Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

1 - SOD > Carbohydrates > Flashcards

Carbohydrates Flashcards

1
Q

What are the 3 key roles of carbohydrates?

A

structure
- form the cell walls in bacteria, plants and the exoskeletons of arthropods
metabolism
- energy carriers = ATP and coenzymes carry phosphorylated sugars
- energy storage = starch and glycogen are broken down into glucose
information
- framework for DNA/RNA
- carbohydrates on cell surface allow for cell-cell recognition

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What are carbohydrates?

A

group of natural products related to simple sugars

- are hydrated carbons

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What is the structure of sugars?

A

sugars (saccharides) are the simplest types of carbohydrates
there are two types
1 - polyhydroxyaldehydes = aldoses = aldehyde group
2 - polyhydroxyketones = ketoses = ketone group

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

How is the stereochemistry of carbohydrates decided/labelled?

A

stereochemistry is labelled with a D or L

  • D = R, meaning it is clockwise
  • L = S, meaning it is anti-clockwise

labelled with respect to glyceraldehyde

  • if last OH next to the carbon furthest from the carbonyl is to the left = L
  • if last OH next to the carbon furthest from the carbonyl is to the right = D
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What are Fischer projections?

A

can be used to represent the carbohydrate structure in a simpler form
- shows the carbonyl group at the top
can be used to represent the sugar rings
- groups on the LEFT of a Fischer projection go ABOVE. the ring
- groups on the RIGHT of a Fischer projection go BELOW the ring

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What re the cyclic isomers that cyclised sugars can form?

A

beta anomer
- cis groups in the aldoses/ketoses
- OH groups both point up in the equatorial position
alpha anomer
- trans groups on the aldoses and ketoses
- OH groups where one points up and one points down in the axial position

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What is the stereocentre of a cyclised sugar called?

A

anomeric carbon

  • has 4 constituent groups
  • has two isomers = beta and alpha
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What is a Hayworth projection?

A

can be used to represent cyclised sugars

  • groups on the LEFT of a Fischer projection go ABOVE. the ring
  • groups on the RIGHT of a Fischer projection go BELOW the ring

CH2OH on the top left of the ring
O on the top right of the ring

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What is mutarotation?

A

process of reaching an equilibrium between the beta and alpha anomers of a cyclised ring in aqueous solution

  • occurs when pure crystalline anomer is dissolved in water
  • process can be catalysed by an acid or base = switches the one in excess to the opposite
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What are the different conformations of rings?

A

chair
- cyclohexane prefer chair conformation
boat
envelope
- furanose (5C) rings prefer envelope conformation = 4C in the ring and 1C is raised
- furanose rings can rapidly interconvert between

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

How does the cyclisation of glucose occur?

A 
O on carbonyl group reacts with water first 
- lone pair attacks H atom 
can form the furanose form
- 4C attacks C1
can form the pyranose form
- 5C attacks C1
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What are the reactions that carbohydrates can go through?

A

due to the sugar functional groups - aldehydes, ketones and hydroxyls

oxidation
reduction
formation of glycosides

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What is acetylation?

A

reaction of glucose with acetic anhydride to form a pentagram-acetate product
- all the H atoms of the hydroxyl group are replaced with an acetyl group

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Why and how are sugars oxidised?

A

sugars are highly oxygenated so undergo a variety of oxidation reactions

these reactions can be used to identify structural information
- use metal ions to oxidise aldehyde groups in aldoses into carboxylic acids (aldonic acids)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What are the three tests for oxidising aldoses?

A

Benedict’s test
Fehling’s test
Tollen’s test

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What is the Bendict’s test?

  • Reagents
  • Products
  • Observations
A

Reagents
- Copper (2+) in aqueous sodium citrate

Products
- Carboxylic acid and copper oxide

Observations
- Red precipitate

17
Q

What is Fehling’s Test?

  • Reagents
  • Products
  • Observations
A 
Reagents 
- Copper (2+) in aqueous sodium tartrate
Products
- Carboxylic acid and copper oxide 
Observations
- Red precipitate
18
Q

What is Tollen’s Test?

  • Reagents
  • Products
  • Observations
A 
Reagents 
- Silver (Ag+) in aqueous ammonia (NH3)
Products
- Carboxylic acid and silver  
Observations
- Silver mirror on glassware
19
Q

Why are sugars reducing agents?

A

they are oxidised by the Benedict’s and Fehling’s reagent and reduce the metal ions (Cu and Ag)

20
Q

How can it be determined whether or not a sugar is a reducing sugar or not?

A

any aldehyde containing sugar that can remain in the open chain form is a reducing sugar
- allows the aldehyde group to be available for oxidation

any any aldehyde containing sugar that cannot remain in the open chain form is not a reducing sugar

sucrose is not a reducing sugar

21
Q

Why can’t oxidation reaction be used preparatively for sugars? When can they be used preparatively?

A

they cannot be used preparatively because these conditions lead to the eventual decomposition of the sugar

aqueous bromine can be used for preparative oxidation

22
Q

Why can some ketoses be used as reducing sugars?

A

some ketoses can be used as reducing sugars due to their rearrangement under basic conditions

23
Q

What are the effects of stronger oxidising agents?

A

example - nitric acid

can result in diacids = oxidation at both ends of the chain

24
Q

What are monosaccharides reduced to?

A

monosaccharides - polyaldoses = ribose, deoxyribose, glucose, fructose, galactose
can be reduced to give polyalcohols = alditols

reducing agent is sodium borohydride

25
Q

What is an example of an alditol (polyalcohol)?

A

D-mannitol

- naturally occurring in mushrooms, olives and onions

26
Q

What is a glycoside?

A

cyclic acetal = glycoside

  • formed when sugars are mixed/combined with alcohols in the presence of an acid
  • forms a glycosidic bond = covalent bond that joins a sugar to another molecule

contains hemi-acetal group
- chiral carbon with 2 R groups and 2 groups with an oxygen (carbon is directly bonded to one O and not the other)

27
Q

How is a glycoside hydrolysed?

A

glycoside is in equilibrium

if a glycoside is mixed with water in the presence of catalytic amount of mineral acid
- hydrolysis favours the formation of a mixture of anomer of the parent sugar and alcohol

28
Q

What happens to a glycoside in neutral aqueous solution?

A

glycoside is in equilibrium

in neutral aqueous solution

  • no hydrolysis
  • no mutarotation

under neutral conditions the glycosides are stable and exist as rings

29
Q

Why are glycosides not reducing sugars?

A

they do not exist as/cannot remain in open chain form

- under neutral conditions they are stable and exists as rings

30
Q

How is glycoside hydrolysis affected by enzymes?

A

hydrolysis can be catalysed by certain enzymes
- they selectively cleave the alpha or beta glycosidic bonds
alpha - OH substituted group is down
beta - OH substituted group is up

1 - SOD (27 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions