CHEM 153A Midterm 2 Exam {fall 2026/2026
Update} Questions and Complete Solutions –
UCLA.
What mechanism allows for the formation of cyclic sugars? - correct answer
cyclization (which is reversible) allowing for mutarotation
cyclization is when the hydroxyl attached to C5 of the straight chain monosaccharide
attacks the anomeric carbon (carbonyl); since the carbonyl is trigonal planar sp2
hybridization, the hydroxyl can attack from the front or back, forming both alpha and
beta anomers
What are anomers? How do they introconvert? - correct answer Anomers are the
alpha and beta forms of a cyclic sugar; the distinguishing factor between them is
whether the alcohol group attached to the anomeric carbon is cis (beta) or trans
(alpha) to C6
They can introconvert because cyclization is a reversible process, therefore the
alcohol of C5 can nucleophilic attack the anomeric carbon from the front or back,
producing both anomers
Be able to identify different anomers - correct answer Draw an alpha and beta
anomer for both L and D sugars
Can a given sugar linearize and switch forms? When can't it? - correct answer α- and
β- forms of a given sugar can readily "flip" between each form in solution, so long as
the anomeric hydroxyl is free
, CHEM 153A Midterm 2 Exam {fall 2026/2026
Update} Questions and Complete Solutions –
UCLA.
Be able to identify or create glycosidic bonds between saccharides - correct answer
Draw an alpha glycosidic bond, beta glycosidic bond, and one that is both alpha and
beta
For all four polysaccharides we've discussed, be able to connect structure with
function, and be able to recognize any of these structures (structural support
polysaccharides) - correct answer Cellulose (plants): beta 1,4 - glycosidic linkages;
alternating structure where every other glucose is inverted; this creates inter and
intra-chain hydrogen bonding which contributes to the straight chain structure,
allowing for stacked fibrils and creates high tensile strength = good for structural
support. Since beta bonds can't be broken down by human enzymes, they are not
good for energy storage or utilization
Chitin (animals): beta 1,4 - glycosidic linkages, alternating structure where every other
glucose is inverted; this creates inter and intra-chain hydrogen bonding which
contributes to the straight chain structure, allowing for stacked fibrils and creates
high tensile strength = good for structural support. Since beta bonds can't be broken
down by human enzymes, they are not good for energy storage or utilization. Are
comprised of N-acetyl-D-glucosamines meaning that there are acetylated amine
groups attached to C2 instead of a hydroxyl group
For all four polysaccharides we've discussed, be able to connect structure with
function, and be able to recognize any of these structures (energy storage
, CHEM 153A Midterm 2 Exam {fall 2026/2026
Update} Questions and Complete Solutions –
UCLA.
polysaccharides) - correct answer Amylose (plants): alpha 1,4 - glycosidic linkages; can
be broken down by human enzymes which makes them good for energy storage and
utilization; since the structure does not have alternating glucose, there is no
interchain hydrogen bonding, so the structure of amylose is helical and not as
structurally sound with 8 glucose residues per turn; is not branched
Glycogen: alpha 1,4 - glycosidic linkages AND alpha 1,6 - glycosidic linkages every 8
to 10 glucose residues; can be broken down by human enzymes which makes them
good for energy storage and utilization; since the structure does not have alternating
glucose, there is no interchain hydrogen bonding, so structure is helical and not as
sound; branched = multiple pts of cleavage = faster parallel breakdown; also good
for storage because links up monomers of glucose, reducing the amount of
hydrophilic surface area that interacts with water to lower the increase in osmotic
pressure and allowing glycogen to be stored in the cell for longer
Understand the basic role of lipids - correct answer Lipids serve as long-term energy
storage (TAGs), provide membrane structure support (phospholipids and
sphingolipids), and can serve as cell signaling molecules (steroids and eicosanoids)
Be able to name a fatty acid using omega naming system - correct answer Create a
fatty acid and name it!
Update} Questions and Complete Solutions –
UCLA.
What mechanism allows for the formation of cyclic sugars? - correct answer
cyclization (which is reversible) allowing for mutarotation
cyclization is when the hydroxyl attached to C5 of the straight chain monosaccharide
attacks the anomeric carbon (carbonyl); since the carbonyl is trigonal planar sp2
hybridization, the hydroxyl can attack from the front or back, forming both alpha and
beta anomers
What are anomers? How do they introconvert? - correct answer Anomers are the
alpha and beta forms of a cyclic sugar; the distinguishing factor between them is
whether the alcohol group attached to the anomeric carbon is cis (beta) or trans
(alpha) to C6
They can introconvert because cyclization is a reversible process, therefore the
alcohol of C5 can nucleophilic attack the anomeric carbon from the front or back,
producing both anomers
Be able to identify different anomers - correct answer Draw an alpha and beta
anomer for both L and D sugars
Can a given sugar linearize and switch forms? When can't it? - correct answer α- and
β- forms of a given sugar can readily "flip" between each form in solution, so long as
the anomeric hydroxyl is free
, CHEM 153A Midterm 2 Exam {fall 2026/2026
Update} Questions and Complete Solutions –
UCLA.
Be able to identify or create glycosidic bonds between saccharides - correct answer
Draw an alpha glycosidic bond, beta glycosidic bond, and one that is both alpha and
beta
For all four polysaccharides we've discussed, be able to connect structure with
function, and be able to recognize any of these structures (structural support
polysaccharides) - correct answer Cellulose (plants): beta 1,4 - glycosidic linkages;
alternating structure where every other glucose is inverted; this creates inter and
intra-chain hydrogen bonding which contributes to the straight chain structure,
allowing for stacked fibrils and creates high tensile strength = good for structural
support. Since beta bonds can't be broken down by human enzymes, they are not
good for energy storage or utilization
Chitin (animals): beta 1,4 - glycosidic linkages, alternating structure where every other
glucose is inverted; this creates inter and intra-chain hydrogen bonding which
contributes to the straight chain structure, allowing for stacked fibrils and creates
high tensile strength = good for structural support. Since beta bonds can't be broken
down by human enzymes, they are not good for energy storage or utilization. Are
comprised of N-acetyl-D-glucosamines meaning that there are acetylated amine
groups attached to C2 instead of a hydroxyl group
For all four polysaccharides we've discussed, be able to connect structure with
function, and be able to recognize any of these structures (energy storage
, CHEM 153A Midterm 2 Exam {fall 2026/2026
Update} Questions and Complete Solutions –
UCLA.
polysaccharides) - correct answer Amylose (plants): alpha 1,4 - glycosidic linkages; can
be broken down by human enzymes which makes them good for energy storage and
utilization; since the structure does not have alternating glucose, there is no
interchain hydrogen bonding, so the structure of amylose is helical and not as
structurally sound with 8 glucose residues per turn; is not branched
Glycogen: alpha 1,4 - glycosidic linkages AND alpha 1,6 - glycosidic linkages every 8
to 10 glucose residues; can be broken down by human enzymes which makes them
good for energy storage and utilization; since the structure does not have alternating
glucose, there is no interchain hydrogen bonding, so structure is helical and not as
sound; branched = multiple pts of cleavage = faster parallel breakdown; also good
for storage because links up monomers of glucose, reducing the amount of
hydrophilic surface area that interacts with water to lower the increase in osmotic
pressure and allowing glycogen to be stored in the cell for longer
Understand the basic role of lipids - correct answer Lipids serve as long-term energy
storage (TAGs), provide membrane structure support (phospholipids and
sphingolipids), and can serve as cell signaling molecules (steroids and eicosanoids)
Be able to name a fatty acid using omega naming system - correct answer Create a
fatty acid and name it!
