- aldohexose - C6H12O6 - blood sugar - monosaccharide of starch, cellulose, and glycogen

- ketohexose - C6H12O6 - sweetest carbohydrate - converts to glucose in the body

- aldohexose - C6H12O6 - not found free in nature - obtained from lactose - essential for the formation of certain glycoproteins and cerbrosides

Test 3: Carbohydrates Flashcards by Julia Styczen

What are carbohydrates? What are they composed of? What are they also called?

major energy source
composed of: C, H, and O
called “saccharides” meaning sugar

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Explain the formation and distruction of carbohydrates.

formation: photosynthesis
- eg. glucose in plants from CO2, H2O and ATP (sun).

destruction: respiration (oxidation)
- produces CO2, H2O and energy

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Give a precise definition of carbohydrates.

polyhydroxyaldegydes,
polyhydroxyketones
substances that give such compounds on hydrolysis.

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What are the different types of carbohydrates? What do they form when water is added?

monosaccharides:
- simplest carbohydrates
- + H2O –> no hydrolysis
- cannot be hydrolysed

disaccharides:
- two monosaccharides
- + H2O –> two monosaccharide units

olgosaccharides:
- 2+ monosaccharides

polysaccharides:
- 100-1000 monosaccharides
- + many H2O –> many monosaccharide units

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How are monosaccharides classified?

number of carbon atoms (3-6 usually)
the carbonyl group: aldehyde or ketone

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What is the colour of monosaccharides? Are they soluble? What taste do they have?

colourless
crystalline solids
soluble in water
insoluble in nonpolar solvents
sweet taste

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State the two major types of monosaccharides.

ketoses
aldoses

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What are aldoses?

monosaccharides with:
- aldehyde group (H-C=O)
- many hydroxyl groups

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What are ketoses?

monosaccharides with:
- ketone group (C=O)
- many hydroxyl groups

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What structure is used to represent carbohydrates? What are the two types? How to tell them apart?

fisher projection:
- L-isomer: OH- is on the left of the chiral carbon
- D-isomer: -OH is on the right of the chiral carbon

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What are the principal rules of the fisher projection?

most oxidised group on top
chiral carbon shown at the intersection of vertical and horizontal lines
-OH of chiral carbon determines L-/D- isomer

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What is D-glucose?

aldohexose
C6H12O6
blood sugar
monosaccharide of starch, cellulose, and glycogen

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What is the normal level of glucose in the blood?

4-6mmol/L

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What is D-fructose?

ketohexose
C6H12O6
sweetest carbohydrate
converts to glucose in the body

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What is D-galactose?

aldohexose
C6H12O6
not found free in nature
obtained from lactose
essential for the formation of certain glycoproteins and cerbrosides

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What are the most important pentoses?

D-ribose and D-deoxyribose

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What is the function of ribose?

coenzyme A
ATP
cyclic AMP
monomeric units of RNR

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What is teh name of the other structure of carbohydrates (not fisher)?

W. Haworth projection

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Explain cyclic structures. When do they form? What are they?

two forms of monosaccharides with 5 or 6 atoms

form when the hydroxyl group on C-5 reacts with the aldehyde/ketone group

How are stable cyclic hemiacetals formed?

C=O group of ketone or aldehyde group
-OH group of C’5

cyclic structure of D-isomer has CH2OH above the ring.

How to draw a W. Haworth projection?

turn chain clockwise (90 * )
bend chain to make hexagon
## draw new -OH on C1

What is the difference between alpha and beta glucose?

alpha and beta glucose have identical configurations except at C-1
alpha glucose: -OH on bottom
beta glucose: -OH on top

What is a reducing sugar?

monosaccharide
carbonyl group which oxidises to form carboxylic acid
undergo fehlings reaction, benedicts reagent
eg. glucose, galactose and fructose

What reactions do reducing sugars undergo?

with Fehling’s reagent (Cu2+ complexed with tartrate ion) –> deep blue colour achieved
with Benedict’s reagent (Cu2+ complexed with citrate ion

State monosaccharide examples of reducing sugars.

- glucose - galactose - fructose

When do ketoses qualify as reducing sugars?

if they can **isomerate** to **aldoses**

What do monosaccharides form when they react with alcohols?

**acetals** - called: **glycosides** - with glycosidic bonds

What is a disaccharide?

- two monosaccarides - glycosidic bond (between *anomeric* *carbon* and *hydroxyl* *group*)

What are the three important disaccharides?

- maltose - lactose - sucrose

What is maltose?

- malt sugar - 2 **D-glucose** molecules - hydrolysis of starch - ***alpha-1,4**-glycosidic bonds*: alpha-OH on C'1 & -OH C'4 of

In what forms is maltose found in?

both alpha and beta

Why is maltose a reducing sugar?

it closes and opens

What bond does maltose have? Between what molecules?

2 alpha glucoses - alpha-1,4-glycosidic bond

What is lactose? What bonds does it contain? What monosaccharides is it formed from? Is it a reducing sugar? Why?

***beta-D*-galactose** and ***alpha/beta-D*-glucose** - ***beta-1,4*-glycosidic bond** - reducing sugar: opens and closes

What is sucrose? What bonds does it contain? What monosaccharides is it formed from? Is it a reducing sugar? Why?

- sugar cane and sugar beets - ***alpha-D-*glucose** + ***beta-D-*fructose** - ***alpha,beta-1,2*-glycosidic** bond - NOT a reducing sugar - easily hydrolysed

What does the hydrolysis of sucrose form?

alpha-glucose and beta-fructose

What are polysaccharides?

- polymers of** D-glucose** - *amylose, amylopectin, starch, glycogen* made of **alpha-D-glucose** - *cellulose* made of beta-D-glucose

What is starch? How can it be seperated?

- energy storing carbohydrate - plants (glucose storage) - seperated into 2 fractions: amylose and amylopectin

What is amylose? What bonds are present? What does it form?

- polymer of **alpha-D-glucos**e units - ***alpha-1,4-glycosidic bonds*** - continuous **unbranched** chain (forms coils 'amyl"O"se')

What is amylopectin? What bonds are present? What does it form?

- polymer of glucose units - **branched** polysaccharide chain - ***alpha-1,4-glycosidic bonds*** (in horizontal lines) - ***alpha-1,6-glycosidic bonds*** (between branches)

Explain the function of the starch iodine test.

**starch**: **deep blue colour** complex with iodine - **iodine** + **amylose** helix = large complex (other polysaccharides give other colours (ie. glycogen- red))

What is glycogen? What is it composed of? What is its function?

- energy storing carbohydrate - made of ***1,4-*** and ***1,6-* linked glucose units** - helps maintain glucose balance in the body - removes and stored excess glucose - **branched**!

What is cellulose? What is it composed of? What is its function?

- polysaccharide of **glucose** - **unbranched** chains - ***beta-1,4-*glycosidic bonds** - cannot be digested by humans

Why can cellulose not be digested by humans?

Humans cannot break down ***beta-1,4-*glycosidic bonds**.

What are the two types of starch?

- amylose - amylopectin

What are *chitins*?

- **nitrogen** containing polysaccharides - forms crustaceans shells + insect exoskeletons

What are *pectins*?

polysaccharides - used for jellies - monomer: galacturonic acid