B1.2 proteins Flashcards
Describe the general structure of an amino acid
Alpha carbon compound has attached to it:
- a hydrogen atom
- an amino group (NH2)
- a carboxyl group (COOH)
- a r group
State the word eqn for a condensation rxn btwn 2 generalised amino acids
Draw the dipeptide formed
amino acid + amino acid = water + dipeptide
peptide bond formed btwn the 2 amino acids - OH removed from the carboxyl group from the left amino acid and H removed from the amino group from the right amino acid. C bonded to N by peptide bond.
what is a peptide bond
covalent bond btwn 2 amino acids
What are essential and non-essential amino acids?
Essential: Body is unable to synthesise and can only be obtained from food
Non-essential: body is able to synthesise from other amino acids
(vegan diets require special attention to ensure that they receive their essential amino acids)
How do genes influence amino acid production
Amino acids are coded for in genetic code.
- genetic code is transcribed to mRNA (transcription), which is then translated by ribosomes into a polypeptide chain (translation) = many polypeptide chains form a protein
(peptide chains can have any number of amino acids which can form in any order [infinite variety] from a few to a thousand)
Examples of polypeptide chains (8)
Found in:
- Haemoglobin (4 polypeptide chains)
- Keratin: found in nails, hair, claws, hooves etc.
- Lipase: digestive enzyme to hydrolyse lipids
- Collagen: Structural protein found in ligaments, tendons - provides high tensile strength (3 chains)
- Insulin: regulate blood sugar
- Histones: proteins found in nucleus involved in formation of chromatin and chromosomes
- Lysozymes: enzyme that kills bacteria by digesting peptidoglycan in their cell walls. (1 chain)
- Integrin: Membrane protein used to make connections btwn structures inside and outside of the cell (2 chains)
Effect of pH on protein structure
if pH is increased/decreased from the optimum pH, the protein is denatured.
- the pH change causes the intramolecular bonds to break within the protein molecule = shape of the protein molecule changes.
(the intramolecular bonds give the protein its precise 3D shape)
Effect of temperature on protein structure
- The intramolecular bonds give the protein molecule its precise 3D shape.
- These bonds are susceptible to changes in temperature, where increased temperature increases molecular motion = increases stress on the relatively weak hydrogen bonds.
- Although the peptide bonds remain, the hydrogen bonds that shape the protein cannot stay in place under the stress = protein loses its shape and function, denatured.
Which part of amino acids determine the properties of assembled polypeptides?
r - group.
They can be:
Hydrophobic
Hydrophilic:
- polar OR non polar,
- acidic (-ve) OR basic (+ve)
Primary structure of proteins - Type of bonds
Peptide bond
Primary structure of proteins - Impact on overall conformation of proteins
Primary structure refers to the sequence of amino acids = determines how folding (of the polypeptide chains) is done and hence the conformation of the protein.
Any changes to the sequence of amino acids would cause the protein to no longer function.
Secondary structure of proteins - structure + bonding
Composed of non-polar amino acids
Primary structure of proteins are pleated and coiled due to HYDROGEN BONDING forming btwn C=O of one amino acid and N-H of another acid.
The h-bonding occurs at regular intervals = adds stability of protein.
Alpha-helixes are COILED
Beta-pleated sheets are pleated..
Tertiary structure - types of intramolecular bonds
- Hydrogen bonds (weak, formed btwn OH and C=O)
- ionic bond (Electrostatic interaction formed btwn oppositely charged ions. Formed btwn +ve/-ve charged AMINE and CARBOXYL groups IN R-GROUPS which become +ve/-ve by binding/dissociation of H+ ions to participate in ionic bonding)
- van del waals forces (occur when 2 molecules are very close tgt)
- hydrophobic interactions
- disulfide bridge (STRONG covalent bond formed by the oxidation of -SH groups of two CYSTEINE side chains = S - S disulfide bond)
These bonds form btwn amino acids in the polypeptide chain, giving each chain its unique structure and shape.
Tertiary structure of proteins - effect of polar and non-polar amino acids
- non-polar hydrophobic amino acid residues/polypeptide chains are clustered in the core of globular proteins. E.g. integral proteins have regions with hydrophobic amino acids to help it embed in the membranes.
- the Polar hydrophilic amino acids are oriented towards water as it makes the protein hydrophilic.
Quaternary protein structure
- Occurs in proteins that have one or more polypeptide chain (Not lysozymes as they only have 1)
- Held together by the same bonds btwn r-groups for tertiary structure. (hydrogen, ionic, covalent [disulfide bridges, hydrophilic and hydrophobic interactions)
