Intro to Cytology HANDOUT Flashcards
Describe eukaryotic cells organelles and particles
contain a number of membranes that form barriers between the cell and external enironment (pm) and also subdivide the cell into compartments
what are organelles
membrane bound compartments within the cell
what do membranes allow
each type of organelle to maintain novel ionic and enzymatic interior environments, which are different from the surrounding cytoplasm.
what are membranes composed of
lipids, proteins, carbs
membranes and visualization
cannot be visualised in a light microscope bc they are too thing (7nm) and do not stain with standard histological dyes (H&E), but can be seen in an electron microscope when stained with osmium tetroxide
Membrane lipid types
phospholipids, cholesterol, glycolipids
polarity of membrane lipids
ampipathic - they have uncharged hydrophobic (dont like water) tails and polar hydrophilic heads .
what does the ampipathic nature of membrane lipids cause
them to spontaeously form a lipid bilayer with the hydrophobic tails facing each other and the hydrophilic heads facing towards the aqueous environment
what is the key to the organization of the membrane
the presence of the hydrophobic center, which acts as an anchor to membrane proteins that can move within the lipid bilayer - FLUID MOSAIC MODEL
Permeability of the membrane
highly permeable for small, uncharged molecules that cross the membrane by simple diffusion. All other molecules such as ions and large molecules require membrane transport proteins to provide them with passage across the membrane.
how can membrane proteins be classified
based on their structure and based on their function
how do you divide structurally membrane proteins
integral and peripheral
describe integral membrane proteins
they have a hydrophobic region which is embedded into the hydrophobic core of the membrane.
what are transmembrane proteins
integral membrane proteins that extend all the way through the membrane
describe peripheral membrane proteins
they are not embedded within the lipid bilayer and attach either to integral proteins or to the hydrophilic heads of the membrane lipids.
How can membrane proteins be divided functionally
into transport proteins, receptors, and structural proteins
transport proteins description
the lipid bilayer forms a barrier which is impassible for charged and polar molecules. Transport proteins selectively allow such molecules to cross the membranes. There are several classes of transport proteins: Channel, carrier, pumps
channel proteins
form “pores”, which allow passage of small molecules across the membrane via passive diffusion. Channels are ion-selective.
Carrier proteins
drag other molecules through the membrane by hiding them in a cleft in the protein
Pumps
use ATP energy to pump ions actively though the membrane
Receptors
Some transmembrane proteins bind to specific molecules in the extracellular matrix. This specific binding can result in a conformational change in the transmembrane protein that can serve as a signal that allows the cell to adapt to its evironment
Structural or anchoring proteins serve to
attach cell to its surroundings. They use their cytoplasmic domains to link to the elements of the cytoskeleton, and their extracellular domains to link to the extracellular proteins
Carbohydrates description
mostly oligosaccharides, are often attached to the extracellular domains of membrane proteins and lipids to form glycoproteins and glycolipids.
What is the glycocalyx
a fuzzy coating on the external surface of a cell due to the large amount of carbohydrates attached to proteins and lipids. This can be seen on an electron microscope