Bio 231

A key trait of a multicellular organism is that a “division of labour” exists among the cells of the organism. That is, the cells are not identical in structure and/or function. Some cells may specialize in harvesting energy, for example, whereas others may serve a specific role in the motility of the organism.

The evolution of multicellularity meant that cells no longer needed to be autonomous (independent). In a multicellular system, the cells cooperate with one another for the benefit of the entire organism.

The oldest known fossil eukaryotes are 2.2 billion years old. If prokaryotic cells first evolved some 3.5 billion years ago, it took up to 1.3 billion years for eukaryotic cells to evolve from prokaryotes.

Most systematists working on living organisms use molecular characters as part of the data set when conducting phylogenetic analyses. Molecular data include nucleotide base sequences of DNA and RNA or the amino acid sequences of the proteins for which they code.

• -they provide abundant data because every amino acid in a protein and every base in a nucleic acid can serve as a separate, independent character for analysis.
• -genes have been conserved by evolution
• -molecular sequences can be compared between distantly related organisms that share no organismal characteristics.
• -molecular characters used to study closely related species with minor morphological differences.
• -many proteins and nucleic acids are not directly affected by the developmental or environmental factors.

• -only 4 alternative character states (the 4 nucleotide bases) at each position in a DNA or RNA sequence and only 20 alternative character states (the 20 amino acids) at each position in a protein.
• -similarity may have evolved independently.
• -As a result, it is difficult to verify that molecular similarities were inherited from a common ancestor.

-A technique for dating the time of divergence of two species or lineages, based on the number of molecular sequence differences between them.

Mutations in DNA appear to arise at a relatively constant rate. Large differences imply divergence in the distant past. Small differences suggest a more recent common ancestor.

• -it is used for dating evolutionary divergences that occurred within the last few million years.
• -Mitochondrial DNA (mtDNA) evolves relatively quickly.

-We compare nucleotide bases or amino acids at exactly the same positions in the nucleic acid or protein molecule because mutations often change along the length of a DNA sequence. This can change the relative locations of specific positions through the insertion or deletion of base pairs. By determining where insertions or deletions have occurred, systematists can match up (align) the positions of nucleotides for comparison.

Bacteria, Archaea, and Eukarya.

The outer limit of the cytoplasm responsible for the regulation of substances moving into and out of cells.

• -acts as a selectively permeable barrier.
• -the plasma membrane allowed for the uptake of key nutrients and elimination of waste products.
• -maintains a protected environment where metabolic processes occur.

Model proposing that the membrane consists of a fluid phospholipid bilayer in which proteins are embedded and float freely.

• Membranes are fluid.
• -Frye and Edidin grew human cells and mouse cells separately in tissue culture.
• -tagged the human or mouse membrane proteins with dye molecules.
• -then fused the human and mouse cells. Within minutes, they found that the two distinctly coloured proteins began to mix. In less than an hour, the two colours had completely intermixed on the fused cells, indicating that the mouse and human proteins had moved around in the fused membranes.
• Membrane Asymmetry
• -membrane asymmetry utilizes the freeze-fracture technique in combination with electron microscopy. A block of cells is rapidly frozen by dipping it in liquid nitrogen (−196°C). Then the block is fractured by hitting it with a microscopically sharp knife edge. Often the fracture splits bilayers into inner and outer halves, exposing the membrane interior. In the electron microscope, the split membranes appear as smooth layers in which individual particles the size of proteins are embedded. From these images, it is clear that the particles on either side of the membrane differ in size, number, and shape, providing evidence that the two sides are distinctly different.

-two fatty acid “tails” linked to one of several types of alcohols or amino acids by a phosphate group.

• each phospholipid molecule contains
• -a region that is hydrophobic- the phosphate-containing head group.
• -and a region that is hydrophilic -the fatty acid chains

Absolutely nothing. Both micelles and bilayers form spontaneously in an aqueous environment because of the tendency of the hydrophobic fatty acids to aggregate together while the polar head groups associate with water. These arrangement are favored because they represent the lowest energy state and are more likely to occur over any other arrangement.

It is dependent on how densely the individual lipid molecules can pack together. This is influenced by two major factors: the composition of the lipid molecules that make up the membrane and the temperature.

Fatty acids composed of saturated hydrocarbons, in which each carbon is bound to a maximum number of hydrogen atoms, tend to have a straight shape, which allows the lipids to pack more tightly together. Alternatively, lipid molecules with unsaturated fatty acids are less straight as the double bonds in an unsaturated fatty acid introduce kinks or bends in its structure.

If the temperature drops low enough, the phospholipid molecules become closely packed, and the membrane forms a highly viscous semisolid gel.

-Normal membrane permeability is inhibited, as well as causing enzymes and other proteins in the membrane to stop functioning. Caused by exposure to low temperatures.

Membranes may become too fluid and liquid due to the increase in molecular motion, which can result in membrane leakage. Ions such as K+, Na+, and Ca2+ begin to freely diffuse across the membrane, resulting in an irreversible disruption of cellular ion balance that can rapidly lead to cell death.

-They are able to increase the relative proportion of unsaturated fatty acids in their membranes. Unsaturated fats have bends in their carbon chains and therefore cannot pack as closely together.

Desaturases

-acts as membrane buffers: at high temperatures, they help restrain the movement of lipid molecules, thus reducing the fluidity of the membrane. At lower temperatures, sterols disrupt fatty acids from associating by occupying space between lipid molecules, thus slowing the transition to the nonfluid gel state. It is found only in animal, not plants are protests.

-Phospholipids

Transport, Enzymatic activity, Signal transduction, and Attachment recognition.

Integral membrane protein (Transport protein)

A protein that is embedded in the phospholipid bilayer.

-Integral proteins are composed of regions (or domains) that consist of predominantly nonpolar amino acids that are usually coiled into alpha helices.

Peripheral membrane protein.

Protein held to membrane surfaces by noncovalent bonds formed with the polar parts of integral membrane proteins or membrane lipids. Mostly on the cytoplasmic side of the membrane.

-held to membrane surfaces by noncovalent bonds—hydrogen bonds and ionic bonds—usually by interacting with the exposed portions of integral proteins as well as directly with membrane lipid molecules.

Peripheral membrane proteins, Integral membrane proteins.

-the movement of a substance across a membrane without the need to expend chemical energy such as ATP.

Diffusion.

the net movement of a substance from a region of higher concentration to a region of lower concentration.

Diffusion.

-increase in entropy. In the initial state, when molecules are more concentrated in one region of a solution or on one side of a membrane, the molecules are highly ordered and in a state of low entropy. As diffusion occurs, the entropy, or disorder, increases until, when the molecules are evenly distributed, entropy reaches its maximum.

The bigger the gradient, the faster the rate of diffusion. Even after their concentration is the same in all regions, there is still constant movement of molecules or ions from one space to another, but there is no net change in concentration. This condition is an example of a dynamic equilibrium

Mechanism by which certain small substances diffuse through the lipid part of a biological membrane.

Simple diffusion and Facilitated diffusion.

-Hydrophobic molecules (O2, CO2, N2) and small uncharged polar molecules (water, indole, glycerol)

True

False

False

Very small, nonpolar, hydrophibic molecules are readily soluble in the hydrophobic interior of a membrane and move rapidly from one side to the other.

False. A membrane is practically impermeable to charged molecules, including ions such as Cl−, Na+, and phosphate (PO4−).

Mechanism by which polar and charged molecules diffuse across membranes with the help of transport proteins.

Channel proteins and carrier proteins.

-forms hydrophilic pathways in the membrane through which water and ions can pass. This provides an avenue such that hydrophilic molecules do not have to interact with the hydrophobic portions of the membrane.

Ion transporter in a membrane that switches between open, closed, or intermediate states.

Transport protein that binds a specific single solute and transports it across the lipid bilayer.

Creates passageways through the lipid bilayer. Each carrier protein binds a specific single solute, such as a sugar molecule or an amino acid, and transports it across.

The carrier protein undergoes conformational changes that progressively move the solute binding site from one side of the membrane.

the net movement of water molecules across a selectively permeable membrane by diffusion, from a solution of lesser solute concentration to a solution of greater solute concentration.

Aquaporins.

Solution containing dissolved substances at lower concentrations than the cells it surrounds.

Solution containing dissolved substances at higher concentrations than the cells it surrounds. Solution containing dissolved substances at higher concentrations than the cells it surrounds.

The mechanism by which ions and molecules move against the concentration gradient across a membrane, from the side with the lower concentration to the side with the higher concentration.

Primary active transport and secondary active transport.

Ions. (H+, Ca2+, Na+, K+)

3 Na+ ions out of the cell and 2 K+ ions into the cell in the same pumping cycle.

Transport in which the same protein that transports a substance also hydrolyzes ATP to power the transport directly.

Transport indirectly driven by ATP hydrolysis.

An electrical voltage that measures the potential inside a cell membrane relative to the fluid just outside; it is negative under resting conditions and becomes positive during an action potential.

Ions and organic molecules.

Symport(cotransport) and antiport.

The transport of two molecules in the same direction across a membrane. Also referred to as cotransport.

Symport

A secondary active transport mechanism in which a molecule moves through a membrane channel into a cell and powers the active transport of a second molecule out of the cell. Also referred to as exchange diffusion.

Antiport. (Or exchange diffusion.)

Peptidoglycan.

A polymeric substance formed from a polysaccharide backbone tied together by short polypeptides, which is the primary structural molecule of bacterial cell walls.

Gram negative and gram postitve.

No. It is one of the defining feature that separate Archaea and Bacteria.

Single, circular in most. Some linear.

Single, circular.

Multiple, linear molecules.

False

True

True

False

True

Only Bacteria.