Question 1

Which of the following best describes the difference between reducing and non-reducing sugars, and why is this distinction important in metabolic pathways such as glycolysis?

Accepted Answer

Reducing sugars have a free aldehyde or ketone group, allowing them to participate in redox reactions; this is crucial in glycolysis because only reducing sugars can be phosphorylated by hexokinase.

Question 2

A carbohydrate is classified as a disaccharide if it contains:

Accepted Answer

Two monosaccharide units joined by a glycosidic bond.

Question 3

Which of the following correctly defines the anomeric carbon in a carbohydrate?

Accepted Answer

The carbon derived from the carbonyl carbon (aldehyde or ketone) during cyclization, which becomes a new stereocenter.

Question 4

Cellulose and glycogen are both polysaccharides. Which structural difference explains why most animals cannot digest cellulose but can digest glycogen?

Accepted Answer

Cellulose contains $$\beta(1 \rightarrow 4)$$ glycosidic bonds, while glycogen contains $$\alpha(1 \rightarrow 4)$$ and $$\alpha(1 \rightarrow 6)$$ bonds; most animals lack enzymes to hydrolyze $$\beta(1 \rightarrow 4)$$ bonds.

Question 5

Which of the following statements about glycoproteins is correct?

Accepted Answer

Glycoproteins are proteins covalently bonded to carbohydrate chains, which can be attached via O-linked (serine/threonine) or N-linked (asparagine) glycosylation.

Question 6

Which of the following best describes the function of lectins?

Accepted Answer

Lectins are proteins that bind specific carbohydrate structures, mediating cell-cell recognition and signaling.

Question 7

Blood group specificity is determined by which of the following molecular features?

Accepted Answer

The specific oligosaccharide structures present on glycoproteins and glycolipids of red blood cell membranes.

Question 8

Which of the following is a storage lipid and what is its backbone structure?

Accepted Answer

Triacylglycerol; glycerol backbone.

Question 9

Which type of lipid is primarily found in biological membranes and contains a sphingosine backbone?

Accepted Answer

Sphingolipids.

Question 10

Which of the following correctly describes the effect of cholesterol on membrane fluidity at different temperatures?

Accepted Answer

Cholesterol decreases membrane fluidity at high temperatures and increases fluidity at low temperatures.

Question 11

What is meant by the term 'fluid mosaic model' of the lipid bilayer?

Accepted Answer

The lipid bilayer is a dynamic structure where lipids and proteins can move laterally, creating a flexible and heterogeneous membrane.

Question 12

Which of the following equations correctly represents the general structure of a triacylglycerol?

Accepted Answer

$$\mathrm{Triacylglycerol:} \ \mathrm{Glycerol} + 3 \ \mathrm{Fatty\ Acids} \rightarrow \mathrm{Triacylglycerol} + 3 \ \mathrm{H_2O}$$

Question 13

A patient has a genetic defect in the enzyme responsible for adding N-linked oligosaccharides to proteins. Which cellular process would be most directly affected?

Accepted Answer

Protein glycosylation in the endoplasmic reticulum.

Question 14

Which of the following best explains why unsaturated fatty acids increase membrane fluidity?

Accepted Answer

Unsaturated fatty acids contain one or more double bonds, introducing kinks that prevent tight packing of lipid tails.

Question 15

Which of the following is the correct formula for the hydrolysis of a glycosidic bond in a disaccharide?

Accepted Answer

$$\mathrm{Disaccharide} + \mathrm{H_2O} \rightarrow 2 \ \mathrm{Monosaccharides}$$

Question 16

Which of the following lipids is NOT amphipathic and therefore does NOT contribute to membrane structure?

Accepted Answer

Triacylglycerols.

Question 17

Which of the following best describes the difference between O-linked and N-linked glycosylation?

Accepted Answer

O-linked glycosylation attaches carbohydrates to the hydroxyl group of serine or threonine, while N-linked glycosylation attaches to the amide nitrogen of asparagine.

Question 18

A mutation causes a protein to lack its glycosylation sites. Which of the following is a likely consequence?

Accepted Answer

Impaired protein folding and reduced stability.

Question 19

Which of the following is a correct description of the reference carbon in a simple carbohydrate?

Accepted Answer

The carbon furthest from the carbonyl group, used to assign D or L configuration.

Biochemistry Study Guide: Carbohydrates, Lipids, and Glycoproteins - Module 5

Guida di studio - Domande di pratica

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