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Membrane proteins

def: carry out most of the membrane functions. (the membranes bitches?)

Info: these proteins, in animals, constitute about 50% of the mass of most plasma membranes
however, because lipids are much smaller then proteins, a cell membrane typically has 50 times more lipid molecules then protein molecules.

They extend through the lipid bilayer, and part of their mass is on either side. They have both hydrophobic and hydrophilic parts. They have their hydrophobic tails in the center of the bilayer like the lipids do, with their hydrophilic heads on the outside.

Some membrane proteins are located entirely in the cytosol, associated with the inner 'leaflet' of the lipid bilayer by an amphipathic alpha helix exposed on the surface of the protein.

Some proteins are entirely outside the bilayer, on one side or the other, attached to the membrane only by one or more covalently attached lipid groups

Proteins can also be bound indirectly to one or the other face of the membrane, held in place only by their interactions with the other membrane proteins.

The proteins that are directly attached to the bilayer can be removed only by disrupting the bilayer with detergents. These are called integral membrane proteins.

All others are called peripheral membrane proteins.

What do:
transport particular nutrients, metabolites, and ions across lipid bilayer
some anchor membrane to macromolecules on either side
some function as receptors that detect chemical signals in the cells environment and relay them to cell interior
some work as enzymes to catalyze specific reactions


Membrane domains

def: functionally specialized regions on the cell or organelle surface.


Membrane transport proteins

def: provide private passageways across the membranes for select substrates


Mobile Genetic Element (chapter 6)

def: Short segment of DNA that can move, sometimes through an RNA intermediate, from one location in a genome to another. They are an important source of genetic variation in most genomes.


Mutation (chapter 6)

def: A randomly produced, heritable change in the nucleotide sequence of a chromosome.


Membrane-Enclosed Organelle (chapter 15)

def: Any organelle in the eukaryotic cell that is surrounded by a lipid bilayer membrane (i.e. the ER, Golgi and lysosome).


Microtubule (chapter 17)

def: Long, stiff, cylindrical structure composed of the protein tubulin. Used by eukaryotic cells to regulate their shape and control their movements.


Motor Protein (chapter 17)

def: protein (such as kinase or myosin) that uses energy derived from ATP hydrolysis to propel itself along a protein filament or polymeric molecule.


Myofibril (chapter 17)

def: Long, highly organized bundle of actin, myosin, and other proteins in the cytoplasm of muscle cells that contracts by a sliding filament mechanism.


Myosin (chapter 17)

def: Type of motor protein that uses ATP to drive movements along actin filaments. Myosin II is a large protein that forms the thick filaments of skeletal muscle. Smaller myosins, such as myosin I, are widely distributed and are responsible for many actin-based movements.


MAP Kinase (chapter 16)

def: Mitogen-activated protein kinase. Protein kinase that performs a crucial step in relaying signals from cell-surface receptors to the nucleus. It is the final kinase in a three-kinase sequence called the MAP kinase cascade.


Molecular Switch (chapter 16)

def: Protein or protein complex that operates in an intracellular signaling pathway and can reversibly switch between an active and inactive state.


Monomeric GTPase (chapter 16)

def: Small, single subunit GTP-binding protein. Proteins of this family, such as Ras and Rho, are part of many different signaling pathways.


Messenger RNA (mRNA) (chapter 7)

def: RNA molecule that specifies the amino acid sequence of a protein. Produced by RNA splicing (in eukaryotes) from a larger RNA molecule made by RNA polymerase as a complementary copy of DNA. It is translated into protein in a process catalyzed by ribosomes.


MicroRNA (miRNA) (chapter 8)

def: Small noncoding RNAs that control gene expression by base-pairing with specific mRNAs to regulate their stability and their translation.


M-Cdk (chapter 18)

def: Active protein complex formed at the start of M phase of the cell cycle by an M-cyclin and the mitotic cyclin-dependent protein kinase (Cdk)


M Cyclin (chapter 18)

def: Cyclin protein that binds to mitotic Cdk to form M-Cdk at the start of M phase of the cell cycle.


M Phase (chapter 18)

def: Period of the eukaryotic cell during which the nucleus and cytoplasm divide.


Metaphase (chapter 18)

def: Stage of mitosis at which chromosomes are firmly attached to the mitotic spindle at its equator but have not yet segregated toward opposite poles.


Mitogen (chapter 18)

def: An extracellular signal molecule that stimulates cell proliferation.


Mitosis (chapter 18)

def: Division of the nucleus of a eukaryotic cell, which involves condensation of the DNA into visible chromosomes (from the Greek mitos, a thread, referring to the threadlike appearance of the condensed chromosomes).


Mitotic Spindle (chapter 18)

def: Array of microtubules and associated molecules that forms between the opposite poles of a eukaryotic cell during mitosis; during the separation of the duplicated chromosomes, the spindle serves to move the two chromosome sets apart.


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