Chapter 8: Biological Membranes Flashcards
Describe the cell membrane.
Semipermeability/selective permeability?
What molecules and compounds can diffuse across the membrane? Which need alternative entry?
What is the name for the theory that underlies the structure and function of the cell membrane?
The cell membrane is a plasma membrane composed of a phospholipid bilayer, the interior of which is nonpolar the cell and environment facing portions are polar.
The cell membrane is semi permeable as it chooses which particles can enter and leave the cell at any point in time.
The selective permeability of the cell membrane is due to its amphipathic nature as well as various transmembrane channels and carriers.
The cell membrane permits fat soluble compounds to cross easily.
Larger and water soluble compounds do not readily diffuse across the membrane and need alternative entry.
This is known as the fluid mosaic model.
Carbohydrates associated with membrane bound proteins are called what?
Carbohydrates associated with membrane-bound proteins, create a glycoprotein coat.
What is the main function of the cell membrane?
How does the cell membrane achieve this?
The main function of the cell membrane is to protect the interior of the cell from the external environment.
The cell membrane achieves this through its phospholipid and amphipathic nature along with embedded proteins that creates a selectively permeable environment.
Cellular membrane selectively regulate traffic into and out of the cell and are involved in both inter and intracellular communication and transport.
The cell membrane is in a constant state of flux on the molecular level.
What are lipid rafts (do they serve a role)?
Flippases (do lipids move between membrane layers)?
Phospholipids move rapidly in the plane of the membrane through simple diffusion.
Lipid rafts are collections of similar lipids with or without associated proteins that serve as attachment points for other biomolecules. Lipid rafts often serve roles in signaling. Lipid rafts move about within the plane of the membrane, but more slowly.
Proteins also travel within the plane of the membrane.
Lipids can also move between the membrane layers, but it is energetically unfavorable because of the polar head groups must be forced through the non-polar tail region.
Flippases facilitate this flipping between the layers (recalling that this is an enzyme, and therefore reduces the energy required for this to happen on its own)
MCAT concept check fluid mosaic model 8.1 page 296 question 1
Describe the role of flippases and lipid rafts in biological membranes.
Flippases are responsible for the movement of phospholipids between the layers of the plasma membrane because it is otherwise energetically unfavorable.
Lipid rafts are aggregate of specific lipids in the membrane that function as attachment points for other biomolecules and play roles and signaling.
MCAT concept check fluid mosaic model 8.1 page 296 question 2
List the following membrane components in order from most plentiful to least plentiful:
Carbohydrates, lipids, proteins, nucleic acids
Lipids, including phospholipids, cholesterol, and others are most plentiful.
Proteins, including transmembrane proteins, channels and receptors, membrane associated proteins, and embedded proteins are the next most plentiful.
Carbohydrates, including the glycoprotein coat, and signaling molecules, are the next most plentiful.
Nucleic acids are essentially absent in the cell membrane.
Many antidepressants increase levels of neurotransmitters in the brain, but the effects take longer to appear than the changes in neural chemistry. Why is that?
The reason for this delay is that the nervous system must still up regulate its post synaptic receptors to respond to the new levels of neurotransmitter.
What molecules lend fluidity and structural integrity to the cell membrane.
Within the cell membrane, there are a large number of phospholipids with very few free fatty acids.
Steroid molecules and cholesterol lend fluidity to the membrane.
Waxes provide membrane stability, help maintain the structural integrity of the cell.
What are fatty acids?
Fatty acids are carboxylic acids that contain a hydrocarbon chain and terminal carboxy group.
Fatty acids are the building blocks of fats in our bodies and food broken down during digestion and absorbed into the blood, forming triglycerides when joined together.
What are triacylglycerols? Whats another name for them?
Triacylglycerols (triglycerides) are storage lipids involved in human metabolism.
Three fatty acid chains esterified to a glycerol molecule.
What is a chylomicron?
Chylomicrons are transport molecules from the intestine that deliver food products to the blood stream to adipose and muscle tissue and liver etc.
What is a phospholipid?
What shape will phospholipids spontaneously assemble into (two answers)?
By substituting one of the fatty acids in triacylglycerol with a phosphate group, a glycerophospholipid is formed, commonly called a phospholipid.
Phospholipid spontaneously assemble into micelles (small mono layer vesicle) and liposomes (bilayered vesicle) due to its amphipathic nature.
What is very low density lipoprotein (VLDL)?
VLDL is a lipoprotein and acts as a lipid transporter.
Glycerophospholipids are used for lipid synthesis and can produce a hydrophilic surface layer on lipoproteins like VLDL.
VLDL, or very-low-density lipoprotein, is a type of lipoprotein, a combination of proteins and fats, that your liver produces and releases into the bloodstream to transport triglycerides (a type of fat) and cholesterol to your tissues.
The phosphate group can also acts as an attachment point for hydrophilic groups. What are some examples of this?
Choline can attach to phosphate groups (phosphatidylcholine aka lecithin)
Inisitol (phosphotidylinositol)
What are sphingolipids?
What differentiates them from glycerophospholipids?
What are the four kinds of sphingolipids?
Sphingolipids are important constituents of cell membranes.
Sphingolipids are similar in structure to glycerophospholipids but they do not contain glycerol, they contain a sphingosine or sphingoid compound rather than glycerol.
Ceramide: simple sphingolipid.
Sphingomyelin: phospholipid as it contains phosphocoline or phosphoethanolamine hydrophilic region.
Glucosphingolipis (CEREBROSIDE): glycolipid containing glucose or galactose as hydrophilic portion.
Gangliosides: glycolipid containing sialic acid (N-acetylneuraminic acid, NANA) linked to oligosaccharides.
What amino acid is important for making sphingolipids?
What are the types of sphingolipids?
What is cholesterol?
Cholesterol regulates membrane fluidity, and is necessary in the synthesis of all steroids.
Is amphipathic, makes up 20% of the cell membrane by mass. Makes up half of the cell membrane by mole fraction.
Cholesterol occupies space between phospholipids and stabilizes them. Cholesterol increases fluidity at lower temperature by preventing the formation of crystal structures in the membrane.
At high temperatures, it decreases the fluidity and helps hold the membrane intact.
What are waxes?
Waxes are a class of lipids that are extremely hydrophobic, rarely found in the cell membranes of animals, sometimes found in the cell membranes of plants.
Composed of long chain fatty acid and long chain alcohol, causing a high melting point.
Provide stability and rigidity within the non-polar tail region.
Waxes serve an extracellular function in protection and waterproofing.
What are the three types of membrane proteins?
Embedded, transmembrane, integral (transmembrane and embedded together), and peripheral.
Embedded proteins are associated with the interior (cytoplasmic) or exterior (extracellular) surface of the cell membrane.
Transmembrane proteins pass completely through the lipid bilayer (transporters, channels, receptors).
Embedded proteins and transmembrane proteins are collectively known as integral proteins.
Membrane associated (peripheral) proteins may be bound through electrostatic interactions with the lipid bilayer or to other transmembrane or embedded proteins like the G proteins found in G protein coupled receptors.
How do carbohydrates relate to the cell membrane?
What are important sphingolipids in the body?
Carbohydrates are attached to protein molecules on the extracellular surface of cells.
Carbohydrates are generally hydrophilic, interactions between glycol proteins and water can form a coat around the cell.
Carbohydrates connective signaling and recognition molecules.
Glycosphingolipids are responsible for ABO blood group antigens on red blood cells. Blood group antigens are sphingolipids connected to carbohydrates that differ only in their carbohydrate sequence.
Immune system and pathogens take advantage of these membrane, carbohydrates and membrane proteins to target particular cells.
What are membrane receptors?
Provide example.
Transporters for facilitated diffusion and active transport can be activated or deactivated by membrane receptors, which tend to be transmembrane proteins.
Ligand gated ion channels are membrane receptors that open a channel in response to binding of a specific ligand.
Other membrane receptors participate in bio signaling, such as G protein coupled receptors (GPCR) involved in several different signal transduction cascades.
Membrane receptors are generally proteins, although there are some carbohydrate and lipid receptors, especially in viruses.
What is a cell cell junction?
What is a cell adhesion molecule?
What are the two types of cell cell junctions?
Cells within tissues can form a cohesive layer via intercellular junctions that provide direct pathways of communication between neighboring cells or between cells and the extracellular matrix.
An important gap junction in myocardial cells are called intercalated discs. Intercalated discs allow the direct passage of ions and small molecules between myocardial cells, facilitating rapid and coordinated electrical conduction throughout the heart
Cell cell junctions are usually comprised of cell adhesion molecules (CAM), proteins that allow cells to recognize each other and contribute to proper cell differentiation and development.
Gap junctions and tight junctions are two types of cell cell junctions.
What is a gap junction?
What is connexin?
What passes through gap junctions, what does not pass through gap junctions?
What are gap junctions found in myocardial cells?
Gap junctions allow for direct cell cell communication and are often found in small bunches together.
Also called connexons and are formed by the alignment in the interaction of pores, composed of six molecules of connexin.
Connexin permit movement of water and some solute directly between cells. Proteins are generally not transferred through gap junctions.
Intercalated discs are gap junctions found in myocardial cells.