Chapter 9 Flashcards
lipids are not polymeric. however, they do …, and it is in this state that they perform their central function as the structural matrix of biological membranes
aggregate
in general, lipids perform three biological functions:
lipid molecules in the form of lipid bilayers are essential components of …
lipids containing hydrocarbon chains serve as …
many intra- and intercellular … involve lipid molecules
biological membranes
energy stores
signaling events
lipids are substances of biological origin that are soluble in ,.. such as chloroform and methanol
organic solvents
fatty acids are … with… side groups
carboxylic acids; long-chain hydrocarbon
fatty acids usually occur in … form as major components of the various lipids described in this chapter
esterified
fatty acids with < … or > …. are uncommon. most fatty acids have an … number of carbon atoms bc they are biosynthesized by the concatenation of C2 units
14; 20; even
the fats and oils that occur in plants and animals consist largely of mixtures of … (also called …)
triacylglycerols; triglycerides
these nonpolar, water-insoluble substances are fatty acid triesters of …
glycerol
triacylglycerols function as … in animals and are therefore their most abundant class of lipids even though they are not components of cellular membranes
energy reservoirs
most triacylglycerols contain … or … different types of fatty acid residues and are named according to their placement on the … moiety
two; three; glycerol
… and … (which differ only in that fats are solid and oils are liquid at room temperature) are complex mixtures of triacylglycerols whose fatty acid compositions vary with the organism that produced them
fats; oils
plant oils are usually richer in … fatty acid residues than …, as the lower melting points of oils imply
unsaturated; animal fats
fats are a highly efficient form in which to store metabolic energy. this is because triacylglycerols are …. than carbs or proteins and hence yield significantly more energy per unit mass on complete oxidation
less oxidized
fats provide about … times the metabolic energy of an equal weight of hydrated glycogen
six
in animals … are specialized for the synthesis and storage of triacylglycerols
adipocytes
whereas other types of cells have only a few small droplets of fat dispersed in their cytosol, adipocytes may be almost entirely filled with …
fat globules
… is most abundant in a subcutaneous layer and in the abdominal cavity
adipose tissue
the fat content of normal humans allows them to survive starvation for … to … months
2; 3;
the body’s glycogen supply, which functions as a short-term energy store, can provide for the body’s energy needs for …
less than a day
the subcutaneous fat layer also provides …
thermal insulation
… (or …) are the major lipid components of biological membranes. they consist of … whose C1 and C2 positions are esterified with fatty acids. In addition, the phosphoryl group is linked to another usually … group, X.
glycerophospholipids; phosphoglycerides; glycerol-3-phosphate
glycerophospholipids are therefore … molecules with … “tails” and … “heads”
amphiphilic; nonpolar aliphatic; polar phosphoryl-X
the simplest glycerophospholipids, in which X = H, are …; they are present in only small amounts in biological membranes
phosphatidic acids
saturated C16 or C18 fatty acids usually occur at the … position of the glycerophospholipids, and the C2 position is often occupied by an … C16 to C20 fatty acid
C1; unsaturated
a glycerophospholipid containing two palmitoyl chains is an important component of …
lung surfactant
the chemical structures–including fatty acyl chains and head groups–of glycerophospholipids can be determined from the products of hydrolytic rxns catalyzed by enzymes known as … , yielding ….
phospholipases; lysophospholipids
lysophospholipids, as their name implies, are powerful detergents that disrupt …, thereby … cells
cell membranes; lysing
enzymes that act on lipids have fascinated biochemists bc the enzymes must gain access to portions of the lipids that are buried in a … environment
nonaqueous
occasionally, the hydrolysis products of lipases are not destined for further degradation but instead serve as intra and extracellular ..
signal molecules
kinases catalyze ATP-dependent …
phosphoryl-transfer rxns
… are glycerophospholipids in which the C1 substituent of the glycerol moiety is linked via an alpha, beta-unsaturated ether linkage in the cis configuration rather than through an ester linkage
plasmalogens
…., …, and … form the most common plasmalogen head groups
ethanolamine; choline; serine
… are also major membrane components. most are derivatives of the C18 amino alcohol sphingosine, whose double bond has the trans configuration
sphingolipids
the N-acyl fatty acid derivatives of sphingosine are known as …
ceramides
…, the most common sphingolipids, are ceramides bearing either a phosphocholine or a phosphoethanolamine head group, so they can also be classified as …
sphingomyelins; sphingophospholipids
although sphingomyelins differ chemically from phosphatidylcholine and phosphatidylethanolamine, their … and … are quite similar. the membranous myelin sheath that surrounds and electrically insulates many nerve cell axons is particularly rich in sphingomyelins
conformations; charge distributions
… are ceramides with head groups that consist of a single sugar residue. these lipids are therefore …
cerebrosides; glycosphingolipids
… and … are the most prevalent. Cerebrosides, in contrast to phospholipids, lack phosphate groups and hence are nonionic.
galactocerebrosides; glucocerebrosides
… are the most complex glycosphingolipids. they are ceramides with attached oligosaccharides that include at least one sialic acid residue.
gangliosides
disorders of ganglioside breakdown are responsible for several hereditary … such as Tay-Sachs disease
sphingolipid storage diseases
sphingomyelin itself, as well as the ceramide portions of more complex sphingolipids, appear to specifically module the activities of … and … that are involved in regulating cell growth and differentiation
protein kinases; protein phosphatases
… are derivatives of cyclopentanoperhydrophenanthrene, a compound that consists of four fused, nonplanar rings
steroids
the much maligned cholesterol, the most abundant steroid in animals, is further classified as a … because of its C3-OH group
sterol
cholesterol’s polar OH group gives it a weak … character, whereas its fused ring system provides it with greater … than other membrane lipids
amphiphilic; rigidity
cholesterol can also be esterified to long-chain fatty acids to form …
cholesteryl esters
cholesterol is the metabolic precursor of …, substances that control a great variety of physiological functions through their regulation of gene expression
steroid hormones
…, such as cortisol, affect carb, protein, and lipid metabolism and influence a wide variety of other vital functions, including inflammatory rxns and the capacity to cope with stress
glucocorticoids
… and other … regulate the excretion of salt and water by the kidneys
aldosterone; mineralocorticoids
the … and … affect sexual development and function.
androgens; estrogens
the various forms of …, which are really hormones, are sterol derivatives in which the steroid B ring is disrupted btwn C9 and C10
vitamin D
active vitamin D increases … by promoting the intestinal absorption of …
serum [Ca2+]; Ca2+
… are nonstructural components of membranes which are built from five carbon units with the same C skeleton as isoprene
isoprenoids
… are organic substances that an animal requires in small amounts but cannot synthesize and hence must acquire in its diet
vitamins
…, or …, is derived mainly from plant products such as beta-carotein. it is oxidized to its corresponding aldehyde, retinal, which functions as the eye’s photoreceptor at low light intensities
vitamin A; retinol
… is a lipid synthesized by plants and bacteria which participates in the carboxylation of Glu residues in some of the proteins involved in blood clotting
vitamin K
… is actually a group of compounds whose most abundant member is alpha-tocopherol–> this highly hydrophobic molecule is incorporated into cell membranes, where it functions as an antioxidant that prevents oxidative damage to membrane proteins and lipids
vitamin E
the … act at very low concentrations and are involved in the production of pain and fever, and in the regulation of blood pressure, blood coagulation, and reproduction
eicosanoids
…: closed, self-sealing solvent-filled vesicles that are bounded by only a single bilayer
liposomes
the transfer of a lipid molecule across a bilayer, a process termed …, or a …, is an extremely rare event
transverse diffusion; flip-flop
lipids are highly mobile in the plane of the …–> …
bilayer; lateral diffusion
the interior of the lipid bilayer is in constant motion due to … of the lipid tails
rotations around the C-C bonds
as a lipid bilayer cools below a characteristic …, it undergoes a sort of phase change in which it becomes a gel-like solid; that is, it loses its fluidity
transition temperature
above the transition temperature, the highly mobile lipids are in a state known as a … because they are ordered in some directions but not others l
liquid crystal
the transition temperature of a bilayer … with the chain length and the …. of its component fatty acid residues for the same reasons that the melting pts of fatty acids increase with these quantities
increases; degree of saturation
cholesterol, which by itself does not form a bilayer, … membrane fluidity bc its rigid steroid ring system interferes with the motions of the fatty acid side chains in other membrane lipids
decreases
cholesterol also broadens the … of the phase transition
temperature
… or … proteins associate tightly with membranes through hydrophobic interactions and can be separated from membranes only by treatment with agents that disrupt membranes
integral; intrinsic
Integral proteins are …; the protein segments immersed in a membrane’s nonpolar interior have predominantly …surface residues, whereas those portions that extend into the aqueous environment are sheathed with …residues
amphiphiles; hydrophobic; polar
…- it completely spans the membrane.
transmembrane (TM) protein
biological membranes are …in that a particular membrane protein is invariably located on only one particular face of a membrane, or in the case of a transmembrane protein, oriented in only one direction with respect to the membrane
asymmetric
the structures of both integral and water soluble proteins are stabilized by the exclusion of their …residues from the surrounding solvent, but in the case of integral proteins, the solvent is the …
interior; lipid bilayer.
A protein segment immersed in the nonpolar interior of a membrane must fold so that it satisfies the …of its polypeptide backbone
hydrogen bonding potential
β Barrels occur in …, which are channel-forming proteins in the outer membrane of gram-negative bacteria
porins
…proteins have covalently attached lipids that are built from isoprene units (Section 9-1F). The most common isoprenoid groups are the C15 farnesyl and C20 geranylgeranyl residues
Prenylated
Two kinds of fatty acids, … acid and …acid, are linked to membrane proteins.
Myristoylated proteins are located in a number of subcellular compartments, including the cytosol, the endoplasmic reticulum, the inner face of the plasma membrane, and the nucleus
In palmitoylation, the saturated C16 fatty acid palmitic acid is joined in thioester linkage to a specifi c Cys residue. Palmitoylated proteins occur almost exclusively on the cytoplasmic face of the plasma membrane, where many participate in transmembrane signaling
myristic; palmitic
Peripheral or extrinsic proteins, unlike integral membrane proteins or lipid linked proteins, can be …from membranes by relatively mild procedures that leave the membrane intact, such as exposure to high ionic strength… or …changes.
dissociated; salt solutions; pH
The demonstrated fluidity of artificial lipid bilayers (Section 9-2B) suggests that biological membranes have …
similar properties
Erythrocyte membranes can be obtained by osmotic lysis, which causes the cell contents to leak out. The resulting membranous particles are known as … because, on return to physiological conditions, they reseal to form colorless particles that retain their original shape but are devoid of cytoplasm
erythrocyte ghosts
Evidently, the membrane rolls across the cell while maintaining its shape, much like the tread of a tractor. This remarkable mechanical property of the erythrocyte membrane results from the presence of a submembranous network of proteins that function as a …
membrane “skeleton.”
The protein …, so called because it was discovered in erythrocyte ghosts, accounts for ∼75% of the erythrocyte membrane skeleton
spectrin
A defect or deficiency in spectrin synthesis causes …, in which erythrocytes are spheroidal and relatively fragile and inflexible.
hereditary spherocytosis
Spectrin also associates with an 1880-residue protein known as …, which binds to an integral membrane ion channel protein. This attachment anchors the membrane skeleton to the membrane.
ankyrin
Some integral proteins are firmly attached to elements of the cytoskeleton or are trapped within the spaces defined by those “fences.” Other membrane proteins may be able to squeeze through gaps or “gates” between cytoskeletal components, whereas still other proteins can diff use freely without interacting with the cytoskeleton at all (Fig. 9-31). Support for this … model comes from the finding that partial destruction of the cytoskeleton results in freer protein diffusion.
gates and fences
, the enzymes that synthesize membrane lipids are mostly integral membrane proteins of the …
endoplasmic reticulum
This observation indicates that newly made PE is synthesized on the …face of the membrane (PE is phosphatidylethanolamine that was labeled with TNBS.
cytoplasmic
Membrane proteins known as …catalyze the flip-flops of specific phospholipids. These proteins tend to equilibrate the distribution of their corresponding phospholipids across a bilayer; that is, the net transport of a phospholipid is from the side of the bilayer with the higher concentration of the phospholipid to the opposite side. Such a process, as we will see in Section 10-1, is a form of …
flippases; facilitated diffusion.
Membrane proteins known as ….transport specific phospholipids across a bilayer in a process that is driven by ATP hydrolysis. These proteins can transport certain phospholipids from the side of a bilayer that has the lower concentration of the phospholipid to the opposite side, thereby establishing a nonequilibrium distribution of the phospholipid. Such a process, as we will see in Section 10-3, is a form of …
phospholipid translocases; active transport
in all cells, new membranes are generated by the … of existing membranes
expansion
In eukaryotic cells, lipids synthesized on the cytoplasmic face of the ER are transported to other parts of the cell by … that bud off from the ER and fuse with other cellular membranes
membranous vesicles
Lipids and proteins in membranes can also be …organized.
laterally
the plasma membranes of epithelial cells (the cells lining body cavities and free surfaces) have an …, which faces the lumen (interior) of the cavity and often has a specialized function (such as the absorption of nutrients in intestinal brush border cells), and a .., which covers the remainder of the cell.
apical domain; basolateral domain
In addition, the hundreds of different lipids and proteins within a given plasma membrane domain may not be uniformly mixed but instead often segregate to form …that are enriched in certain lipids and proteins. This may result from specific interactions between integral membrane proteins and particular types of membrane lipids
microdomains
One type of microdomain, termed a…, appears to consist of closely packed glycosphingolipids (which occur only in the outer leafl et of the plasma membrane) and cholesterol
lipid raft
the glycosphingolipids in lipid rafts associate …via weak interactions between their carbohydrate head groups, and the voids between their tails are fi lled in by cholesterol.
laterally
…ribosomes synthesize mostly soluble and mitochondrial proteins, whereas … ribosomes manufacture transmembrane proteins and proteins destined for secretion, operation within the ER, and incorporation into lysosomes
Free; membrane-bound
∼40% of the various types of proteins that a cell synthesizes must be processed via the …pathway or some other protein targeting pathway.
secretory
(secretory pathway)
- All secreted, ER-resident, and lysosomal proteins, as well as many TM proteins, are synthesized with leading (N-terminal) 13- to 36-residue ….
- When the signal peptide first protrudes beyond the ribosomal surface the …), a 325-kD complex of six diff erent polypeptides and a 300-nucleotide RNA molecule, binds to both the signal peptide and the ribosome. At the same time, the SRP’s bound guanosine diphosphate (GDP; the guanine analog of ADP) is replaced by guanosine triphosphate (GTP; the guanine analog of ATP). The resulting conformational change in the SRP causes the ribosome to…, thereby preventing the RER-destined protein from being released into the cytosol.
signal peptides; signal recognition particle (SRP); arrest further polypeptide growth
(secretory pathway) 3. The SRP–ribosome complex diff uses to the RER surface, where it binds to the … (SR; also called docking protein) in complex with the …, a protein pore in the ER membrane through which the growing polypeptide will be extruded. In forming the SR–translocon complex, the SR’s bound GDP is replaced by GTP
SRP receptor; translocon
(secretory pathway) 4. The SRP and SR stimulate each other to hydrolyze their bound GTP to GDP (which is energetically equivalent to ATP hydrolysis), resulting in conformational changes that cause them to dissociate from each other and from the … complex. This permits the bound ribosome to resume … such that the growing polypeptide’s N-terminus passes through the translocon into the lumen of the ER. Most ribosomal processes, as we will see in Section 27-4, are driven by GTP hydrolysis.
ribosome–translocon; polypeptide synthesis
(secretory pathway) 5. Shortly after the signal peptide enters the ER lumen, it is specifi cally cleaved from the growing polypeptide by a membrane-bound signal peptidase (polypeptide chains with their signal peptide still attached are known as …; signal peptides are alternatively called presequences
preproteins
(secretory pathway) 6. The nascent (growing) polypeptide starts to fold to its native conformation, a process that is facilitated by its interaction with the ER-resident chaperone protein Hsp70 (Section 6-5B). Enzymes in the ER lumen then initiate … of the polypeptide, such as the specifi c attachments of “core” carbohydrates to form glycoproteins (Section 8-3C) and the formation of disulfi de bonds as facilitated by protein disulfi de isomerase (Section 6-5A). Once the protein has folded, it cannot be pulled back through the membrane. Secretory, ER-resident, and lysosomal proteins pass completely through the RER membrane into the lumen. TM proteins, in contrast, contain one or more hydrophobic ∼22-residue membrane anchor sequences that remain embedded in the membrane.
posttranslational modification;
secretory pathway) When the synthesis of the polypeptide is completed, it is released from both the ribosome and the …. The ribosome detaches from the RER, and its two subunits dissociate.
translocon
the translocon must mediate the insertion of an integral protein’s … into the membrane
TM segments
The signal peptides of many TM proteins are not cleaved by signal peptidase but, instead, are …. Such so-called signal-anchor sequences may be oriented with either their N- or C-termini in the cytosol
inserted into the membrane
proteins are conveyed between successive Golgi compartments in the cis to trans direction as cargo within membranous vesicles that bud off of one compartment and fuse with a successive compartment, a process known as forward or …
anterograde transport
proteins are carried as passengers in Golgi compartments that transit the Golgi stack; that is, the cis cisternae eventually become trans cisternae, a process called … or …. (Golgi-resident proteins may migrate backward by retrograde transport from one compartment to the preceding one via membranous vesicles.)
cisternal progression; maturation
The vehicles in which proteins are transported between the RER, the different compartments of the Golgi apparatus, and their final destinations are known as …
coated vesicles
a vesicle buds off from its membrane of origin and later fuses to its target membrane. This process preserves the orientation of the transmembrane protein (Fig. 9-42), because the lumens of the ER and the Golgi cisternae are topologically equivalent to the …
outside of the cell
Coated vesicles transport membrane-embedded and luminal proteins from the ER to the Golgi apparatus for further processing, and from there to other membranes. The proteins coating these vesicles may consist largely of …, which forms polyhedral cages, or …or …, which form coats with an amorphous appearance
clathrin; COPI; COPII
The fusion of vesicles with membranes occurs via a complex process that involves …. These form four-helix bundles that bring two membranes into proximity, which in turn induces membrane fusion.
SNAREs
…mediate the fusion of membrane-enveloped viruses such as infl uenza virus with their host cell membranes so as to release the viral nucleic acids into the host cell cytoplasm
Viral fusion proteins
In all cells, new membranes are generated by the expansion of existing membranes. In eukaryotes, this process occurs mainly via… in which a vesicle buds off from one membrane (e.g., that of the Golgi apparatus) and fuses to a different membrane
vesicle trafficking
Biological membranes do not spontaneously …
fuse
After budding from the original host cell, an influenza virus particle can infect a new host cell. The virus binds to the plasma membrane of the new cell and is taken into the cell by the invagination of the membrane via a process known as …(Section 20-1B) that superficially resembles the reverse of the fusion of a vesicle with a membrane (Fig. 9-42). The resulting intracellular vesicle with the virus bound to its inner surface then fuses with a vesicle known as an …that has an internal pH of ∼5.
receptor-mediated endocytosis; endosome
