Module 2- chapter 3 carbohydrates Flashcards
(98 cards)
1
Q
What is the general formula of carbohydrates?
A
Cₓ(H₂O)ᵧ
2
Q
What are carbohydrates in general also known as?
A
saccharides/ sugars
3
Q
What are the three types of carbohydrates?
A
- Monosaccharides
- Disaccharides
- Polysaccharides
4
Q
What are monosaccharides?
A
small, simple sugars which will reduce
5
Q
What are disaccharides?
A
Large sugars formed from two monosaccharides
6
Q
what are polysaccharides?
A
long chain carbohydrates. a type of polymer made up of monosaccharides as monomers
7
Q
What are some examples of monosaccharides?
A
glucose, fructose, ribose
8
Q
what are some examples of disaccharides?
A
lactose, sucrose, maltose
9
Q
what are some examples of polysaccharides?
A
glycogen, cellulose, starch
10
Q
What is the formula of glucose?
A
C₆H₁₂O₆
11
Q
What type of monosaccharide is glucose due to its number of carbons?
A
hexose monosaccharide (6 carbons)
12
Q
What is a key property of glucose? Why is this useful?
A
Highly soluble. Useful because glucose is a major energy source for most cells and is the main form in which carbohydrates are transported around the body of animals.
13
Q
What makes glucose highly soluble?
A
- The oxygen in the water molecules as a partial negative charge whilst the hydrogens in the water molecules have a partial positive charge, therefore the overall partial charge of the water is positive.
- The OH groups on the glucose have a partial negative charge so the water and hydroxyl groups bond by dipole bonding.
- The dipole dipole attraction of the water with the glucose hydroxyl groups is stronger than the attraction of the OH group to the carbon chain of glucose.
14
Q
What are the three ways of drawing the structure of glucose?
A
Straight chain, ring (most commonly used), simplified ring
15
Q
What are the two structural variations of the glucose molecule?
A
Alpha and beta glucose
16
Q
What can structural variations of molecules be referred to as?
A
structural isomers
17
Q
How are alpha and beta glucose different?
A
Alpha glucose has the hydroxyl group below carbon 1. Beta glucose has the hydroxyl group above carbon 1.
18
Q
In molecular structure diagrams, how are the carbons numbered?
A
clockwise from the oxygen atom within the ring
19
Q
What are condensation reactions?
A
\when two hydroxyl groups react to bond the two molecules and produce a water molecule. A glycosidic bond forms between the two molecules and oxygen is left behind where the two hydroxyl groups were.
20
Q
What is a glycosidic bond?
A
a type of covalent bond formed in condensation reactions between monosaccharides
21
Q
What do condensation reactions form?
A
Disaccharides and polysaccharides when two or more monosaccharides are bonded.
22
Q
How is maltose formed?
A
by two alpha glucose molecules joined by an alpha 1,4 glycosidic bond.
23
Q
what type of carbohydrate is maltose?
A
disaccharide
24
Q
what type of carbohydrate is fructose?
A
hexose monosaccharide
25
what type of carbohydrate is galactose?
hexose monosaccharide
26
How is sucrose formed?
by glucose and fructose, joined by an alpha 1,4 glycosidic bond
27
what type of carbohydrate is sucrose?
disaccharide
28
how is lactose formed?
by galactose and glucose, joined by a beta 1,4 glycosidic bond
29
what type of carbohydrate is lactose?
disaccharide
30
is fructose more or less sweet than glucose?
more (sweeter)
31
is galactose more or less sweet than glucose?
less sweet
32
is glucose more or less sweet than galactose?
more (sweeter)
33
is glucose more or less sweet than fructose?
less sweet
34
Do pentose monosaccharides have alpha and beta isomers?
no
35
How many carbons do pentose monosaccharides have?
5
36
which structure is used to draw pentose monosaccharides?
ring
37
what are two examples of pentose monosaccharides?
ribose and deoxyribose (structural isomers)
38
What is the difference between ribose and deoyribose?
ribose has one hydrogen atom and one hydroxyl group attached to carbon 2. Deoxyribose has two H atoms and no OH groups on carbon 2.
39
How can you remember the difference between ribose and dexoyribose?
DEOXYribose is DEOXYgenated compared to ribose (no OH groups so no oxygen on carbon 2)
40
What important biological molecule is ribose part of?
RNA - ribonucleic acid
41
What important biological molecule is deoxyribose part of?
DNA - deoxyribonucleic acid
42
What are polysaccharides mainly used as?
an energy store
43
What are three examples of polysaccharides?
- starch
- glycogen
- cellulose
44
what are the two types of starch polysaccharides?
amylose and amylopectin
45
what is starch stored as in plastids?
intracellular starch grains
46
what are examples of plastids?
chloroplasts (leaf cells) and amyloplasts (found in potatoes)
47
How is amylose formed?
by two alpha glucose molecules joined together by 1,4 glycosidic bonds.
48
describe the structure of amylose
-the long chain of glucose forms a helix because of the bond angle. the helix is stabilised by the hydrogen bonding in the molecule.
49
how does its structure give amylose its properties?
the helical structure makes amylose more compact and less soluble than the glucose molecules used to make it
50
how is amylopectin formed?
by alpha glucose molecules with 1,4 glycosidic bonds but also some 1,6 glycosidic bonds formed by condensation reactions.
51
describe the structure of amylopectin
the 1,6 glycosidic bonds mean that amylopectin is branched with the 1,6 branching points occurring every 25 glucose subunits
52
how does its structure give amylopectin its properties?
branching makes amylopectin more compact so ideal for storage. amylopectin is also insoluble
53
how is glycogen formed?
by alpha glucose molecules with 1,4 glycosidic bonds and 1,6 glycosidic bond.
54
describe the structure of glycogen
forms more branches than amylopectin so is more compact and less space required for it to be stored
55
how does its structure give glycogen its properties?
- branching makes the molecules more compact and means that there are free ends where glucose molecules can be added or removed, this increases the speed of processes for storing and releasing glucose molecules required by the cell.
- broken down more quickly due to free ends from branching, indicates higher metabolic requirements of animals compared with plants
- insoluble but less dense and more soluble than starch
56
how is glucose stored in animals and fungi?
as glycogen
57
What are hydrolysis reactions?
the opposite of condensation reactions, break polysaccharides and disaccharides into monosaccharides by the addition of water molecules
58
key points about cellulose
- main component of plant cell walls
- most abundant organic polymer
- very strong so prevents cells from bursting when take in excess water
59
how is cellulose formed?
beta glucose molecules in long chains. the glucose molecules alternate (every other one inverted 180 degrees) so the hydroxyl groups are adjacent and react to form 1,4 glycosidic bonds
60
describe the structure of cellulose
- a straight, linear chain as unable to coil or form branches.
- the chains of cellulose molecules make hydrogen bonds with each other to form microfibrils. the microfibrils join together to from macrofibrils, which combine to form fibres.
61
link the properties of cellulose to function
the fibres are strong and insoluble and are used to make cell walls. cellulose is hard to break down into its monomers and acts as fibre/roughage in the diet due to this
62
what is used to test for starch?
iodine dissolved in potassium iodide solution
63
what is a positive result for the test for starch?
a colour change from yellow-brown to purple-black
64
what is a negative result for the test for starch?
the solution will remain yellow-brown
65
what are reducing sugars?
sugars which can donate electrons or reduce another molecule/ chemical.
66
what type(s) of carbohydrates are reducing sugars?
all monosaccharides and some disaccharides are reducing sugars
67
what are examples of disaccharides which are reducing sugars?
maltose and lactose
68
what can be used to test reducing sugars?
Benedict's solution
69
what is Benedict's solution/reagent?
an alkaline solution for copper (II) sulfate
70
Describe the method for testing for reducing sugars.
1) Place the sample to tested in a test tube, the sample must be in liquid form.
2) Add an equal volume of Benedict's reagent as the volume of the sample.
3) Heat the mixture gently in a water boiling bath for 5 minutes.
71
what is a negative result for the test for reducing sugars?
The solution will remain blue (the original colour of Benedict's reagent)
72
What is a positive result for the test for reducing sugars?
- a very low concentration of reducing sugar will a colour of green
- a low concentration of reducing sugar will a colour of yellow
- a medium concentration of reducing sugar will a colour of orange
- a high concentration of reducing sugar will a colour of brick red
73
Why is a positive result for the test for reducing sugars a range of colour changes?
- The reducing sugars react with the copper ions in the Benedict's reagent. This adds electrons to the blue Cu²⁺ ions, reducing them to red Cu⁺ ions.
- When the test is carried out, a brick-red precipitate being formed indicates a positive result. The more reducing sugar present, the more precipitate formed and the fewer blue Cu²⁺ ions remaining in solution.
- The colour observed will be a mixture of red Cu⁺ and blue Cu²⁺ ions so the colour is different for different concentrations of reducing sugars.
74
what is the test for non-reducing sugars?
the Benedict's test but modified
75
Describe the method for testing for non-reducing sugars.
1) Add the sample to be tested to a test tube and add an equal volume of hydrochloric acid.
2) Heat the mixture for a few minutes in a water bath.
3) Add the sodium hydrogen carbonate to neutralise the solution. Continue adding the sodium hydrogen carbonate until there is no effervescence.
4) Add the same volume of Benedict's reagent as HCl and the sample.
5) Heat the mixture gently in a boiling water bath for 5 minutes.
76
what is a positive result in the test for non-reducing sugars and what is the negative result?
both the same as the results in the test for reducing sugars (unmodified Benedict's test)
77
What are the modifications to the Benedict's test when testing for non-reducing sugars?
adding hydrochloric acid and neutralising the solution with sodium hydrogen carbonate.
78
why is HCl added as a modification to the Benedict's test when testing for non-reducing sugars?
the HCl hydrolyses (breaks down) the glycosidic bond between the reducing sugars which make up the non-reducing sugars.
79
why is sodium hydrogen carbonate added as a modification to the Benedict's test when testing for non-reducing sugars?
the sodium hydrogen carbonate neutralises the solution after the HCl is added, simply because Benedict's reagent won't work in acidic environments.
80
What type of test is the Benedict's test (qualitative etc)? why?
qualitative and semi-quantitative as it doesn't give a numerical value for the concentration of reducing sugars present, yet the relative concentration of reducing sugars can be estimated by the colour change.
81
Describe the term "qualitative" in relation to the Benedict's test.
A red precipitate (copper oxide) shows that a reducing sugar is present, with NO indication of the exact amount
82
Describe the term "semi-quantitative" in relation to the Benedict's test.
The more colour changes seen on heating with Benedict's, the more reducing sugar can be estimated to be in the sample being tested
83
Describe the term "quantitative" in relation to the Benedict's test.
If you weighed the amount of copper oxide precipitate then this would give you a numerical value for the amount.
84
What is a colorimeter?
Equipment which quantitatively measures the absorbance or transmission of light by a coloured solution.
85
As the concentration of a solution increases, what happens to the absorbance and transmission of light?
more light is absorbed and less light is transmitted
86
how should an appropriate filter be chosen when using a colorimeter?
use a filter with a complementary colour to the colour of the solution to maximise the absorption of light
87
how is Benedict's reagent used with a colorimeter?
quantitative Benedict's is used, this forms a white precipitate and the blue colour of the solution fades with the presence of reducing sugars. the opacity of the precipitate increases with reducing sugar concentration
88
what colour filter is used with Benedict's in a colorimeter?
a red filter because the solution is blue and red is complementary of blue
89
how is a colorimeter calibrated?
using distilled water as a reference solution or by setting the colorimeter to 100%
90
how can percentage absorption be calculated from percentage transmission with a colorimeter?
100% - (% transmission) = % absorption
91
how are solutions prepared before being tested in the colorimeter?
filtering the solutions to remove the precipitate and leaving the unreacted Benedict's solution. The unreacted solution is also known as the supernatant
92
what are biosensors?
when biological components are used to determine the presence and concentration of molecule
93
what are the three components of biosensors?
molecular recognition, transduction and display
94
what is molecular recognition in biosensors?
when a protein (enzyme/antibody) or single strand of DNA (ssDNA) is immobilised to a surface such as a test strip. The molecule interacts/binds to the analyte.
95
what is the analyte in biosensors?
the compound or molecule under investigation
96
What is transduction in biosensors?
when the molecular recognition/interaction causes a change in a transducer. the transducer detects changes in the molecule (changes in pH etc) then responds.
The response may be the release of an immobilised dye (in a test strip) or an electric current if in a testing machine.
97
what is the display in biosensors?
when a visible qualitative or quantitative signal is given. e.g. a colour change on a test strip or a reading on a test machine
98
What type of graph is used with a colorimeter?
A calibration curve
