B1.2 Proteins HL Flashcards
what clusters in the core of a globular protein?
hydrophobic amino acids
give examples of important amino acids and state whether they are hydrophobic or hydrophilic
- Glutamic acid (hydrophilic)
- Vallne (hydrophobic)
- sickle cell anaemia: one diff base changes glutamic acid to vallne, hydrophilic to hydrophobic
- Cysteine (hydrophobic) → contains sulphur *only amino acid
- Methlonine (hydrophobic)
what are used in membrane channels?
polar and non-polar amino acids
explain how polar and non-polar amino acids are used in membrane channels
-polar amino acids are positions on external surfaces and line the protein channels for facilitated diffusion
- polar sections allow ions through (charged or polar molecules cannot normally pas through the hydrophobic layers)
- non-polar sections bond with hydrophobic tails
what are the 4 structures in protein folding and state the order
Primary structure 1° → Secondary structure 2° → Tertiary structure 3° → Quaternary structure 4°
what is the process when a protein goes from secondary structure to primary structure, and is it easy or hard compared tertiary structure to secondary structure
denaturation
sec to pri: hard because a lot of energy is needed to break hydrogen bonds
ter to sec is easier than sec to pri
what is primary structure of protein
the unfolded chain of polypeptide
what is secondary structure of protein
repeating local structures, held by H-holds
repeating units
- α-helix (hydrogen bonds)
- β-pleated sheets
what is tertiary structure of protein?
state and explain the features
3D folded structure
- folding of a single protein into a 3D structure
- hydrophobic core
- this 3D structure gives proteins their functional properties, such as active sites on enzymes
- R group interactions: the below are all dependent on the R-group
- hydrophilic polar amino acids orient to the outside
- hydrophobic non-polar amino acids protected in the core
- oppositely-charged ions attract (ionic bond)
- disulphide bridges globular protein
what is the quaternary structure of proteins?
- multiple subunits
- protein complex
- made of two or more subunits
what are R group interactions and give examples of R group interactions in tertiary structure
the below are all dependent on the R-group
-
hydrophilic polar amino acids orient to the outside
- hydrophobic non-polar amino acids protected in the core
- oppositely-charged ions attract (ionic bond)
- disulphide bridges globular protein
give an example of quaternary structure of proteins
e.g. haemoglobin, bc it needs to bind onto iron? or oxygen; 4 haem inside contains iron;; (beta chain & alpha chain on outside, haem on inside)
e.g. DNA Polymerase
e.g. Ion channels in the plasma membrane
what is temperature sensitive?
hydrogen bonds
hydrogen bonds are very weak → heat a little and it will break → but reforms very easily
what is pH sensitive? why?
ionic bonds
if make pH more acidic = add more H+ protons
what cannot reform is disulphide bridges are broken?
cysteine cannot reform
(a type of amino acid)
denaturation is mostly irreversible, why?
- if in water, if broken into primary structure
- water react to inside of protein → does not want to fold back into original shape
what are the 2 types of quaternary structure in protein
non-conjugated and conjugated
give examples of non-conjugated quaternary structure of protein
insulin, collagen
give examples of conjugated quaternary structure of protein
haemoglobin have 4 polypeptide chain + 4 haem groups
how do conjugated and non-conjugated quaternary structure of protein differ?
Non-conjugated only have polypeptide chain
Conjugated have non-polypeptide component (e.g. haem)
Describe the structure of insulin
polypeptide chains are separate, but held together using disulphide bridges from R group (cystine)
describe the structure of collagen
- quaternary structure = 3 polypeptides, wound together into a triple helix
- fibrous protein → more structural role
- repeating amino acid unit
- primary structure of polypeptides = repeating sequence of 3 amino acids: P-G-X
- can’t change P or G or else will fold differently)
- P = proline
- G = glycine
- X → R group
why does collagen have to have amino acid P and G?
- P = proline/hydroxyproline
- prevents formation of an α-helix
- winding together of 3 polypeptides would be impossible if they were α-helices
- R group is every 3rd amino acid faces inwards towards the centre of the triple helix and glycine is the only amino acid with an R-group small enough to fit → single hydrogen atom
if many repeats in bases what does it indicate about the protein?
fibrous protein instead of globular
