Generalised Eukaryotic Cells Flashcards
Whats defines a Eukaryotic Cell - what are examples of these cells.
Those with a true nucleus - found in all multicellular and nonbacterial unicellular organisms (animal, fungal and plant). Contains genetic information (DNA) which can be divided into 2 by mitosis.
What is the plasma membrane - what defines its structure. What can cross this barrier
Is a semipermeable barrier which defines the outer cell perimeter. Permeable to small uncharged substances (02, CO2, urea) which diffuse freely across the membrane. Impermeable to charged or large substances which may require transport proteins (ions, amino acids, sugars).
What are 3 processes in which substances can cross the membrane
simple diffusion, carrier-mediated transport, endo/exocytosis.
What are the plasma membranes mainly composed of. How are they mainly structured.
lipids (fats and protein). The membrane is dynamic, active and fluid. Contain two ‘layers’ of phospholipids (bilipid)
What is the main lipid in the plasma membrane - define these. What is its structure.
Contains phospholipids (amphipathic molecules) - because their tail end contains fatty acids which are insoluble in water (hydrophobic), opposite end contains charged phosphate head which are soluble in water (hydrophilic). Hydrophobic heads project to the outside, hydrophilic heads project to the inside of the membrane.
How do phospholipids move within the plasma membrane - what increases and decreases the fluidity of the membrane.
Phospholipids are fluid - they move freely within the membrane. Fluidity increases with increased temperature and decreased saturation of fatty acyl tails. Fluidity decreases with decreased temperature, increased saturation of fatty acyl tails and increase in membrane cholesterol content.
What are glycoproteins - where are they found, what is the function.
Limited to extracellular aspect of membrane. Carbohydrate portion of glycolipids extends from outer leaflet into extracellular space and forms part of the glycocalyx (sugar coat on outer surface of outer leaflet of plasma membrane). Glycocalyx aids in the attachment of some cells, facilitates cell recognition, helps bind antigen and antigen-presenting cells to cell surface.
Where are proteins found within the membrane - what is their mobility. What are the two different types and where are they found
Distributed throughout membrane (mosaic of proteins) with limited mobility. Are either outside of membrane (extrinsic) or spanning the membrane (intrinsic). Intrinsic proteins are dissolved in the lipid bilayer. Extrinsic proteins don’t extend into the lipid bilayer - but can temporarily adhere to either side of the plasma membrane, bond to phospholipids groups or intrinsic proteins of the membrane via noncovalent interactions.
What are some functions of proteins
regulatory protein subunits of ion channels or transmembrane receptors, associations with the cytoskeleton and extracellular matrix, and as part of the intracellular second messenger system.
What are the methods of substances crossing the membrane
simple diffusion, carrier-mediated transport or by endo/exocytosis
What is the process of simple diffusion - what are the different types.
Spontaneous spreading of a substance going from high concentrated area to low concentrated areas (concentration gradient). Can either be a chemical gradient or electrical gradient.
Define osmosis and osmotic pressure. When will a substance have an osmotic pressure of zero.
Diffusion of water across semipermeable membrane moving from an area of high water concentration (lower solute concentration = hypotonic) to area of lower water concentration (higher solute concentration = hypertonic).
Osmotic pressure = hydrostatic pressure needed to oppose the movement of water. Isotonic solution (concentration of solute on both sides of the membrane is equal) would have an osmotic pressure of zero.
Define endocytosis - what is it called if a particle is ingested vs fluid.
Cell actually invaginates, pinches off and is released intracellularly (endocytotic vesicle).
Solid particle ingested by the cell (i.e bacterium) = phagocytosis.
Fluid ingested = pinocytosis.
What are the two substances that coat vesicles in endocytosis. What are examples of substances these two can be found in
Clathrin - protein plays major role in formation of coated vesicles. Receptor-mediated endocytosis of ligands (e.g. low density lipoprotein, growth factors, anti-bodies, etc) is due to Clathrin-coated vesicles. Found in all cells.
Caveolae = most common non-clathrin-coated plasma membrane buds which exist on surface of some cells. Consist of cholesterol-binding protein caveolin with a bilayer enriched in cholesterol and glycolipids.
How do amino acids, sugars and other solutes get across the membrane
Carrier-mediated transport: need to reversibly bind to proteins (carriers) in the membrane to get across.
Define exocytosis. What are some examples of substances that undergo this process
A cell directs an intracellular vesicle to fuse with the plasma membrane - releasing its contents to the exterior.
Neurotransmitters, pancreatic enzymes, cell membrane proteins/lipids, etc)
In exocytosis, what is the name of the structure that forms when the transient vesicle fuses with the cell membrane.
What are the main types of proteins in these structures - what is their role.
Porosome (shaped like a pore) - which are cupped shaped structures where vesicles dock in the process of fusion and secretion.
Main proteins including chloride and calcium channels, actin, and SNARE proteins - which mediate the docking and fusion of vesicles with the cell membrane.
What is the main role of SNARE proteins (2 types of fusion).
Mediate vesicle fusion through full fusion exocytosis (vesicle collapses fully into the plasma membrane) or open and close exocytosis (vesicle docks transiently with the membrane and is recycles - i.e. kiss and run).
List the typical components of the interior of a Eukaryotic Cell
Cytoplasm, Cytosol, Cytoskeleton, Flagellum,. Cilia, pseudopod, microvilli.
Define cytoplasm - what does it contain, how does transport occur.
Cytoplasm is the interior of the cell - refers to all cell components enclosed by cells membrane.
Includes: cytosol, cytoskeleton, and membrane bound organelles.
Transport: Occurs by cyclosis (circular motion of cytoplasm around the cell).
What is cytosol
The solution which bathes the organelles and contains numerous solutes like amino acids, sugars, proteins, etc.
What is the cytoskeleton. What is the importance of the cytoskeleton (intracellularly and extracellularly.
The cytoskeleton extends throughout the entire cell and has importance in shape and intracellular transportation. Also makes extracellular complexes with other proteins forming a matrix so that cells ‘‘stick together’’ (known as cellular adhesion).
What are the three main components of the cytoskeleton (which is the biggest).
In increasing order of size: Microfilaments, intermediate filaments, and microtubules.
What is the role of microfilaments in phagocytosis and cytokinesis
Microfilaments squeeze the membrane together in phagocytosis and cytokinesis. They are also important for muscle contraction and microvilli movement.
What is the main function of microfilaments, what are they composed of.
What is the polarity of microfilaments
Also known as Actin filaments - important in cell movement and contraction (i.e. actin and myosin). Composed of actin monomer (G actin) linked into a double helix.
They display polarity (having distinct and opposite poles), with polymerization and depolymerization preferentially occurring at the barbed end (+ end - where ATP bound to G actin).
Where are intermediate filaments and microtubules located within a cell. What does this permit
What structures do microtubules also form
They extend along axons and dendrites of neurons (acting like railroad tracks). This allows organelles or protein particles to shuttle to or from the cell body.
Microtubules also form:
i) the core of the cilia and flagella.
ii) the mitotic spindles
iii) centrioles.
