The Cell - The smallest living human subunit Flashcards
Why are we interested in Compartmentalisation?
Allows for regions of different composition and function to co-exist (maintains low entropy)
Separators cause different regions to have different composition: different chemical reactions and different molecular composition.
What makes a good separator?
Insoluble in water (does not dissolve in water)
Non-rigid; Flexible to accommodate expansion and contraction in response to cellular dynamics
Why are lipids a good and bad separator?
Lipids are good separators as oil and water don’t mix
However, they have minimal surface area as parts of a lipid repels water
Define amphipathic molecules
Molecules with a polar/hydrophilic region and a non-polar/hydrophobic region
Describe the features of a phospholipid
Long chain of fatty acids (two per molecule)
A bridging organic molecule (typically glycerol or some form of sphingosine)
A phosphate group
A polar small organic molecule (typically choline or serine)
What structures do phospholipids form?
Phospholipids (as amphipathic molecules) form lipid bilayers and hence cell membranes.
The hydrophobic tails repel water coming together exposing the hydrophilic region to the aqueous environment
What characteristic does fatty acids determine in phospholipid?
Fluidity and Flexibility
What characteristic does polar groups determine in a phospholipid?
Chemical properties of surface
What characteristic do both fatty acids and polar groups determine in a phospholipid molecule?
Protein binding
How does communication between compartments occur in a cell?
Exchange of small molecules
Exchange of large molecular assemblies
Signalling (without transit of molecules across compartments)
How does exchange of small molecules occur?
- Non-polar molecules diffuse through lipid bilayer
- Polar molecules can’t diffuse through lipid bilayer. They use transporter proteins (usually contain hydrophobic regions embedded in bilayer and hydrophilic regions in contact with aqueous solution)
What are the ways of classifying membrane transporters?
Specificity of the solute that they will allow through
Direction in which the solute passes across the membrane in relation to their concentration gradients
Describe the features of a channel protein
Allow many solutes through such as ions
Moves solutes down concentration gradients (from higher concentration to lower concentration)
Carrier proteins also moves solutes down concentration gradients
Describe the features of a pump
Doesn’t allow as many solutes through (more selective than channel and carrier proteins)
Pumps move solutes upwards from low concentration to high concentrations.
This requires energy in the form of ATP that lowers the entropy to make the system more organised
This means pumps cause different composition in their compartments
What are the three ways in which large molecular assemblies are exchanged?
- Vesicle Formation/membrane fusion
- Nuclear Pore Complex (NPC)
- Clathrin
Describe the features of the mitochondria
Biochemistry is prokaryote, not eukaryote
Have own “bacterial” genome and replicates autonomously - this is another whole genome in our cells
Main function is respiration - depending on forming a H+ gradient across the mitochondrial membrane
Double Membrane
How does the electron transport chain help with the formation of ATP
Electron transport chain pumps proton out the inner membrane and the pH gradient is maintained by the presence of the outer membrane
Then relaxation of the H+ gradient drives ATP synthesis
Describe the features of the Endoplasmic Reticulum
Receives newly synthesised proteins (coated with ribosomes - “Rough” ER)
Ensures proper protein folding (chaperoning)
Performs protein quality control with misfolded proteins tagged for degradation - Endoplasmic Reticulum
Associated Degradation
From these two functions, the ER is a stress-response organelle and is actively researched as a drug target
Other compartmentalised synthetic functions apart from protein synthesis is the smooth ER are lipid synthesis and hepatic enzymatic activity
Describe the features of the Golgi Apparatus
Initial step of the vesicular transport system that delivers proteins to specific compartments or to the cell exterior
Proteins are tagged, typically by glycosylation according to the compartment in which they must be delivered.
Both ER and Golgi display directional movement, from protein synthesis near the nucleus to vesicle formation and delivery to the cell membrane
Membranes move inside the cell, and do so with a well define direction
Describe the features of microtubules
Microtubules are formed by the polymerisation of two proteins: alpha and beta tubulin
A microtubule grows in one direction only
Hence, microtubules are asymmetric with a + end and a - end.
The - end is usually attached to a structure e.g. a centriole or microtubule organising centre - MTOC containing y-tubulin while the + end is free to grow
What are the name of ATP-dependent motor proteins?
Kinesins and dyneins
What is the function of kinesins and dyneins
ATP-dependent motor proteins that drag cargo (e.g. vesicles) along microtubules towards either the + end (anterograde) or the - end (retrograde), respectively.
This ATP-powered motor system provides directional movement for membranes and vesicles
How is cell motility achieved?
Cell motility is achieved by polymerisation of a protein called actin (G-actin when in globular, unpolymerized form)
Fibres of polymerised actin (F-actin) push cell membranes forward
Actin fibres also provide “tracks” for myosin, which cause contraction of muscle cells
How is DNA packaged into chromatin?
DNA wraps around four histone molecules: H2a, H2b, H3 and H4 (plus a “linker” histone H1)
Histone acetylation determines chromatin opening and DNA accessibility for transcription
What is the name of the membraneless organelle?
Nucleolus
Describe the features of nucleolus
Synthesises ribosomal RNA (RNA polymerase I)
Process initial RNA into smaller fragments
Pre-assembles and exports ribosomes
Many viral proteins “piggyback” on nuclear export
Highly sensitive to stress - particular metabolic stress due to high energy demand of RNA synthesis
Define Karyokinesis
The separation of chromosomes is termed karyokinesis
What is the name of the motors that pull the daughter chromatids along the microtubules towards the daughter of the cells?
Kinetochore
Define kinetochore
Motors that pull the daughter chromatids along the microtubules towards the daughter of the cells
Where is the minus end of the microtubules situated in mitosis?
In the centriole of the chromosome
