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BIOLOGY CHAPTER 6-7 (Life at the edge (Evolution of differences in…
BIOLOGY CHAPTER 6-7
Life at the edge
The plasma membrane is the boundary that separates the living cell from its surroundings
The plasma membrane exhibits selective permeability.
Phospholipids
They are the most abundant lipid in the plasma membrane
Phospholipids are amphipathic molecules, containing hydrophobic (water-fearing). And hydrophilic (water-loving)
The hydrophobic tails of the phospholipids are sheltered inside the membrane, while the hydrophilic heads are exposed to water on either side.
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Evolution of differences in membrane lipid composition
Variations in lipid composition of cell membranes of many species appear to be adaptations to specific environmental conditions
Ability to change the lipid compositions in response to temperature changes has involved in organisms that live where temperatures vary.
Membane proteins and their functions
A tile mosaic, a membrane is a collage of different proteins, often clustered in goups, embedded in the fluid matrix of the lipid bilayer.
Phospholipids from the main fabric of the membrane
Proteins determine most of the membrane's functions
Effects of osmosis on water balance
Osmosis: is the diffusion of water across a selectively permeable membrane
Water diffuses across a membrane from the region of lower solute concentration to the region of higher solute concentration until the solute concentration is equal on both sides.
Tonocity; is the ability of a surrounding solution to cause a cell to gain or lose water.
The tonicity of a solution depends on its concentration of solutes that cannot cross the membrane relative to that inside the cell
Isotonic solution; Solute concentration is the same as the inside the cell; not net water movement across the plasma mmebrane.
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Active transport uses energy to move solutes against their gradients
Facilitated diffusion is still passive becuase the solute moves down its concentration gradient, and the transport requires no energy.
Some transport proteins, however, can move solutes against their concentration gradients.
Active transport; requires energy, usually in the form of ATP hydrolisis, to move substances against their concentration gradients.
All proteins involved in active transport are carrier proteins.
Active transport allows cells to maitain concentration gradients that differ from their surroundings
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Microscopy
Microscopes were invented in 1590 and further refined during the 1600's.
Microscopes are used to visualize cells.
A light microscope (LM), visible light is passed through a specimen and then through glass lenses.
Lenses refract (bend) the light so that the image is magnified.
Three important parameters of microscopy
Resolution
The measure of the clarity of the image, or the minimum distance of two distinguishable points.
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Contrast
Visible differences in brightness between parts of the sample.
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Magnification
The ratio of an object's image size to its real size.
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Cell fractination
Takes cells apart and separates the major organelles from one another.
Centrifuges fractionate cells into their component parts.
Cell fractionation anables scientists to determine the functions of organelles.
Biochemistry and cytology help correlate cell function with structure.
Eukaryotic cells have internal membranes that compartmentalize their functions.
The basic structural and functional unit of every organism is one of two types of cells; prokaryotic or eukaryotic.
Only organisms of the domains bacteria and archaea consist of prokaryotic cells.
Protists, fungi, animals, and plants all consist of eukarytic cells.
Comparing prokaryotic and eukaryotic cells
Basic features of all cells.
Plasma membrane
Prokaryotic cells
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Semifluid substance called cytosol.
Chromosomes (carry genes)
Ribososmes (make proteins)
The eukaryotic cell's genetic instructions are housed in the nucleus and carried our by the ribososmes.
The nucleus contains most of the DNA in a eukaryotic cell
Ribosomes use the information from the DNA to make proteins.
The nucleus
The nuclear envelope encloses the nucleus, separation it from the cytoplasm
The nuclear envelope is a double membrane; each membrane consist of a lipid bilayer.
The nucleus contains most of the cell's genes and is usually teh most conspicuous organelle
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The cytoskeleton is a network of fibers that organizes structures and activities in the cell.
The cytoskeleton is a network of fibers extending throughout the cytoplasm
It organizes the cell's structures and activities, anchoring many organelles
it is composed of three types of molecular structures
Microfilaments
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Microtubules
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Intermediate Filaments
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Roles of the cytoskeleton
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There are types
