Non-enzymatic protein function Flashcards
A cell cytoskeleton is composed of several different types of protein fibers namely?
Microfilaments, intermediate filaments, and microtubules
Actin is a microfilament. What is its functions?
Motion, structure, cell division, and muscle contraction
Individual actin monomers are known as
G actin (have a globular shape)- each is a protein an d have sites where and ADP and ATP can bind
G actin bind to each other to form what?
Filamentous actin (F-actin)
How many F-actin are stuck together to form a microfilament?
2
2 ends of actin
- Plus end heavy in ATP bound actin
2. Minus end heavy in ADP bound actin
Which end of the actin is most likely to have beads dissociate
ADP bound end
Treadmilling
When actin filament simultaneously grow at one and and shrinks on the other end. A process derived by ATP hydrolysis
What can be used to block addition or removal of monomeric actin
Capping end
These are composed of various types of protein subunits and are generally more stable and do not bind nucleotides like the other 2 classes of cytoskeleton fibers
Intermediate filaments
These can be stretched like a rubber band. they are typically found in the cytoplasm between the nucleus and plasma membrane
Intermediate filaments
Their main function is structural support and helps cell adhere to neighboring cells and in positioning organelles
Intermediate filaments
Ex. Keratin
These provides structural support for cilia and eukaryotic flagella, chromosome separation during mitosis and meiosis, and intracellular support
Microtubules
The largest of the cytoskeleton fibers and is composed of a diner of an alpha-tubulin and a beta-tubulin
Microtubules
Microtubule dimers have nucleotide binding sites for ?
GTP and GDP
Polymerization of microtubule dimers are driven by
Large number of dimers in the cell
*think Le Chatelier’s principle
Polymerization and Depolymerization preferentially occurs at which end of microtubules?
Positive end
Presence of GDP at the positive end of the microtubules favor polymerization or depolymerization?
Depolymerization
Motor proteins functions
- Transport
- Motility in unicellular organisms
- Generating force during muscle contraction
These motor proteins are ATP-ashes which consumes energy from ATP hydrolysis. They can also do anterograde cargo transport
Kinesins
Kinesics move through the (positive / negative) end of the microtubule, which faces the periphery of the cell
Positive
Kinesins are made up of how many subunits? Describe them
4- heterotetramer
- 2 heavy chains and 2 head groups attached to thin flexible stocks
- 2 light chains on top to which the cargo that the kinesin is transporting attaches to.
Kinesins attach to which protein fiber. What drives this mechanism?
It attaches to microtubule and ATP hydrolysis is used to push movement of the Kinesins to the positive end
Which motor protein walk towards the minus end of microtubules (retrograde transport)- towards the cell center
Dyneins
2 main groups of dyneins
Axonemal and cytoplasmic
This type of dyneins are only found in cell with cilia or flagella. They can help generate the sliding motion between microtubules that are necessary for these structures to move
Axonemal
This type of dyneins transport cargo for cell functions such as organelle and vesicle components
Cytoplasmic
This type of motor proteins are also ATP-ase and attaches to actin filaments during muscle contraction
Myosins
Myosin’s structure and function of each
- Head motor domain- binds actin and hydrolyzes ATP to power myosin’s movement
- neck- linker region that hold the structure together
- tail effector domain- binds to cargo or other myosin molecules
These are proteins located on the cell surface or periphery that glue cells together to stabilize tissues and organs
Cell Adhesion Molecules (CAM)
Different functions of different types of CAMs
- Associate with cytoskeletal elements to help the cytoskeletons stay in place
- Anchor cells to each other and the extra cellular matrix
This type of CAM mediate the inflammatory response and are important in blood clotting
Selectins
Where are selectins found?
Immune cells, platelets, and endothelial cells lining blood vessels
Selectin binding is which ion dependent?
Calcium-ion dependent
*also heterophilic
This CAM plays a role in cell growth and development. They are calcium-ion dependent and play major role in cell adhesion
Cadherins
Cadherins bind to other Cadherins which makes it?
Homophilic
Type of CAM that are membrane-spanning heterodimers with alpha and beta subunits and ligand binding sites that attract metal ions and proteins
Integrins
This type of CAM helps cell adhere to this extracellular matrix by linking microfilaments in the cytoskeleton to the matrix proteins outside of the cell
Integrins
This type of CAM play a role in cell signaling by binding ligands and interacting with various receptors on the cell surface
Integrins
3 types of cell junctions
Anchoring junctions, gap junctions, and tight junctions
This junction connects one cell with the cytoskeleton of other cells or with the extracellular matrix- helps stabilize cells an tissues
Anchoring junctions
Adherens junctions created by cadherin proteins to interact with actin filaments and desmosomes are what type of junctions
Anchoring junction
Desmosomes tend to be found in cells that have to withstand a lot of force regularly such as heart muscle. The cadherin proteins attach to what protein fibers?
Intermediate filaments
Gap junctions are connected by which proteins
Connexin
T or F. The connexin proteins connect cells in such a way that there’s a small passage between them through which small ions can diffuse
TRUE
What ions can pass through gap junctions
Sugars, vitamins, nucleotides, and amino acids, cAMP, and Ca2+
