Chemistry of the Kitchen:   Proteins

X.  Proteins

A.  Functions of Proteins

1.  proteins have the most diverse roles in the cell (cf carbohydrates/lipids)

a.  structural proteins

b.  hormonal proteins

c.  receptor proteins

d.  transport proteins

e.  sensory proteins

f.  storage proteins

g.  defensive protein

h.  regulatory proteins

i.  motor proteins

2.  Is this all that proteins do?

3.  What role does shape play in protein function?

B.  Models of Proteins

1.  proteins are polymers of _____________________

2.  structural elements of the polymer:   main chain (backbone) and side chains

3.  so complex, must use models that omit the details

a.  bead-chain model

b.  ribbon model

c.  space-filling model

C.  Levels of Structure

1.  four levels of structure

a.  primary structure

b.  secondary structure

c.  tertiary structure

d.  quaternary structure

2.  Where can I see the structures of real proteins?

http://molbio.info.nih.gov/cgi-bin/pdb

http://expasy.hcuge.ch/

D.  Primary Structure (1^o)

1.  Intro

a.  primary structure = sequence of amino acids

b.  amino acids:

i.  ________ different kinds of amino acids

ii.  What are the amino acids and their abbreviations?

 

c.  How important is primary structure?

d.  Why is such a great variety of proteins possible?

2.  Amino Acid Residue

a.  side chain (R)

b.  backbone

3.  Free Amino Acid

a.  parts of a free amino acid:

 

b.  How does water affect free amino acids?

 

4.  Linking Amino Acids

a.  amino acids linked together in the protein chain by peptide bonds

b.  anatomy of a peptide bond:

 

c.  What determines the amino acid sequence?

5.  Types of amino acids

a.  types of amino acids

i.  polar

 

ii.  nonpolar

 

iii.  acidic

 

iv.  basic

 

b.  Why do we need to know the four catagories of side chains?

E.  Secondary Structure (2^o)

1.  Intro

a.   repeating patterns of the backbone

b.   stabilized by hydrogen bonds

c.  ribbon models show outline of backbone

d.  examples

e.  How important is secondary structure?

2.  Alpha Helix

a.  corkscrew pattern

b.  where are the side chains?

c.  hydrogen bonds

3.  Pleated Sheet

a.  flat, pleated pattern

b.  where are the side chains?

c.  hydrogen bonds

F.  Tertiary Structure (3^o)

1.  Intro

a.  tertiary structure = overall folding pattern

b.  three kinds of forces maintain tertiary structure:

i.  ionic

ii.  disulfide bridge

iii.  polar

c.  What do the three stabilizing forces have in common?

d.  Why is tertiary structure different for each kind of protein?

2.  Proteins in water

a.  water forms a cage that keeps a protein folded...

b.  Is it true that cold alcohol can cook an egg by replacing water?

3.  Polar Forces in 3^o structure

a.  folding depends on polar side chains and nonpolar side chains

b.  two proteins fold differently because the nonpolar side chains are in different locations within the protein

4.  Protein temperature sensitivity

a.  tertiary structure is delicate because it depends on weak polar forces

b.  causes protein structure to be dependent on T

c.  What happens to the structure of the protein as it gets hot?

d.  What's denaturation?

e.  Why does a little heat make enzymes work better?

5.  Ionic forcces in 3^o structure

a.  positively charged side chains attracted to negatively charged side chains

b.  what happens to these structures as the pH changes?

6.  Protein pH sensitivity

a.  Because folding depends on ionic bonds, changes in pH can reshape a protein (denature it)

b.  Why does protein function depend on pH?

7.  Disulfide bridges in 3^o structure

a.  occurs:

b.  covalent bond, therefore less sensitive to environment

 

G.  Quaternary Structure

1.  Intro

a.  two or more protein units binding together to form a functional protein

b.  What do proteins gain by binding together?

2.  Polar forces in 4^o structure

 

3.  Disulfide bridges in 4^o structure

a. 

b.  Does a hair stylist make disulfide bridges?

 

H.  Quality of protein

1.  do not store amino acids

2.  must get essential amino acids from diet

3.  animal sources are excellent sources of all 10 essential amino acids:  high quality proteins

4.  plant sources are less valuable:   low quality proteins

5.  vegetarians:  mix incomplete protein sources

I.  Structural changes in proteins

1.  taste change

2.  easier to digest

3.  change color, texture

4.  change enzyme function helps preserve food

5.  physical disruption

6.  chemical disruption

 

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