Porphyrins

Question 1

Porphyrins

Answer 1

• heterocyclic macrocycles
• composed of four modified pyrrole subunits interconnected at their α carbon via methine bridges (=CH-)
• aromatic
• they obey Huckel´s rule for aromaticity

Question 2

What is the most abundant porphyrin in the human body called?

Answer 2

heme

Question 3

What is heme?

Answer 3

• the pigment in red blood cells

- a cofactor of the protein hemoglobin

Question 4

What is the parent porphyrin called?

Answer 4

porphine

Question 5

What is the substituted porphines called?

Answer 5

pophyrin

Question 6

What is heme?

Answer 6

the prosthetic group of proteins called homoproteins.

Question 7

Homoproteins

Answer 7

• hemoglobin
• myoglobin
• cytochromes
• catalase
• peroxidase

Question 8

Homoproteins facts

Answer 8

they are rapidly synthesized and degraded

Question 9

What is the synthesis and degradations of porphyrins an important part of?

Answer 9

synthesis and degradation of porphyrins is an important part in the nitrogen balance

Question 10

What does porphyrin consist of?

Answer 10

porphyrin consist of four pyrrole rings, A, B, C, and D interconnected by methine bridges (=CH-), and different lateral substituents (O)

Question 11

What is the precursor of porphyrin called?

Answer 11

porphyrogens

Question 12

What color is porphyrin?

Answer 12

• purple (?)

- colorful

Question 13

What is the most abundant derivative of porphyrin?

Answer 13

porphyrin IX - i.e. heme

Question 14

What varieties of heme do we have?

Answer 14

• A
• B
• C

Question 15

Heme A

Answer 15

• found in cytochrome a+a3

- differs from heme B and C by side substituents

Question 16

Heme C

Answer 16

• acts in cytochrome C, where it binds to the atom residues His 18 and Met80
• vinyl groups of heme C forms covalent bonds with -SH residues of Cys14 and Cys 17 of the enzyme protein

Question 17

Ion Fe2+/Fe3+ forming a part of Heme B of cytochrome b

Answer 17

• is not able to bond with O2 or with H2O

- participates in the transport of electrons through respiratory chain only

Question 18

Heme B

Answer 18

• creates two additional coordination bonds with a water molecule and O2 and the nitrogen atom og His being the part of globin
• in this way the heme of hemoglobin or myoglobin can alternatively attach and detach the molecule of oxygen

Question 19

Chlorophyl

Answer 19

• a green pigment found in almost all plants, algae, and cyanobacteria
• allows plants to obtain energy from lights

Question 20

What does the pophyrins rings of chlorophyl contain?

Answer 20

Mg2+ ion

Question 21

Chlorophyl a:

Answer 21

contains unsaturated alcohol -pythol- bounded at position 7 by ester bond

Question 22

Chlorophyl b:

Answer 22

differs from “chlorophyl a” by formyl group at position 3

Question 23

Chlorophyl c:

Answer 23

does not contain phytol, and at the position 4, instead of ethyl group, propanate is connected

Question 24

Chlorophyl d

Answer 24

instead vinyl group at the 2 position, contains formyl group

Question 25

Where does synthesis of heme occur?

Answer 25

in the bone marrow precursor´s red blood cells and in the liver