Chapter 3: The Cellular Level of Organization

**cell membrane**

is an extremely pliable structure composed primarily of back-to-back phospholipids (a “bilayer”).

**hydrophilic**

molecule (or region of a molecule) is one that is attracted to water.

**hydrophobic**

molecule (or region of a molecule) repels and is repelled by water.

**amphipathic**

molecule is one that contains both a hydrophilic and a hydrophobic region

**Intracellular fluid (ICF)**

is the fluid interior of the cell.

**Extracellular fluid (ECF)**

is the fluid environment outside the enclosure of the cell membrane.

**Interstitial fluid (IF)**

is the term given to extracellular fluid not contained within blood vessels.

**integral protein**

An **integral protein** is a protein that is embedded in the membrane.

**channel protein**

is an example of an integral protein that selectively allows particular materials, such as certain ions, to pass into or out of the cell.

**receptor**

is a type of recognition protein that can selectively bind a specific molecule outside the cell, and this binding induces a chemical reaction within the cell.

**ligand**

is the specific molecule that binds to and activates a receptor.

**glycoprotein**

is a protein that has carbohydrate molecules attached, which extend into the extracellular matrix.

**glycocalyx**

is a fuzzy-appearing coating around the cell formed from glycoproteins and other carbohydrates attached to the cell membrane.

**Peripheral protein**s

are typically found on the inner or outer surface of the lipid bilayer but can also be attached to the internal or external surface of an integral protein.

**Passive transport**

is the movement of substances across the membrane without the expenditure of cellular energy.

**concentration gradient**

is the difference in concentration of a substance across a space.

**Diffusion**

is the movement of particles from an area of higher concentration to an area of lower concentration.

**Facilitated diffusion**

is the diffusion process used for those substances that cannot cross the lipid bilayer due to their size and/or polarity

**Osmosis**

is the diffusion of water through a semipermeable membrane.

**Active transport**

is the movement of substances across the membrane using energy from adenosine triphosphate (ATP).

**electrical gradient**

is a difference in electrical charge across a space.

**Endocytosis**

(bringing “into the cell”) is the process of a cell ingesting material by enveloping it in a portion of its cell membrane, and then pinching off that portion of membrane

**vesicle**

is a membranous sac—a spherical and hollow organelle bounded by a lipid bilayer membrane.

**Phagocytosis**

(“cell eating”) is the endocytosis of large particles.

**Pinocytosis**

(“cell drinking”) brings fluid containing dissolved substances into a cell through membrane vesicles.

**Receptor-mediated endocytosis**

is endocytosis by a portion of the cell membrane that contains many receptors that are specific for a certain substance.

**Exocytosis**

(taking “out of the cell”) is the process of a cell exporting material using vesicular transport.

**Cytosol**

, the jelly-like substance within the cell, provides the fluid medium necessary for biochemical reactions.

**organelle**

(“little organ”) is one of several different types of membrane-enclosed bodies in the cell, each performing a unique function.

**cytoplasm**

The organelles and cytosol, taken together, compose the cell’s

**nucleus**

is a cell’s central organelle, which contains the cell’s DNA.

**endoplasmic reticulum**

is a system of channels that is continuous with the nuclear membrane (or “envelope”) covering the nucleus and composed of the same lipid bilayer material.

**ribosome**

is an organelle that serves as the site of protein synthesis.

**Golgi apparatus**

is responsible for sorting, modifying, and shipping off the products that come from the rough ER, much like a post-office.

**lysosome**

is an organelle that contains enzymes that break down and digest unneeded cellular components, such as a damaged organelle

**Autophagy**

(“self-eating”) is the process of a cell digesting its own structures.

**mitochondrion**

(plural = mitochondria) is a membranous, bean-shaped organelle that is the “energy transformer” of the cell.

**cristae**

The inner membrane is highly folded into winding structures with a great deal of surface area, called

**Reactive oxygen species**

such as peroxides and free radicals are the highly reactive products of many normal cellular processes, including the mitochondrial reactions that produce ATP and oxygen metabolism.

**mutation**

is a change in the nucleotide sequence in a gene within a cell’s DNA, potentially altering the protein coded by that gene.

**cytoskeleton**

is a group of fibrous proteins that provide structural support for cells, but this is only one of the functions of the cytoskeleton.

**Cilia**

are found on many cells of the body, including the epithelial cells that line the airways of the respiratory system.

**flagellum**

(plural = flagella) is an appendage larger than a cilium and specialized for cell locomotion.

**Centriole**

can serve as the cellular origin point for microtubules extending outward as cilia or flagella or can assist with the separation of DNA during cell division

**microfilament**

is a thinner type of cytoskeletal filament.

**intermediate filament**

is a filament intermediate in thickness between the microtubules and microfilaments

**nuclear envelope**

Like most other cellular organelles, the nucleus is surrounded by a membrane called the

**nucleosome**

is a single, wrapped DNA-histone complex.

**chromosome**

is composed of DNA and proteins; it is the condensed form of chromatin.

**DNA replication**

is the copying of DNA that occurs before cell division can take place.

**gene**

is a functional segment of DNA that provides the genetic information necessary to build a protein.

**Gene expression**

, which transforms the information coded in a gene to a final gene product, ultimately dictates the structure and function of a cell by determining which proteins are made.

**triplet**

is a section of three DNA bases in a row that codes for a specific amino acid.

**transcription**

Gene expression begins with the process called **__** which is the synthesis of a strand of mRNA that is complementary to the gene of interest.

**spliceosome**

—a structure composed of various proteins and other molecules—attaches to the mRNA and “splices” or cuts out the non-coding regions.

**intron**

The removed segment of the transcript is called an

**exon**

is a segment of RNA that remains after splicing

**polypeptide**

**Translation** is the process of synthesizing a chain of amino acids called a

**Ribosomal RNA (rRNA)**

is a type of RNA that, together with proteins, composes the structure of the ribosome.

**Transfer RNA (tRNA)**

**I**s a type of RNA that ferries the appropriate corresponding amino acids to the ribosome, and attaches each new amino acid to the last, building the polypeptide chain one-by-one.

**anticodon**

This sequence of three bases on the tRNA molecule is called an

**somatic cell**

is a general term for a body cell, and all human cells, except for the cells that produce eggs and sperm (which are referred to as germ cells), are somatic cells.

**homologous**

pair of chromosomes is the two copies of a single chromosome found in each somatic cell.

**diploid**

The human is a **__** organism, having 23 homologous pairs of chromosomes in each of the somatic cells.

**cell cycle**

The **__** is the sequence of events in the life of the cell from the moment it is created at the end of a previous cycle of cell division until it then divides itself, generating two new cells.

**Interphase**

is the period of the cell cycle during which the cell is not dividing.

**Mitosis**

is the division of genetic material, during which the cell nucleus breaks down and two new, fully functional, nuclei are formed.

**Cytokinesis**

divides the cytoplasm into two distinctive cells.

**G1 phase (gap 1 phase)**

is the first gap, or growth phase in the cell cycle.

**S phase** (synthesis phase)

is the period during which a cell replicates its DNA.

**G2 phase**

is a second gap phase, during which the cell continues to grow and makes the necessary preparations for mitosis.

**G0 phase**

is a resting phase of the cell cycle.

**centromere**

is the structure that attaches one sister chromatid to another.

**mitotic phase**

The **__** of the cell typically takes between 1 and 2 hours

**Prophase**

is the first phase of mitosis, during which the loosely packed chromatin coils and condenses into visible chromosomes.

**centrosome**

is a pair of centrioles together.

**mitotic spindle**

is the structure composed of the centrosomes and their emerging microtubules.

**kinetochore**

is a protein structure on the centromere that is the point of attachment between the mitotic spindle and the sister chromatids.

**Metaphas**e

is the second stage of mitosis

**metaphase plate**

is the name for the plane through the center of the spindle on which the sister chromatids are positioned.

**Anaphase**

is the third stage of mitosis.

**Telophase**

is the final stage of mitosis.

**cleavage furrow**

is a contractile band made up of microfilaments that forms around the midline of the cell during cytokinesis.

**checkpoint**

is a point in the cell cycle at which the cycle can be signaled to move forward or stopped.

**cyclin**

is one of the primary classes of cell cycle control molecules.

**cyclindependent kinase (CDK)**

is one of a group of molecules that work together with cyclins to determine progression past cell checkpoints.

**stem cell**

is an unspecialized cell that can divide without limit as needed and can, under specific conditions, differentiate into specialized cells.

**pluripotent**

stem cell is one that has the potential to differentiate into any type of human tissue but cannot support the full development of an organism.

**multipotent**

stem cell has the potential to differentiate into different types of cells within a given cell lineage or small number of lineages, such as a red blood cell or white blood cell.

**oligopotent**

An stem cell is limited to becoming one of a few different cell types.

**unipotent**

cell is fully specialized and can only reproduce to generate more of its own specific cell type.

**transcription**

factor is one of a class of proteins that bind to specific genes on the DNA molecule and either promote or inhibit their transcription.