Chp. 18 Protein Structure/Function Flashcards
Exam 2
What does the term ‘protein’ mean?
Of first importance
List the biological functions of proteins
- Enzymes
- Defense proteins
- Transport proteins
- Regulatory proteins
- Structural proteins
- Movement proteins
- Nutrient proteins
What is the general structure of an α-amino acid?
Contains both an amine and an acid
How many common α-amino acids are found in nature?
20
19/20 stereoisomers, not glycine
What is a zwitterion?
A neutral molecule with equal number of + and − charges
What is the isoelectric point?
The pH point at which there is no net charge on the zwitterions
Which amino acid is not chiral?
Glycine
What are the classes of amino acids based on their R groups?
- Hydrophobic amino acids
- Hydrophilic amino acids
- Polar, neutral amino acids
- Negatively charged amino acids
- Positively charged amino acids
What is the peptide bond?
Linkage between the carboxyl group of one amino acid and the amino group of another
What is the primary structure of proteins?
The amino acid sequence of the polypeptide chain; A result of covalent bonding between the peptide bonds (amino acids)
What results in the formation of secondary structure in proteins?
Hydrogen bonding between amide hydrogens and carbonyl oxygens of the peptide bonds (how they fold in a repeated primary sequence)
What is the most common type of secondary structure?
α-Helix
Describe the structure of an α-helix
- Coiled, helical
- Right-handed (clockwise)
- 3.6 amino acids per turn
- Carbonyl O links with Amide H: 4 amino acids away
What is the second most common type of secondary structure?
β-Pleated sheet
What defines tertiary structure in proteins?
The overall 3-D folding of the entire polypeptide chain
List the types of interactions that maintain tertiary structure
- Disulfide bridges
- Salt bridges
- Hydrogen bonds
- Hydrophobic interactions
What is quaternary structure?
The arrangement of subunits or peptides that form a larger protein; tertiary structures coming together
What types of proteins require prosthetic groups?
- Nucleoproteins
- Lipoproteins
- Glycoproteins
- Phosphoproteins
- Hemoproteins
- Metalloproteins
What is the role of myoglobin?
Oxygen storage protein of skeletal muscle
What causes denaturation of proteins?
Extremes of temperature and pH
What is the difference between denaturation and hydrolysis?
Denaturation is the loss of organized structure; hydrolysis breaks proteins into smaller peptides or amino acids
What are essential amino acids?
Amino acids that cannot be made in the body
What are nonessential amino acids?
Amino acids that can be made in the body
List the essential amino acids
- Isoleucine
- Leucine
- Lysine
- Methionine
- Phenylalanine
- Threonine
- Tryptophan
- Valine
- Histidine (for infants)
List the nonessential amino acids
- Alanine
- Arginine (conditionally essential)
- Asparagine
- Aspartate
- Cysteine (conditionally essential)
- Glutamate
- Glutamine
- Glycine
- Proline
- Serine
- Tyrosine (conditionally essential)
What is the primary effect of increasing temperature on proteins?
Increases the rate of molecular movement
How does changing pH affect protein structure?
Interferes with salt bridges and hydrogen bonds stabilizing the tertiary structure
Protein Biological Function: Enzymes
Example?
Biological Catalyst
Protein Biological Function: Defense Proteins
Example?
Antibodies: produced by the immune system in response to antigens
Protein Biological Function: Transport Proteins
Example?
Hemoglobin: carries oxygen from the lungs to the tissues/organs
Protein Biological Function: Regulatory Proteins
Example?
Glucose Regulation
Protein Biological Function: Structural Proteins
Example?
Actin: gives structure/shape in the cytoskeleton
Protein Biological Function: Movement Proteins
Example?
Actin & Myosin Proteins work together to create movement inside the cell
Protein Biological Function: Nutrient Proteins
Example?
Food from Diet (further broken down into amino acids for energy)
Amino Acid Configuration Isolated From Proteins is
L-
(most oxidized end of the molecule: carbonyl is at the top when drawing)
What is a dipeptide?
A dipeptide is a molecule formed from two amino acids linked by a peptide bond.
True or False: Dipeptides are the simplest form of peptides.
True
Fill in the blank: A dipeptide consists of __ amino acids.
2
Which type of bond connects the amino acids in a dipeptide?
Peptide bond
What Produces a Dipeptide
Condensing/Dehydrating 2 amino acids
N-terminal Amino Acid
Amino Acid with a free α-NH3+ group
C-terminal Amino Acid
Amino Acid with a free
-COO (carboxyl) group
β-Pleated Sheet
*All of Carbonyl O and Amide H are involved in H bonding
*Parallel if the N termini are head to head
*Perpendicular (antiparallel) if the N-terminus of one chain is aligned with the C-terminus of the other
Globular Proteins
*Formed Spontaneously
*Maintained by interactions among the side chains/R-groups
*Apart of tertiary structure of proteins
Tertiary Structure: Disulfide Bridges
Between 2 cysteine Residues ex. Curling/Straightening Hair
Tertiary Structure: Salt Bridges
Between ionic side chains
-COO and NH3+ (carboxyl and amine)
Tertiary Structure: Hydrogen Bonds
Between polar residue side chains
Tertiary Structure: Hydrophobic Interactions
2 nonpolar groups are attracted by a mutual repulsion of water
prosthetic groups
a special tool that gets attached to a protein, and it helps the protein do its job better. It’s not made of protein itself, but it sticks to the protein really tightly
Fibrous Protein Functions
*Mechanical strength
*Structural Components (actin, keratin)
*Movement (actin, myosin)
Globular Protein Functions
*Transport: nonpolar, hemoglobin, myoglobin
*Regulatory: polar insulin
*Enzymes
Hemoglobin
oxygen transport protein of higher animals
Denature Agents
*Organic Solvents
-interfere w/ hydrophobic interactions
*Detergents
-polar head and hydrophobic tail & interferes w/ hydrophobic interactions
*Heavy Metals
-bind to (-) charged amino acid & interfere w/ disulfide bridges
*Mechanical Stress
-lots of force on proteins break weak interactions
Myoglobin
oxygen storage protein of skeletal muscle
