Exam 1 Study Guide (Cells & Organelles) pt 3 Flashcards
What actual cell type most closely resembles the theoretical “typical” cell?
There are over 200 different types of cells, each specialized in its makeup to carry out its own particular function, so no one cell type represents a true “typical” cell.
Describe the basic makeup of a typical cell membrane (Plasma membrane)
Fluid but relatively stable
A phospholipid bilayer with associated integral and peripheral proteins.
What is the “catch phrase” for the plasma membrane (and cell membranes in general)?
Fluid mosaic model
A sea of fluid lipids contains a mosaic of many different proteins, including those that:
- float freely like icebergs in the lipid sea
- are constrained in their movement like a ship at anchor
Describe the ability to view membranes of cells through the light microscope versus the ability to view membranes of cells using the electron microscope.
Too thin to see with light microscope, but can be observed with electron microscope
As a general category, what type of substances are allowed by membrane lipids to move across membranes?
- Membrane allows passage of many lipid soluble substances
As a general category, what type of substances are not allowed by membrane lipids to move across membranes?
- barrier to passage of charged or polar substances
“like dissolves like”. (Water is polar, oil is non-polar)
Sequence the following constituents of the lipid bilayer from greatest proportion to least proportion within the membrane
Phospholipids (about 75% of the membrane)
Cholesterol (about 20 % of the membrane)
Glycolipids (about 5% of the membrane)
Describe phospholipid molecules comprising cell membranes with regard to placement and orientation within the membrane
Bilayer occurs because lipids are amphipathic, having both polar and nonpolar parts
Describe phospholipid molecules comprising cell membranes with regard to nature and polarity of different parts of the phospholipid
Phosphate-containing head is polar (hydrophilic)
Fatty acid tails are nonpolar (hydrophobic)
How does the amphipathic nature of phospholipids relate to the bilayer structure of membranes and the parts of the bilayer that face the environment within the bilayer itself, as well as the environment away from the bilayer?
The polar head of the phospholipid is looking for other polar molecules to bond to i.e. H2O. Because both intracellular fluid and extracellular fluid are mostly composed of H2O the heads of the phospholipids naturally orient themselves toward the ECF and ICF. The hydrophobic tails are both nonpolar and naturally orient themselves toward one another also.
Describe phospholipid molecules comprising cell membranes with regard to types of atoms that comprise the different parts of the phospholipid and their effect on polarity
The head of the lipid is mostly hydrogen and oxygen bonds resulting in a polar non-covalent bond. The tail of the lipid is mostly composed of a carbon tail this is covalently bonded and also non polar.
What is the function of cholesterol in the membrane bilayer?
forms hydrogen bonds with heads of phospholipids and glycolipids, and fills the space between fatty acid tails
mediates membrane fluidity, makes lipid bilayer less fluid (and stronger) at normal body temperatures
increases membrane fluidity at lower temperatures
What are the two categories of membrane proteins based on location relative to the overall structure of the membrane?
integral proteins and peripheral proteins
Integral proteins go throughout the ECF side and ICF side of the lipid bilayer.
Peripheral proteins are located on one side of the membrane. Attach to phospholipid heads or to integral proteins
Compare the variability of lipids that are constituents of different types of cellular membranes with the variability of proteins that are constituents of different types of cellular membranes.
Membranes of different cell types and of different intracellular organelles exhibit a great variety of proteins, and are determiners of many of the membrane’s functions
In contrast with lipids in membranes of cells which vary only slightly
Compare and contrast integral (membrane) protein(s), peripheral (membrane) protein(s), and transmembrane protein(s)
Integral proteins are amphipathic (like membrane lipids) and extend through or well into the bilayer
Most are transmembrane proteins (go all the way through the membrane bilayer)
- Form ion channels (channel proteins)
- Transporters (carriers)
Peripheral proteins are on one side of the membrane and attach to phospholipid heads or to integral proteins
Compare the relative degree to which membrane cholesterol, membrane lipids, and the two types of membrane proteins are amphipathic.
Cholesterol is weakly amphipathic, having a small –OH group as its only polar part
What is the composition of the glycocalyx?
proteins (to form glycoproteins)
lipids (to form glycolipids)
What are the functions of the glycocalyx?
To protect cells from enzymatic action
For cell adhesion
For cell recognition
How can the glycocalyx be used to identify the exterior plasma membrane surface?
Makes the outer membrane asymmetric, and provides a way to tell the outer surface from the inner surface.
What features of the lipid bilayer of a plasma membrane cause it to be asymmetric?
Glycocalyx
How do alterations of the glycocalyx enable cancer cells to avoid detection by the body’s immune system?
A cancer cell’s glycocalyx may change almost continuously, allowing it to keep ahead of immune system recognition systems and avoid destruction.
The lipid bilayer is permeable to_____
nonpolar, uncharged molecules such as oxygen, carbon dioxide, and steroids
The lipid bilayer is impermeable to______
ions and large uncharged polar molecules such as glucose
The lipid bilayer is slightly permeable to_______
small uncharged polar molecules such as water and urea
What are the three types of gradients that are important in living systems?
Concentration Gradients, in which the attribute is concentration of a chemical
Electrical Gradient, in which the attribute is electrical charges
Electrochemical Gradient, the combined influence of the above two
