Proteins Flashcards
(37 cards)
Describe the functions of proteins
Proteins have a huge range of functions within the body. o Movement o Protection o Transport o Enzymes o Receptors o Structural o Storage o Hormones o Control of gene expression
Define the primary structure of a protein
The sequence of amino acids in a polypeptide chain. This is the source of versatility in protein structure and function.
Define the secondary structure of a protein
The spatial arrangement of amino acid residues that are near each other in the linear sequence.
• Alpha Helices
A telephone cord shape held in place by H Bonds between the N-H group and the C=O group of the amino acid in the next turn of the helix.
• Beta Sheet
The pleated structure is held together by H bonds between the amide groups of linear polypeptide chains.
Define the tertiary structure of a protein
The spatial arrangement of amino acid residues that are far apart in the linear sequence. This depends on: • Van der Waals • Ionic Interactions • Hydrogen Bonding • Disulphide bridges • Hydrophobic interactions
Define the quarternary structure of a protein
Refers to the spatial arrangement of individual polypeptide chains in a multi-subunit protein.
Define the 4 classes of naturally occurring amino acids.
Basic
Acidic
Uncharged polar
Polar
Name some acidic amino acids
- Aspartic Acid
* Glutamic Acid
Name some basic amino acids
- Lysine
- Arginine
- Histidine
HAL is basic af
Name some uncharged polar amino acids
- Asparagine
- Glutamine
- Serine
- Threonine
- Tyrosine
STTAG (e.g. stag horns)
Name some polar amino acids
- Glycine
- Alanine
- Valine
- Leucine
- Isoleucine
- Proline
- Phenylalanine
- Methionine
- Tryptophan
- Cysteine
Name some sulphur containing amino acids
Cysteine
Methionine
Name some aromatic amino acids
Phenylalanine
Tyrosine
Tryptophan
Describe the basic structure of an amino acid
Amino acids are biologically important organic compounds containing amine (-NH2) and carboxylic acid (-COOH) functional groups, along with a side-chain (R group) specific to each amino acid
How many codons are there in the genetic code?
64, some redundancy
What occurs in protein denaturation?
- Denaturation of proteins involves the disruption and possible destruction of both the secondary and tertiary structures.
- Denaturation reactions are not strong enough to break the peptide bonds, so the primary structure remains the same after a denaturation process
What can cause protein denaturation?
- Acids
- Heat
- Solvents - Ethanol, methanol
- Cross linking reagents - Formaldehyde
- Chaotropic agents – Urea (disrupts hydrogen bonding between water molecules, affects stability of other molecules in solution)
- Disulphide bond reducers - 2 mercaptoethanol
What effects does denaturation have on proteins?
- Decreased solubility
- Altered water binding capacity
- Loss of biological activity
- Improved digestibility
Name the enzyme involved in protein degradation and describe its different activity
Peptidases - cleave peptide bonds
Endopeptidases - cleavage of internal bonds
Exopeptidases - cleave off one aa at a time
Carboxypeptidases - cleave from carboxylic end
Aminopeptidase - cleave at amine end
Describe the composition of a glycoprotein
Protein + carbohydrate
Formed by post translational modification reaction glycosylation, e.g. immunoglobulins
Describe glycosylation and where it occurs in a cell
- Glycosylation is the reaction in which a carbohydrate, i.e. a glycosyl donor, is attached to a hydroxyl or other functional group of another molecule (a glycosyl acceptor). In biology glycosylation mainly refers in particular to the enzymatic process that attaches glycans to proteins, lipids, or other organic molecules.
- Process occurs in the ER and Golgi network.
Describe lipoproteins and their function, including some examples
Protein and lipids that are either covalently or non-covalently bonded together. Their main function is for the transport of water-insoluble fats and cholesterol in the blood e.g. HDL, LDL
Describe some metalloproteins and their functions
Protein molecule with a bound metal ion. Functions include:
o Enzymes
o Storage
o Signalling
o Transport
Importance can be seen in anaemia, when there is an iron deficiency that affects the functionality of haemoglobin.
Describe haemoglobin’s structure, and the role of its structure in its function
Haemoglobin is the iron-containing oxygen-transport metalloprotein in the red blood cells of all vertebrates as well as the tissues of some invertebrates.
The hemoglobin molecule is an assembly of four globular protein (2 x α + 2 x β) subunits. Each subunit is composed of a protein chain tightly associated with a non-protein heme group. Each protein chain arranges into a set of alpha-helix structural segments connected together in a globin fold arrangement, so called because this arrangement is the same folding motif used in other heme/globin proteins such as myoglobin. This folding pattern contains a pocket that strongly binds the heme group.
A heme group consists of an iron (Fe) ion (charged atom) held in a heterocyclic ring, known as a porphyrin.
Haem group at the centre of each polypeptide chain binds one molecule of oxygen.
So that one haemoglobin molecule can bind four molecules of oxygen
Cooperative binding
What is cooperative binding?
Seen in oxygen binding to haemoglobin.• The binding of O2 to one sub-unit alters its shape.
This in turn causes a change in the shape of the other sub-units, so that they bind O2 more easily.
