Proteins Flashcards
Proteome
The entire set of proteins expressed by a genome
The proteome is larger than the number of genes because…?
more than one protein can be produced from a single gene as a result of alternative RNA
splicing
The endoplasmic reticulum (ER)
forms a network of membrane tubules continuous with the
nuclear membrane
The Golgi apparatus
is a series of flattened membrane discs
Lysosomes
are membrane-bound organelles containing a variety of hydrolases that digest
proteins, lipids, nucleic acids and carbohydrates
Vesicles
transport materials between membrane compartments
Lipids and proteins are synthesised in…
the ER
The synthesis of all proteins begins in…
cytosolic ribosomes
signal sequence
Transmembrane proteins carry these which halt translation and directs the ribosome synthesising the protein to dock with the ER to form RER
Once the proteins are in the ER, they are transported by…
vesicles that bud off from the ER
and fuse with the Golgi apparatus
post-translational modification
occurs in the Golgi apparatus as proteins move through it. This is the addition of carbohydrates to the protein.
Vesicles that leave the Golgi apparatus take proteins to…
the plasma membrane and
lysosomes
Vesicles move along…
microtubules to other membranes and fuse with them within the cell
Secreted proteins are translated in
ribosomes on the RER and enter its lumen. The proteins move through the Golgi apparatus and are then packaged into secretory
vesicles
How are secretory proteins released from the cell?
vesicles move to and fuse with the plasma membrane, releasing the proteins out of
the cell
How are inactivated secretory proteins activated?
proteolytic cleavage
Primary structure
the sequence in which the amino acids are synthesised into the polypeptide
How are secondary structures formed and what are they?
Hydrogen bonding along the backbone of the protein strand results in regions of secondary
structure — alpha helices, parallel or anti-parallel beta-pleated sheets, or turns
tertiary structure
The polypeptide folds into a conformation that is stabilised by interactions between R groups: hydrophobic interactions;
ionic bonds; London dispersion forces; hydrogen bonds; disulfide bridges
Quaternary structure
exists in proteins with two or more connected polypeptide subunits
prosthetic group
a non-protein unit tightly bound to a protein and necessary for its function
ligand
a substance that can bind to a protein. R groups not involved in protein folding can allow binding to ligands.
When a ligand binds to a protein…
The conformation of the protein changes and therefore its function changes.
Allosteric interactions occur between..
spatially distinct sites
allosteric proteins consist of
multiple sub-units (quaternary structure)
co-operativity
changes in binding at one subunit alter the affinity of the remaining subunits
Modulators
Modulators regulate the activity of the enzyme when they bind to the allosteric site. Following binding of a modulator, the conformation of the enzyme changes and this alters
the affinity of the active site for the substrate
co-operativity in haemoglobin
When oxygen binds at one sub-unit of
haemoglobin this changes the conformation of
the remaining sub-units, increasing their affinity.
A decrease in pH and an increase in temperature…
lowers the affinity of haemoglobin for oxygen. Therefore the binding of oxygen to haemoglobin
is reduced.
common form of post-translational modification
The addition or removal of phosphate can cause reversible conformational change in
proteins
Protein kinases
catalyse the transfer of a phosphate group to other proteins
The terminal phosphate of ATP is transferred to specific R groups
Protein phosphatases
catalyses the removal of a phosphate group from a protein
Phosphorylation
brings about conformational changes, which can affect a protein’s activity
The activity of many cellular proteins, such as enzymes and receptors, is regulated in this
way
Some proteins are activated by phosphorylation while others are inhibited
