Biological Molecules - Proteins Flashcards
What polymer is an amino acid the monomer of?
A protein (polypeptide)
How many amino acids occur naturally in proteins?
20
How many amino acids are essential? (can only be obtained through food)
9
What does it mean that amino acids are amphoteric?
Amino acids can act as both an acid and a base.
Amino acids therefore work as buffer solutions.
What is the central atom of an amino acid?
Carbon
What are the 4 groups of an amino acid?
Amine group (-NH2) Carboxyl group (-COOH) Hydrogen group (-H) R group (variable chemical group)
Draw the structure of an amino acid.
See bio book
What is a polypeptide?
A chain of multiple amino acids.
What is a protein?
one or multiple folded and modified polypeptide chains bonded together
What bonds form between amino acids and between which groups?
Peptide bonds between C of carboxyl group and N of amine group.
What kind of reaction breaks the bond between two amino acids?
Hydrolysis reaction (water used up)
What kind of reaction forms a peptide bond?
Condensation reaction (water produced)
What is the primary structure of a protein?
The specific sequence of amino acids in a polypeptide chain.
This decides the structure and the function of the protein.
What are the two structures formed as part of the secondary structure of a protein?
Alpha-helix
Beta-pleated sheet
What is an alpha-helix?
When a polypeptide chain stabilises by coiling into a cylindrical shape held together by hydrogen bonds between carboxyl and amine groups.
What is a beta-pleated sheet?
Polypeptide chains become linked in parallel flat strands joined by hydrogen bonds between carboxyl and amine/hydroxyl groups.
What is the tertiary structure of a protein?
The secondary structures fold up to form a precise 3D structure.
The R-groups on amino acids result in further folding.
What is the quaternary structure of a protein?
Multiple proteins interact to form a larger molecule.
May have identical or non-identical subunits.
Made of more than one polypeptide chain.
May contain prosthetic groups (non protein groups)
What is an example of a prosthetic group in a protein?
Haemoglobin contains proteins attached to haem groups.
What are the 4 types of bonds between R-groups of polypeptides that form their precise 3D structure?
Disulphide bonds
Ionic bonds
Hydrophobic interactions
Hydrogen bonding
What kind of bond is a disulphide bond and between which amino acids does it form?
Covalent bond between two cysteine monomers
Disulphide bridge
Which types of protein bonding are the first to break when a protein is denatured due to temperature or PH?
Ionic bonds
Hydrogen bonds
What groups on amino acids do ionic bonds form between?
Ionic bonds form between amine and carboxyl groups, ionising them.
What are hydrophobic interactions and to what amino acids do they occur?
Hydrophobic interactions involve amino acids with non-polar (hydrophobic) R groups.
Hydrophobic R groups twist the protein to take position in the centre of a loop, away from water.
In proteins, what do hydrogen bonds form between?
Delta negative oxygen and delta positive hydrogen.
What are the features of a fibrous protein?
Little/no tertiary structure. Long, parallel polypeptide chains. Cross linkages at intervals forming long fibres or sheets. Usually insoluble. Usually play a structural role. Very strong.
What are 4 examples of fibrous proteins?
Keratin
Elastin
Collagen
Myosin
Where is collagen found in the body?
Skin, bones, cartilage, blood vessels
structural protein
What is the structure of collagen?
3 polypeptide chains in a helical shape to form a “rope”.
Held together by hydrogen bonds.
What feature of collagen’s primary structure allows it to be so strong?
Small glycine R-group allows the closeness of polypeptide chains, increasing the strength of the intermolecular forces.
What is the general structure of a globular protein?
Globular proteins have complex tertiary and quaternary structures.
They are folded into globular (spherical) shapes.
What role do globular proteins usually play in the cell?
Roles in metabolic reactions (enzymes)
Are globular proteins usually soluble or insoluble and why?
Globular proteins are usually soluble as all the hydrophobic R-groups are in the centre of the 3D structure.
What are 4 examples of globular proteins?
Enzymes, haemoglobin, insulin, actin
What is the structure of haemoglobin?
Made of 4 polypeptide chains.
2 identical alpha chains and 2 identical beta chains.
Each polypeptide contains a prosthetic haem group, so haemoglobin is a conjugated protein.
What ion is contained in a haem group and what is its function?
Haem group contains an iron (Fe2+) ion at its centre. This combines with oxygen at high oxygen concentrations.
How many haem groups does haemoglobin have and how many oxygen molecules can it carry?
4 haem groups
4 oxygen molecules
What is a conjugated protein?
A protein containing a prosthetic group
