Protein: Difference between revisions
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A protein is a biological polymer which is made up of [[Amino acid|amino acids]]. The [[Amino acids|amino acids]] are joined together with a [[Peptide bond|peptide bond]] to form a [[Polypeptide|polypeptide]] chain. The [[Peptide bond|peptide bond]] is formed by joining the ɑ-carboxyl group of an [[Amino acid|amino acid to]] the ɑ-amino group of another [[Amino acid|amino acid]]<ref name="null">Berg et al., (2006) Biochemistry, 6th edition, New York. Pg 34</ref>. A protein can be made up of a single polypeptide chain or multiple [[Polypeptides|polypeptides]] linked together. There are three types of proteins: [ | A protein is a biological polymer which is made up of [[Amino acid|amino acids]]. The [[Amino acids|amino acids]] are joined together with a [[Peptide bond|peptide bond]] to form a [[Polypeptide|polypeptide]] chain. The [[Peptide bond|peptide bond]] is formed by joining the ɑ-carboxyl group of an [[Amino acid|amino acid to]] the ɑ-amino group of another [[Amino acid|amino acid]]<ref name="null">Berg et al., (2006) Biochemistry, 6th edition, New York. Pg 34</ref>. A protein can be made up of a single polypeptide chain or multiple [[Polypeptides|polypeptides]] linked together. There are three types of proteins: [[fibrous|fibrous]], [[Globular protein|globular]] and [[Membrane protein|membrane proteins]]. Examples of proteins include [[Enzyme|enzymes]], [[Receptor|receptors]] and [[Hormone|hormones.]] They are found in every form of life from [[Virus|viruses]] to [[Bacteria|bacteria]]; [[Yeast|yeasts]] to [[humans|humans]]. One important technique used to analyse proteins is [[SDS polyacrylamide-gel electrophoresis|SDS polyacrylamide-gel electrophoresis]] ([[SDS polyacrylamide-gel electrophoresis|SDS-PAGE]]). | ||
== Structure<br> == | == Structure<br> == | ||
A protein has several 'layers' of structure <ref>Elliott.W.H, Elliott.D.C (1997) Biochemistry and Molecular Biology. New York, United States:Oxford University Press.pp.47-49.ISBN 0199271992</ref>. The function of the protein is determined by its structure, therefore each layer is dependent on the next.<ref>Berg J., Tymoczko J and Stryer L. (2007) Biochemistry, 6th edition, New York: WH Freeman.</ref> | A protein has several 'layers' of structure <ref>Elliott.W.H, Elliott.D.C (1997) Biochemistry and Molecular Biology. New York, United States:Oxford University Press.pp.47-49.ISBN 0199271992</ref>. The function of the protein is determined by its structure, therefore each layer is dependent on the next.<ref>Berg J., Tymoczko J and Stryer L. (2007) Biochemistry, 6th edition, New York: WH Freeman.</ref> | ||
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=== Primary Structure === | === Primary Structure === | ||
The [[Primary structure|primary structure]] is the specific sequence of [[Amino acids|amino acids]] joined together by peptide bonds in a polypeptide chain. There are 20 different [[Amino acids|amino acids]] found in nature. The sequence of amino acids is determined by the [[DNA|DNA]] sequence that encodes for that particular protein. This is know as the [[Gene|gene]]. <br> | The [[Primary structure|primary structure]] is the specific sequence of [[Amino acids|amino acids]] joined together by peptide bonds in a polypeptide chain. There are 20 different [[Amino acids|amino acids]] found in nature. The sequence of amino acids is determined by the [[DNA|DNA]] sequence that encodes for that particular protein. This is know as the [[Gene|gene]]. <br> | ||
=== Secondary Structure<br> === | === Secondary Structure<br> === | ||
[[Secondary structure|Secondary structure]] is the first level of protein folding. The two main folding structures of a protein are the [[Alpha-helix|alpha-helix]] or the [[Beta-sheet|beta-sheet]] depending on the sequence of [[Amino acids|amino acids]]. This, in turn, allows the protein to have a [[Hydrophobic|hydrophobic]] core and a [[Hydrophilic|hydrophilic]] surface. The secondary structure is stabilised by [ | [[Secondary structure|Secondary structure]] is the first level of protein folding. The two main folding structures of a protein are the [[Alpha-helix|alpha-helix]] or the [[Beta-sheet|beta-sheet]] depending on the sequence of [[Amino acids|amino acids]]. This, in turn, allows the protein to have a [[Hydrophobic|hydrophobic]] core and a [[Hydrophilic|hydrophilic]] surface. The secondary structure is stabilised by [[hydrogen bonds|hydrogen bonds]] between the C=O and H-N groups<ref>Clark, J (2004) The Structure of Proteins. [Internet], Available from: http://www.chemguide.co.uk/organicprops/aminoacids/proteinstruct.html;[Accessed 20 October 2015].</ref> for the peptide backbone. | ||
=== Tertiary Structure<br> === | === Tertiary Structure<br> === | ||
[[Tertiary structure|Tertiary structure]] relates to the protein function. If the [[Tertiary structure|tertiary structure]] is altered, then the protein is unlikely to function properly. [[Tertiary structure|Tertiary structure]] is held together by either [[Hydrogen bonds|hydrogen bonds]] or [[Disulphide bridges|disulphide bridges]] depending on the [[Amino acids|amio acids]] present. Disulphide bridges are formed between the amino acid [[Cysteine|Cysteine]] <ref>Berg J., Tymoczko J and Stryer L. (2007) Biochemistry, 6th edition, New York: WH Freeman.</ref>.<br> | [[Tertiary structure|Tertiary structure]] relates to the protein function. If the [[Tertiary structure|tertiary structure]] is altered, then the protein is unlikely to function properly. [[Tertiary structure|Tertiary structure]] is held together by either [[Hydrogen bonds|hydrogen bonds]] or [[Disulphide bridges|disulphide bridges]] depending on the [[Amino acids|amio acids]] present. Disulphide bridges are formed between the amino acid [[Cysteine|Cysteine]] <ref>Berg J., Tymoczko J and Stryer L. (2007) Biochemistry, 6th edition, New York: WH Freeman.</ref>.<br> | ||
=== Quaternary Structure<br> === | === Quaternary Structure<br> === | ||
One or more tertiary stuctures of protein linked together build up a [[Quaternary structure|quaternary structure]]. Quaternary structure can also refer to proteins with an inorganic prosthetic group attached, an example being [ | One or more tertiary stuctures of protein linked together build up a [[Quaternary structure|quaternary structure]]. Quaternary structure can also refer to proteins with an inorganic prosthetic group attached, an example being [[haemoglobin|haemoglobin]]: a tetramer consisting of four myoglobin subunits and an iron-containing haem group. Two of the subunits are alpha, and two are beta <ref>Berg J., Tymoczko J and Stryer L. (2007) Biochemistry, 6th edition, New York: WH Freeman.</ref>.<br> | ||
== Functions of Proteins == | == Functions of Proteins == | ||
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Proteins make up 50% of each cell and have both structural and functional importance. [[Enzymes|Enzymes]] are globular proteins that act as biological [[Catalysts|catalysts, and]] collagen is a fibrous protein which provides strength and structural support in many tissues. | Proteins make up 50% of each cell and have both structural and functional importance. [[Enzymes|Enzymes]] are globular proteins that act as biological [[Catalysts|catalysts, and]] collagen is a fibrous protein which provides strength and structural support in many tissues. | ||
Enzymes work by binding substrate at their active sites, which is a specific region dependant on amino acid sequence forming an enzyme-substrate complex. This causes a conformational change in the shape of the enzyme which encourages catalysis by putting strain on the bonds in the substrate (and/or by other means).<br> | Enzymes work by binding substrate at their active sites, which is a specific region dependant on amino acid sequence forming an enzyme-substrate complex. This causes a conformational change in the shape of the enzyme which encourages catalysis by putting strain on the bonds in the substrate (and/or by other means).<br> | ||
A group of protein structures called motor proteins are responsible for activities such as muscle contraction, cell movement, migration of [[Chromosomes]] during [[Mitosis]] and the direction of organelles. There are two different types of [[Microtubules|microtubule]] motor proteins known as [[Kinesin|kinesins]] and [[Dynein|dyneins]]. Kinesins facilitate the carrying of organelles toward the positive end of the [https://teaching.ncl.ac.uk/bms/wiki/index.php/Microtubules microtubule] and dyneins are important of the movement of [[Cilia|cilia]] or [[Flagella|flagella]] in organisms <ref>Alberts.B et al, (Fifth Edition); Molecular Biology of the Cell; Taylor and Francis Group, pp 1014-1015</ref>. | A group of protein structures called motor proteins are responsible for activities such as muscle contraction, cell movement, migration of [[Chromosomes]] during [[Mitosis]] and the direction of organelles. There are two different types of [[Microtubules|microtubule]] motor proteins known as [[Kinesin|kinesins]] and [[Dynein|dyneins]]. Kinesins facilitate the carrying of organelles toward the positive end of the [https://teaching.ncl.ac.uk/bms/wiki/index.php/Microtubules microtubule] and dyneins are important of the movement of [[Cilia|cilia]] or [[Flagella|flagella]] in organisms <ref>Alberts.B et al, (Fifth Edition); Molecular Biology of the Cell; Taylor and Francis Group, pp 1014-1015</ref>. | ||
== See also<br> == | == See also<br> == | ||
*[[Amino acid|Amino acid]]<br> | *[[Amino acid|Amino acid]]<br> | ||
== References<br> == | == References<br> == | ||
<references /><br> | <references /><br> | ||
Revision as of 13:42, 1 December 2015
A protein is a biological polymer which is made up of amino acids. The amino acids are joined together with a peptide bond to form a polypeptide chain. The peptide bond is formed by joining the ɑ-carboxyl group of an amino acid to the ɑ-amino group of another amino acid[1]. A protein can be made up of a single polypeptide chain or multiple polypeptides linked together. There are three types of proteins: fibrous, globular and membrane proteins. Examples of proteins include enzymes, receptors and hormones. They are found in every form of life from viruses to bacteria; yeasts to humans. One important technique used to analyse proteins is SDS polyacrylamide-gel electrophoresis (SDS-PAGE).
Structure
A protein has several 'layers' of structure [2]. The function of the protein is determined by its structure, therefore each layer is dependent on the next.[3]
Primary Structure
The primary structure is the specific sequence of amino acids joined together by peptide bonds in a polypeptide chain. There are 20 different amino acids found in nature. The sequence of amino acids is determined by the DNA sequence that encodes for that particular protein. This is know as the gene.
Secondary Structure
Secondary structure is the first level of protein folding. The two main folding structures of a protein are the alpha-helix or the beta-sheet depending on the sequence of amino acids. This, in turn, allows the protein to have a hydrophobic core and a hydrophilic surface. The secondary structure is stabilised by hydrogen bonds between the C=O and H-N groups[4] for the peptide backbone.
Tertiary Structure
Tertiary structure relates to the protein function. If the tertiary structure is altered, then the protein is unlikely to function properly. Tertiary structure is held together by either hydrogen bonds or disulphide bridges depending on the amio acids present. Disulphide bridges are formed between the amino acid Cysteine [5].
Quaternary Structure
One or more tertiary stuctures of protein linked together build up a quaternary structure. Quaternary structure can also refer to proteins with an inorganic prosthetic group attached, an example being haemoglobin: a tetramer consisting of four myoglobin subunits and an iron-containing haem group. Two of the subunits are alpha, and two are beta [6].
Functions of Proteins
Proteins make up 50% of each cell and have both structural and functional importance. Enzymes are globular proteins that act as biological catalysts, and collagen is a fibrous protein which provides strength and structural support in many tissues.
Enzymes work by binding substrate at their active sites, which is a specific region dependant on amino acid sequence forming an enzyme-substrate complex. This causes a conformational change in the shape of the enzyme which encourages catalysis by putting strain on the bonds in the substrate (and/or by other means).
A group of protein structures called motor proteins are responsible for activities such as muscle contraction, cell movement, migration of Chromosomes during Mitosis and the direction of organelles. There are two different types of microtubule motor proteins known as kinesins and dyneins. Kinesins facilitate the carrying of organelles toward the positive end of the microtubule and dyneins are important of the movement of cilia or flagella in organisms [7].
See also
References
- ↑ Berg et al., (2006) Biochemistry, 6th edition, New York. Pg 34
- ↑ Elliott.W.H, Elliott.D.C (1997) Biochemistry and Molecular Biology. New York, United States:Oxford University Press.pp.47-49.ISBN 0199271992
- ↑ Berg J., Tymoczko J and Stryer L. (2007) Biochemistry, 6th edition, New York: WH Freeman.
- ↑ Clark, J (2004) The Structure of Proteins. [Internet], Available from: http://www.chemguide.co.uk/organicprops/aminoacids/proteinstruct.html;[Accessed 20 October 2015].
- ↑ Berg J., Tymoczko J and Stryer L. (2007) Biochemistry, 6th edition, New York: WH Freeman.
- ↑ Berg J., Tymoczko J and Stryer L. (2007) Biochemistry, 6th edition, New York: WH Freeman.
- ↑ Alberts.B et al, (Fifth Edition); Molecular Biology of the Cell; Taylor and Francis Group, pp 1014-1015