Protiens Flashcards
What is a protein?
One or more polypeptide chain arranged in a complex macromolecule
State the 4 protein structures?
- primary
- secondary
- tertiary
- quaternary
What is a Primary structure?
- A sequence of amino acids held together by covalent peptide bonds via condensation reaction (removal of water)
- Directed by the DNA
- amino acids determine how the polypeptide folds into its structure and its function
What is a Secondary structure
- The simple fold of polypeptide into either 2 structure/shapes.
- hydrogen bonds between an amine group of a amino acid and carboxyl group of another amino acid.
- Alpha helix shape: Hydrogen bonds within the amino acid chain pulls into a helix shape
- beta pleated sheet: polypeptide chain is parallel to each other and joined by hydrogen bonds forming a sheet like structure. Appear Pleated due to the patterns formed by individual amino acids
What is a Tertiary structure?
- The complex folding of a single polypeptide chain into its final structure and function
- R groups of a amino acid joins with a R group of another amino acid forming additional bonding.
- Additional bonding: Disulphide, hydrogen, ionic bonding and hydrophobic and hydrophilic interactions.
State and describe the additional bonding’s you can find in both tertiary and quaternary structure.
- Disulphide bonds = between cysteine (amino acids containing sulphur atoms) = strongest but not common (used to stabilise) = Broken down by oxidation
- Ionic bonds = between non polar R groups = stronger than hydrogen bonding but not common = Broken down by pH changes
- Hydrogen bonds = between polar R groups = weakest but most common.
- Hydrophilic interactions
- Hydrophobic interactions
What is Quaternary structure?
- The final/compete fold of more than one polypeptide chain into is structure and function
- Contains the additional bonding’s found in Tertiary structure
Globular proteins shape/structure & Amino acid sequence.
Shape: compact, spherical shape that folds into a tertiary structure because of..
- The polar hydrophobic R groups orientate towards the centre of the protein away from the aqueous environment and the non polar R groups orientate themselves to the surface of the protein.
possesses a specific shape due to the interactions between R groups.
Amino acid sequence: Irregular
Globular proteins Function & Examples
Function: Physiological/Functional.
- Roles used for catalysing enzymes metabolic reactions and antibodies to respond to antigens.
Examples:
Insulin
- A hormone that is involved in regulating the concentration of glucose in the blood. Needs to fit into specific receptors to function so a specific shape is needed
Globular proteins Solubility
Soluble in water
Conjugated protein: Haemoglobin
A pigment that can combine and carry oxygen, is found in red blood cells.
- Quaternary protein made up of 4 subunits( 2 alpha and 2 beta subunits)
- Each subunit contains a prosthetic haem group
- The Fe2+ ions in the haem group are each able to combine reversibly with an oxygen molecule in the lung + transport the 02 to the tissue to be used for aerobic metabolic pathways.
Fibrous protein: Keratin
- strong, insoluble and inflexible.
- Structure contains a lot of cysteine(Amino acids containing sulphur atoms) which has many disulphide bonds (strong bonds)
Fibrous protein: Collagen
- connective tissue found in the tendons, ligaments, and nervous system.
- made up of 3 polypeptides wound together in a long, thin, strong rope-like structure.
Fibrous protein: Keratin
- Strong, inflexible and insoluble due to may cysteine(amino acids contain sulphur atoms) which haave alot of disulphide bonds(strong bonds)
- Found in hair, nails and skin
Fibrous proteins structure/shape & Amino acid sequence
Shape/Structure:
- thin and structural/organized proteins
- Don’t fold into 3D shapes like globular proteins
Amino acid sequence: Repetitive = organized structure
Fibrous protein: Function
Structural functions
Conjugated protein: Enzyme
Intracellular Enzyme, Catalase.
Conjugated proteins that are biological catalysts.
Need a complementary substrate to fit into its active site to function.
- quaternary protein contains 4 prosthetic haem groups
-interacts with hydrogen peroxide and speeds up the breakdown due to the presence of Fe2+ ions in the haem groups
- Hydrogen peroxide = common by-product of metabolism that’s damaging to cells
Extracellular Enzymes, Amylase
Catalyses the breakdown of starch into maltose. Extracellular molecules are too big to fit into cells so need to be digested first. Amylase secreted by the pancreas and salivary glands, is found in saliva.
Fibrous protein: Examples
- Keratin
- Elastin
- Collagen
Fibrous protein: Solubility
Insoluble = high proportion of amino acids with hydrophobic R groups in their primary structure
