Carbohydrates (3.1.2) Flashcards

You may prefer our related Brainscape-certified flashcards:
1
Q

what are monosaccharides?

A

the monomers from which larger carbohydrates are made

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

what are examples of monosaccharides?

A

glucose, galactose and fructose

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

what does a condensation reaction between two monosaccharides do?

A

form a glycosidic bond

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

how are disaccharides formed?

A

from the condensation of two monosaccharides

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

what is maltose?

A

a disaccharide formed from the condensation of two glucose molecules

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

what is sucrose?

A

a disaccharide formed from the condensation of a glucose molecule and a fructose molecule

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

what is lactose?

A

a disaccharide formed from the condensation of a glucose molecule and a galactose molecule

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

what are isomers?

A

two or more compounds with the same formula but a different arrangement of atoms in the molecule and different properties

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

what are the isomers of glucose?

A

alpha glucose and beta glucose

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

what is the key difference between alpha and beta glucose?

A

in alpha glucose, the carbon 1 hydroxyl points below the plane but in beta glucose it points above

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

how are polysaccharides formed?

A

from the condensation of many glucose units

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

what does the condensation of alpha glucose form?

A

glycogen and starch

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

what does the condensation of beta glucose form?

A

cellulose

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

what is a reducing sugar?

A

a sugar which can donate an electron to another molecule

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

what are examples of reducing sugars?

A

all monosaccharides and some disaccharides (maltose and lactose)

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

give an example of a non-reducing sugar?

A

sucrose

17
Q

what do reducing sugars do when they have Benedict’s solution added to them?

A

they reduce the copper sulphate in the reagent (by adding an electron so it goes from a Cu2+ ion to a Cu+ ion) to produce a red precipitate of copper oxide - the amount of precipitate produced depends on the concentration of reducing sugars present

18
Q

how do you carry out a test for reducing sugars?

A

add 1cm^3 of your sample to a boiling tube
add 1cm^3 of Benedict’s solution (blue) to the boiling tube
place the boiling tube into a water bath and leave for three minutes
remove the tube and observe the colour

19
Q

how do you identify if there is a reducing sugar present?

A

there will be a colour change depending on the amount of reducing sugar present so the solution is no longer blue:
small amount - green
more - yellow
higher level - orange
lots - brick-red

20
Q

why is the Benedict’s test semi-quantitative?

A

it only gives an approximate idea of the amount of reducing sugar present because it only shows a narrow range of colour changes and all humans perceive colour differently

21
Q

how do you test for a non-reducing sugar?

A

first you need to see if the solution also contains some reducing sugar by carrying out a Benedict’s test on it and recording any colour change that occurs
take 1cm3 of the solution and add 1cm3 of dilute HCl then boil in a water bath for two minutes
remove from the water bath and leave to cool slightly
add 1cm3 of NaOH to neutralise (Benedict’s test doesn’t work in acidic conditions)
carry out another Benedict’s test and record any colour change

22
Q

what happens when HCl is added to a solution if a non-reducing sugar is present?

A

the acid hydrolyses the glycosidic bonds which releases the monosaccharides

23
Q

how do you interpret results of a non-reducing sugar test?

A

if there is a colour change in the first Benedict’s test then that tells you that there is a reducing sugar present in some amount
if there is a colour change in the second Benedict’s test then that tells you that there is also a non-reducing sugar present in some amount
if the colour change in the first Benedict’s test is red that tells you that there is a large amount of reducing sugar present - in this case you can’t test for a non-reducing sugar as you can’t see a colour change beyond red

24
Q

when quantifying the Benedict’s test, what is the relationship between glucose concentration and mean light transmission and why?

A

As concentration increases, transmission increases, but at higher concentrations it levels off
This is because as concentration increases, more copper sulphate in the Benedict’s solution is reduced to produce copper oxide, meaning a greater amount of red precipitate forms. Therefore the solution contains less copper sulphate when filtered so it loses more of its blue colour, and this means that more light can be transmitted through

25
Q

what is glycogen?

A

a glucose storage molecule found in animals

26
Q

how would you describe the structure of glycogen?

A

it is a polymer of alpha glucose and each glucose molecule is joined by 1,4 glycosidic bonds
it is a branched molecule and at the branch points there are 1,6 glycosidic bonds

27
Q

how is glycogen suitable for its function?

A

because it has many branches it has lots of free ends, which means there is a large surface area for enzymes to rapidly convert glycogen back to glucose, allowing them to accommodate the rapid changes in energy needs in animals
it is insoluble in water so it doesn’t dissolve into glucose and cause water to move into the animal cell via osmosis
it is a large molecule so cannot move out of the cell

28
Q

what is cellulose?

A

a polysaccharide which is found in the cell wall of plant cells

29
Q

how would you describe the structure of cellulose?

A

it is a polymer of beta glucose, so in a molecule every second beta glucose molecule flips to allow 1,4 glycosidic bonds to be created
large numbers of hydrogen bonds form between cellulose chains making it very strong
cellulose chains group together to form microfibrils, which then group together to form macrofibrils, which group together to form cellulose fibres

30
Q

how is cellulose suitable for its function?

A

it creates a cellulose cell wall which is permeable to water
cellulose is very strong so when water moves into the cell and causes it to become turgid, the cell wall can withstand the high pressure caused by this
this allows plant cells to have a rigid structure which keeps the plant upright

31
Q

why do plant cells store glucose as starch?

A

glucose has many hydroxyl groups which makes it very soluble in water, and if cells had lots of glucose this could cause too much water to move into the cell by osmosis

32
Q

what are the two molecules that make up starch?

A

amylose and amylopectin

33
Q

how would you describe the structure of amylose?

A

it is a polymer of alpha glucose with 1,4 glycosidic bonds
the molecule twists into a compact helix and hydrogen bonds form between glucose molecules along the chain

34
Q

how would you describe the structure of amylopectin?

A

it is a polymer of alpha glucose with 1,4 glycosidic bonds
it has a branch every 25-30 glucose molecules and the branches are connected to the main chain by 1,6 glycosidic bonds

35
Q

how is starch suitable for its function?

A

it is a very compact molecule
it is insoluble in water so doesn’t cause water to enter the cell
amylose and amylopectin are large so can’t diffuse out of the cell
because amylopectin is branched there are many ends for enzymes to hydrolyse the glycosidic bonds when the cell needs glucose

36
Q

what do you need to do to prepare a food sample for carrying out a food test?

A
  1. grind the food with a small amount of distilled water in a mortar and pestle
  2. once the food is a paste add more water and stir
  3. filter the mixture to remove any solid food particles - you do the test on the solution which passes through the filter
37
Q

how do you test for starch?

A
  1. add 3cm^3 of food solution to a test tube
  2. add 1cm^3 of a solution containing iodine and potassium iodide
  3. if starch is present, the solution will turn blue-black, and if not, it will remain orange