4.12
タンパク質とは?
タンパク質は、ペプチド結合によって結合したアミノ酸のポリマーです。 タンパク質とポリペプチドは、アミノ酸の長鎖を指すために同じ意味で使用されます。 ただし、ポリペプチドの分子量は 10,000 ダルトン未満ですが、タンパク質の分子量はそれより大きくなります。 アミノ酸が 20 個未満のポリペプチドは…
タンパク質は、アミノ酸の鎖であり、アミン基とカルボキシル基を含む化合物であり、Rで示されるさまざまな側鎖とともに、コアカーボンに結合しています。
アミノ酸は共有結合ペプチド結合を介して結合されており、コアに沿って繰り返される一連の原子はポリペプチド骨格と呼ばれます。
シーケンスはN末端から始まり、フリーアミノグループNH3+で、C末端、自由なカルボキシル基で終わります、COO-。
各タンパク質は、アミノ酸の数とその側鎖によって異なります。
20種類のサイドチェーンがあり、4つのグループのいずれかに分類されます。酸性アミノ酸は、アスパラギン酸やグルタミン酸と同様に、カルボキシル基を持つ側鎖を持っています。このため、生理学的pHで酸のように作用します。
塩基性アミノ酸は、側鎖にアミノ基を持ち、塩基のように働きます。
いくつかのアミノ酸は極性ですが、帯電していません。それらは親水性である傾向があり、折り畳まれたタンパク質の外側部分を構成し、そこで水性環境と自由に相互作用します。
最後に、アミノ酸の大きなグループには非極性側鎖が含まれています。それらは、グリシンのように単純なものから、プロリンやトリプトファンのように複雑なものまであります。
View the full transcript and gain access to JoVE Core videos
Q1: What are the basic building blocks that make up proteins?
Proteins are polymers composed of amino acids linked together by peptide bonds. These amino acids contain a central carbon atom bonded to an amino group, a carboxyl group, a hydrogen atom, and a distinctive side chain. The sequence and arrangement of these amino acids determine each protein's unique structure and function.
Q2: How do proteins differ from other biological macromolecules?
Proteins are distinct macromolecules composed of amino acids, while other compounds essential to human function include carbohydrates, lipids, and nucleic acids. Each macromolecule type has different elemental composition and structural organization. Proteins specifically contain nitrogen in their amino groups, making them unique among major biological polymers.
Q3: What are the two main categories of protein structure?
Proteins are classified into fibrous proteins and globular proteins based on their three-dimensional shape. Fibrous proteins are elongated and typically provide structural support, while globular proteins are compact and spherical, often serving dynamic roles like catalysis and transport. Both types are essential for different physiological functions.
Q4: Why is protein structure important for biological function?
A protein's three-dimensional structure determines its ability to perform specific functions in cells and tissues. The folding of amino acid chains creates active sites, binding regions, and structural features necessary for the role of proteins in the human body. Disruptions to this structure can impair or eliminate protein function.
Q5: What factors can cause proteins to lose their functional structure?
Proteins can undergo protein denaturation when exposed to extreme conditions such as high temperature, extreme pH, or certain chemical solvents. Denaturation disrupts the bonds maintaining protein structure, causing the molecule to unfold and lose its three-dimensional shape. This structural change typically results in loss of biological activity.
Q6: How do amino acid side chains influence protein properties?
Amino acid side chains vary in chemical composition, ranging from nonpolar hydrophobic groups to polar and charged groups. These differences determine how amino acids interact with each other and their environment, influencing protein solubility, charge, and overall three-dimensional folding. Side chain properties are fundamental to protein diversity and function.
Q7: What role do peptide bonds play in protein formation?
Peptide bonds are covalent linkages that connect amino acids together in a linear chain, forming the protein backbone. These bonds form between the carboxyl group of one amino acid and the amino group of the next through a dehydration reaction. The sequence of amino acids linked by peptide bonds determines the primary structure of every protein.