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H2 Biology > Carbohydrates > Flashcards

Carbohydrates Flashcards

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AP® Biology flashcards
1
Q

what elements are carbohydrates composed of?

A

carbon, hydrogen, water (hydrated carbon)

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2
Q

what are the functional groups of a carbohydrate?

A

a carbonyl group (C=O, its position determines whether it is a ketone or aldehyde) and multiple hydroxyl groups (OH)

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3
Q

how are carbohydrates classified based on their number of monomer units?

A

1 monomer: monosaccharide
2 monomers: disaccharide
3-10 monomers: oligosaccharide
>10 monomers: polysaccharide

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4
Q

general formula of saccharides

A

(CH2O)n

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5
Q

what are the characteristics of monosaccharides? (appearance and solubilities)

A

colourless, crystalline solids

freely soluble in water, insoluble in nonpolar solvents

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6
Q

generic names of monosaccharides according to number of carbon atoms (and where glucose belongs)

A

trioses (3 carbons), tetroses (4 carbons), pentoses (5 carbons), hexoses (6 carbons, including glucose)

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7
Q

what is the formula and function of glucose?

A

C6H12O6, key energy source for cells

polysaccharides composed of only glucose used as energy stores (glycogen in animals, starch in plants)

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8
Q

what are the uses of monosaccharides?

A

important energy sources and respiratory substrate to produce ATP during cellular respiration
building blocks for synthesis of disaccharides and polysaccharides
raw material for synthesis of other organic molecules, such as nucleotides, amino acids and fatty acids

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9
Q

what is the difference between aldo and keto sugars?

A

aldose / aldo sugars have an aldehyde group, where C=O is bonded to carbon at the end of the chain
ketose / keto sugars have a ketone group, where C=O is bonded to carbon in the middle of the chain

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10
Q

what are the different structures of monosaccharides (with examples)?

A

linear (open-chain) or ring (more predominant, energetically more stable) structures
glucose (6 carbon) ring form is created when O on fifth carbon links with first carbon comprising the carbonyl group, transferring H to carbonyl O to create a hydroxyl group

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11
Q

what is the anomeric carbon, and how is it formed

A

it is the carbon bonded to two oxygen atoms, found in ring structures

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12
Q

what is the difference between an alpha and beta glucose molecule?

A

ABBA (Alpha is Below, Beta is Above)
the hydroxyl group bonded to the anomeric carbon in a ring structured monosaccharide either lies above or below the plane of the ring

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13
Q

how is a disaccharide formed?

A

a condensation reaction, involving the loss of a single water molecule, forms a glycosidic bond (C-O-C) between:
the anomeric carbon of one sugar unit
and
another carbon on the other sugar unit

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14
Q

how is a disaccharide broken down?

A

a hydrolysis reaction, where one molecule of water is added via
either
incubation with dilute acid at 100 degrees Celcius (acid hydrolysis)
or
incubation with an enzyme

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15
Q

what is the nomenclature of glycosidic bonds dependent on?

A

the numbering of carbons attached to hydroxyl (OH) groups involved
the orientation of the hydroxyl (OH) group, whether it is alpha or beta

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16
Q

describe the benedict’s test for reducing sugars in detail (principle, method, observation)

A

principle: a free carbonyl (C=O) group in a reducing sugar can reduce copper from Cu2+ to Cu+, under alkaline conditions, from a blue solution to brick-red precipitate
method: add 2cm^3 of Benedict’s solution to an equal volume of food sample, and heat
observation: if reducing sugars are not present, Benedict’s solution will remain blue. with increasing quantities of reducing sugars present, the suspension formed will gradually turn from green to yellow to orange then to brick-red

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17
Q

for non-reducing sugars, what changes have to be made to the Benedict’s test, and why?

A

for non-reducing sugars (eg. sucrose): prior acid hydrolysis step, where equal volume of dilute HCl is added over heat to break down sugars into reducing sugars
they have no free carbonyl (C=O) group since both are linked in a glycosidic bond

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18
Q

what are polysaccharides, and their uses?

A

macromolecules with a few hundred to a few hundred thousand monosaccharides joined by glycosidic bonds
they serve as storage or structural materials

19
Q

what are glycosidic bonds / linkages?

A

a covalent bond between the anomeric carbon of one saccharide and a carbon of another saccharide

20
Q

state each of the three monosaccharides, disaccharides, and polysaccharides

A

monosaccharides: glucose, fructose, galactose
disaccharides: lactose, maltose, sucrose
polysaccharides: starch (amylose and amylopectin), glycogen, cellulose

21
Q

describe the function, monomer, and type of glycosidic bond of starch

A

storage in plants, alpha-glucose, alpha (1,4) for amylose and alpha (1,4) + alpha (1,6) for amylopectin
10-30% unbranched amylose, 70-90% branched amylopectin

22
Q

describe the function, monomer, and type of glycosidic bond of glycogen

A

storage in humans, alpha-glucose, alpha (1,4) + alpha (1,6) every 8-12 glucose units

23
Q

describe the function, monomer, and type of glycosidic bond of cellulose

A

structural support in plants, beta-glucose, beta (1,4)

typically makes up 50% of plant cell wall

24
Q

what monomers make up each type of starch, glycogen, cellulose?

A

alpha-glucose for starch and glycogen, beta-glucose for cellulose

25
Q

what are the types of glycosidic bonds present in each of the polysaccharides?

A

alpha (1,4) only for amylose
alpha (1,4) and alpha (1,6) for amylopectin
alpha (1,4) and alpha (1,6) for glycogen
beta (1,4) for starch

26
Q

what are the structural features of storage polysaccharides (amylose, amylopectin, glycogen) that help with their function?
hint: large molecule, alpha (1,4), alpha (1,6)

A

large molecules, stores large number of glucose, insoluble, no effect on cell’s water potential
alpha (1,4) glycosidic bond, easily hydrolysed by enzymes, helical coil, compact shape
alpha (1,6) glycosidic bond, highly branched, more free ends, faster hydrolysis by enzymes, more compact

27
Q

what are the structural features of cellulose that help its function?

A

alternate inverted beta-glucose units linked by beta (1,4) glycosidic bonds, long unbranched chains, with OH groups projecting from cellulose chains, extensive hydrogen bonding between parallel chains, extensive cross-linkages, microfibrils form, high tensile strength
microfibrils associate to form macrofibrils, further increase strength
beta (1,4) glycosidic bonds are not easily hydrolysed by acid or enzymes, structurally stable

28
Q

what are the features of each type of glycosidic bond?

A

alpha (1,4) glycosidic bonds: linear, unbranched chains

alpha (1,6) glycosidic bonds: branched chains (and only at the point where it branches off)

29
Q

starch: when is it synthesised, what is its purpose, what is its monomer, what is it composed of in what percentages, and what is it stored as and where?

A

formed from excess glucose synthesised via photosynthesis
serves as a carbon source
only made of alpha-glucose monomers
10-30% unbranched amylose and 70-90% branched amylopectin
stored as starch grains either within chloroplasts or amyloplasts

30
Q

describe the principle, method, and observation of the starch test

A

principle: centre of starch helix is hydrophobic, where iodine in potassium iodide solution packs within the helix’s core to give rise to a blue-black colouration
method: add 3 drops of iodine in dilute potassium iodide solution (I2/KI) to the sample
observation: if starch is present, the sample will turn blue-black. if starch is absent, the sample remains yellow / brown

31
Q

what is the structure of amylose? (branched / unbranched, number and type of monomers, type of glycosidic bonds, structure and size, solubility in water)

A

unbranched chain, hundreds to thousands of alpha-glucose residues with alpha (1,4) glycosidic bonds
helical, compact structure, six glucose units per turn
bulky, poorly soluble in water

32
Q

what is the structure of amylopectin? (branched / unbranched, number and type of monomers, type of glycosidic bonds, structure and size, rate of hydrolysis)

A

branched at every 12-30 residues due to alpha (1,6) glycosidic bonds, but also has alpha (1,4) for unbranched sections, average branch length of 24-30 residues
alpha-glucose residues
many branch ends allow more enzymes to act on it at once, easily hydrolysed
highly compact, twice as many alpha-glucose residues as amylose bc of extensive branching (and coiling)
- free end in the middle

33
Q

what colours are amylose and amylopectin when stained with iodine, and what are their relative molecular masses and number of units per molecule?

A

amylose: deep blue, Mr up to 50,000, up to 300 glucose per molecule
amylopectin: red to purple, Mr up to 500,000, 1300-1500 glucose per molecule

34
Q

how does the structure of starch relate to its storage function?

hint: large, many monomers, alpha (1,4) glycosidic bonds, amylose is helical, amylopectin is highly branched, anomeric carbon involved in glycosidic bond formation

A

large and insoluble, does not affect cell’s water potential
large store of carbon (respiratory substrate)
alpha (1,4) glycosidic bonds, easily hydrolysed by enzymes
helical amylose is compact, highly branched amylopectin is compact and has many free ends for more enzymes to work on at once
anomeric carbon used in glycosidic bond formation, few free anomeric hydroxyl groups, so starch is unreactive and chemically stable

35
Q

what is glycogen, where is it found, and what is its purpose?

A

in the liver (amounting up to 10% of liver mass), skeletal muscle (accounts for 1-2% of muscle mass), cytoplasmic granules
in liver, used as a source of glucose to maintain blood sugar levels.
in muscle, serves as fuel source to generate ATP for muscle contraction

36
Q

how does the structure of glycogen relate to its storage function?

hint: large, several hundreds to thousands of monomers, alpha (1,4) glycosidic bonds, highly branched, a

A

large and insoluble, does not affect cell’s water potential
large store of carbon (respiratory substrate)
alpha (1,4) glycosidic bonds, easily hydrolysed by enzymes
highly compact, many free ends for more enzymes to work on at once
anomeric carbon used in glycosidic bond formation, few free anomeric hydroxyl groups, so starch is unreactive and chemically stable

37
Q

why are alternate beta-glucose monomers inverted in cellulose, what type of chain does it form with how many monomers, and how do the chains run?

A

to obtain beta (1,4) glycosidic bonds, forming a long and unbranched straight chain of up to 10,000 beta-glucose monomers, with hydroxyl (OH) groups projecting outwards from each parallel chains

38
Q

how are parallel cellulose molecules held together, and how are microfibrils formed?

A

extensive hydrogen bonds form between the protruding OH groups of neighbouring chains, establishing rigid cross-links between chains, where 60-70 of them form a microfibril with a diameter of up to 25nm

39
Q

how are macrofibrils made in cellulose?

A

microfibrils (cross-linked cellulose chains with extensive hydrogen bonds) associate in groups

40
Q

what confers high tensile strength to cellulose?

A

alternate inverted beta-glucose units linked by beta (1,4) glycosidic bonds allow the formation of long, unbranched, straight and parallel chains with extensive hydrogen bonds that group into microfibrils, then macrofibrils

41
Q

how are cellulose macrofibrils laid down in plant cell walls, and what purpose does this serve?

A

celloluse fibres are laid down in different orientations in the different layers of the plant cell wall, permitting the cell wall to withstand forces exerted in all directions

42
Q

what is the permeability of cellulose plant cell walls, and its function?

A

full permeability to water and solutes, important for proper functioning of plant cells

43
Q

what is cellulose’s use for animals (snails, insects, ruminants), algae, bacteria, and fungi?

A

a food source, since they can break cellulose down into glucose with the enzyme cellulase that they all possess

H2 Biology (24 decks)

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