Cell Sorting (Biomedical Science)

Cells To Systems - Cell Sorting
Cell Sorting - Endocytosis & Exocytosis

Location:

 Right protein, right place, right time is essential to properly function
 Being in the wrong location does not allow it to fulfil its functions
 Location of organs/organ system within the body is essential for function
 Location within the cell e.g. right protein in the right organelle is essential for function
 Eukaryotes have multiple sub-cellular organelles, where each have specific functions, so it is important to have the
correct proteins
 Specialised function requires proteins
- Nucleus needs nuclear proteins as it has all the nuclear functions to replicate e.g. DNA needs DNA polymerase
- ER needs ER proteins

‘Roadmap’ Of Protein Traffic:

 A lot of trafficking in the cell

3 Mechanisms Of Protein Transport:

1. Gated transport
2. Transmembrane transport
3. Vesicular transport

Gated Transport:

 Occurs in both directions
 Changes molecules between the cytosol and the nucleus

Transmembrane Transport:

 Occurs in 1 direction
 From cell cytosol to different organelles but selects certain organelles e.g. peroxisomes, plastids, endoplasmic
reticulum, mitochondria

Vesicular Transport:

 Occurs in 1 and both directions
 Traffic of molecules between Golgi and other organelles in the cell surface

 All proteins are translated in ribosomes and cell cytosol, and have to reach the final destination
e.g. Golgi enzyme in Golgi, whether it’s a secreted protein, or if it has to stay in the ER, or go to the nucleus (needs
to know where it’s going and how to get there)

Direction:

 Proteins know where to go as it is encoded in the protein structure
 Destination depends on amino acid sequence, some part of it will encode an address (sorting signal) or where
destination proteins need to go
 Most proteins lack sorting signal/address added, meaning they will remain in cytosol
 If a protein needs to go to a specific organelle, it will have a specific signal sequence or sorting signal that directs it
to its final destination




Topological Relationship Between Compartments:
1

, Cells To Systems - Cell Sorting
 If a eukaryotic cell is injected with a dye, it fills the cytosol and nucleus
 Extracellular space is the same colour as/connects with lumen of some organelles that
are membrane bound e.g. ER, Golgi, vesicles, lysosomes, perinuclear space
 Cytosol connects with inside of the nucleus and lumen of certain organelles
is the same as the extracellular space
Eukaryotic Cell
Signal Sequences:
Signal Sequence/Address - Tells proteins where to go

 Sequences that are encoded in amino acid structural protein are recognised
by complementary receptor proteins (address will be recognised by certain receptor and will guide it to where it
needs to go)
 Can be continuous (either 1 or other side of protein) or discontinuous
 Signal is removed after sorting by enzymes
 Signal may or may not be part of the final protein

Can Be In The Middle:

 Consists of several patches of the protein
 Protein folds together in the final confirmation and makes a 3D structure
 The signal parts are coming together and forming a signal patch
 Localised in 1 location
 Can be recognised by the receptor and guide the protein to its final destination




Import = Charged
Export = Hydrophobic

What Happens When The Address Is Changed?
Make mutations to these signal sequences



 Protein will localise in the nucleus
 Has positively charged amino acid stretch



 Change 1 amino acid (Thr)
 Localisation of proteins becomes very different
2
 Cell nuclei hasn’t gone to the nucleus, but has
stayed in the cell cytosol
 Address has been changed, can’t reach its final
destination so stays in the cell cytosol