Lecture 1 Flashcards
What are cells
Highly dynamic; constituent elements all in continuous state of flux; dynamic self organising system.
Self-organising
Cell scale phenomena - spatial and temporal organisation. Cell has to manage interactions between actin monomers and other constituent elements.
Self organising systems require continuous energy input. => Entropy; not favourable to greater organisation.
1 human lifetime
10^9 seconds
Cells are made out of
Atoms, mostly C, H2O.
Macromolecules - proteins, nucleic acids, lipids, sugars.
size of protein
Median size = approx 400 AAs, 40kDa, 5nm.
But, large range.
Median lifetime of protein
in human cells, 2 days; varies based on type of protein.
Size of bacterial cell
1um.
Generally, cells tend to be in micron range; but there’s a huge amount of morphological diversity - relative sizes are important. Proteins are at least 3 orders of magnitude smaller than cells.
Size of nucleus
Tends to scale with cell size.
Diameter approx 10 um in human cells.
Size of human genome
1 m, which is much bigger than 10um nucleus diameter.
The human genome contains approximately
one billion base pairs.
Each base pair is approximately 1 nm long.
Typical lifetime of a cell
Cells can live up to 4
orders of magnitude
longer than the
typical protein
Neurons - most mitotic. Red blood cells - live 4 months, but no nucleus. Haemoglobin is very stable - approx 120 day lifetime.
How do cells regulate interactions among macromolecules
and thus large-scale cellular phenomena?
Cells control:
- Localization patterns
- Expression levels (changes probability of interactions)
- Binding affinities (strength of binding between molecule A and B).
TOR
master regulator of cell growth. Regulates binding affinities; determined by non covalent bonds between macromolecules. TOR modifies likelihood of these bonds forming.
TOR = kinase; Kinase - adds P group to protein. Post-translational modifications can change morphology of protein, changing the binding ability.
How do cells control binding affinities?
By regulating post-translational modifications, protein conformation, and formation of non-covalent bonds.
Impact of TOR-mediate phosphorylation on localisation patterns and expression levels?
Regulates the localisation of TFs ==> expression levels.
How do cells control expression levels
Cells control expression levels by regulating transcription,
translation, and degradation
Cell type diversity in multicellular organisms is dependent on what
on cell type-dependent
differences in gene expression
6 points of control of protein expression from transcription to degradation
- transcriptional control
- RNA processing control
- RNA transport and localisation control
- translational control OR 5. mRNA degradation control.
- If translated, protein degradation control.
How long does up regulation of protein expression take
Hours to days.
Cells controlling binding affinities vs contolling expression levels
1st is FAST. 2nd is SLOW.
How do cells control localisation patterns
Cells control localization patterns via active and passive transport
mechanisms and compartmentalization
Role of membrane bound organelles
Organise the cell.
Membranes are physical barriers between
organelles and the surrounding cytoplasm.
Active and passive transport mechanisms
allow molecules to cross membranes.
Membrane bound organelles
Include Golgi apparatus, ER, nucleus, mitochondria, and cytoplasmic membrane.
Membrane-less organelles
Germ granules, stress granules, nuclear bodies, balbiani body, centrosomes. P bodies.
Protein, RNA condensates form via intracellular phase transitions.
How do cells regulate interactions among constituent elements
by controlling
binding affinities, expression levels, and localization patterns
