《食品化学 Food Chemistry》课程教学课件（讲稿，英文版）Proteins

Proteins

Proteins

Definition z Protein from the Greek proteios, meaning primary. z Proteins are the work horses of biological systems. – They play key roles in constructing and maintaining living cells z Our genes code for proteins z Proteins are polymers of amino acids

Definition z Protein from the Greek proteios, meaning primary. z Proteins are the work horses of biological systems. – They play key roles in constructing and maintaining living cells z Our genes code for proteins z Proteins are polymers of amino acids

Proteins are: Polypeptides + (cofactors, coenzymes, prosthetic groups, other modifications) z Polypeptides are covalently linked α-amino acids z Cofactors are non-amino acid components e.g. metal ions like Zn2+ in carboxypeptidase z Coenzymes are organic cofactors e.g. nucleotides in lactate dehydrogenase z Prosthetic groups are covalently attached cofactors e.g. heme in myoglobin

Proteins are: Polypeptides + (cofactors, coenzymes, prosthetic groups, other modifications) z Polypeptides are covalently linked α-amino acids z Cofactors are non-amino acid components e.g. metal ions like Zn2+ in carboxypeptidase z Coenzymes are organic cofactors e.g. nucleotides in lactate dehydrogenase z Prosthetic groups are covalently attached cofactors e.g. heme in myoglobin

Roles played by proteins include z Enzymes (biological catalysts) z Hormones z Storage proteins z Transport proteins z Structural proteins z Protective proteins z Contractile proteins z Toxic proteins

Roles played by proteins include z Enzymes (biological catalysts) z Hormones z Storage proteins z Transport proteins z Structural proteins z Protective proteins z Contractile proteins z Toxic proteins

Food Proteins z Palatable z Digestible z Non-toxic z Available Economically

Food Proteins z Palatable z Digestible z Non-toxic z Available Economically

Proteins in the Diet z 9 of the 20 amino acids must be obtained from the diet z These are referred to as the essential amino acids. – Histidine – Isoleucine – Leucine – Lysine – Methionine – Phenylalanine – Threonine – Tryptophan – Valine z Proteins are also the major source of nitrogen in the diet

Proteins in the Diet z 9 of the 20 amino acids must be obtained from the diet z These are referred to as the essential amino acids. – Histidine – Isoleucine – Leucine – Lysine – Methionine – Phenylalanine – Threonine – Tryptophan – Valine z Proteins are also the major source of nitrogen in the diet

( ) 20 Amino Acids Primary Secondary Tertiary Quaternary Denatured Coded in DNA Self assembly to a single (native) structure. Depends on primary structure and solution conditions Common in foods. Many non-native forms depending on protein structure, solution conditions (& history) and ingredient interactions Protein Structure

( ) 20 Amino Acids Primary Secondary Tertiary Quaternary Denatured Coded in DNA Self assembly to a single (native) structure. Depends on primary structure and solution conditions Common in foods. Many non-native forms depending on protein structure, solution conditions (& history) and ingredient interactions Protein Structure

z Protein are polymers of α-amino acids z The amino acids used to make proteins are 2-amino￾carboxylic acids. z The α (alpha) carbon is the carbon to which a functional group is attached. Protein Structure and Function

z Protein are polymers of α-amino acids z The amino acids used to make proteins are 2-amino￾carboxylic acids. z The α (alpha) carbon is the carbon to which a functional group is attached. Protein Structure and Function

z structure and chemical functionality z chirality z acid-base properties z capacity to polymerize Properties of Amino Acids

z structure and chemical functionality z chirality z acid-base properties z capacity to polymerize Properties of Amino Acids

Properties of Amino acids z Aliphatic chains: Gly, Ala, Val, Leu, and Ile – Pro? z Hydroxyl or sulfur side chains: Ser, Thr, Cys, Met z Aromatic: Phe, Trp, Tyr z Basic: His, Lys, Arg z Acidic and their amides: Asp, Asn, Glu, Gln hydrophobicity

Properties of Amino acids z Aliphatic chains: Gly, Ala, Val, Leu, and Ile – Pro? z Hydroxyl or sulfur side chains: Ser, Thr, Cys, Met z Aromatic: Phe, Trp, Tyr z Basic: His, Lys, Arg z Acidic and their amides: Asp, Asn, Glu, Gln hydrophobicity