Cell Signaling, Enzymes, and Cellular Processes: A Comprehensive Biology Review

Autocrine signaling

Involves cell signaling to itself, usually with the goal of growth regulation.

Paracrine signaling

Involves cell signaling between nearby cells.

Endocrine signaling

Occurs between distant cells, with the chemical signal usually carried by the blood.

Feedback Inhibition

Involves the use of the product of a reaction to regulate its own further production.

Gap junctions

Connections between the plasma membranes of neighboring cells allowing small signaling molecules to pass directly.

Homeostasis

The state of steady physical and chemical internal conditions within an organism.

Kinase

An enzyme that transfers phosphate groups from ATP to another protein.

Ligand

Any molecule or atom that binds to a receiving protein molecule (a receptor).

Negative feedback loop

A feedback system that counteracts a change in the organism.

Neurotransmitters

Ligands released from the axon of one nerve cell to the dendrite of another nerve cell.

Positive feedback loop

A process in which the product reinforces or amplifies a response.

Receptors

Complex proteins that can be located in the plasma membrane or within the cell.

G-protein coupled receptors (GPCR)

Ligand binding activates an associated protein called a G-protein.

Enzyme-linked receptors

Ligand binding turns on the enzymatic activity of the receptor.

Ion channel-linked receptors

Ligand binding leads to the opening of a pore in the receptor for ion passage.

Internal receptors

Receptors located inside the cell that bind to hydrophobic ligands.

Second messengers

Small molecules that help the continued transmission of a signal after receptor binding.

Set Point

The ideal target value or range of values that the body works to maintain.

Target cells

The cells that are affected by chemical signals or ligands.

Transduction

The process by which the cell converts an external signal into an internal response.

Passive Transport

The movement of molecules across the cell membrane without the need of energy.

Concentration

The amount of solutes per unit volume of a solution.

Concentration Gradient

The difference in concentration between two points in space or across a cell membrane.

Diffusion

The movement of solute molecules from high concentration to low concentration.

Facilitated Diffusion

The movement of solutes across the cell membrane from high to low concentration with the help of a protein.

Hypertonic

A solution that is more concentrated relative to another solution.

Hypotonic

A solution that is less concentrated (fewer solute molecules) relative to another solution; in biology this will always refer to a solution OUTSIDE the cell that has a lower solute concentration.

Isotonic

Two solutions that have the same number of solute molecules, or the same solute concentration.

Osmosis

The movement of water from an area of low solute concentration to an area of high solute concentration; does not require energy.

Plasmolysis

The loss of water from a plant cell (specifically from the central vacuole of the plant cell) leading to the collapse of the cell membrane as it pulls away from the cell wall.

Lysis

The breakdown or disintegration of a cell due to the rupture of the cell membrane. This occurs when animal cells are placed in a hypotonic solution and the water flows into the cell.

Solute

In a solution, this is the molecule; for example in sugar water, the solute is the sugar molecule.

Active Site

The site in the enzyme protein where the substrate binds. The active site of each enzyme is specific for 1 substrate.

Denaturation

The breaking down of the structure of the protein so that it no longer performs its function. This can happen when the temperature or the pH of the environment is not at the ideal setting for the enzyme to function properly.

Enzyme

A special protein that controls biochemical reactions in the cell. It is reusable, specific, and is sensitive to temperature and pH.

Product

What is produced during an enzyme-catalyzed biochemical reaction.

Substrate

What the enzyme acts on during an enzyme-catalyzed biochemical reaction.

Induced fit

The change in shape of the active site of an enzyme so that it binds more snugly to the substrate.

Cofactors

Any nonprotein molecule or ion that is required for the proper functioning of an enzyme.

Coenzymes

Any organic molecule (one containing carbon atoms) that is required for the proper functioning of an enzyme. Examples of coenzymes are most vitamins.

Allosteric Site

A site in the enzyme where a cofactor or coenzyme binds thus altering the shape of the enzyme and the active site to either impair or enhance the binding of the substrate at the active site.

Competitive Inhibitor

A substance that reduces the activity of an enzyme by entering the active site in place of the substrate whose structure it mimics.

Non-competitive Inhibitor

A substance that reduces the activity of an enzyme by binding to a location remote from the active site (an allosteric site) changing the enzyme's shape so that the active site no longer binds to the substrate.

Allosteric Inhibitor

A substance that reduces the activity of an enzyme by binding to a site on the enzyme that is remote from the active site.

Allosteric Activator

A substance that increases the activity of an enzyme by binding to a site on the enzyme that is remote from the active site.

Activation Energy

The amount of energy that reactants must absorb before a chemical reaction will start.

Primary Protein Structure

The sequence of amino acids that make up a protein.

Secondary Protein Structure

The folding or coiling of the primary protein structure due to hydrogen bonding between the amine and carboxyl groups of the amino acids in the chain.

Tertiary Protein Structure

The folding of the secondary protein structure due to interactions between the R side chains of the amino acids in the protein.

Quaternary Protein Structure

The particular shape of a complex protein made up of several tertiary protein structures.

Amino Acids

The monomers or building blocks of proteins; there are 20 different amino acids that all living organisms use to build proteins.

Carbohydrates

An organic macromolecule made up of carbon and water (hydrogen and oxygen); important for short term energy and structure in cells and organisms.

Cellulose

A carbohydrate polymer made up of glucose monomers; found in plants where it provides structure to the cell (makes up the cell wall).

Cholesterol

A complex lipid molecule in the group called steroids; it is important for structure in the cell membrane.

Fatty Acid

A building block (monomer) of lipid molecules; contains a hydrophobic (water-hating) tail.

Fructose

A carbohydrate monomer and a component of sugar (sucrose).

Glucose

A carbohydrate monomer; a component of sucrose; also the primary carbohydrate used for energy in cells.

Glycerol

A building block (monomer) of lipid molecules.

Glycogen

A carbohydrate; polysaccharide (polymer) made up of glucose molecules linked together; storage of glucose in animals.

Lipid

An organic macromolecule made up of carbon, hydrogen, oxygen and phosphate; important for long term energy storage, insulation, and protection in organisms.

Monomer

The single unit of all complex organic macromolecules.

Nucleic Acids

An organic macromolecule made up of carbon, hydrogen, oxygen, phosphate and nitrogen; important for storage and transmission of genetic (hereditary) information; include DNA and RNA.

Nucleotides

The building blocks (monomers) of nucleic acids; nucleotides are composed of phosphates, a sugar, and a nitrogenous base.

Polymer

The large complex structure of organic macromolecules; made up of monomers that are linked together with chemical bonds.

Proteins

An organic macromolecule made up of carbon, hydrogen, oxygen, nitrogen and sulfur; important for bones and muscles, reactions in the cell, fighting disease, and transporting other molecules.

Starch

A complex carbohydrate made up of glucose molecules; found in plant cells where it is used to store glucose.

Steroid

A lipid molecule made of many ring-like structures; includes cholesterol, testosterone, vitamin D, and cortisone.

Triglyceride

A complex lipid molecule made up of 1 glycerol and 3 fatty acids; examples of triglycerides are liquid (oil) and solid (butter) fats.

Adenosine Triphosphate

A nucleotide; the energy molecule (or currency) of the cell.

Dehydration Synthesis

The process of forming a bond between two molecules by removing a molecule of water.

Hydrolysis

The process of breaking the bond between two molecules by adding a molecule of water.

Hydrogen Bonds

Weak attraction between a partially positive hydrogen and a partially negative element such as oxygen or nitrogen.

Polarity

The property of having poles (or regions of a molecule) with opposite charges.

Polar

A molecule in which one end is slightly negative and the other is slightly positive.

Nonpolar

A molecule in which NO oppositely charged poles form.

Cohesion

The property of polar molecules (such as water) being attracted to each other and forming hydrogen bonds.

Adhesion

The property of a polar molecule (such as water) being attracted to different polar molecules and forming hydrogen bonds.

Capillary Action

The property of water to climb a surface against gravity due to the adhesion between the water molecules and the molecules along the surface.

Surface Tension

The property of the surface of water to resist force due to the cohesion between water molecules.

Hydrophobic

The property of repelling water.

Hydrophilic

The property of being attracted to water.

Specific Heat Capacity

The amount of heat energy required to change the temperature of 1 gram of a substance by 1 degree Celsius.

Heat of Vaporization

The amount of heat energy required to turn 1 gram of a liquid into vapor without increasing the temperature.

Water Density

The density of water INCREASES as the temperature decreases.

Solvent Properties

The ability of a solvent to dissolve substances (solutes); water is a universal solvent because of its polarity.

Aerobic Respiration

A process that requires oxygen.

Alcoholic Fermentation

The process by which yeast cells produce energy in the absence of oxygen.

Cellular Respiration

The process by which a cell produces energy in the form of ATP from glucose and oxygen in the mitochondria.

Electron Transport Chain

The final step of cellular respiration where the cell produces the most ATP (34 molecules).

Fermentation

The process by which cells produce energy in the absence of oxygen.

Glycolysis

The first step of cellular respiration where the cell produces 2 pyruvic acid molecules and 2 molecules of ATP from 1 molecule of glucose.

Inner Mitochondrial Membrane

The inner membrane of the mitochondria where the electron transport chain occurs.

Kreb's Cycle

The second step of cellular respiration where the cell produces 2 molecules of ATP and 6 molecules of carbon dioxide from every molecule of glucose.

Lactic Acid Fermentation

The process by which animal cells produce energy in the absence of oxygen.

Mitochondria

The power house of the cell.

NAD+ and FAD

The oxidized state of the electron carriers that harness the energy in the bonds of glucose.

Pyruvic Acid

The molecule formed in the first step of cellular respiration (glycolysis).

Calvin Cycle

The reaction of photosynthesis where glucose is made using carbon dioxide and energy harnessed from the sun.

Chlorophyll

The light absorbing pigment in chloroplasts.

Chloroplast

The organelle in plants that uses solar energy to produce glucose.