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Carbohydrates Flashcards

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Biology 101 flashcards
1
Q

What elements do carbs contain ?

A

C, H, O

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2
Q

What’s the general formula of carbs ?

A

Cx(H2O)y

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3
Q

What are monosaccharides ?

A

Simplest form of carbohydrates which cannot be hydrolysed to any simpler carbs

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4
Q

What is the general formula of monosaccharides ?

A

(CH2O)n
- can range from 3-7 carbons long
- have a carbonyl group and multiple hydroxyl groups attached

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5
Q

What are the different types of monosaccharides ?

A

Aldoses and ketones
Open chain and ring form
a-isomer (alpha) and ß-isomer (beta)

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6
Q

What is the difference between aldoses and ketoses?

A

Aldoses (aldehyde sugar) - have carbonato group attached at the end of the carbon chain (-CHO)
Ketoses (ketone sugar) - have carbonyl group within the carbon skeleton (C=O)

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7
Q

What’s the most common type of carbon skeletons in monosaccharide ?

A

Pentose (5C) and hexose (6C)

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8
Q

Is open chain or ring form the most usual forms and why?

A

In aqueous solutions, pentose and hexose form stable ring structures which are the usual forms (due to the bond angle between carbon atoms)

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9
Q

What is a pyranose ring?

A

A six membered ring in hexoses (6C) which are aldoses
- the first carbon atom combines with oxygen on carbon atom 5
- eg. Glucose
- count carbon starting from the C after oxygen, count clockwise

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10
Q

What is a furanose ring ?

A

Five membered ring in hexoses (6C) which are ketoses
- the carbonyl group of Caron atom 2 reduces the -OH group on carbon 5
- eg. Fructose
- count carbon starting from the carbon in CH2OH on top, count anticlockwise

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11
Q

What are the two ring forms that glucose exists in ?

A

a (alpha) and ß (beta)

Alpha - the -OH group on carbon 1 projects below the ring
Beta - the -OH group on carbon 1 projects above the ring

(Carbon 1 is the first carbon atom to the right of the oxygen in the ring, count clockwise)

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12
Q

What are the properties of monosaccharides ?

A
  • sweet
  • crystalline in appearance
  • readily soluble in water (-OH groups form H bond with water)
  • all are reducing sugars (have the ability to reduce Cu2+ in benedict’s reagent to Cu+ which results in formation of Cu2O, brick red ppt)
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13
Q

What are disaccharides made of ?

A

2 monosaccharides joined by glycosidic bonds

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14
Q

What are the three disaccharides ?

A

Lactose - glucose + galactose
Maltose - glucose + glucose
Sucrose - glucose + fructose

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15
Q

What is the name of the reaction in which disaccharides are formed from monosaccharides and vice versa ?

A

Disaccharides from monosaccharides - condensation, a single H2O molecule is lost
Disaccharides split into monosaccharide - hydrolysis, addition of water

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16
Q

What are monosaccharides in disaccharides / once they are linked called ?

A

Residue

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17
Q

Which of the three disaccharides is non-reducing ?

A

Sucrose

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18
Q

What bond is formed between two monosaccharides ?

A

Glycosidic bond

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19
Q

What are the properties of disaccharides ?

A

Sweet
Crystalline in appearance
Readily soluble in water
Can be hydrolysed to a monosaccharide under certain condition

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20
Q

What are the two methods in which a disaccharide can be hydrolysed into a monosaccharide ?

A

Chemical method - incubating the disaccharide with dilute acid at 100ºC
Enzymatic method - incubating the disaccharide with an enzyme at room temperature
( sucrose : sucrase, invertase | Maltose : Maltase | lactose : lactase )

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21
Q

What is maltose and where can it be found ?

A

A breakdown product during starch digestion by amylases
It occurs commonly in animals and germinating seeds

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22
Q

Characteristics of lactose ?

A

Exclusively found in milk (milk sugar)
Is slowly digested so gives a steady release of energy

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23
Q

Characteristics of sucrose ?

A

Cane sugar
Most plentiful disaccharide in nature
Most commonly found in plants

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24
Q

Why is sucrose commonly found in plants ?

A

Good transport sugar - highly soluble
Good storage sugar - chemically unreactive

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25
Q

What are macromolecules ?

A

Polymers with a few hundred to a few thousand monosaccharides joined together by glycosidic bonds

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26
Q

Characteristic of polysaccharides ?

A

Macromolecules
Insoluble in water due to its big size
Chain can be branched or unbranched

27
Q

What are the two groups of polysaccharides ?

A

Storage polysaccharides
Structural polysaccharides

28
Q

What are the two storage polysaccharides ?

A

Starch - amylose + amylopectin
Glucose

29
Q

What is an example of a storage polysaccharide ?

A

Cellulose

30
Q

Characteristics of starch ?

A

Polymer of a-glucose
Found in most parts of plants in the form of small granules - Serves as an energy store formed from excess glucose produced during photosynthesis

31
Q

What are the two substances that starch is made up of ?

A

Amylose and amylopectin

32
Q

What is the structure of amylose ?

A

a-glucose residues joined together by (a 1-4 glycosidic bonds) with bond angle of 109º causing the polymer to form a helix (like loops)
The -OH on carbon 2 of each glucose residue projects into the middle of the spiral

33
Q

What residues make up amylose ?

A

a-glucose residues

34
Q

What bond is in amylose ? bond angle ?

A

a 1-4 glycosidic bond \
109º

35
Q

How does amylose hold its helical shape?

A

The -OH groups on each carbon 2 pointing inside the helix forms H bonds with each other, stabilising the shape of the polymer

36
Q

Characteristic of amylopectin

A

a-glucose residues joined by either (a 1-4 glycosidic bonds) or (a 1-6 glycosidic bonds)
Multi-branched compact polymer

37
Q

Why is amylopectin branched while amylose is not ?

A

The formation of the (a 1-6 glycosidic bond) in amylopectin puts a branch point into the polymer making it branched

38
Q

How is both amylose and amylopectin compact ?

A

Amylose - coiled up into a compact helical shape
Amylopectin - branched to form a closely packed brush shape

39
Q

Characteristics of glycogen

A

Major polysaccharide storage material in animals and fungi (mainly stored in liver and muscles)
Exist as granules usually associated with the smooth endoplasmic reticulum

40
Q

What type of monosaccharide is glycogen made up of ?

A

a-glucose

41
Q

Structure and bonding in glycogen ?

A

Branched
a-glucose residues bonded by (a 1-4) and (a 1-6) glycosidic bonds

42
Q

What are the differences between glycogen and amylopectin ?

A

Glycogen has shorter chains an is more highly branched

43
Q

Why is glycogen highly branched ?

A

It has multiple ends where enzymes can cleave off glycogen molecules resulting in quick release of many glucose

44
Q

Characteristics of cellulose

A

Most abundant organic molecule on earth
A structural component of all plant cell walls

45
Q

Type of residue in cellulose and bond formed

A

ß-glucose linked by ß 1-4 glycosidic bonds

46
Q

How is the ß 1-4 bond formed between the residues ?

A

Every alternate ß–glucose residue is flipped upside down (180º) so that the -OH groups are lined up to form the bonds

47
Q

Formation of cellulose from ß-glucose chains

A
  1. -OH groups project outwards form each chain in all directions and form H bonds with neighbouring chains (cross-linking binds the chains rigidly together)
  2. The chains are aggregated into bundles to form cellulose micelles (~40 chains)
  3. The micelles are embedded in other polysaccharides and arranged in larger bundles to form microfibrils (3.5nm in diameter)
  4. Microfibrils combine to form macrofibrils
48
Q

Where is cellulose formed and assembled ?

A

NOT the Golgi apparatus
Made by specific enzyme on the cell surface membrane

49
Q

What are the five structures of storage molecules (which can be related to properties) ?

A

Large molecule
Composed of many a-glucose monomers
Compact shape
Stable
Organisation of chain

50
Q

How does being a large molecule enable starch and glycogen to be storage molecules ?

A

Large thus insoluble in water making them an ideal storage material as it has little effect on the water potential of the cell - can be stored in large quantities in cell

51
Q

How is starch and glycogen insoluble even when they have -OH groups to form H bonds with water ?

A

The molecule is so large that there are not enough H bonds between the -OH groups and water to dissolve the entire macromolecule

52
Q

Is starch or glycogen less soluble in water ?

A

Starch

53
Q

Why is starch less soluble in water than glycogen ?

A

Tight spirals of amylopectin in starch reduce the ability of -OH groups interacting with water molecules
While glycogen is branched thus -OH groups more exposed

54
Q

How does being composed of many a-glucose monomers enable starch and glycogen to be storage molecules ?

A

Starch and glycogen act as large store of carbon (building blocks) and energy (respiratory substrate broken down in the process of respiration)

55
Q

How does having a compact shape enable starch and glycogen to be storage molecules ?

A

Compact and ideal for storage as many glucose residues can be stored in a small volume within the cell - saves space

(Compact due to the helical coils formed)

56
Q

How does being stable enable starch and glycogen to be storage molecules ?

A

Most -OH groups of glucose residues are projected into the interior of the helices
-OH groups form H bonds with each other to stabilise the shape

57
Q

How does organisation of chains enable starch and glycogen to be storage molecules ?

A

Organisation : Starch and glucose are not cross-linked to form a bundle

Can be readily hydrolysed to release their monomers when required

58
Q

How is starch readily hydrolysed ?

A

The (a 1-4) glycosidic bonds of amylose and amylopectin can be easily hydrolysed by enzymes present in plants and most organisms

The (a 1-4) glycosidic bonds create many branch points which increases the SA for enzyme action, allowing many enzymes to hydrolyse amylopectin at the same to release many glucose molecules

59
Q

How is glycogen readily hydrolysed ?

A

The (a 1-4) glycosidic bond can be easily hydrolysed by enzyme glycogen phosphorylase to form glucose-1-phosphate molecules (the phosphate group must be removed so that glucose can leave the cell)

The (a 1-6) glycosidic bonds creates many branch points which allows many enzymes to hydrolysed it at the same time, releasing many glucose molecules

60
Q

What are the structures of cellulose (that can be linked to properties)?

A

Large molecule
Straight chain
Effective inter-chain bonding
Microfibrils and macrofibrils

61
Q

How does being a large molecule enable cellulose to be a structural molecule ?

A

Large therefore insoluble in water therefore an ideal structural material as it will remain intact in the presence of water to provide structural support to the plant cells

62
Q

How does being a straight chain enable cellulose to be a structural molecule ?

A

Straight chain due to every alternate ß-glucose residue being flipped upside down to form (ß 1-4) glycosidic bonds which are not easliy hydrolysed so cellulose is stable which is important for serving structural function

63
Q

How does effective inter-chain bonding enable cellulose to be a structural molecule ?

A

Cross-linking between the -OH groups of neighbouring chains binds the chains rigidly together conferring great tensile strength and inelastic nature

64
Q

How does microfibrils and macrofibrils enable cellulose to be a structural molecule ?

A

Association of chains into microfibrils and macrofibrils resulting high tensile strength which translates further into mechanical strength
- allows cellulose cell wall to withstand stress and prevents cell from bursting when water enters by osmosis
- cellulose cell wall helps determine shape of cells

Microfibrils and macrofibrils are not easily broken down

bio (23 decks)

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