Carbohydrates Flashcards by Ariyaana Khanom

What are three types of carbohydrates?

Monosaccharide
Disaccharide
Polysaccharide

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What is the general formula for monosaccharides?

(CH₂O)n

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What is an example of a pentose (type of monosaccharide)?

Ribose -> found in ATP and RNA
Formula: C₅H₁₀O₅

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What is an example of a hexose (type of monosaccharide)?

Glucose -> alpha or beta (animal transport sugar)
Fructose -> found in plant transport sugar (sucrose)
Galactose (in milk)
Formula: C₆H₁₂O₆

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What is the difference between alpha (α) glucose and beta (β) glucose?

In α-glucose, the OH group on carbon 1 is below the plane of the ring
In β-glucose, the OH group on carbon 1 is above the plane of the ring

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What are disaccharides?

2 monosaccharides joined together in a condensation reaction
Joined by a glycosidic bond

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What is maltose (disaccharide) made up of?

α-glucose + α-glucose

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What is sucrose (disaccharide) made of?

α-glucose + fructose

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What is lactose (disaccharide) made of?

Glucose + galactose

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What are polysaccharides?

Long chain of monosaccharides, joined in condensation reactions

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What are the two polysaccharides of starch?

Amylose
Amylopectin

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What is the structure/bonding of amylose (plants)

α-glucose monomers
α 1,4 glycosidic bonds
Helical structure (held together by intermolecular hydrogen bonds
20% of starch

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What is the structure/bonding of amylopectin (plants)?

α-glucose monomers
α 1,4 and 1,6 glycosidic bonds
Branched structure
80% of starch

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What is the structure/bonding of glycogen (animals)?

α-glucose monomers
α 1,4 and 1,6 glycosidic bonds
Highly branched structure

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What is the structure/bonding of cellulose?

β-glucose monomers
β 1,4 glycosidic bonds
Linear structure-> every other monomer is flipped, so unable to coil
Chains of cellulose molecules lie parallel -> joined by hydrogen bonds to form microfibrils.

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Amylopectin and glycogen are both compact. Why does this property make them good storage molecules?

As it means many glucose monomers can be packed in a small space -> lots of energy can be stored in cell

Amylopectin and glycogen are both insoluble. Why does this property make them good storage molecules?

Because it does not affect the water potential of the cell -> so no swelling due to osmosis

Amylopectin and glycogen are both branched. Why does this property make them good storage molecules?

Many glucose monomers at branched endings -> are rapidly released for respiration (faster in glycogen as it is more branched so animals are more metabolically active)

What makes cellulose insoluble and unreactive?

Intermolecular hydrogen bonds prevent water bonding with and hydrolysing polar –OH groups

What makes cellulose flexible?

Microfibrils can slide over each other

What makes cellulose have high tensile strength?

The intermolecular hydrogen bonds

What makes cellulose have an unbranched structure?

Only has β 1,4 glycosidic bonds (no 1,6 bonds)

What makes cellulose linear?

Every other monomer is flipped 180° so forms parallel strands

What is a reducing sugar and an example?

A saccharide (sugar) that donates electrons which results in the reduction (gain of electrons) of other molecules
Glucose

What is the qualitative test for reducing sugars?

- **Benedict's solution** is added to solution being tested and **heated** - Colour change: from blue- green- yellow- orange- brick red (colour depends on conc. of sugar in solution) - The more sugar that is present, the more blue Cu²⁺ ions in benedict’s solution are reduced to red Cu⁺ ions in CuO precipitate

What is the qualitative test for non-reducing sugars (e.g sucrose)?

- Heat with HCl to hydrolyse solution into reducing monosaccharides - Neutralise with an alkaline solution (sodium hydrogencarbonate) - Heat with Benedict's solution

What is the quantitative test for reducing sugars?

- Carry out the test for reducing sugars - Filter the solution to remove the precipitate formed because it may obstruct the transmission of light through the solution - Calibrate a colorimeter using distilled water for the transmission of red light - Add a sample of the solution to the cuvette and place it in the colorimeter to measure the transmission of red light through it - Repeat with different concentrations and plot a calibration curve.

How do you test for starch?

- Use **iodine** solution - Colour change: yellow/orange to blue/black - Because the iodine molecules enter the helical amylose structure, forming blue-black starch-iodine complex - When heated, the iodine is released as intramolecular hydrogen bonds in the helix break, turning yellow again

Which molecule consists of many alpha glucose molecules joined together by alpha (1-4) glycosidic bonds and alpha (1-6) glycosidic bonds to form a branched polysaccharide that is the storage carbohydrate in animals?

Glycogen

Amylopectin

Which elements are found in carbohydrates?

Carbon, hydrogen and oxygen

What is the transport carbohydrate in animals?

Glucose

Which disaccharide is the transport carbohydrate in plants?

Sucrose