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Biology > carbohydrates > Flashcards

carbohydrates Flashcards

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1
Q

what elements do carbohydrates contain

A
  • carbon
  • hydrogen
  • oxygen
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2
Q

what is the general formula for carbohydrates

A

Cx(H2O)y

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3
Q

monosaccharide examples

A

glucose
fructose
ribose

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4
Q

disaccharide examples

A

lactose
sucrose
maltose

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5
Q

polysaccharide examples

A

glycogen
cellulose
starch

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6
Q

what is a monosaccharide

A

a single sugar unit

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7
Q

formula of glucose

A

C6H12O6

hexose monosaccharide (6 carbons)

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8
Q

what is the difference between alpha and beta glucose

A

alpha glucose has its OH ion on carbon 1 below
beta glucose has its OH ion from carbon 1 above

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9
Q

characteristics of glucose

A
  • polar
  • soluble due to hydrogen bonds that form between the hydroxyl groups and the water molecules
  • solubility means glucose is dissolved in the cytosol of the cell
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10
Q

condensation reaction between 2 alpha glucose

A
  • 2 hydroxyl groups interact
  • forms a water molecule
  • carbon 1 and carbon 4 bond
  • glycosidic bond made
  • maltose is made (disaccharide)
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11
Q

what is sucrose made from

A

glucose and fructose

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12
Q

examples of hexose monosaccharides

A

glucose
fructose
galactose

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13
Q

what is the disaccharide lactose made from

A

glucose
galactose

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14
Q

pentose monosaccharides

A
  • 5 carbon atoms
  • ribose in RNA nucleotides
  • deoxyribose in DNA nucleotides
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15
Q

what is starch made from

A
  • many alpha glucose molecules joined by glycosidic bonds
  • form 2 slightly different polysaccharides
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16
Q

what is amylose

A

one of the polysaccharides in starch
- formed by alpha glucose molecules joined by 1-4 glycosidic bonds
- angle of the bond means that this long chain of glucose twists to form a helix which is further stabilised by hydrogen bonding
-makes the polysaccharide more compact and less soluble than the glucose molecules used to make it

17
Q

what is amylopectin

A
  • one of the polysaccharides in starch
  • made by 1-4 glycosidic bonds between alpha glucose molecules
  • also some glycosidic bonds formed by condensation reactions between carbon 1 and 6 on 2 glucose molecules
  • this means that amylopectin has a branched structure
    (1-6 branching points every 25 subunits)
  • insoluble, compact
18
Q

what is glycogen in relation to starch

A

the functionally equivalent molecule to starch in animals and fungi

19
Q

structure of glycogen

A
  • forms more branches than amylopectin
  • so its more compact and less space is needed for it to be stored
  • this is important as animals are mobile, unlike plants
  • branching means there are many free ends where glucose can be added/removed which speeds up processes of storing/releasing glucose molecules required by the cell
20
Q

how is cellulose made

A
  • chain of beta glucose molecules
  • beta glucose molecules can only bond if alternate subunits are turned upside down
  • so that their hydroxyl groups can interact
  • when a polysaccharide is formed from glucose this way, it is unable to coil or form branches
  • so forms a straight chain molecule called cellulose
21
Q

what are microfibrils and macrofibrils

A
  • when cellulose molecules make hydrogen bonds with each other, they form microfibrils
  • microfibrils join to form macrofibrils
  • macrofibrils combine to produce fibres
  • fibres are strong and insoluble (cell walls)
22
Q

what are reducing sugars

A

all monosaccharides and some disaccharides
they can donate electrons or reduce another molecule or chemical

23
Q

what is the test for reducing sugars

A

Benedict’s reagent

an alkaline solution of copper(II) sulfate

24
Q

how to carry out the test for reducing sugars

A
  • place sample in boiling tube
  • add equal volume of Benedict’s
  • heat mixture gently in boiling water bath for 5 minutes
  • reducing sugars will react with copper ions
  • results in addition of electrons to the blue Cu2+ ions
  • reduces them to brick red Cu+ ions
  • the more reducing sugar present, the more precipitate formed and the less blue ions left in solution
  • so the colour seen is a mixture of brick red and blue
  • this will depend on the concentration of the reducing sugar present
  • so this test is qualitative
25
Q

how to carry out the test for non-reducing sugars

A
  • boil sample with dilute HCl
  • warm the sample with Benedict’s solution

this is because the non reducing sugar has been hydrolysed to reducing sugars
(e.g. sucrose goes to fructose and glucose)

26
Q

test for starch

A

iodine test
-a few drops of iodine dissolved in potassium iodide solution are mixed with sample
- solution changes from yellow/brown to purple/black

Biology (12 decks)

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