Topic 7.5 Proteins Flashcards
7.5.1 Explain the primary level of protein structure, indicating the significance.
Primary Structure
- unique sequence of amino acids bonded by peptide bonds in protein
- 20 amino acids, arranged in any order (nucleotide base seqence in DNA determines order)
- significance: if order is changed, shape & function of protein are changed –> determines next 3 levels of protein organization
7.5.1 Explain the secondary level of protein structure, indicating the significance.
Secondary Structure
- regular repeating structures stabilized by H-bonds between groups in the main chain of polypeptides
- common configurations of secondary structure are α-helix & β-pleated sheet (both have regular repeating patterns)
- created by formation of H-bonds between oxygen from carboxyl group of 1 amino acid & hydrogen from amino group of another
- doesn’t involve side chains, R groups
7.5.1 Explain the tertiary level of protein structure, indicating the significance.
Tertiary Structure
- polypeptide chain bends & folds over itself b/c of interactions among R-groups & peptide backbone –> results in 3D shape
- significance: important in determining specificity of enzymes
- interactions causing tertiary organizations are:
- disulfide (covalent) bonds - strong, often called bridges
- hydrogen bonds b/w polar side chains
- Van der Waals interactions among hydrophobic side chains of amino acids – strong b/c hydrophobic side chains are forced inwards when hydrophilic side chains interact w/ water towards outside of molecule
- ionic bonds b/w (+) and (-) charged side chains
7.5.1 Explain the quaternary level of protein structure, indicating the significance.
Quaternary Structure
multiple polypeptide chains combine to form single structure
- not all proteins have quaternary structure
- primary, secondary & tertiary bonds are involved on this level
- conjugated proteins exist at this level (include prosthetic or non-polypeptide groups)
- e.g. Hemoglobin contains 4 polypeptide chains with heme (non-polypeptide group; contains iron atom that binds to oxygen) on each chain
7.5.2 Outline the difference between fibrous and globular proteins, with reference to two examples of each protein type.
Fibrous
- many polypeptide chains, long narrow shape
- usually insoluble in water
- e.g. collagen (structural role in connective tissues of humans) & actin + myosin (major component of human muscle, involved in contraction)
Globular
- more 3D shape
- mostly water soluble
- e.g. hemoglobin (delivers O2 to body tissues) & insulin (regulates blood glucose level in humans)
7.5.3 Explain the significance of polar and non-polar amino acids.
Amino acids are grouped according to properties of their side chains (R-groups) –> important in determining enzyme specificity. Specific substrates only combine with particular enzyme’s active sites (combination possible when “fitting” occurs)
Polar
- hydrophilic
- found in regions of proteins exposed to water
- membrane proteins include polar amino acids towards interior & exterior of membrane – > creates hydrophilic channels in proteins through which polar substances can move
Non-polar
- hydrophobic
- when in centre of water-soluble proteins, can stabilize structure
- found in regions of proteins linked to hydrophobic area of cell membrane
7.5.4 State four functions of proteins, giving a named example of each.
Proteins: HAM In Im Am
- hemoglobin: protein containing iron that transports O2 from lungs to all parts of body in vertebrates
- actin & myosin: proteins that interact to bring about muscle movement (contraction) in animals
- insulin: hormone secreted in pancreas that aids in maintaining blood glucose levels in vertebrates
- immunoglobulins: group of proteins that act as anti-bodies to fight bacteria & viruses
- amylase: digestive enzyme that catalyzes hydrolysis of starch
