Proteins. protein domains. protein families Flashcards
what do proteins do?
responsible for almost all life functions:
* Support ( structural protein)
* Movement (motor proteins)
* Catalysis (enzymes)
* Membrane transport (transporter)
* Recognition, specific binding and reaction to molecules (receptor, transcription regulator antibodies etc)
* Homeostasis (hemoglobin, albumin etc)
* Genes work by encoding proteins
what are proteins composed of?
- Proteins are polymers of alpha amino acids
- Amino acids bind together to form polypeptide chains
what are some characteristics you can tell me about a polypeptide chain?
- C-Terminus : ends with carboxylgroup (COOH)
- N-Terminus: ends with aminogroup (H2N-)
- polypeptide chain has a monotonous “backbone”; (-NH-CH-CO-)n
what are the four levels of organization of proteins?
- primary structure
- secondary structure
- tertiary structure
- quaternary structure
what can you tell me about the primary structure of a protein?
sequence of polypeptide chain
it includes;
* Number of amino acids (from <60 to >1500)
* Composition of amino acids (more basic, more acidic, more polar neutral, more hydrophobic)
* Order of amino acids (how they are arranged in polypeptide chain)
determines all other levels of structure + function
what are some examples of proteins with primary structure?
- protamine; 58 amino acids- major protein of spem nucleus
- glycophorin A; 131 amino acids responsible for separating erythrocytes from each other
what is the secondary structure of a protein?
regular folding of parts of polypeptide chain in α-helix or ß-sheet based on interactions between group of (-NH-CH-CO-)n
backbone stabilized by hydrogen bond
what are the types of secondary structure?
there are two types;
α-helix
* e.g in myoglobin
ß-sheet
* e.g in immunoglobin
* anti parallel or parallel
a particular polypeptide will form a α-helix, parallel ß-sheet, antiparallel ß-sheet or neither depending on interaction within monotonous backbone (primary structure)
what is the tertiary structure of a protein and what can you tell me about it?
- final 3D folding of polypeptide chain as a result of irregular but non-random bending parts
- determines final shape of protein molecule
- subdivided into globular, fibrous and membrane
what can you tell me about the interactions of tertiary structure?
(mainly) non covalent;
* ionic
* hydrogen
* hydrophobic
* Covalent disulfide bonds (can support tertiary structure)
* hydrophobic interactions force the globular protein to fold in a way that hydrophobic amino acids are clustered in the
middle and isolated from water
* hydrophilic interactions force amino acids to remain on the surface of the folded chain their polar side will interact with water mdecules
what is the quaterenary structure of a protein
- two or more polypeptide chains must bind together into functional complex
- the individual polypeptides called subunits
- based on interaction between amino acid chains belonging to different subunits
what are some examples of quaternary structures?
Myoglobin-only tertiary structure
Hemoglobin
* formed by 4 subunits (2 α & 2 ß chains) bound non covalently
* This quat. structure facilitates binding of Oz in lungs
**Immunoglobulin **
* formed by 4 polypeptide chains
* 2 heavy and 2 light chains, (4 domains, 2 domains)
* Connected by disulfide bonds
what is a protein domain and what can you tell me about them?
- region of polypeptide chain that is self-stabilizing and folds independently from the rest
- Tertiay structure packs the alpha helixes and/or beta sheets in globular units
- Some proteins have a single while others have 2 or more
- different domains have different structure and different functions
what is a protein motif
Proteins can be composed of different domains and one domain may appear in a variety of different proteins -such folding patterns called protein motifs
what is a protein family
group of proteins that share a common evolutionary origin, often arranged into hierarchies, with proteins that share a common ancestor subdivided into smaller groups (reflected by their related functions and similarities in sequence or structure)
