2.2 Carbohydrates Flashcards by Lou eung

Define carbohydrates

A group of molecules containing C,H and O molecules

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What bond is formed between two monosaccharides by a condensation reaction?

Glycosidic bond

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What are carbohydrates for?

•Act as a source of energy (e.g. sugars such as sucrose in cakes/biscuits, starch in pasta and rice)
•Act as a store of energy (e.g. starch and glycogen)
•Act as structural units (e.g. cellulose in plants and chitin in insects)
•Some carbohydrates are also part of other molecules, such as nucleic acid and glycolipids

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What is the structure of sugar glucose?

•glucose has a ring shape
•all carbohydrates including glucose contain only the elements of carbon, hydrogen and oxygen
•glucose contains 6 carbon atoms
•monosaccharide (one sugar)

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What are sugars with 6 carbon atoms called? And give examples

Hexose sugars

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What are examples of hexose monosaccharides?

fructose and galactos, beta and alpha glucose

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What do you call monosaccharides with 5 carbon atoms? and give examples

Pentose sugars eg ribose, deoxyribose

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What are OH groups called?

Hydroxyl groups

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What are isomers

The two different forms of glucose, these 2 different forms are called isomers of glucose

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Similarity between isomers?

•In both isomers of glucose, carbon 1 is bonded to a hydrogen atom and alsoto a hydroxyl group

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Difference between isomers?

The position of the hydroxyl group on carbon 1

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Which one is alpha and beta glucose?
(How can you differentiate them?)

•Alpha glucose has the hydroxyl group below the ring
•Beta glucose had the hydroxyl group above the ring

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What reaction occurs when a glycosidic bond is formed? And what is produced?

A condensation reaction, one molecule of water is produced

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What reaction occurs when a glycosidic bond are broken? And what is needed?

A hydrolysis reaction, which requires addition of water.

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What are polysaccharides?

Polysaccharides are polymers of monosaccharides

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What are polysaccharides that are made solely of one kind of monosaccharide called?

Homopolysaccharides

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What are polysaccharides that are made of more than one monomer called?

Heteropolysaccharides

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What is the formula of glucose?

C6H12O*6

What are the properties of monosaccharides?

•Soluble in water

Why are monosaccharides soluble in water?

They have a large number of OH groups/ hydroxyl groups are polar due to the small negative charge on the oxygen atom and the small positive charge on the hydrogen so hydroxyl groups can form hydrogen bonds with water molecules- monosaccharides are hydrophilic

When do Disaccharides form?

When two monosaccharides chemically react together ( and form a glycosidic bond, and a molecule of water is produced)

When two alpha glucose molecules are reacted together, what is the name of the disaccharide we make?

Maltose

Why is a water molecule formed during a condensation reaction, when making a disaccharide?

The water molecule is formed from a hydrogen atom from one of the monosaccharides and a hydroxyl group from the other

How is the disaccharide sucrose formed?

From the monosaccharides glucose and fructose.
Sucrose= glucose + fructose

How is the disaccharide Lactose formed?

From the monosaccharides glucose and galactose Lactose= glucose +galactos

Where is starch found?

In starch grains

What two molecules does starch consist of?

Amylose and amylopectin

What is the structure of amylopectin?

•branched polymer braches are held by 1,6 glycosidic bonds ( polysaccharide) of alpha of glucose joined by 1,4 glycosidic bonds •Have a branch for every 25-30 glucose molecules •also forms a helical shape with hydrogen bonds

What is the structure of amylose?

•unbranched polymer (polysaccharide) of alpha glucose molecules joined by 1,4 glycosidic bonds •Forms a compact helix with hydrogen bonds forming between glucose molecules along the chain ——> helical shape makes starch a compact molecule

How is the structure of starch related to its function?

•Amylose forms a tight helix which makes starch compact (it can store a large amount of glucose molecules for it’s size) •Starch is insoluble in water so starcg does not cayse water to enter the cell by osmosis •Polysaccharides hold glucose molecules in chains so they can easily be snipped off from the end of the chain by hydrolysis when needed for respiration • amylopectin has a large number of branches therefore a large number of ends which means the enzymes can break down starch rapidly

What is the glucose storage molecule in plants?

Starch

What is the glucose storage molecule in animals?

Glycogen

Where are the major stores of glycogen located?

The liver and in muscle cells.

What is the structure of glycogen?

• Branched polymer of alpha glucose joined by 1,4 glycosidic bonds • Glucose molecules at the branch points are joined by 1,6 glycosidic bonds (Similar structure to amylopectin HOWEVER glycogen is more branched which makes it a VERY compact molecule)

What does having lots of branches mean in a polysaccharide?

More free ends so enzymes can convert glycogen or amylopectin back to glucose very rapidly

Why is it important that glycogen is very branched?

It means it will have more free ends so enzymes can convert glycogen back to glucose very rapidly —-> important as animals often have a high rate of respiration and the energy needs of animals can change very rapidly e.g move quickly to escape a predator—> if this happened then the rate of respiration would increase and glycogen in the animal’s muscles could be converted to glucose for respiration

What does starch’s and glycogen’s insolubility mean? And how does it make them ideal storage molecules?

-Glycogen and Starch do not draw water into cells by osmosis, being a large molecule they cannot diffuse out of the cell—-> makes them ideal storage molecules

What is the structure of cellulose?

•Unbranched polymer (polysaccharide) of beta glucose •Every second beta glucose molecule is flipped

How does cellulose’s structure match with its function?

• Cellulose forms a straight chain without any branches allowing the cellulose molecules to get close together, hydrogen bonds form between neighbouring chains AND due to their huge number it makes cellulose extremely strong

Microfibril

When cellulose chains group together.

Macrofibrils

Microfibrils grouped together

Cellulose fibre

Macrofibrils group together. • form the plant cell wall Microfibrils—> Macrofibrils—> Cellulose fibre—> plant cell wall

What are two features of starch that makes it a good storage molecule?

•branched so there is a faster breakdown •insoluble in water so it does not effect water potential

What do you call monosaccharides containing 5 carbon atoms?

Pentose monosaccharides