Lesson Four - Levels of Protein Structure Flashcards
What are the levels of protein structure?
Primary - amino acid sequence
Secondary - regular sub structures (alpha helix or beta sheets
Tertiary - 3D structure
Quaternary - Complex of protein molecules
How many levels are there of protein structure?
Four
What is the Primary structure?
Simply the sequence of amino acids in a protein
Where are the chains of amino acids written from?
The amino terminus to teh carbxyl terminus
What are the two types of the secondary structure?
a-helix
b-sheet
What types of bonds are present is the secondary structure?
Hydrogen bonding
Explain a-helix
The helix is right-handed with 4 residues (amino acids) per ture
How many models are there of a-helix?
3
What are the models of a-helix?
Ball and stick
The ribbon and then those combined
Hydrogen bonds between oxygen and hydrogen stabiles the helix
Explain b-sheets
Can be parallel or antiparallel
The different parallels will have different structures and hence different hydrogen bonds in different places
What is the Tertiary Structure?
It is all about the interactions between the R groups
This involves the folding of the polypeptide chains to give a more complex 3D structure
What interactions can be found within the R-groups in tertiary structure?
Hydrophobic interactions Ionic bonds Hydrogen bonds LDF Disulfide bridges
Which techniques can be used to identify a tertiary structure?
X-ray crystallography
NMR (nuclear magnetic resonance)
Where about in a molecule does the non-polar R groups tent to be placed?
In the centre
They are classically found embedded in the phospholipid bilayer of a cell
What do hydrophobic and hydrophilic interactions influence and why?
The location of cellular proteins
R-groups at surface of a protein determine its location within a cell. Hydrophilic R groups will predominate at the surface of a soluble protein, hydrophobic R groups may cluster at the centre to form a globular structure
What are disulphide bonds/bridges?
Strong covalent bonds which can form between -SH groups
Which amino acid contains the -SH group?
Cysteine
What are prosthetic groups?
They are associated non-protein groups
Where are prosthetic groups found?
Within some proteins
Name four types of prosthetic groups
Haeme
Carbohydrate
Lipid
Nucleic Acid
What is myoglobin?
A red protein containing haem, which carries and stores oxygen in muscle cells. It is structurally similar to a subunit of haemoglobin.
How is myoglobin held together and what does it contain?
By a-helices which link together with nonhelical sections
It contains a haeme groups that is protected in a hydrophobic pocket
How are protein structures held together in a tertiary structure?
By weak hydrogen bonds and a few disulphide bonds
Why are tertiary structure proteins surprisingly stable?
As in the most part to the evolution of proteins that have useful yet stable conformations
Why do proteins fold?
To give a structure with the lowest free energy
When would the structure of the protein change?
When there is a change in the chemical environment
How does the temperature affect a protein molecule?
It increases the kinetic energy which places stress on bonds which breaks them
What types of bonds are particularly susceptible to temperature in a protein?
Hydrogen bonds
Ionic bonds
Van der Waals
What effect does pH have on a solution?
It changes the concentration of Hydrogen ions and hydroxide ions
How does pH affect a protein?
It changes the relative charge of the protein and places stress on polar interactions s
What does a change in temperature and pH result in?
It denatures the protein and causes the loss of tertiary structure and function
What is a quaternary sturcture?
A protein which is made up of two or more polypeptide subunits
What cell is an example of quaternary structure and why?
Haemoglobin as it is tetrameric
What does tetrameric mean?
It is made up of 4 parts
What is haemoglobin made up of?
2 a-helices and 2 b-sheets
Some integral proteins can be…
Transmembrane
What are some examples of transmembrane proteins?
Channels
Transporters
Receptors
What type of protein are transmembrane?
Hydrophobic
FINISH FLASHCARdS ON PERIPHERAL PROTEINS< JUNCTIONS BETWEEN CELLS +HIV
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