CHEM 153A Midterm 2 Exam {fall 2025/26
Update} Questions and Complete Solutions –
UCLA.
What mechanism allows for the formation of cyclic sugars? - correct answer Rotate
the bond of the linear sugar, tip it on its side, the hydroxyl at C5 acts as a nucleophile
and attacks the carbonyl.
What are anomers? - correct answer They differ only in the newly formed chiral
carbon (after ring formation). Can be α vs β.
Glucose the α anomer is trans and the β anomer is cis (both pointing up!)
How can the sugar anomers interconvert? - correct answer Cyclization is a reversible
process. Depending on what side the nucleophile attacks, the orientation of the OH
on the C1 can be pointing up or down.
What does the anomeric carbon serve as? - correct answer the connection to other
monosaccharides
Can a given sugar linearize and switch forms? - correct answer It can as long as it is
not the monomer using the anomeric carbon to bind. Whichever molecule that is
using the anomeric carbon in a bond is the one that cannot linearize and switch
forms. If both anomeric carbons (the carbons bound to two oxygens) are blocked it
cannot linearize since the ring cannot open or close.
, CHEM 153A Midterm 2 Exam {fall 2025/26
Update} Questions and Complete Solutions –
UCLA.
Glycosidic bonds - correct answer covalent bonds that form between the hemiacetal
group of a carbohydrate and a hydroxyl group on another compound (like other
carbohydrates). This is how polysaccharides form.
β-1,4-glycosidic bonds - correct answer lactose
α-1,4-glycosidic bond - correct answer maltose
α-1, β-2-glycosidic bond - correct answer sucrose
Cellulose - correct answer polysaccharide of β-D-glucose that's used for structure in
plants. Has an alternating structure. Has β-1,4 linkages that can form strong
intrachain and interchain hydrogen bonds.
Can human enzymes break down β linkages? - correct answer Nope!
How does the structure of cellulose affect its strength? - correct answer The
alternating structure of cellulose causes the hydrogens to be in an optimal position to
form strong intrachain and interchain hydrogen bonds.
Amylose - correct answer a polysaccharide of α-D-glucose that's used for energy
storage in plants. It is a starch. Human enzymes can break down α linkages and utilize
for energy. Just regular 1,4 linkages.
, CHEM 153A Midterm 2 Exam {fall 2025/26
Update} Questions and Complete Solutions –
UCLA.
is amylose straight chain or branched? - correct answer amylose is not a straight
chain. It's in a helix because the helix optimizes H bonding and makes the structure
more stable. There is about 8 glucose residues per turn.
Glycogen - correct answer a polysaccharide of α-D-glucose that's used for energy
storage in animals. Has α-1,4 and α-1,6 every 8-10 residues creating a branch
Is Glycogen branched or straight chained? - correct answer It is branched since
multiple branches reduce the time it takes for breakdown and utilization.
Lipids - correct answer a class of organic compounds that are insoluble in water, and
soluble in organic solvents.
How are lipids useful in structure? - correct answer they are part of cell membranes
How do lipids compare to carbohydrates as energy stores? - correct answer They are
long term energy stores compared to carbohydrates since they are harder to break
down and utilize. They need to be broken down and used in cellular respiration.
Fatty acids - correct answer carboxylic acids with open chains. Can be saturated or
unsaturated based on whether they have double bonds.
Update} Questions and Complete Solutions –
UCLA.
What mechanism allows for the formation of cyclic sugars? - correct answer Rotate
the bond of the linear sugar, tip it on its side, the hydroxyl at C5 acts as a nucleophile
and attacks the carbonyl.
What are anomers? - correct answer They differ only in the newly formed chiral
carbon (after ring formation). Can be α vs β.
Glucose the α anomer is trans and the β anomer is cis (both pointing up!)
How can the sugar anomers interconvert? - correct answer Cyclization is a reversible
process. Depending on what side the nucleophile attacks, the orientation of the OH
on the C1 can be pointing up or down.
What does the anomeric carbon serve as? - correct answer the connection to other
monosaccharides
Can a given sugar linearize and switch forms? - correct answer It can as long as it is
not the monomer using the anomeric carbon to bind. Whichever molecule that is
using the anomeric carbon in a bond is the one that cannot linearize and switch
forms. If both anomeric carbons (the carbons bound to two oxygens) are blocked it
cannot linearize since the ring cannot open or close.
, CHEM 153A Midterm 2 Exam {fall 2025/26
Update} Questions and Complete Solutions –
UCLA.
Glycosidic bonds - correct answer covalent bonds that form between the hemiacetal
group of a carbohydrate and a hydroxyl group on another compound (like other
carbohydrates). This is how polysaccharides form.
β-1,4-glycosidic bonds - correct answer lactose
α-1,4-glycosidic bond - correct answer maltose
α-1, β-2-glycosidic bond - correct answer sucrose
Cellulose - correct answer polysaccharide of β-D-glucose that's used for structure in
plants. Has an alternating structure. Has β-1,4 linkages that can form strong
intrachain and interchain hydrogen bonds.
Can human enzymes break down β linkages? - correct answer Nope!
How does the structure of cellulose affect its strength? - correct answer The
alternating structure of cellulose causes the hydrogens to be in an optimal position to
form strong intrachain and interchain hydrogen bonds.
Amylose - correct answer a polysaccharide of α-D-glucose that's used for energy
storage in plants. It is a starch. Human enzymes can break down α linkages and utilize
for energy. Just regular 1,4 linkages.
, CHEM 153A Midterm 2 Exam {fall 2025/26
Update} Questions and Complete Solutions –
UCLA.
is amylose straight chain or branched? - correct answer amylose is not a straight
chain. It's in a helix because the helix optimizes H bonding and makes the structure
more stable. There is about 8 glucose residues per turn.
Glycogen - correct answer a polysaccharide of α-D-glucose that's used for energy
storage in animals. Has α-1,4 and α-1,6 every 8-10 residues creating a branch
Is Glycogen branched or straight chained? - correct answer It is branched since
multiple branches reduce the time it takes for breakdown and utilization.
Lipids - correct answer a class of organic compounds that are insoluble in water, and
soluble in organic solvents.
How are lipids useful in structure? - correct answer they are part of cell membranes
How do lipids compare to carbohydrates as energy stores? - correct answer They are
long term energy stores compared to carbohydrates since they are harder to break
down and utilize. They need to be broken down and used in cellular respiration.
Fatty acids - correct answer carboxylic acids with open chains. Can be saturated or
unsaturated based on whether they have double bonds.
