The Structure and Function of Large Biological Molecules

Page
11

Fig. 5-22c

Normal red blood

cells are full of

individual

hemoglobin

molecules, each

carrying oxygen.

Fibers of abnormal

hemoglobin deform

red blood cell into

sickle shape.

10 µm

10 µm

Slide 92

What Determines Protein Structure?

In addition to primary structure, physical and chemical conditions can affect structure

Alterations in pH, salt concentration, temperature, or other environmental factors can cause a protein to unravel

This loss of a protein’s native structure is called denaturation

A denatured protein is biologically inactive

Slide 93

Fig. 5-23

Normal protein

Denatured protein

Denaturation

Renaturation

Slide 94

Protein Folding in the Cell

It is hard to predict a protein’s structure from its primary structure

Most proteins probably go through several states on their way to a stable structure

Chaperonins are protein molecules that assist the proper folding of other proteins

Slide 95

Fig. 5-24

Hollow

cylinder

Cap

Chaperonin

(fully assembled)

Polypeptide

Steps of Chaperonin

Action:

An unfolded poly-

peptide enters the

cylinder from one end.

1

2

3

The cap attaches, causing the

cylinder to change shape in

such a way that it creates a

hydrophilic environment for

the folding of the polypeptide.

The cap comes

off, and the properly

folded protein is

released.

Correctly

folded

protein

Slide 96

Fig. 5-24a

Hollow

cylinder

Chaperonin

(fully assembled)

Cap

Slide 97

Fig. 5-24b

Correctly

folded

protein

Polypeptide

Steps of Chaperonin

Action:

1

2

An unfolded poly-

peptide enters the

cylinder from one end.

The cap attaches, causing the

cylinder to change shape in

such a way that it creates a

hydrophilic environment for

the folding of the polypeptide.

The cap comes

off, and the properly

folded protein is

released.

3

Slide 98

Scientists use X-ray crystallography to determine a protein’s structure

Another method is nuclear magnetic resonance (NMR) spectroscopy, which does not require protein crystallization

Bioinformatics uses computer programs to predict protein structure from amino acid sequences