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Option Chemistry > Biological Pigments > Flashcards

Biological Pigments Flashcards

1
Q

What is the function of pigment molecules

A

absorb light in the visible region of the spectrum (400-700nm)

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2
Q

Define biological pigments

A

coloured compounds produced by living organisms

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3
Q

What are the characteristics of conjugated systems

A

alternating single and double bonds
- region of overlapping p orbitals with delocalised pi electrons

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4
Q

What is the effect of a conjugated system on their ability to absorb light

A
  • Large conjugated systems absorb light of lower energy (longer wavelength)
  • Small conjugated systems absorb light of higher energy (shorter wavelength)
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5
Q

What are the characteristics of Porphyrin Pigments

A
  • planar ring structures with extensive conjugated systems
  • chelates of metals with large nitrogen containing macrocyclic ligands
  • made up of four rings that act as ligands
  • non-bonding pairs of electrons on the nitrogen atoms form coordinate covalent bonds with the central metal ion
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6
Q

What is the metal ion in chlorophyll

A

magnesium ion

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7
Q

Where is chlorophyll found

A

in plants (a biological pigment)

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8
Q

What does the thermal stability of chlorophyll depend on

A

The thermal stability of chlorophyll depends on the pH

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9
Q

Outline the thermal stability of chlorophyll

A

When heated, the cell membrane of the plant deteriorates releasing acids which decrease the pH
This magnesium ion in the porphyrin ring is displaced by 2H+ ions resulting in the formation of a brown colour

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10
Q

Examples of porphyrin pigments

A

Chlorophyll(s) (Magnesium)
Cytochromes (iron)
- Haemoglobin
- Myoglobin

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11
Q

The function/importance of nitrogen in porphyrin pigments

A
  • allows the ring to form 4 coordinate bonds. Because of this, porphyrin pigments are always found as chelates, the 4 nitrogens are bound to a central metal atom
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12
Q

What is a heme

A

the prosthetic group of haemoglobin, myoglobin and the cytochromes

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13
Q

How many coordinate bonds can iron(II) heme form

A

2

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14
Q

Properties of haemoglobin

A

It contains 4 heme groups, each bound within a polypeptide chain (quaternary structure)
The porphyrin group is bonded to an iron(III) ion

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15
Q

Properties of myoglobin

A

A protein composed of a single polypeptide chain and one heme group
The porphyrin group is bonded to an iron(III) ion
Myoglobin only binds to 1 O2 molecule compared to 4 in haemoglobin

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16
Q

Characteristics of Carotenoids

A
  • have extensive conjugated systems
  • exhibit strong light absorption in the blue portions of the visible spectrum
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17
Q

How are biological pigments produced

A

metabolism

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18
Q

What is the function of haemoglobin

A

carries oxygen in the blood

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19
Q

What is the function of myoglobin

A

stores oxygen

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20
Q

How many heme groups does hemoglobin contain

A

4 (oxygen molecules)

21
Q

How many heme groups does myoglobin contain

A

1 (oxygen molecule)

22
Q

What central metal ion do cytochromes have

A

iron

23
Q

Cytochromes can interconvert between what and when

A

iron (II) –> iron (III)
- redox reactions

24
Q

Outline the first step of oxygen dissociation

A
  • binding of oxygen is known as cooperative binding
  • when oxygen binds to to protein it changes its conformational shape (active site)
  • then binding affinity for oxygen increases
25
Q

Outline the second step of oxygen dissociation

A

After a lot of oxygen is bound, the haemoglobin is saturated, and binding more oxygen is therefore difficult.
- lower binding affinity for oxygen

26
Q

What is the shape of the graph for oxygen dissociation

A

sigmoidal shape

27
Q

Label the axis for the oxygen dissociation graph

A

x-axis: partial pressure of O2
y-axis: % saturation of O2

28
Q

outline the relationship between partial pressure and the amount of oxygen carried by haemoglobin

A
  • high partial pressure = each haemoglobin can carry maxim. of 4 oxygen molecules
  • low partial pressure = each haemoglobin releases some of the oxygen it’s carrying
29
Q

Factors that favour oxygen release

A
  • increased CO2
  • increased acidity (due to CO2)
  • increased temperature
30
Q

Describe the oxygen dissociation graph when there is an increase in CO2

A

the graph moves inwards, the curve shifts to the right

31
Q

Foetal vs Adult Haemoglobin oxygen dissociation

A

foetal has a higher affinity for oxygen (binds better)

32
Q

Why does foetal haemoglobin have a higher affinity than adult haemoglobin

A

foetal: 2 alpha + 2 gamma chains
adult: 2 alpha + 2 beta chains

33
Q

Describe the oxygen dissociation graph when comparing foetal and adult haemoglobin

A

graph shifts to the left for foetal (goes outwards)

34
Q

What is the effect of carbon monoxide on the binding of oxygen to haemoglobin

A

it acts as a competitive inhibitor of oxygen and prevents oxygen from binding to the haemoglobin

35
Q

What are the con’s of CO

A

toxic for humans

36
Q

What are the properties of Anthocyanins

A
  • aromatic
  • water-soluble
  • found in plants
37
Q

What affects the colour of Anthocyanins

A

ph and metal ions
- react with H+ or OH-
- leads to changes in the conjugation of the molecule, therefore changing its colour.

38
Q

What could be one of the uses of Anthocyanins

A

indicator

39
Q

HOW TO BREAK ANTHROCYANINS

A
  • break down at high temperatures
  • also at extreme pHs
  • the rings break which breaks the conjugation
  • destroys the colour
40
Q

Properties of chlorophyll and carotenoids

A
  • non-polar/lipid-soluble
  • involved in photosynthesis
41
Q

What are the factors that affect the stability of chlorophyll

A
  • temperature
  • ph
  • light
42
Q

How does temperature affect the stability of chlorophyll

A

Magnesium ion is lost from porphyrin ring
Damaged more easily than carotenoids (easier to lose Mg ion than break carotenoid)

43
Q

How does pH affect the stability of chlorophyll

A

Hydrogen ions react with nitrogens in the porphyrin ring and kick out the magnesium ion

44
Q

How does light affect the stability of chlorophyll

A

Double bonds are oxidised as catalysed by light (destroys them)

45
Q

Difference between α-carotene and β-carotene

A

β-carotene: more conjugated so absorbs lower wavelengths
α-carotene: less conjugated so absorbs higher wavelengths

46
Q

What affects the stability of carotenoids

A

heat and light

47
Q

How does heat/temperature affect the stability of carotenoids

A

Heat breaks double bonds and therefore conjugation

48
Q

How does light affect the stability of carotenoids

A

Light oxidises the double bonds and thus destroys them

49
Q

Why do biological pigments absorb light

A

for photosynthesis (production of glucose)

Option Chemistry (10 decks)

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