Protein Flashcards
Different amino acids
there are 20 different amino acids
1) Selenocysteine
2) Pyrrolysine
these two are modified variants
where are amino acids joined
Amino acids are joined together on the ribosome to form long chains called polypeptides, which make up proteins.
Each type of amino acid differs in the composition of the variable side chain
Peptide bonds
joined together amino acids in a condensation reaction form dipeptide and water
The covalent bond between the amino acids is called a peptide bond
Polypeptide chains
Polypeptide chains can be broken down via hydrolysis reactions, which requires water to reverse the process
Primary structure (amino sequence)
Primary structure is the order of the amino acid sequences which determine the way the chain will fold
secondary structure (amino sequence)
Alpha helices occur when the amino acid sequence folds into a coil / spiral arrangement
Beta-pleated sheets occur when the amino acid sequence adopts a directionally-oriented staggered strand conformation
Tertiary structure (amino sequence)
The tertiary structure of a polypeptide chain will be determined by the interactions between the variable side chains.
These interactions may include hydrogen bonds, disulphide bridges, ionic interactions, polar associations, etc.
Quaternary structure (amino sequence)
Quaternary structures are found in proteins that consist of more than one polypeptide chain linked together.
Alternatively, proteins may have a quaternary structure if they include inorganic prosthetic groups as part of their structure
Denaturation
Denaturation is a structural change in a protein that results in the loss of its biological properties. Denaturation of proteins can usually be due to: temperature or PH
Temperature (denaturation)
High levels of thermal energy can disrupt the hydrogen bonds holding the protein together, causing the protein to loose its function
PH (denaturation)
Changing the pH will alter the charge of the protein, which in turn will alter protein solubility and overall shape
Gene
A gene is a sequence of DNA of which encodes a polypeptide sequence
gene sequence to polypeptide sequence
1) Transcription – making an mRNA transcript based on a DNA template (occurs within the nucleus)
2) Translation – using the instructions of the mRNA transcript to link amino acids together (occurs at the ribosome)
exceptions to rule: 1 gene will code for 1 polypeptide
- Genes may be alternatively spliced to generate multiple polypeptide variants
- Genes encoding tRNA sequences are transcribed but never translated
- Genes may be mutated (their base sequence is changed) and consequently produce an alternative polypeptide sequence
Proteome
The Proteome is the totality of proteins expressed within a cell, tissue or organism at a certain time