B1.2 Proteins Flashcards
Two amino acids join together
forms dipeptide bond - CONH
release H2O
Peptides
Oligopeptide - upto 20 amino acids in a chain
Polypeptide - anything more
Protein - combination of polypeptides
Essential and non essential amino acids
essential - not produced in body, obtained by food (threonine, leaucine, isoleucine, tryptophan)
non essential - amino acids that can be made from other amino acids (aspartic acid, glutamic acid, alanine)
infinite variety of possible peptide chains
the amino acid sequence of each polypeptide is stored in a coded form in the base sequence of a gene
Protein synthesis in 2 stages
1) Transcription - DNA to mRNA
2) Translation - mRNA to proteins
ribosomes read and bring in correct amino acids. THey link amino acids together one at a time until polypeptide is fully formed
types of protein structures
primary structure - amino acid sequence
secondary structure: (peptide bond + inter and intramolecular H-bonding)
1) alpha helix - CO of the 1st amino acid bonds with the 3rd amino acid through H-bond creating an alpha helix
2) beta pleated sheet - formed by the parallel arrangement of the amino acid chains forming intermolecular H-bonds between the amino acid chains
tertiary structure - folding of a single protein chain into a 3D structure with a hydrophobic core. This 3D structure gives proteins their functional properties such as active sites on enzymes
Types of bonds
H-bond - bond between hydrogen and electronegative atom which is partially negative
Ionic bond - electrostatic force of attraction between negatively charged anion and positively charged cation
Hydrophobic - bond between two nonpolar molecules
Disulfide bridge - bond formed between two sulphur containing R groups, type of covalent bond
Quarternary structure
- made up of 2 or more polypeptide chains
- same bonds as tertiary
Conjugated protein
- has one or more non-polypeptide subunits in addition ot polypeptide (prosthetic group)
Non conjugated
- composed only of polypeptides
- formed by linking several polypeptide chains
- doesn’t have to be globular
Hemoglobin
- Made of two type of polypeptide chains - alpha and beta
- has 4 subunits, each subunit has a heme group conjugated with an iron atom
Collagen
- non conjugated, quarternary, fibrous
- most abundant protein in body, form dermis of the skin
- rope-like protein with 3 polypeptides wound together
- triple helix - 3 different types of polypeptide chains (alpha-1, alpha-2, alpha-3)
- alpha chains form collagen molecules to collagen fibrils to collagen
- forms mesh of fibres in skin and blood vessels that resist tearing
- found in tendons and other connective ligaments - structural component in teeth bones, tendons
- lack of collagen makes susceptible to skin tear
Insulin
- peptide hormone with site of secretion in pancreas beta cells
- decreases blood sugar
- secreted in inactive state by pancreas
- exist as dimers and hexamers
- becomes active when pH level changes, breaking bonds between dimers and hexamers
- inactive dimers and hexamers are quartnerary
- active is separated and exist as monomers in tertiary state
Integral protein
polar amino acids of an integral membrane protein are located on outside, extend into extracellular fluid - hydrophilic
non polar amino acids anchor protein into the membrane - associate with hydrophilic parts of membrance
Eg: transport channel
rhodopsin
- quarternary, globular
- retina of eye
- light sensitive pigment
- absorbs photons of light and changes its shape in response to this
- change in shape causes nerve impulse to be sent to the brain
keratin
- fibrous, quarternary
- two polypeptide chains
- high tensile strength
- hair, nails, claws, and hooves as structural component
