Molecules and Cells in Animal Physiology

GENPHYSIO

Cell membrane (plasma membrane)

Each cell is enclosed in this membrane

Intracellular membranes (subcellular membranes)

This includes the endoplasmic reticulum, the inner and outer membranes of each mitochondrion, and the two closely associated membranes that form the nuclear envelope.

Bilayer (double layer) of phospholipid molecules

The cell membrane is ordinarily composed primarily of this, in which protein molecules are embedded​

Phospholipases

An enzyme found in snakes such as puff adder or rattlesnake which break up phospholipids​

Distribution of electrons

A property that determines whether the molecule is polar or nonpolar.

Polar Molecule

Electrons here are unevenly distributed; thus some regions are relatively negative, whereas others are relatively positive.​

Nonpolar Molecule

Electrons here are evenly distributed and there are no charge imbalances between different molecular regions

Phospholipids

• contain phosphate groups.

• the principal constituents of the matrix in which proteins are embedded in cell membranes and intracellular membranes.​

Amphipathic

This term means each molecule consists of a polar part and a nonpolar part​

Two layers of phospholipid molecules

Known as the two leaflets of the membrane, typically are composed of different mixes of phospholipid molecules.​

Fluid

The phospholipids in a cell membrane or intracellular membrane are in this state

Fluidity

• The ease of motion of the phospholipid molecules in a membrane leaflet.

• also depends in part on the degree of chemical saturation of the hydrocarbons that make up the phospholipid tails.​

Saturated

A hydrocarbon if it contains no double bonds

Unsaturated

A hydrocarborn if it includes one or more double bonds

Bent tails of membrane phospholipids

Prevent tight, crystal-like packing of the tails in the hydrophobic interior of the membrane.

Temperature

In addition to chemical composition, this factor also affects the fluidity of membranes​

Alteration of the numbers of double bonds​

During evolution, one important way in which cells have become adapted to different temperatures is through this

Sterols

Besides phospholipids, cell membranes and intracellular Membranes contain other classes of lipids such as this

Cholesterol and Cholesterol Esters​

The principal membrane sterols

Proteins

second major constituents of cell membranes and intracellular membranes ​

Fluid Mosaic Model of Membranes

According to this, membrane consists of a mosaic of protein and lipid molecules, all of which move about in directions parallel to the membrane faces because of the fluid state of the lipid matrix

Integral and Peripheral

Membrane proteins are structurally of two principal kinds

Integral Membrane Protein

• These proteins are parts of the membrane and cannot be removed without taking the membrane apart

• Most of these span the membrane and thus are called transmembrane proteins.​

Peripheral Membrane Proteins

These proteins are associated with the membrane but can be removed without destroying the membrane.

Channels, Carriers (Transporters), Enzymes, Receptors, Structural

Five functional types of membrane proteins

Channels

It creates a direct water path from one side to the other of a membrane (i.e., an aqueous pore) through which solutes in aqueous solution may diffuse or water may undergo osmosis

Transporters (carriers)

• Binds noncovalently and reversibly with specific molecules or ions to move them across a membrane intact.

• active transport if it employs metabolic energy;

• it is facilitated diffusion if metabolic energy is not employed.​

Enzymes

Catalyzes a chemical reaction in which covalent bonds are made or broken​

Receptors

• Binds noncovalently with specific molecules

• initiates a change in membrane permeability or cell metabolism

• mediate the responses of a cell to chemical messages (signals) arriving at the outside face of the cell membrane​

Structural Proteins

• attaches to other molecules to anchor intracellular elements to the cell membrane.

• creates junctions between adjacent cells or establishes other structural relations.

Carbohydrates

• also a component of cell membrane and intracellular membrane

• occurs mostly in covalently bonded combinations with lipids or proteins

• hydrophilic

Glycolipids, Glycoproteins, and Proteoglycans​

Major categories of Carbohydrate-containing membrane compounds

Epithelium (plural epithelia)

• a sheet of cells that covers a body surface or organ, or lines a cavity​

• compartmentalize the body by forming boundaries between body regions.

• also form a boundary between an animal and its external environment​

Simple Epithelium

• single layer of cells

• exceedingly common;

• found in the intestines, kidney tubules, blood vessels, and sweat glands

• rests or found on basal lamina

• has two polarities: apical and basal surface

Basement membrane (basal lamina)

• positioned beneath the basal cell surfaces

• a thin, permeable, noncellular, and nonliving sheet of matrix material

• composed of glycoproteins and particular types of collagen​

Apical Surface (mucosal surface)

facing into a cavity or open space​

Basal surface (serosal surface)

facing toward the underlying tissue to which the epithelium is attached

• Squamous - cells are low and flat

• Cuboidal - cells as about as tall as they are wide​

• Columnar - cells are high relative to their basal dimensions​

Classifications of Simple Epithelia​

Tight, Septate, Desmosome, Gap

Types of Junction

Tight Junction

• place where the cell membranes of adjacent cells are tightly joined so that there is no intercellular space between the cells​

• demarcates the apical surface of the cell from its lateral and basal surfaces

• giving rise the distinction between the apical region and the basolateral region of each cell membrane

• block some paracellular movement of substances

• permit extensive paracellular movement of certain sorts of molecules or ions

Septate Junction

• common in invertebrate groups

• differ from tight junctions in their fine structure

• tight and septate junctions are sometimes aptly called occluding junctions

• block or occlude the spaces between adjacent epithelial cells, preventing open passage between the fluids on either side of an epithelium​

Desmosome

• a junction at which mutually adhering glycoprotein filaments from two adjacent cells intermingle across the space between the cells​

• principal function: strengthen and stabilize contacts between adjacent cells.​

Gap Junction

• they occur at discrete spots

• very different from all the other junctions because within a gap junction there are open pores between cells​

• pores are created by connexin proteins

Asymmetric

Central feature of epithelia

Control and mediate the transport of substances between the apical and basal sides

Important function of an epithelium

• Transcellular Path - may pass through cell

• Paracellular Path - may pass between cells

Two types of paths in which substances pass through

Metabolism

Set of processes by which cells and organisms acquire, rearrange, and void commodities in ways that sustain life

• Nitrogen metabolism

  • set of processes by which nitrogen is acquired

  • synthetic reactions to create proteins and other functional nitrogenous compounds

  • transferred to elimination compounds such as urea or ammonia

• Energy metabolism

  • processes by which energy is acquired, transformed, channeled into useful functions, and dissipated

Metabolism according to specific commodities

• Catabolism

  • complex chemical compounds are broken down to release energy, create smaller chemical building blocks, or prepare chemical constituents for elimination

  • destructive

• Anabolism

  • synthesize larger or more complex chemical compounds from smaller chemical building blocks, using energy

  • constructive

Metabolism according to type of transformation

Enzyme

Protein catalysts that play two principles:

• speed chemical reactions

• regulate reactions

Catalyst

A molecule that accelerates a reaction without, in the end, being altered itself

Substrate

Initial reactants of the reaction that the enzyme catalyzes

Products

are the compounds produced by the reaction

Denature

Tertiary structure of Protein is altered ​

Physical and chemical stresses

high tissue temperatures, low cellular levels of O2, and exposure to toxic chemicals

Molecular Chaperones

Can repair damage to other proteins by correcting reversible denaturation

Heat-shock proteins

• also known as stress proteins

• function as molecular chaperones

• most famous and best understood molecular chaperones