BIOL 1090 Study Guide - Midterm Guide: Inner Mitochondrial Membrane, Integral Membrane Protein, Peripheral Membrane Protein

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Published on 1 Mar 2013
Department
Course
BIOL 1090 Midterm Notes
50 Marks
- MC
- SA
- Paragraph/point form/label diagram
Basic Properties of Cells
- Complex and organized
o Contain large number of parts
o Organized with respect to time and
space
o Interaction with little tolerance for
error
o Control and regulation is maintained
o Complexity allows cells to be diverse
o Cellular organization is consistent and conserved through evolution
therefore there may be similarities between many cells in specific
parts and pieces
- Maintain and use a genetic program
- Reproduction
- Acquire and utilize energy
- Support enzyme-catalyzed chemical reactions
- Mechanical activities
- Response to stimuli
- Self-regulation
- Evolve
Two Classes of Cells on Earth
1) Prokaryotic
- Bacteria
- Structurally simpler
2) Eukaryotic
- Protists, fungi, plants and animals
- Structurally more complex
Viruses
- Non-cellular macromolecular
packages
- Reproduce only in living cells
- Virus outside of a cell is called a virion
- Virion is comprised of a small amount of DNA/RNA and a protein
capsule (capsid)
- Very small compared to other eukaryotic and prokaryotic cells
- Can bind to a cell surface via specific proteins
o Narrow host versus wide host range
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- Two main types of viral infections
o Lytic: production of virus particles ruptures and kills the cell
(e.g. influenza)
o Non-lytic (or integrative): viral DNA is inserted into the host
genome (provirus) and the viral progeny buds at the cell
surface and the cell can survive, but often with impaired
function (e.g. HIV)
Fluid-Mosaic Model (Singer/Nicolson, 1972)
- Bilayer of amphipathic lipids
o Amphipathic: both hydrophilic and hydrophobic
- Integral (transmembrane), peripheral and lipid-anchored proteins
- Components are mobile and can interact
The Cell Membrane
- Layer of lipids interacting with another layer
- Biological membranes contain a hydrated lipid bilayer
- All membranes share common properties
o Approximately 6nm thick (with associated water)
o Stable
o Flexible
o Capable of self assembly
- Different membranes contain different types of lipids and proteins
- Membranes have different functions, in different cells and within an
individual cell
- Inner membrane of mitochondria contains a very high concentration
of protein because it is a metabolic centre (ATP synthesis)
- Myelin sheath of a neuron contains very low amounts of protein and
consists of layers of plasma membrane wrapped around the nerve
axon for insulation
- Contain specific proteins that are needed at that specific location to
complete a job
- Asymmetrical
- Two leaflets have distinct lipid composition
- In many plasma membranes, the outer leaflet contains glycolipids and
glycoproteins
- Lipids move easily, laterally, within leaflet (or layer)
- Lipid movement from leaflet to another leaflet is slow because of
physical restriction and must be done by an enzymatic process
- Membrane proteins can diffuse within the bilayer
o Movement of proteins is restricted and some proteins do not
move
o Biochemical modification can dramatically alter protein’s
mobility in the membrane
Membrane Proteins
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- Integral Membrane Proteins
o Span the lipid bilayer
o Can stick out on either side
o Compatible with the hydrophobic environment in the membrane
o Very stable
- Lipid-anchored proteins
o Attached to a lipid in the bilayer
o Interacts with the hydrophobic nature and holds the molecule that I
associated with the membrane
- Peripheral membrane proteins
o Associate with the surfaces of the lipid bilayer
o Not permanently attached to the membrane
o Allows them to associate with hydrophilic parts of membranes or will
associate with another part of another protein
o Charged, electrostatic interactions and usually hydrophilic
o Not as stably associated as integral membranes
Membrane Fluidity
- Determined by the nature of lipids in the membrane, temperature
o Unsaturated lipids increase fluidity while unsaturated lipids reduce
fluidity
o An increase of temperature increases fluidity (because of more
molecular motion) into a liquid crystal while cooling decrease fluidity,
turning the membrane into a crystalline gel
- Balance between ordered (rigid) structure and disordered structure
- Allows mechanical support and flexibility
- Dynamic interactions between components of the membrane
- Important for membrane assembly and modification
- Lipid composition of membranes can be altered by the desaturation of lipids
or the exchange of lipid chains, but usually only occurs in response to
temperature changes in eukaryotes who do not have control over their
internal temperature
- Cholesterol regulates membrane fluidity
o Cholesterol is hydrophobic and has contrasting effects depending on
the situation
o Alters packing and flexibility of lipids
o If added to a liquid crystal membrane, fluidity will decrease
o If added to a crystalline gel membrane, fluidity
will increase
Lipid Rafts
- Small areas of the plasma membrane that are enriched
in certain types of lipids (e.g. cholesterol)
- Rafts are relatively rigid
- Some membrane proteins accumulate in rafts
- Specialized component of the membrane
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