Biochemistry Quiz on Proteins and Amino Acids

Cysteine

• Cysteine contains a sulfhydryl group (-SH) which is unique among standard amino acids
• This sulfhydryl group is crucial for disulfide bond formation, which contributes to the tertiary structure of proteins
• Cysteine dimerizes through a disulfide bond, a covalent link formed between the sulfhydryl groups of two cysteine residues
• The dimerization process is reversible and can be influenced by factors such as pH and reducing agents

Zwitterions

• Amino acids are considered zwitterions because they contain both a positively charged amino group (-NH3+) and a negatively charged carboxyl group (-COO-)
• In their zwitterionic form, amino acids exist in solution

Carboxyl Groups

• When carboxyl groups in amino acids release protons, they become negatively charged (COO-)

Peptide Chains

• The suffix "-peptide" is used to name peptide chains

Peptides

• Peptides are polymers formed by the linkage of amino acids through peptide bonds
• Peptide bonds are formed through a dehydration reaction between the carboxyl group of one amino acid and the amino group of another

α-amino acids in solution:

• In solution, α-amino acids exist in equilibrium between their zwitterionic and non-zwitterionic forms

The sulfhydryl group:

• The sulfhydryl group in cysteine contributes to its reactivity and allows it to participate in disulfide bond formation, which is vital for protein structure.

Myoglobin

• Myoglobin's primary function in muscles is to store oxygen

Albumin

• Albumin, a type of protein, plays a crucial role in maintaining fluid balance between blood and surrounding tissue

Collagen

• Collagen is a protein composed of three polypeptide chains twisted together to form a triple helix
• This unique structure is a key component of collagen's strength and flexibility

Ferritin

• Ferritin is an iron-storage protein

Globular proteins

• Globular proteins are characterized by their compact, spherical shape

Transmembrane Channels

• Transmembrane channels belong to the class of integral membrane proteins

Protein Denaturation

• During protein denaturation, the 3D structure of a protein is disrupted, leading to loss of function
• Denaturation can be caused by factors like heat, pH changes, and chemical agents
• Denaturation disrupts non-covalent bonds such as hydrogen bonds, hydrophobic interactions, and ionic interactions

Glycoproteins

• Glycoproteins play essential roles in various biological systems, including cell recognition, adhesion, and immune response

Structural Proteins

• Actin, collagen, elastin, and keratin are primarily structural proteins

Proteins and Cooking

• Cooking can denature proteins, causing them to lose their native shape and function
• Denaturation alters their texture and taste

Collagen's structural role

• Collagen is a major structural protein in the human body, providing strength and support to connective tissues like skin, tendons, and bones

Buffer Proteins

• Buffer proteins in the body help maintain a stable pH by resisting changes in pH

Hydrophobic Amino Acid Residues in Membrane Proteins

• The hydrophobic amino acid residues in membrane proteins are responsible for anchoring the protein within the hydrophobic interior of the cell membrane

α-Keratin

• α-Keratin is a protein that is primarily composed of α-helices
• It is a key component of hair, skin, and nails

The functional versatility of proteins

• Proteins are incredibly versatile molecules, performing a wide range of functions in living organisms
• Their structure, function, and location are intricately linked, enabling them to perform diverse tasks.

Coagulation:

• Coagulation in the context of proteins refers to the process of protein aggregation or clumping
• Coagulation usually involves the formation of a gel-like network

Secondary structure stabilization

• Hydrogen bonds are the primary force that stabilizes the secondary structure of proteins, such as α-helices and β-sheets

Stabilizing forces in proteins

• Disulfide bonds are covalent and strong stabilizing forces in proteins

Hydrogen bonds and α-helices

• Hydrogen bonds in α-helices form between the carbonyl oxygen of one amino acid and the amino hydrogen of an amino acid that is four residues away

Interactions between charged side chains

• Ionic interactions are attractive forces between charged side chains of amino acids

β-pleated sheet structure

• The β-pleated sheet structure in proteins is characterized by polypeptide chains arranged side by side, forming a sheetlike structure

Hydrophobic Interactions:

• Hydrophobic interactions stabilize protein structures due to the tendency of nonpolar amino acids to avoid contact with water, clustering together within the protein

Stabilizing Interactions

• Hydrophobic interactions, hydrogen bonds, ionic interactions, and disulfide bonds are essential for protein structure stabilization
• Van der Waals interactions are another type of stabilizing force

Amino acid R groups orientation in α-helix

• In an alpha helix, the amino acid R groups (side chains) point outwards from the helix axis

Insulin's Primary Structure

• The primary structure of insulin is highly conserved across different species

Peptide linkages

• Peptide linkages are rigid due to partial double-bond character

Isomerism in peptide bonds

• Cis-trans isomerism can occur around the C—N bond in peptides
• The trans isomer is more stable and commonly found due to steric hindrance in the cis isomer

Secondary arrangement of proteins

• The secondary structure of proteins refers to the local, regular arrangement of polypeptide chains

Preferred orientation of the trans isomer

• The trans isomer in peptide bonds is preferred due to its lower steric hindrance

Alpha-helix:

• The α-helix structure resembles a coiled spring

Peptide bond planar structure

• Six atoms lie in the same plane formed by a peptide bond: Cα, C, N, O, Cα', and H
• These atoms are linked by a peptide bond and form a planar structure

Primary protein structure

• The primary structure of a protein refers to the linear sequence of amino acids connected through peptide bonds

Test your knowledge on unique features of amino acids, particularly cysteine, and their roles in proteins. This quiz covers aspects of protein structure, function, and characteristics of various types of proteins. Challenge yourself to understand the complexities of biochemistry relating to peptides and their functions in biological systems.