LM7 Flashcards
Sterochemistry D or L and its relation to OH group
determined by the position of the OH group on the last chiral carbon in the linear chain (left or right)
stereochemistry beta or alpha OH group position
beta - OH group is up
alpha - OH group is down
what does it mean to have an alpha1->4 glycosidic bond (acetal)
The linkage between the sugar units (themselves known as hemiacetals) is an acetal bond. Biochemists have named the linking acetal bond a ‘glycosidic’ bond. The α1→4 notation means the link is made between C1 (the anomeric carbon) of the first sugar unit (left hand side) to the C4 of the 2nd sugar unit. The 1st sugar unit will have originally had its reacting OH group in the ‘downward’ orientation, which is the α anomer.
Cellulose is not highly branched because it
does not have β1→6 linkages
Branches in polysaccharides are formed on reaction of the anomeric carbon of a glucose monomer with the C6 of a monomer within the forming chain (in cellulose, since the monomers are β anomers, the linkage is a β1→6 linkage). The sugar unit to form the branch, will also have its C4 available to form another chain by reaction with another glucose monomer at C1 (β1→4 linkages)
Lipids may be either hydrophobic or
amphipathic
what does amphipathic mean
Amphipathic means have separate hydrophobic and polar patches. This description indeed applies to most (though not all) lipids
Triacylglycerols cannot form lipid bilayers because they
do not have polar heads.
TAGs have hydrocarbon tails whic would tend to associate to bury the non-polar groups from water. However, there are no polar head groups to interact favourably with water on the surface of bilayers. Lipids that form membrane bilayers are amphipathic.
In a sphingolipid, how are the two long hydrocarbon chains (‘fatty’ chains) linked to the three-carbon backbone structure?
One hydrocarbon chain is linked to the sphingosine unit by an amide bond and the other is part of the sphingosine unit
One hydrocarbon chain is indeed an integral part of the sphingosine backbone unit itself. The other is attached to the central carbon of the three-carbon backbone via an amide (CONH) linking bond
Glycosphingolipids are lipids that contain one or more monosaccharide residues or oligosaccharide moieties. Which of the following statements are true?
A. A glycosphingolipid with one monosaccharide attached is called a ceramide.
B. A glycosphingolipid with one monosaccharide attached is called a cerebroside.
C. Gangliosides are lipids containing diverse oligosaccharide chains.
D. Cerebrosides present diverse repertoires of oligosaccharide chains and are important markers in cell recognition.
B and C
In a membrane lipid bilayer, lipid fluidity is reduced by an increase in __________ bearing ____________
Lipid fluidity is reduced by an increase in glycerophospholipids bearing saturated fatty acid tails.
Lipids provide cells with an impermeable barrier. Transport of polar molecules across a membrane requires proteins. Which of the following statements is accurate?
A. Integral membrane proteins can form a channel across a membrane that selectively accommodates passage of molecules or ions.
B. Peripheral membrane proteins are required for uniport movement of molecules across a membrane.
C. Secondary active transport requires a complex of two integral membrane proteins, both driven by ATP hydrolysis.
D. Passive transport constitutes ion movement up a concentration gradient.
A only
B is incorrect as peripheral membrane proteins are not known as being required for uniport transport. C is incorrect as in secondary active transport, only one protein (the primary active transporter) is driven by such a direct source of energy - the other protein usually benefits from a concentration gradient that is established as a result of the active transport by the first. D is incorrect as ions cannot be moved passively (without energy) against their concentration gradient.
