protein structure Flashcards
What is the primary structure of a protein
sequence of amino acids in a polypeptide chain bonded by covalent peptide bonds
the DNA of the cell determines the primary structure if the primary structure is altered it alters the entire structure and therefore protein function
What is the secondary structure of a protein
2 structures?
Weak negatively charged nitrogen and oxygen from the amine and carboxyl groups interact with weak positively charged hydrogen
This creates weak hydrogen chains
ONLY RELATES TO HYDROGEN BOND BETWEEN AMINE AND CARBOXYL GROUP
they are either
Alpha helix or Beta pleats
What is an Alpha helix and a Beta pleat in the secondary structure
Alpha helix
structured like a coil
can be between each 4th peptide bond
beta pleats
zig zag and are opposite eachother
(there are 2)
What is the tertiary structure of a protein and what are the 3 bonds and 1 interaction
Additional bonds formed between R groups
bonds :
- ionic
- hydrogen
- disulphide
interaction :
- hydrophobic interaction
What is the properties of the Disulphide and ionic bonds in the tertiary structure
Disulphide - between cysteine amino acids only because its the only one with an available sulphur
- broken by reduction
- strongest used to help stabilise a protein
ionic - form between positive and negative R groups
- Brocken by the wrong PH
What are the properties of the hydrogen bonds and the hydrophobic interaction in the tertiary structure of proteins
Hydrogen bonds - Between strong polar R groups
- most common but the weakest
hydrophobic interaction - between non polar (hydrophobic) R groups within the interior of the protein
What is the quaternary structure in proteins
Occurs in proteins with more than one polypeptide chain e.g. haemoglobin
What is the structure of a a globular protein
why is it that structure
- Compact and roughly spherical in shape and soluble in water
it is spherical because: . . . . their non polar hydrophobic R groups face outwards
. polar hydrophilic R groups face inwards - They have an irregular range of R groups
- Have a specific shapes
What are the roles of globular proteins
Play an important part in physiological roles as they can be easily transported
- metabolic rate
some globular proteins can be conjugated proteins that contain a prosthetic group
What is the structure of a fibrous protein
- Long strands of of polypeptide chains that have cross-linkages due to hydrogen bonds
- little to no tertiary structure due to hydrophobic R groups meaning they are insoluble
- limited number of amino acids so they are repetitive
What are the roles of fibrous structures
due to them being repetitive and insoluble they are suitable for structural roles
e.g. hair, nails
made from keratin and collagen
What is an example of a globular protein and what is its structure
It has a quaternary structure as there are four polypeptide chains. These chains or subunits are called globin proteins
( 2 alpha globin and 2 beta globin )
- 4 globin subunits are held by disulphide bonds
- Each subunit has a prosthetic haem
- hydrophobic R-group faces in hydrophilic R-group faces out
What happens to the quaternary structure of haemoglobin as oxygen binds?
it alters causing higher affinity so more oxygen can bind
what is an example of a fibrous protein and its structure
collagen
- insoluble
- formed from 3 polypeptide chains held by hydrogen binds to form a triple helix
- Almost every third amino acid in the primary structure is glycine (single hydrogen R group)
- Covalent bonds also form cross-links between R-groups (contain fibrils)
What is the function of collogen
- flexible structural protein forming connective tissues
- great tensile strength due to triple helix
- Stable protein
