Protein structure
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Transcript of Protein structure
1
Amino Acids, Proteins, and Enzymes
Primary and Secondary Structure
Tertiary and Quaternary Structure
Protein Hydrolysis and Denaturation
2
Primary Structure of Proteins
The particular sequence of amino acids that is the backbone of a peptide chain or protein
H3N CH
CH3
C
O
N
H
CH C
O
N
H
CH C
O
N
H
CH C O-
OCH
CH CH3
CH3
CH2
SH
CH2
CH2
S
CH3
+
Ala-Leu-Cys-Met
3
Secondary Structure – Alpha Helix
• Three-dimensional arrangement of amino acids with the polypeptide chain in a corkscrew shape
• Held by H bonds between the H of –N-H group and the –O of C=O of the fourth amino acid along the chain
• Looks like a coiled “telephone cord”
4
Secondary Structure – Beta Pleated Sheet
• Polypeptide chains are arranged side by side
• Hydrogen bonds form between chains
• R groups of extend above and below the sheet
• Typical of fibrous proteins such as silk
5
Secondary Structure – Triple Helix
• Three polypeptide chains woven together
• Glycine, proline, hydroxy proline and hydroxylysine
• H bonding between –OH groups gives a strong structure
• Typical of collagen, connective tissue, skin, tendons, and cartilage
6
Learning Check P1
Indicate the type of structure as
(1) primary (2) alpha helix
(3) beta pleated sheet (4) triple helix
A. Polypeptide chain held side by side by H bonds
B. Sequence of amino acids in a polypeptide chain
C. Corkscrew shape with H bonds between amino acids
D. Three peptide chains woven like a rope
7
Solution P1
Indicate the type of structure as
(1) primary (2) alpha helix
(3) beta pleated sheet (4) triple helix
A. 3 Polypeptide chain held side by side by H bonds
B. 1 Sequence of amino acids in a polypeptide chain
C. 2 Corkscrew shape with H bonds between amino acids
D. 4 Three peptide chains woven like a rope
8
Tertiary Structure
• Specific overall shape of a protein• Cross links between R groups of amino
acids in chain
disulfide –S–S– +
ionic –COO– H3N–
H bonds C=O HO–
hydrophobic –CH3 H3C–
9
Learning Check P2
Select the type of tertiary interaction as
(1) disulfide (2) ionic
(3) H bonds (4) hydrophobic
A. Leucine and valine
B. Two cysteines
C. Aspartic acid and lysine
D. Serine and threonine
10
Solution P2
Select the type of tertiary interaction as
(1) disulfide (2) ionic
(3) H bonds (4) hydrophobic
A. 4 Leucine and valine
B. 1 Two cysteines
C. 2 Aspartic acid and lysine
D. 3 Serine and threonine
11
Globular and Fibrous Proteins
Globular proteins Fibrous proteins
“spherical” shape long, thin fibers
Insulin Hair
Hemoglobin Wool
Enzymes Skin
Antibodies Nails
12
Quaternary Structure
• Proteins with two or more chains• Example is hemoglobin
Carries oxygen in blood
Four polypeptide chains
Each chain has a heme group to
bind oxygen
13
Learning Check P3
Identify the level of protein structure1. Primary 2. Secondary3. Tertiary 4. Quaternary
A. Beta pleated sheetB. Order of amino acids in a proteinC. A protein with two or more peptide chainsD. The shape of a globular proteinE. Disulfide bonds between R groups
14
Solution P3
Identify the level of protein structure1. Primary 2. Secondary3. Tertiary 4. Quaternary
A. 2 Beta pleated sheetB. 1 Order of amino acids in a proteinC. 4 A protein with two or more peptide chainsD. 3 The shape of a globular proteinE. 3 Disulfide bonds between R groups
15
Protein Hydrolysis
• Break down of peptide bonds • Requires acid or base, water and
heat• Gives smaller peptides and
amino acids • Similar to digestion of proteins
using enzymes• Occurs in cells to provide amino
acids to synthesize other proteins and tissues
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Hydrolysis of a Dipeptide
H3N CH
CH3
C
O
N
H
CH C
OCH2
OH
OH
+
H3N CH
CH3
COH
O
+ CH C
OCH2
OH
OHH3N
H2O, H+
++
heat
17
Denaturation
Disruption of secondary, tertiary and quaternary protein structure byheat/organics
Break apart H bonds and disrupt hydrophobic attractions acids/ bases
Break H bonds between polar R groups andionic bonds
heavy metal ions React with S-S bonds to form solids
agitation Stretches chains until bonds break
18
Applications of Denaturation
• Hard boiling an egg• Wiping the skin with alcohol swab for
injection• Cooking food to destroy E. coli.• Heat used to cauterize blood vessels• Autoclave sterilizes instruments• Milk is heated to make yogurt
19
Learning Check P4
What are the products of the complete hydrolysis of Ala-Ser-Val?
20
Solution P4
The products of the complete hydrolysis of Ala-Ser-Val are
alanine
serine
valine
21
Learning Check P5
Tannic acid is used to form a scab on a burn. An egg becomes hard boiled when placed in hot water. What is similar about these two events?
22
Solution P5
Acid and heat cause a denaturation of protein. They both break bonds in the secondary and tertiary structure of protein.