Exam 2: Biochem 2.1

Front 1

Where does myoglobin transport 02? Hemoglobin?

Back 1

Through cytosol to mitochondria; (Hb) from lungs to peripheral tissues, and C02 and H+ from periph to lungs

Front 2

simple protein

Back 2

polypeptide only

Front 3

conjugated protein

Back 3

polypeptide and cofactor

Front 4

cofactor (prosthetic group)

Back 4

nonpeptide group essential for protein's function

Front 5

Mb & Hb are __________ proteins

Back 5

conjugated

Front 6

What prosthetic group does Mb contain? Hb?

Back 6

Both contain heme

Front 7

Structure of Hb

Back 7

4 subunits, each with 1 polypeptide chain (alpha or beta) and 1 heme. Subunits are similar to Mb

Front 8

Ionic metal bonding

Back 8

-electrons not shared
-ion-ion/ion-dipole
-transient complexes
-ex. Na+, K+, Mg2+. Ca2+ (alkali and alkaline earth metals)

Front 9

Covalent metal bonding

Back 9

-electrons shared
-both elec. from ther nonmetal atom (coordinate covalent)
-stable
-ex. iron, zinc, copper (transitional metals)

Front 10

Ferrous Iron

Back 10

Fe2+

Front 11

Ferric Iron

Back 11

Fe3+ (hemin)

Front 12

Heme structure (6)

Back 12

1) Protoporphyrin IX (organic part) + heme
2) Large (>70 atoms)
3) Planar
4) aromatic
5) Nonpolar except for 2 COO-
6) Unshared e- pairs of N bonded to Fe/delocalized into ring system

Front 13

Iron in heme (3)

Back 13

1) Tightly bound to 4 N (coordinate covalent bond)
2) Can bind 2 more atoms
3) ferrous (Fe2+)

Front 14

Heme-polypeptide interactions (3)

Back 14

1)Nonpolar. Pep has pocket for heme
2) coordinate covalent bond (btw hist and iron
3) Ion pairing (heme COO- groups with 2 cationic side chains - arg45 and his97)

Front 15

Coordinate covalent bond of heme-polypeptide

Back 15

1)btw his side chain and iron
2) 5th coordination position of iron (?)
3) Proximal his: 93, or F8 in Mb helix (?)

Front 16

O2 binding site (4)

Back 16

1)Fe2+ (e-'s come from O)
2)6th coordination position
3)opposite of proximal his binding
4)near to a distal his chain, which stablizes

Front 17

Oxygenation vs Oxidation of Heme

Back 17

Oxygenation: heme+O2 <==> heme-O2
-fast, reversible.
-e- pair shared
Oxidation: heme-O2 --> hemin +O2- (superoxide)
-irreversible
-e- transferred
-hemin cannot bind O2

Front 18

Methemoglobinemia

Back 18

1) metHb or metMb. Hb/Mb with hemin instead of heme
2) result of oxidation
3) reversed in vivo by enzymes and reductants
4) can result in cyanosis
5) possible causes: food additives, drugs, enzyme deficiency
6) treated with reducing agents (eg - vita C)

Front 19

What is the result of methemoglobinemia

Back 19

Cyanosis (>10% Hb is met Hb)

Front 20

Main chain structure of Mb

Back 20

75% alpha helixes
8 helixes in 2 layers linked by loops
common structure - "globin fold"

Front 21

Mb structure: Side chains

Back 21

1) Polar on surface/Nonpolar in interior
2) Folded has heme site
3) Bound heme is less oxidizable

Front 22

O2 disassociation equation

Back 22

Y = pO2/(pO2+P50)

Y = fractional saturation
p50 = pO2 required for 50% saturation

Front 23

p50 for Mb

Back 23

1 torr

Front 24

O2 binding curve of Mb (3)

Back 24

-hyperbolic
-as the pressure of O2 increases, the amount of O2 needed for half saturation (p50) of Mb increases.
-i.e. as the amount of O2 increases, the affinity for O2 decreases

Front 25

p50 (3)

Back 25

-O2 level needed for half saturation
-pO2 where [Mb=MbO2]
-p50 INCREASE means O2 affinity DECREASE

Front 26

p50 of Hb

Back 26

26 torrs

Front 27

Diff btw Mb & Hb binding curves

Back 27

- Hb more to right :. Hb is ALWAYS less saturated than Mb
- Hb curve sigmoidal (Mb is hyperbolic)
- Hb curve is steeper in middle :. Hb is more sensitive to pO2 changes in middle