Biological Molecules : Proteins Flashcards
What are proteins ?
Are polypeptides made up of monomers called amino acids
General structure of amino acids ?
AMINE GROUP - NH2
CARBOXYLIC ACID - COOH
Hydrogen atom
R group
How is a peptide bond formed?
CONDENSATION REACTION - water released
A hydroxyl (-OH) is lost from COOH group and H is lost from amine group on another amino acid
- so the carbon atom and nitrogen atom bond tgt
What is primary structure of amino acid? How does DNA effect primary structure ?
Sequence of amino acid bonded by covalent peptide bonds
- DNA effects primary structure of protein by instructing cell to add certain amino acids in specific quantities in a certain sequence
What is the secondary structure?
Occurs when negative charged (nitrogen and oxygen) interact with weak positive hydrogen atoms to form HYDROGEN BONDS
- forms alpha helix/beta pleated sheet - way the polypeptide chain is folded/packaged
What is the tertiary structure?
More complex 3D structure of protein containing :
HYDROGEN BONDS - between polar R groups
DISULPHIDE BONDS - between sulphur atoms in cysteine amino acids
IONIC - between + charged amine group and - charged (COO-) R group
HYDROPHOBIC INTERACTIONS - between non polar R groups IN INTERIOR OF PROTEINS
What is the quaternary structure ?
proteins that have more than one polypeptide chain working together
E.g haemoglobin
Properties of globular proteins and function/examples?
Compact /type of tertiary structure
spherical - non polar hydrophobic R groups are orientated towards centre of protein/polar hydrophilic R groups orientated towards outside of protein
- soluble in water- easily transported/involved in metabolic reactions
- Some are conjugated - contain a prosthetic group (eg HAEM for haemoglobin)
E.g insulin (hormone) - cell signalling
enzymes - metabolic reactions
haemoglobin - transport blood
Antibodies - antitoxins/oppsonins/agglutinins
How are the arrangement of the R groups important for haemoglobin’s function?
If changes occur to sequence of amino acids in the 4 subunits , properties of haemoglobin change
How does the prosthetic group in haemoglobin help its function?
Oxygen can bind to the HAEM (Fe2+) group and oxygen is released when required
Properties and function/ examples of fibrous proteins?
Long strands of polypeptide chains that have cross links due too hydrogen bonds -SECONDARY STRUCTURE - repetitive amino acids
Insoluble - large no. Hydrophobic R groups
Strong / flexible
Unreactive
E.g Keratin - strength IN HAIR/NAILS
Elastin (connective tissue,tendons) - elasticity in blood vessels /alveoli
, Collagen (skin,tendons,ligaments) - structural
Structure and function of collagen?
- three polypeptide chains held together by hydrogen bonds to form TRIPLE HELIX
- EVERY 3RD amino acid is GLYCINE in primary structure
- covalent bonds form CROSS LINKS between R groups of amino acids when arranged parallel to each other
Function : structural protein - hydrogen bonds in triple helix structure —> TENSILE STRENGTH
- Staggered ends within fibrils provide strength
What are the essential inorganic ions in the body?
Hydrogen ions - determine pH
Iron ions - components of haemoglobin
Sodium ion - involved in co transport of glucose/amino acids
Phosphate ions - components of DNA and ATP
Potassium ions - electrolyte/nerve transmission
Calcium ions - bone/enamel structures and muscle contraction
Ammonium ions - deaminating of proteins
Test for proteins ?
Add sodium hydroxide (NaOH) to make solution alkaline AND Add few drops of copper (II) sulfate solution (BIURET REAGENT)
- colour change from blue to lilac
