Topic 4 - Proteins Flashcards
Less than 50 amino acids = a protein or a peptide?
Peptide
List the biological roles of proteins
- Enzymes
- Transport
- Nutrient & storage
- Contractile or motile
- Structural
- Defence
- Regulatory
What determines protein function?
number of amino acids
amino acid composition
Number of aa chains
different aa’s in each chain
Non-amino acid parts of proteins are called…?
prosthetic groups
Proteins containing prosthetic groups (non-aa parts) are called…?
conjugated proteins
Identify the 4 levels of protein structure
Describe primary (covalent) structure of proteins
based on the linear sequence of amino acids.
Determines function & shape (protein configuration)
What is configuration (in relation to proteins)?
the AMINO ACID SEQUENCE (primary structure)
-covalent bonds have to be broken for change in configuration
What is conformation (in relation to proteins)? and how is it stabilised?
How the chain is ARRANGED
Stabilised by weak interactions
- hydrogen bonds
- Hydrophobic interactions
- ionic interactions
- disulfide bonds (outside cell)
ALL ARE VERY IMPORTANT
What is the purpose of disulfide bonds and where do they occur?
DO NOT OCCUR IN CELLS. ARE OUTSIDE CELLS
Used to make cells more robust
What is the driving force behind protein folding?
Minimising the number of hydrophobic amino acid R-groups exposed to water
Are peptide bonds covalent or non-covalent?
covalent
Describe seconday structure of proteins and name the two kinds of folding
How the primary sequence folds -spatial arrangement of aa’s that are close together in a peptide due to H-bonding
Describe the structure of the alpha helix (secondary structure)
commonly associated w/ globular proteins
right handed
simplest arrangement a polypeptide can make w/ a rigid (double) peptode bond
backbone wound around imaginary axis
R-groups protrude to outside
stabilised by H bonds
Describe the structure of Beta-pleated sheets (secondary structure)
Can be parallel or anitparallel
stabilised by h bonding b/w different strands
What is a beta turn and what is its purpose?
a connecting element b/w a-helix or b-sheet in globular proteins
used for change of direction (gly and pro often occur)
stabilised by H bonding
Describe the tertiary structure of a protein and how it is stabilised
the overall 3D structure incl. assemblage of a-helix, b-sheet and connecting elements
forms fibrous (support) and globular (often enzymes) proteins
Maintained by weak interaction b/w R-groups =>H bonding b/w polar side chains, ionic interactions, hydrophobic interactions, Van der Waals & covalent cross-links (disulfide bonds)
Describe the quaternary structure of a protein
proteins composed of multiple subunits (polypeptides). Polypeptides are held together by non-covalent interactions
Describe protein denaturation, its effects and how it is caused
The unfolding of proteins
caused by changes in heat, pH & organic solvents
Causes loss of tertiary structure (disulphide bonds, aa side chain interactions) & secondary structure (folding). Most does NOT affect primary structure.
How to hydrophobic effects allow proteins to spontaneously refold (renaturation)?
Hydrophobic aa’s want to release their ordered water
Name the 3 kinds of proteins and give a brief description.
- Fibrous proteins =>long strands or sheets e.g. keratin, collagen
- Globular proteins =>chains folded into globular shape e.g. myoglobin (tertiary), haemoglobin (quaternary)
- Membrane proteins
Describe the structure and function of keratin
fibrous protein
right handed a-helix as secondary structure
many cysteine residues, therefore disulfide linkages b/w chains (protofilaments).
Describe the structure and function of Collagen
structural protein
right handed triple a-CHAIN
typically consists of Glycine, Alanine and Proline
assembly of collagen fibres requires vitamin C as a cofactor
Describe the structure and function of Myoglobin
conjugated protein
single polypeptide chain w/ 8 a-helices
Oxygen storage
haem is its prosthetic group
