The Structure and Function of Large Biological Molecules

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10

Sickle-Cell Disease: A Change in Primary Structure

A slight change in primary structure can affect a protein’s structure and ability to function

Sickle-cell disease, an inherited blood disorder, results from a single amino acid substitution in the protein hemoglobin

Slide 88

Fig. 5-22

Primary

structure

Secondary

and tertiary

structures

Quaternary

structure

Normal

hemoglobin

(top view)

Primary

structure

Secondary

and tertiary

structures

Quaternary

structure

Function

Function

 subunit

Molecules do

not associate

with one

another; each

carries oxygen.

Red blood

cell shape

Normal red blood

cells are full of

individual

hemoglobin

moledules, each

carrying oxygen.

10 µm

Normal hemoglobin









1

2

3

4

5

6

7

Val

His

Leu

Thr

Pro

Glu

Glu

Red blood

cell shape

 subunit

Exposed

hydrophobic

region

Sickle-cell

hemoglobin





Molecules

interact with

one another and

crystallize into

a fiber; capacity

to carry oxygen

is greatly reduced.





Fibers of abnormal

hemoglobin deform

red blood cell into

sickle shape.

10 µm

Sickle-cell hemoglobin

Glu

Pro

Thr

Leu

His

Val

Val

1

2

3

4

5

6

7

Slide 89

Fig. 5-22a

Primary

structure

Secondary

and tertiary

structures

Function

Quaternary

structure

Molecules do

not associate

with one

another; each

carries oxygen.

Normal

hemoglobin

(top view)

 subunit

Normal hemoglobin

7

6

5

4

3

2

1









Glu

Val

His

Leu

Thr

Pro

Glu

Slide 90

Fig. 5-22b

Primary

structure

Secondary

and tertiary

structures

Function

Quaternary

structure

Molecules

interact with

one another and

crystallize into

a fiber; capacity

to carry oxygen

is greatly reduced.

Sickle-cell

hemoglobin

 subunit

Sickle-cell hemoglobin

7

6

5

4

3

2

1









Val

Val

His

Leu

Thr

Pro

Glu

Exposed

hydrophobic

region

Slide 91