Biochem Session 9- Carbohydrates/Fatty Acids and Lipids

Sucrose→ monosaccharides and bond type

Glucose→Fructose

Linkage is alpha for glucose and beta for fructose (1→2)

Glucose in alpha, fructose in beta

Lactose→ monosaccharides and bond type

Galactose→Glucose

B-1,4-glycosidic bond

Galactose in beta, glucose in alpha

Maltose→ monosaccharides and bond type

Glucose→Glucose

a-1,4-glycosidic bond

Glucose 1 in alpha, glucose 2 in alpha

Define “aldose” and “ketose.”

Aldose→ sugar containing an aldehyde moiety (carbonyl at C1)

Ketose→ sugar containing a ketone moiety (carbonyl at C2)

What is the “anomeric carbon” in a monosaccharide, and why is it important?

The anomeric carbon is linked to both the aldehyde or ketone moiety in the open chain form and the anomeric hydroxyl that can form glycosidic bonds/position determines anomeric isomer designation (a/B) in the cyclic form

What is mutarotation, and which carbon atom’s stereochemistry is changing during this process?

Mutarotation is the active fluctuation between a/B anomers→ position of the -OH is changing about the anomeric carbon

Compare α- and β-glycosidic linkages and give an example of a disaccharide with each.

α-glycosidic linkages→ located above the plane of the ring

• Ex: Maltose→ α-1,4 linkage between two glucoses

β-glycosidic linkages→ located above the plane of the ring

• Ex: Lactose→ β-1,4 linkage between galactose and glucose

Name the three most common disaccharides and list their component monosaccharides.

1. Sucrose→ Glucose (alpha) and fructose (beta) 1→2

2. Lactose→ Galactose (beta) and glucose (alpha) B-1,4

3. Maltose→ Glucose (alpha) and glucose (alpha) a-1,4

Describe the main structural difference between amylose, amylopectin, and glycogen.

Amylose→ linear/all a-1,4 linkages

Amylopectin→ branched/1 a-1,6 linkage for every 30 a-1,4 linkages

Glycogen→ most branched/1 a-1,6 linkage for every 8 a-1,4 linkages

What are glycoproteins? Give two examples of where they are commonly found.

Glycoproteins→ proteins covalently bonded to a carbohydrate (protein=major component and carbohydrate=minor component)

Commonly found in biological membranes (receptors) and extracellular matrix proteins

What is the repeating disaccharide unit of chitin?

β-1,4 linked N-acetyl-D-glucosamine

Define “essential fatty acids” and give one example

Essential fatty acids are fatty acids that are required in the diet but are not produced by humans

Ex: linoleic acid, α-linolenic acid

What is the difference between cis and trans double bonds in fatty acids, and what health impacts are associated with trans fats?

Cis double bonds→ cause kinks in the acyl chain (alkene H’s on same side)

Trans double bonds→ allow acyl chain to be more linear (alkene H’s on opposite sides)

Trans fats industrially produced and are associated with coronary heart disease, inflammation, etc.→ form stronger VdW interactions and human’s cannot effectively break them down

What is meant by “omega-3 fatty acid”? Give one example.

First double bond in a saturated fatty acid is located 3 carbons from the omega (terminal/methyl) carbon.

Ex: EPA (20:5 Δ5,8,11,14,17) is an omega-3 FA

Name the three major classes of membrane lipids

1. Phospholipids

2. Sphingolipids

3. Cholesterol

What is the structural difference between glycerophospholipids and sphingolipids?

Glycerophospholipids→ glycerol backbone

Sphingolipids→ sphingosine backbone

What is a liposome, and how are they used in biomedical research?

A liposome is a lipid vesicle made of a phospholipid bilayer→ has an inner aqueous compartment lined with H-philic heads and outer aqueous compartment (interacts with solution) lined with H-philic heads. H-phobic tails interact with each other within the bilayer

They are used for drug delivery (drug placed in inner aqueous compartment) and for studying membrane proteins

What is the driving force for spontaneous bilayer formation?

Hydrophobic interactions/the hydrophobic effect→ nonpolar tails cluster away from water and interact with each other to form the bilayer

Which molecule makes up roughly 25% of plasma membrane lipids in some nerve cells but is absent from some intracellular membranes?

Cholesterol

In what way are cerebrosides and gangliosides structurally different?

Both contain a sphingosine backbone

Cerebrosides→ contain 1 sugar group (glucose or galactose)

Gangliosides→ contain up to 7 sugar groups

Define “micelle” and explain why fatty acids form them in aqueous solution.

A micelle is a spherical aggregate of fatty acids that forms in aqueous solution as a result of the hydrophobic effect (clustering of nonpolar tails). Fatty acids are cylindrical in shape (single tail→ head cross section larger than tail cross section), so they favor the formation of spherical aggregates

Draw the chair and boat conformations of glucose. Which is energetically favored and why?

Chair is more stable because all of the axial groups are H’s and all bulky groups are in the equatorial position (more stable due to reduced steric clash)

You dissolve pure α-D-glucose in water and measure its optical rotation over time. What do you expect to observe and why?

The optical rotation would continue changing until equilibrium between anomers is established

You test sucrose and maltose with Fehling’s reagent. Which one gives a positive test and why?

Maltose because it has a free anomeric -OH that can reduce Cu²⁺ to Cu⁺ which will form a red precipitate with water→ positive. Sucrose does not have a free anomeric carbon and is non-reducing→ negative.

Explain how glycogen’s branching pattern contributes to its rapid mobilization compared to amylose.

Glycogens branching pattern allows it to have more glycosidic bonds than amylose. This means it can undergo rapid glycogen phosphorylase activity→ releases glucose more efficiently to meet metabolic needs

Given a fatty acid notation “18:3 all cis-Δ9, Δ12, Δ15,” draw its general structure and classify it as omega-3 or omega-6

Omega-3 polyunsaturated fatty acid

If a cell membrane had a very high cholesterol content, how would this affect membrane fluidity at (a) low temperature and (b) high temperature?

Low temp→ increased fluidity

• The bulky nature of cholesterol’s polycyclic ring structure interrupts VdW interactions between fatty acid chains (prevents packing) that stabilize the gel phase

High temp→ decreased fluidity

• The constrained nature of cholesterol’s polycyclic ring structure restricts movement (lateral diffusion) in the membrane

Explain how partial hydrogenation of vegetable oil leads to trans fats, and why this is a health concern.

Partial hydrogenation converts some cis double bonds to trans→ results in straighter chains that are more difficult to break down→ leads to inflammation and coronary heart disease