1.2 proteins Flashcards
what is the proteome?
the entire set of proteins expressed by a genome
why is the proteome larger than the genome?
due to alternative splicing and post-transational modification (more than one protein being produced by a single gene)
what is the name for genes that do not code for a protein?
non-coding RNA genes
which genes are included in non-coding RNA genes?
those that are needed to transcribe tRNA, rRNA, and other RNA molecules that directly control the expression of other genes
the set of proteins expressed by a given cell
type can vary over time and under different
conditions. what are some factors that affect this?
metabolic activity
cellular stress
response to signalling molecules
diseased vs healthy cells
eukaryotes have a relatively small surface area : volume ratio. what does this mean?
the plasma membranes of these cells are too small to carry out the vital functions required
what is present in eukaryotic cells to account for the small plasma membrane?
a system of internal membranes to increase the total surface area
what are the endoplasmic reticula? (ER)
a network of membrane tubules that are continuous with the nuclear membrane
what are the golgi apparatus?
a series of flattened membrane discs
what are lysosomes?
membrane-bound organelles that contain a variety of hydrolases that digest
proteins, lipids, nucleic acids and
carbohydrates
what is the role of vesicles?
transport materials between membrane compartments
where are lipids made before being inserted into the membrane?
in the SER
in which type of ribosome are all proteins made?
in the cytosolic ribosomes
what happens once cytosolic proteins are synthesised?
they remain in the cytosol (liquid part of the cytoplasm)
what is the purpose of the signal sequence carried by transmembrane proteins?
to halt translation and direct the ribosome synthesising the protein to dock
with the ER, forming RER
what is a signal sequence?
a short stretch of amino
acids at one end of the polypeptide that
determines the eventual location of a protein
in a cell
what happens after docking?
translation continues and the protein is inserted into membrane of the ER
what happens once proteins have been synthesised at the ER?
they are transported to the Golgi apparatus by vesicles that bud off of the ER
how do molecules move through the Golgi?
in vesicles that come from one disc and fuse to another
what happens at the Golgi apparatus?
post-translational modification
what is classed as major protein modification?
the addition of sugars in steps to form carbohydrates (catalysed by enzymes)
what happens once post-translational modification is completed?
vesicles take the modified proteins to the plasma membrane and lysosomes, which bind to the membrane and allow the proteins to be released
how to vesicles move from one structure to another?
along microtubules, fusing to other membranes within the cell
what are examples of secreted proteins?
peptide hormones and digestive enzymes
what are the steps of the secretory pathway?
1) translation in RER, proteins enter lumen
2) proteins move through Golgi and packaged into vesicles
3) vesicles fuse to pm and proteins are released
many proteins are synthesised as inactive precursors. what is required to produce active proteins from them?
proteolytic cleavage