles within a cell that ensures circulation of nutrients, proteins and other cellular materials; also referred to as cytoplasmic streaming. Cyclosis is particularly evident in large plant cells.
Microtubule organising Centre (MTOC)
Amorphous region of cytoplasm from which microtubules radiate. The pattern and number of microtubules is determined by the MTOC. Animal cells typically contain a single MTOC called the centrosome, which is usually located near the nucleus.
Kinesins
A family of microtubule-binding motor proteins that are involved in cytokinesis (e.g. in movement of chromosomes) and intracellular transport of vesicles and organelles. They bind to and move towards the plus end of a microtubule (towards the cell surface), carrying cargo vesicles and particles along as they do so. Kinesins move along microtubules in the opposite direction to cytoplasmic dyneins, another family of motor proteins.
Dyneins
A family of microtubule-binding motor proteins that bind to and move towards the minus end of a microtubule. Cytoplasmic dyneins carry cargo of vesicles and particles along microtubules whilst axonemal dynein constitutes the side arms of the outer microtubule doublets in the ciliary axoneme and is responsible for generating movement of this structure. Cytoplasmic dyneins move along microtubules in the opposite direction to kinesins, another family of motor proteins; they are particularly important in vesicle trafficking and localisation of the Golgi apparatus.
Syncytia
singular, syncytium). Membrane-bound masses of cytoplasm containing multiple nuclei, formed by fusion of cells (usually during embryogenesis). Skeletal muscle fibres are syncytia, formed by the fusion of hundreds of individual cells called myoblasts.
Myofibrils
Highly organised linear structures in the cytoplasm of muscle fibre cells, consisting of actin filaments and myosin filaments. Under the microscope, myofibrils can be seen to consist of a regular series of light and dark bands in repeating units termed sarcomeres.
Sarcomeres
Repeating structural unit in the myofibrils of striated muscle, readily identified by electron microscopy.
Sliding filament model
A model to describe the process by which skeletal muscle contracts. The interdigitating actin and myosin filaments of myofibrils slide past each other, without shortening of either. The myosin heads act as ‘cross-bridges’ between the myosin filament and the actin filament, applying power-strokes to pull the actin filaments towards the centre of the sarcomere. As the actin filaments are anchored at the Z disc, the sarcomere is effectively shortened.
Cross-bridge cycle
The mechanism by which sarcomere shortening is achieved in skeletal muscle; in principle the same as the general motor protein mechanism. The myosin heads (the motor proteins) act as ‘cross-bridges’ between the myosin filament and the actin filament and, through a series of conformational changes, pull the actin filament toward the centre of the sarcomere, thereby shortening the sarcomere.
Chemotaxis
Orientation and movement of a cell along a concentration gradient of a diffusible chemical or movement in the direction of the gradient (either toward or away from the higher concentration).
Tumbling
Changes in direction of swim of motile bacteria in response to chemotactic signals, caused by reversal of direction of rotation of bacterial flagella. Re-orientation occurs more often when repellents are sensed, and is reduced when attractants are sensed.
Proton motive force
The free energy stored in an electrochemical proton gradient such as that which is established across the inner mitochondrial membrane or the thylakoid membrane in chloroplasts. It is this that drives synthesis of ATP in mitochondria and in chloroplasts.
Methyl accepting chemotaxis proteins (MCPs)
Receptors involved in chemotactic regulation of flagellar movement in bacteria, whose activity is regulated by methylation. They have a periplasmic domain that binds the ligand (attractant or repellent), a transmembrane domain and a highly conserved cytosolic domain that interacts with a series of downstream signalling proteins called Che proteins
Che proteins
A series of intracellular signalling proteins involved in chemotactic regulation of flagellar movement in bacteria.
Integrins
Type of cell surface proteins that are involved in binding to extracellular matrix components such as fibronectin, which links to collagen. On the inside of the cell, integrins link, via other proteins, to actin filaments.
