protein and protein structure Flashcards
What are three different types of protein shapes
- globular (round, tightly folded)
- fibrous (more elongated)
- membrane spanning (part of protein hydrophobic allowing interaction with lipids in cell membrane)
what does overall shape of protein determine
- function
- what is binds to, flexibility, solubility, how easy it can degrade
4 protein structure
- primary - linear sequence of amino acid
- secondary - local region of proteins formed/folded
- tertiary - folding of secondary structure into 3d structure
- quaternary - only some proteins - where different proteins interact together - polypeptide chains
what five factors determine the shape of protein
- amino acid sequence
- chaperones - proteins in cells involved in helping of folding of other proteins
- water - proteins naturally fold with hydrophilic residues exposed to aq environment and hydrophobic residue hidden away inside protein
- cysteine - carries out role in formation of disulphide linkages
- h bonds - have to align correctly
- flexibility - more flexible more bend
what are chaperones
- barrel shaped proteins allowing other proteins to enter them and allow proteins to have interaction to form folded proteins
- by folding the protein in the barrel means water kept out allowing polar interactions without water
- energy required
what are two examples of secondary protein structure
- alpha helix
- beta pleated sheets
have structural motifs which help with turns
have non regular coils and loops more flexible
alpha helix structure
- tightly coiled rod of amino acids
- found in globular proteins, dna binding, membrane spanning proteins
- hydrogen bonding holds helix in place - bonds formed between amino acids
- in haemoglobin alpha helix main structural element
- in keratin - 2 or more helices intertwine together
how are hydrogen bonds formed in beta pleated sheets
- hydrogen bonds from between two pars of proteins that may be far apart
- h bonds forms when the atoms involved are co linear can also happen when sheets are slightly bent
- pleated sheets can be between polypeptide chains that are parallel to each other or in opposite direction to each other
antiparallel beta pleated sheets
- this structure can be achieved by a beta turn
- 4 amino acids involved and hydrogen bond together
- resulting in a hair pin loop
- the h bonds helps make structure v stable
what are structural motifs responsible for and what is an example
- responsible for a particular property of protein
- example; zinc finger protein = alpha helix, b sheet, zinc held by 2 his and 2 cys - these proteins are found in proteins that bond to dna and rna
tertiary structure
- highest level of structure for most proteins
- folding pattern of secondary structure giving molecule a 3d structure
- 3d structure; binding sites for ligands, maintains appropriate residues on surface
- have an independent, specialised structure to carry out a particular function
what are quaternary proteins and an example
- some proteins have an association with other separate
proteins that come together - forms one functional unit
- sub units can be same (homo) or different (hetero)
- increases stability
what happens when oxygen binds to haemoglobin
- when haemoglobin binds to oxygen there is a subtle change in structure of haemoglobin
- becomes more flattened therefore changing structure and function allowing other oxygen molecules to bind to haemoglobin
- allows haemoglobin to be loaded with as much oxygen as possible to carry around the body
protein switches
- GTP binds to proteins and affects structure
- G proteins activity is dependent on whether it binds to GDP or GTP
- when binds to GDP essentially inactive - meaning does not interact with other molecules
- when promotes exchange of GDP to GTP becomes activated
what happens when a protein denature and the cause of denaturation
- shape change, bonds disrupted, function lost
- due to changes in pH, temp, acid bases, high salt, solvent
