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What are the two types of exocytosis?
Constitutive and regulated
What happens in constitutive exocytosis?
Substances travel to the cell surface and are released immediately
Give examples of products that are released through constitutive exocytosis
Mucus, glycoproteins of the extracellular matrix, blood proteins
What happens in regulated exocytosis?
Substances travel to the cell surface but are not released immediately
Give examples of products that are released through regulated exocytosis
Neurotransmitters, hormones, zymogen granules
What are zymogen granules?
Specialised organelles in pancreatic acinar cells for digestive enzyme storage and regulated secretion
Why is budding yeast (s. cerevisiae) used to investigate membrane traffic in the lab?
Simpler than human cells
Polarised (express asymmetry of form)
Grow in simple conditions
Easy to isolate mutations
How is budding yeast (s. cerevisiae) used to investigate membrane traffic in the lab?
Grow a beaker with a wild-type yeast cell
Use a mutagen such as radiation to induce random mutations
Isolate colonies of mutant clones which can be kept and analysed
Sec mutants are secretory mutants
What are SNARE proteins?
Proteins on the vesicle (V-SNAREs) and targets (T-SNAREs) which recognise each other and facilitate docking and fusion by carrying out a ‘molecular handshake‘
Give an example of evidence for SNARE protein docking
Scientists have engineered cells which have been ‘flipped‘ to have their SNARE proteins on the outside. Cells which have blue fluorescently-labelled external SNAREs and those with red SNAREs approach each other and fuse.
What is the name of transport towards the cell membrane?
Secretion
What is the name of transport away from the cell membrane?
Endocytosis
What are the two types of endocytosis?
Phagocytosis and pinocytosis (‘cell-eating‘ and ‘cell-drinking‘ respectively)
What is the proteasome?
A complex of proteinases involved in breaking down selected intracellular proteins
Which protein mediates the degradation of proteins?
Ubiquitin
What is the protein concentration in the cytoplasm?
20%
What state of matter is the cytoplasm?
Non-newtonian fluid (can behave like a solid when under force and resists sudden impacts but ‘melts‘ under slow, shear pressure)
What does it mean that the cytoplasm is non-uniform?
It has different microdomains
What are three effector functions of the cytoskeleton?
integration of compartments (traffic) and cell-cell signals
organelle distribution
cell motility and division
For which types of molecules is diffusion by thermal motion FAST?
ions and small molecules (ATP, tRNA, majority of mRNA)
For which types of molecules is diffusion by thermal motion SLOW?
Macromolecules and some mRNA
What are vimentin networks?
Vimentin is a major constituent of the intermediate filament protein family. Vimentin networks are known to maintain cellular integrity and provide resistance against stress.
What is thought to be the role of an actin-like substance in ancestral unicellular organisms?
Maintaining the asymmetrical shape of the cell
Why is it thought that an actin-like protein was not used as a vectoral transport system in ancestral unicellular organisms?
Because the cells were so small they would not have needed vectorial transport and could rely on diffusion alone
