Chapter 2 Flashcards
The surface of a cell is made of a ___ (general word):
Membrane
What is the cell membrane primarily composed of?
Phospholipids
What do phospholipids do when placed in aqueous solution?
Form complex structures
What is the diffusion of individual lipids in the bilayer dependent on?
The independent structure of phospholipids that may contain biochemical steric hindrances.
What is the phospholipid bilayer impermeable to?
Charged (polar) molecules
How are membrane proteins and the phospholipid bilayer associated with each other?
Membrane proteins are either integrated into the bilayer or are attached peripherally on the exterior or interior of the cell (with respect to the membrane).
Transmembrane proteins embedded in the membrane are composed of:
Hydrophobic alpha-helices
Can proteins be mobile in the bilayer?
Yes! (Fluid-mosaic model)
Integral receptor proteins can function to do what? (3)
- Adhesion molecules 2. Enzymes 3. Intracellular signaling
What type of proteins are responsible for transporting water-soluble molecules into/out of the cell?
Integral membrane proteins
Enzymes can also be thought of as?
Proteins
Peripheral membrane proteins can function to do what? (2)
- Intracellular signaling 2. Form a submembranous cytoskeleton
What is the nucleus responsible for?
Stores, replicates, and reads the cell’s genetic information.
What do lysosomes do?
Digest material with origins from the interior, as well as the exterior, environments of the cell.
Where is the site of oxidative energy production?
Mitchondria (pl.) (Mitochondrion - sing.)
How are the cytoplasm and the organelles within the cell organized (as opposed to be scattered randomly?)?
The cytoskeleton organizes the cellular components.
What are intermediate filaments responsible for?
Structural support for the cell.
What are microtubules responsible for? (2)
- Structural support 2. Subcellular motility/transportation.
What component of the cytoskeleton is present in every type of cell throughout the body?
Thin and thick filaments
What are thin filaments, (or microfilaments) known as?
Actin
What are thick filaments known as?
Myosin - a motor protein
How/where are secretory and membrane proteins synthesized?
Translation in the rough endoplasmic reticulum (Rough ER)
What else occurs at the rough endoplasmic reticulum besides translation?
- Signal peptide recognition in docking to the rough ER. 2. Translocation of the generated peptide chain into the rough ER (for post-translational modifications).
What are start-transfer and stop-transfer sequences generally responsible for?
Proper insertion of proteins into the membrane
Why are newly synthesized secretory and membrane proteins translocated into the rough ER after translation?
To undergo post-translational modifications and protein folding in the lumen of the rough ER.
How do proteins and enzymes travel throughout the cell to other locations or the exterior environment?
Secretory vesicles
How are vesicles formed or secreted into/out of the cell?
Through protein complexes, such as clathrin and coatamers.
What do clathrin and coatamers do?
Form complexes with each other to create budding/formation of vesicles.
What can happen to proteins as they go through the secretory pathway?
More post-translational modification.
Where are newly-synthesized proteins sorted?
trans-Golgi
How are hydrolytic enzymes organized to be sent to lysosomes?
A mannose-6 recognition marker is responsible for the transportation of these hydrolytic enzymes to lysosomes.
What is the role of endocytosis? (general)
To internalize extracellular material.
How is the process of endocytosis activated?
Receptor-mediated activation that results in endocytosis.
What happens to stuff that is endocytosed into the cell?
Sent to lysosomes for degradation or recycled back to the cell membrane.
What is another way extracellular stuff can be internalized into the cell aside from endocytosis?
Through caveolae
What type of cell separates the milieu interior from the milieu exterior?
Epithelial cells
What does polarization mean when referring to epithelial cells?
That there is an apical surface versus a basolateral surface.
What does the cytoplasm consist of?
- Proteins 2. Nucleic Acids 3. Nucleotides 4. Sugars
Why is it important not to lose a lot of cytoplasm?
Because a lot of energy was used up to create the stuff inside the cytoplasm.
What is a phospholipid composed of?
- Glycerol backbone 2. Fatty acid or fatty acyl groups 3. Phosphate group 4. Head group
What is the plasma membrane impermeable to?
Proteins, nucleic acids, and other large molecules.
What is the plasma membrane selectively permeable to?
Ions and metabolites
If biochemical analysis were done on the membrane of a cell, what components would it find?
Lipids and proteins.
Visualize a monolayer of phospholipids placed in an aqueous solution.
Heads are interacting with aqueous solution while standing upright, with nonpolar tails erected upwards.
Define amphipathic:
Having polar and nonpolar segments in one molecule (ex. phospholipid)
Define a micelle:
When phospholipids combine to form a sphere (head groups facing outwards) in aqueous solution.
What determines how densely pack the lipid bilayer is in terms of adjacent phospholipids?
The nature of the head group of the phospholipid.
What determines how densely pack the lipid bilayer is in terms of thickness of the bilayer?
How long the fatty acid chains of the phospholipid is.
Define leaflet:
Refers to a single sheet of phospholipids. Two leaflets produces a phospholipid bilayer.
Why can detergents dissolve and disintegrate lipid complexes?
Because they are amphipathic in structure (like phospholipids) and can easily dissolve them by forming dimers with them or mixed micelles.
Why are detergents useful?
- Laundry 2. Help to determine the structure and composition of lipid membranes
Define sol state:
When leaflets are exposed to high temperatures, they are more easily able to diffuse around their adjacent phospholipids, as the intermolecular forces between the two lipids are overcome by the high temperature.
Define gel state:
When leaflets are exposed to low temperatures that inhibit the ability of adjacent phospholipids to diffuse around each other, resulting in a more rigid leaflet.
Define transition temperature:
The equilibrium temperature when the gel is “melting” into the sol state.
Would long-chain phospholipids interacting with each have a higher or lower transition temperature than short-chain phospholipids? Why?
Higher, because the intermolecular forces that need to be overcome are greater than the short-chain intermolecular forces.
What happens to a transition temperature if you were to incorporate a double bond (a “kink”) instead of a single bond into the fatty acid chain of a phospholipid?
The transition temperature would decrease dramatically because the chains are now less “stackable” and can diffuse more readily.
What are the 3 classes of membrane lipids?
- Glycerol-based phospholipids 2. Sphingolipids 3. Cholesterol
What are the 4 common types of glycerol-based phospholipids?
- Phosphatidylethanolamine 2. Phosphatidylinositols 3. Phosphatidylserines 4. Phosphatidylcholines
What are the 3 subgroups of sphigolipids?
- Sphingomyelins 2. Glycosphingolipids 3. Gangliosides
Draw the components of phosphoinositol:
Inositol –> Phosphate –> Glycerol –> Fatty acid chains
Draw the components of phosphoserine:
Serine –> Phosphate –> Glycerol –> Fatty acid chains
Draw the components of phosphatidylcholine:
Choline –> Phosphate –> Glycerol –> Fatty acid chains
Draw the components of sphingomyelin:
Choline –> Phosphate –> Sphingosine –> Fatty acid chain (x1)
Draw the components of glucocerebroside:
Galactose –> Phosphate –> Sphingosine –> Fatty acid chain (x1)
What are thecomponents of cholesterol?
Hydroxyl group, 4 ring structure (3 hexagons, 1 pentagon), hydrocarbon chain
Why are the existence of sphingolipids and cholesterol, as opposed to only glycerol-based phospholipids important for cell membrane characteristics?
Because these other forms of lipids can allow for change in the transition temperature of the membrane by preventing lipids from diffusing as easily, causing a more rigid state.
How can cholesterol concentration in the cell membrane impact cell diffusability?
At modest concentrations, cholesterol decreases fluidity (because the 4 ring structure can bind to lipids and partially immobilize them).
At high concentrations, cholesteral increases the fluidity/diffusability of the membrane and thus lowers the gel state transition temperature.
Lakes located within the membrane refer to:
Regions in the membrane where some lipids are more in the gel state (lipids with longer chains) while other regions are more in the sol state (lipids with shorter chains), creating a mosaic like feel.
What does flip-flop mean? How often does this occur?
When a phospholipid flip-flops from one leaflet of the bilayer to the other leaflet. This does not occur often because it is a non-spontaneous reaction. However, cholesterol is more likely to flip-flop because the only polar part of cholesterol is the hydroxyl group, so it is more easily able to flip flop.
