Proteins Flashcards
What is the proteome?
The entire set of proteins expressed by a genome
Why is the proteome smaller/larger than the number of genes, particularly in eukaryotes?
It is larger because more than one protein can be produced from a single gene as a result of alternative RNA splicing
What do non-coding RNA genes, code for?
tRNA, rRNA and RNA molecules that control the expression of other genes
Name some factors affecting the set of proteins expressed by a given cell type
Metabolic activity of the cell, cellular stress, response to signalling molecules and diseased vs healthy cells
What is unique about eukaryotic cells?
They have a system of internal membranes, which increases the total area of the membrane
Why is it eukaryotic cells have their unique feature?
Eukaryotes have a relatively small surface area to volume ratio (because of their size) and therefore the plasma membrane is too small an area to carry out all the vital functions carried out by membranes
Describe the structure of the endoplasmic reticulum
It forms a network of membrane tubules continuous with the nuclear membrane
What is the job of the endoplasmic reticulum?
To fold proteins and transport translated proteins to the Golgi apparatus
What is different between the RER and the SER
RER has ribosomes on its cytosolic face and SER lacks ribosomes
Describe the structure of the Golgi apparatus
A series of flattened membrane discs
What is the job of the Golgi apparatus?
To process and package the proteins to be used inside/outside the cell
What are lysosomes?
Membrane-bound protein bound organelles containing a variety of hydrolases that digest proteins, lipids, nucleic acids and carbohydrates
What are vesicles and what do they do?
They are fluid filled sacs which transport materials between different membrane compartments
Where does the synthesis of all proteins begin?
In the cytosolic ribosomes
Where does the synthesis of cytosolic proteins occur?
In the cytosolic ribosomes
How do transmembrane proteins end up on the ER
A signal sequence halts translation at the cytosolic ribosome and directs the ribosome to the ER to form the 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 the ribosome is docked to the ER
Translation continues again and the protein gets inserted into the membrane of the ER. Once translation is finished, the ribosome detaches.
Summarise the 5 stages of transmembrane protein synthesis
- Protein synthesised by ribosomes in cytoplasm
- SRP binds to ribosome and stops translation
- SRP binds to receptor which directs the ribosome to attach to the ER
- Translation restarts and protein inserted into ER membrane
- Ribosome detaches once translation is completed
What transports proteins from the ER to the Golgi apparatus
Vesicles
What happens once lipids are synthesised in the SER
They are inserted into its membrane
