Chapter 3: The Cellular Level of Organization

cell membrane

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 proteins

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)

Is 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.

Metaphase

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.