1. Key Area 2- Proteins Flashcards
Define proteome
The entire set of proteins expressed by a genome
Explain why the proteome is larger than the number of genes particularly in eukaryotes
As more than one protein can be produced from a single gene as a result of alternative RNA splicing
Not all genes are expressed as proteins in a particular cell type. What is the term to describe genes that do not code for proteins?
non-coding RNA genes
What do non-coding RNA genes include?
Those that are transcribed to produce tRNA, rRNA and RNA molecules that 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 the factors that affect the set of proteins expressed by a given cell type?
- metabolic activity of the cell
- cellular stress
- the response to signalling molecules
- whether the cell is diseased or healthy
Why do eukaryotes have a relatively small surface area to volume ration?
Because of their size
What is the function of Eukaryotic cells having a system of internal membranes?
Increases the total area of membrane which allows vital functions to be carried out
What is the Endoplasmic reticulum (ER)?
Forms a network of membrane tubules continuous with the nuclear membrane
What is the difference between the rough endoplasmic reticulum (RER) and the soft endoplasmic reticulum (SER)
The RER has ribosomes on its cytosolic face while the SER lacks ribosomes
What is the Golgi Apparatus
A series of flattened membrane discs
What are lysosomes?
Membrane-bound organelles containing a variety of hydrolases (class of enzymes) that digest proteins, lipids, nucleic acids and carbohydrates
What is the function of vesicles?
To transport materials between membrane compartments
What are the two types of vesicles and their functions?
- transport vesicles which move molecules within the cytosol
- secretory vesicles which transport molecules to the plasma membrane
What are the two types of vesicles and their functions?
- transport vesicles which move molecules within the cytosol
- secretory vesicles which transport molecules to the plasma membrane
Where are lipids and proteins synthesised in general
in the endoplasmic reticulum (ER)
Where are lipids synthesised
In the smooth endoplasmic reticulum (SER) and inserted into its membrane
Where does the synthesis of all proteins begin?
In the cytosolic ribosomes
Where is the synthesis of cytosolic proteins completed?
In cytosolic ribosomes and remain in the cytosol
What is the cytosol?
Is the intra-cellular fluid that is present in the cytoplasm
What are examples of cytosolic proteins?
Enzymes of glycolysis, enzymes that attach amino acids to tRNA molecules for use in protein synthesis
Describe the synthesis of transmembrane proteins?
Transmembrane proteins carry a signal sequence which temporarily halts translation and directs the ribosome synthesising the protein to dock with the ER, forming the RER.
Describe what happens after docking
Translation continues after docking and the protein is inserted into the membrane of the ER
How are proteins moved between membranes?
Once the protein is in the ER, they are transported by vesicles that bud off from the ER and fuse with the Golgi apparatus. Molecules move through the golgi discs in vesicles that bud off from one disc and fuse to the next one in the stack
What happens when proteins move through the Golgi apparatus?
They undergo post-translational modification where the major modification is the addition of carbohydrate groups
When vesicles leave the Golgi apparatus where do they take the proteins? and what happens to the vesicles?
To the plasma membrane and lysosomes. Vesicles move along microtubules to other membranes and fuse with them within the cell.
Where are secreted proteins translated?
In ribosomes on the RER and enter its lumen
What are examples of secreted proteins?
Peptide hormones (insulin) and digestive enzymes (pepsin)
Describe the secretory pathway
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. These vesicles move to and fuse with the plasma membrane releasing the proteins out of the cell.
What is the function of proteolytic cleavage?
To produce active proteins
Why do many secreted proteins require proteolytic cleavage?
Due to many secreted proteins being synthesised as inactive precursors and require proteolytic cleavage to produce active proteins