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BIOL*1090
Introduction To Molecular and Cellular Biology Fall 2014 Lecture 3 - Sept. 15, 2014
• Viruses • Biological Membranes Karp 7th ed: Chpt. 4; sections 4-1, 4-3 to 4-7 1
2
VIRUS Non-cellular macromolecular packages that can function and reproduce only within living cells
• outside of cells, a virus exists as an inanimate particle (= VIRION)
Tobacco Mosaic Virus (TMV)
• VIRION comprised of - small amount of DNA or RNA (encoding a few to hundreds of genes) Fig 1.21
- PROTEIN capsule (= capsid)
4
3
Viruses bind to a cell surface via specific proteins and enter into cell - this defines the cell types the virus can infect and the host range Adenovirus WIDE host range: - rabies can infect cells in dogs, bats, and humans Human immunodeficiency virus (HIV)
NARROW host range - human cold and influenza viruses infect epithelial cells of human respiratory system
T-even bacteriophage
Fig 1.21 5
6
Once inside a cell, the virus hijacks cellular machinery to synthesize nucleic acids and proteins
Virus Life Cycle
‣ assembles new virus particles Two main types of viral infection: 1) LYTIC: production of virus particles ruptures (and kills) cell (e.g. influenza) 2) NON-lytic or INTEGRATIVE: viral DNA is inserted in host genome DNA = PROVIRUS; viral progeny bud at cell surface; cell can survive, often with impaired function (e.g HIV) 8
7
Function of Biological Membranes • cell boundary *
The Plasma Membrane
• define /enclose compartments • control movement of material into/out of cell * • allow response to external stimuli *
Fig 4.1
• enable interactions between cells * • provide scaffold for biochemical activities ** * plasma membrane only ** including energy transduction
Electron micrograph of a muscle cell
9
10
The Fluid-Mosaic model of biological membranes
~ 6 nm thick
trilaminar Fig 4.4
11
Fluid - individual lipid molecules can move Mosaic - different particles penetrate the lipid layer 12
Structure of Biological Membranes
Biological membranes contain a hydrated lipid bilayer
• Fluid-mosaic Model (Singer/Nicolson, 1972) - bilayer of amphipathic lipids - proteins:
- integral (transmembrane) - peripheral - lipid-anchored
• components are mobile • components can interact
Fig 4.3 Fig 4.4 13
14
Structure of Biological Membranes • all membranes share common properties ~ 6 nm thick (with associated water) - stable - flexible - 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 15
Structure of Biological Membranes An example of differential membrane structure:
• The inner membrane of mitochondria contains a very high concentration of protein.
16
Electron micrograph of a nerve cell axon (cross section) showing myelin sheath, a modified plasma membrane structure.
- Why?
• The myelin sheath of a neuron contains very low amounts of protein. Myelin sheath consists of layers of plasma membrane, forming insulation around the nerve axon.
Fig 4.5 17
18
3 Classes of Membrane Proteins:
Different areas of the plasma membrane perform different functions
INTEGRAL membrane proteins span the lipid bilayer
e.g. epithelial cell LIPID-ANCHORED proteins attach to a lipid in the bilayer
PERIPHERAL membrane proteins associate with the surfaces of the lipid bilayer Fig 4.13
19
20
Fig 4.30
Fluidity: an Important Feature of Biological Membranes Membrane fluidity is determined by:
• nature of lipids in membrane - unsaturated lipids increase fluidity - saturated lipids reduce fluidity Fig 4.4
• temperature - warming increases fluidity
Biological Membranes are Asymmetrical • two leaflets have distinct lipid composition
= liquid crystal
• in many plasma membranes, the outer leaflet contains glycolipids and glycoproteins (lipids and proteins with carbohydrate attached)
- cooling decreases fluidity 21
Transition temperature
warm
= crystalline gel
22
Membrane Fluidity is Crucial to Cell Function cool
• BALANCE between ordered (rigid) structure and disordered structure allows: - mechanical support and flexibility
Fig 4.23
liquid crystal state
crystalline gel state
- dynamic interactions between membrane components (e.g. proteins can come together reversibly) - membrane assembly and modification
23
24
Dynamic properties of the plasma membrane
Membrane Fluidity is Crucial to Cell Function • membrane fluidity must be maintained • in response to changes in temperature*, lipid composition of membranes can be changed by: 1) desaturation of lipids 2) exchange of lipid chains
Fig 4.8
Fig 8.45
Ruffles on the plasma membrane of a moving cell
A leukocyte ingesting a yeast cell
(e.g. Listeria monocytogenes changes the lipid content of its plasma membrane while growing at 10o C) 25
Biological Membranes are Dynamic • lipids move easily, laterally, within leaflet • lipid movement to other leaflet is slow • membrane proteins can diffuse within bilayer - movement of proteins is restricted - some proteins do not move - rapid movement is spatially limited - long range diffusion is slow - biochemical modification can dramatically alter protein mobility in the membrane (part of signal transduction) 27
26
BIOL*1090
Introduction To Molecular and Cellular Biology Fall 2014 Lecture 3 - Sept. 15, 2014
• Viruses • Biological Membranes Karp 7th ed: Chpt. 4; sections 4-1, 4-3 to 4-7 1
2
VIRUS Non-cellular macromolecular packages that can function and reproduce only within living cells
• outside of cells, a virus exists as an inanimate particle (= VIRION)
Tobacco Mosaic Virus (TMV)
• VIRION comprised of - small amount of DNA or RNA (encoding a few to hundreds of genes) Fig 1.21
- PROTEIN capsule (= capsid)
4
3
Viruses bind to a cell surface via specific proteins and enter into cell - this defines the cell types the virus can infect and the host range Adenovirus WIDE host range: - rabies can infect cells in dogs, bats, and humans Human immunodeficiency virus (HIV)
NARROW host range - human cold and influenza viruses infect epithelial cells of human respiratory system
T-even bacteriophage
Fig 1.21 5
6
Once inside a cell, the virus hijacks cellular machinery to synthesize nucleic acids and proteins
Virus Life Cycle
‣ assembles new virus particles Two main types of viral infection: 1) LYTIC: production of virus particles ruptures (and kills) cell (e.g. influenza) 2) NON-lytic or INTEGRATIVE: viral DNA is inserted in host genome DNA = PROVIRUS; viral progeny bud at cell surface; cell can survive, often with impaired function (e.g HIV) 8
7
Function of Biological Membranes • cell boundary *
The Plasma Membrane
• define /enclose compartments • control movement of material into/out of cell * • allow response to external stimuli *
Fig 4.1
• enable interactions between cells * • provide scaffold for biochemical activities ** * plasma membrane only ** including energy transduction
Electron micrograph of a muscle cell
9
10
The Fluid-Mosaic model of biological membranes
~ 6 nm thick
trilaminar Fig 4.4
11
Fluid - individual lipid molecules can move Mosaic - different particles penetrate the lipid layer 12
Structure of Biological Membranes
Biological membranes contain a hydrated lipid bilayer
• Fluid-mosaic Model (Singer/Nicolson, 1972) - bilayer of amphipathic lipids - proteins:
- integral (transmembrane) - peripheral - lipid-anchored
• components are mobile • components can interact
Fig 4.3 Fig 4.4 13
14
Structure of Biological Membranes • all membranes share common properties ~ 6 nm thick (with associated water) - stable - flexible - 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 15
Structure of Biological Membranes An example of differential membrane structure:
• The inner membrane of mitochondria contains a very high concentration of protein.
16
Electron micrograph of a nerve cell axon (cross section) showing myelin sheath, a modified plasma membrane structure.
- Why?
• The myelin sheath of a neuron contains very low amounts of protein. Myelin sheath consists of layers of plasma membrane, forming insulation around the nerve axon.
Fig 4.5 17
18
3 Classes of Membrane Proteins:
Different areas of the plasma membrane perform different functions
INTEGRAL membrane proteins span the lipid bilayer
e.g. epithelial cell LIPID-ANCHORED proteins attach to a lipid in the bilayer
PERIPHERAL membrane proteins associate with the surfaces of the lipid bilayer Fig 4.13
19
20
Fig 4.30
Fluidity: an Important Feature of Biological Membranes Membrane fluidity is determined by:
• nature of lipids in membrane - unsaturated lipids increase fluidity - saturated lipids reduce fluidity Fig 4.4
• temperature - warming increases fluidity
Biological Membranes are Asymmetrical • two leaflets have distinct lipid composition
= liquid crystal
• in many plasma membranes, the outer leaflet contains glycolipids and glycoproteins (lipids and proteins with carbohydrate attached)
- cooling decreases fluidity 21
Transition temperature
warm
= crystalline gel
22
Membrane Fluidity is Crucial to Cell Function cool
• BALANCE between ordered (rigid) structure and disordered structure allows: - mechanical support and flexibility
Fig 4.23
liquid crystal state
crystalline gel state
- dynamic interactions between membrane components (e.g. proteins can come together reversibly) - membrane assembly and modification
23
24
Dynamic properties of the plasma membrane
Membrane Fluidity is Crucial to Cell Function • membrane fluidity must be maintained • in response to changes in temperature*, lipid composition of membranes can be changed by: 1) desaturation of lipids 2) exchange of lipid chains
Fig 4.8
Fig 8.45
Ruffles on the plasma membrane of a moving cell
A leukocyte ingesting a yeast cell
(e.g. Listeria monocytogenes changes the lipid content of its plasma membrane while growing at 10o C) 25
Biological Membranes are Dynamic • lipids move easily, laterally, within leaflet • lipid movement to other leaflet is slow • membrane proteins can diffuse within bilayer - movement of proteins is restricted - some proteins do not move - rapid movement is spatially limited - long range diffusion is slow - biochemical modification can dramatically alter protein mobility in the membrane (part of signal transduction) 27
26
