Synthesis and transport of proteins Flashcards
Endoplasmic reticulum
forms
Transportation system
Forms a network of membrane tubules continuous with nuclear membrane.
Transportation system used to create and transport
- proteins
- enzymes
- and lipids.
Rough ER
Cytosolic face covered with ribosomes, connected to the nuclear membrane and smooth ER, flattened sacs called cisternae.
Smooth ER roles
No ribosomes,
- Synthesises lipids and proteins to be exported by cell
- controls calcium level in muscles
- detoxifies poisions.
Synthesis of all proteins begins in
Cytosolic Ribosomes
Cytosol
cytoplasm’s matrix, surrounds the cell organelles, fluid present in the cell membrane, while cytoplasm is all the contents of cell excluding nucleus.
Proteins within the membrane
Intrinsic proteins and external
Intrinsic proteins
Embedded in the membrane, from one side to the other
Signal sequence
short stretch of amino acids at one end of polypeptide that determines final location of protein in a cell.
Transmembrane protein
Inserted into phospholipid bi layer, permit the transport of specific substances across the membrane
So what do transmembrane proteins do
Carry a signal sequence, which halts translation and directs the ribosome to dock with the ER, forming Rough ER!
Translation continues and protein is inserted into membrane of the ER
Locations proteins can be taken to by vesicles
- Cytoplasm
- organelles like lysosomes
- cell membrane like receptor proteins
- secreted from the cell like hormones and antibodies.
Vesicles
Transport materials between membrane compartments
Movement of proteins between membranes
Proteins in the lumen of the ER are transported by vesicles that bud off and fuse with the golgie apparatus
Golgi apparatus
Series of flattened membrane discs, stacks of single membrane compartments.
Proteins moving through golgi discs
They do so in vesicles that bud off from one disc and fuse to the next one in the stack, undergoing post translational modification,
What do enzymes catalyse while proteins move through golgi
The addition of various sugars in multiple steps to form the carbohydrates
What is the major modification to proteins
addition of a carbohydrate group, now forming a fully functioning protein
Vesicles leaving Golgie
Take proteins to the plasma membrane and lysosomes, they move along microtubulea and fuse with membranes within the cell.
Secretory pathway
Secreted proteins are translated in ribosomes on the RER and enter its lumen, proteins move through Golgi and are packaged into secretory vesicles, which fuse with plasma membrane releasing the proteins from the cell.
Examples of secreted proteins
peptide hormones and digestive enzymes
Many are synthesised as inactive precursors and require proteolytic cleavage to produce proteins
Proteolytic cleavage
Process of breaking the peptide bonds between amino acids in proteins.
Type of PTM
Digestive enzymes are an example of
Secreted proteins that require Proteolytic cleavage to become active!
Proteome
Entire set of proteins expressed by a genome
Why is the proteome larger thsan the genome
More than one protein can be expressed from a single gene because of Alternative RNA splicing. Though not all genes are expressed as proteins in a particular cell type.
Genes that dont code for protein
Called non coding rna genes and include those that are transcribed to produce tRNA rRNA and RNA molecules that control the expression of other genes.
Factors affecting the set of proteins expressed by a cell type are
The metabolic activity of a cell, cellular stress, response to signalling molecules, and diseased vs healthy cells
