Unit 6: Cell Communication and Division

paracrine signaling

local signaling between nearby cells

local regulator

A secreted molecule that influences cells near where it is secreted

endocrine signaling

hormone release in the bloodstream

hormone

In multicellular organisms, one of many types of secreted chemicals that are formed in specialized cells, travel in body fluids, and act on specific target cells in other parts of the organism, changing the target cells’ functioning

autocrine signaling

form of cell communication where a cell secretes signaling molecules that bind to receptors on its own surface, leading to self-regulation of its functions

signal transduction pathway

A series of steps linking a mechanical, chemical, or electrical stimulus to a specific cellular response

reception

In cellular communication, the first step of a signaling pathway in which a signaling molecule is detected by a receptor molecule on or in the cell

ligand

A molecule that binds specifically to another molecule, usually a larger one

ion channel receptor

A transmembrane protein containing a pore that opens or closes as it changes shape in response to a signaling molecule (ligand), allowing or blocking the flow of specific ions; also called an ionotropic receptor

g-protein coupled receptor

A signal receptor protein in the plasma membrane that responds to the binding of a signaling molecule by activating a G protein. Also called a G protein-linked receptor

receptor tyrosine kinase

A receptor protein spanning the plasma membrane, the cytoplasmic (intracellular) part of which can catalyze the transfer of a phosphate group from ATP to a tyrosine on another protein. Receptor tyrosine kinases often respond to the binding of a signaling molecule by dimerizing and then phosphorylating a tyrosine on the cytoplasmic portion of the other receptor in the dimer

transduction

A process in which phages (viruses) carry bacterial DNA from one bacterial cell to another. When these two cells are members of different species, transduction results in horizontal gene transfer; A series of steps linking a mechanical, chemical, or electrical stimulus to a specific cellular response

second messenger

A molecule that relays messages in a cell from a receptor to a target where an action within the cell takes place

cAMP

Cyclic adenosine monophosphate, named because of its ring structure, is a common chemical signal that has a diversity of roles, including as a second messenger in many eukaryotic cells, and as a regulator of some bacterial operons

Ca++

A second messenger that functions as an intermediate between certain signaling molecules and a subsequent second messenger, a calcium ion (Ca superscript 2-plus), causing a rise in cytoplasmic calcium ion concentration

IP3

A second messenger that functions as an intermediate between certain signaling molecules and a subsequent second messenger, a calcium ion (Ca superscript 2-plus), causing a rise in cytoplasmic calcium ion concentration

phosphorylation cascade

A series of chemical reactions during cell signaling mediated by enzymes (kinases), in which each kinase in turn phosphorylates and activates another, ultimately leading to phosphorylation of many proteins.

kinase

An enzyme that transfers phosphate groups from ATP to a protein, thus phosphorylating the protein

phosphatase

An enzyme that removes phosphate groups from (dephosphorylates) proteins, often functioning to reverse the effect of a protein kinase

amplification

The strengthening of stimulus energy during transduction

response

(1) In cellular communication, the change in a specific cellular activity brought about by a transduced signal from outside the cell. (2) In feedback regulation, a physiological activity triggered by a change in a variable

apoptosis

A type of programmed cell death, which is brought about by activation of enzymes that break down many chemical components in the cell

prophase

The first stage of mitosis, in which the chromatin condenses into discrete chromosomes visible with a light microscope, the mitotic spindle begins to form, and the nucleolus disappears but the nucleus remains intact

metaphase

The third stage of mitosis, in which the spindle is complete and the chromosomes, attached to microtubules at their kinetochores, are all aligned at the metaphase plate

anaphase

The fourth stage of mitosis, in which the chromatids of each chromosome have separated and the daughter chromosomes are moving to the poles of the cell

telophase

the fifth and final stage of mitosis, in which daughter nuclei are forming and cytokinesis has typically begun

cytokinesis

Any of a group of small proteins secreted by a number of cell types, including macrophages and helper T cells, that regulate the function of other cells, particularly immune cells. Examples include interferons and interleukins

cell cycle

An ordered sequence of events in the life of a cell, from its origin in the division of a parent cell until its own division into two. The eukaryotic cell cycle is composed of interphase (including G1, S, and G2 phases) and M phase (including mitosis and cytokinesis)

interphase

The period in the cell cycle when the cell is not dividing. During interphase, cellular metabolic activity is high, chromosomes and organelles are duplicated, and cell size may increase. Interphase often accounts for about 90 percent of the cell cycle

gap 1 (G1)

The first gap, or growth phase, of the cell cycle, consisting of the portion of interphase before DNA synthesis begins

gap 2 (G2)

The second gap, or growth phase, of the cell cycle, consisting of the portion of interphase after DNA synthesis occurs

chromatin

The complex of DNA and proteins that makes up eukaryotic chromosomes. When the cell is not dividing, chromatin exists in its dispersed form, as a mass of very long, thin fibers that are not visible with a light microscope

chromosome

A cellular structure consisting of one DNA molecule and associated protein molecules. A duplicated chromosome has two DNA molecules. (In some contexts, such as genome sequencing, the term may refer to the DNA alone.) A eukaryotic cell typically has multiple, linear chromosomes, which are located in the nucleus. A prokaryotic cell often has a single, circular chromosome, which is found in the nucleoid, a region that is not enclosed by a membrane; The complex of DNA and proteins that makes up eukaryotic chromosomes. When the cell is not dividing, chromatin exists in its dispersed form, as a mass of very long, thin fibers that are not visible with a light microscope

centromere

In a duplicated chromosome, the region on each sister chromatid where it is most closely attached to its sister chromatid by proteins that bind to the centromeric DNA. Other proteins condense the chromatin in that region, so it appears as a narrow “waist” on the duplicated chromosome. (An unduplicated chromosome has a single centromere, identified by the proteins bound there.)

sister chromatids

Two copies of a duplicated chromosome attached to each other by proteins at the centromere and, sometimes, along the arms. While joined, two sister chromatids make up one chromosome. Chromatids are eventually separated during mitosis or meiosis II.

gene

A discrete unit of hereditary information consisting of a specific nucleotide sequence in DNA (or RNA, in some viruses)

homologous chromosomes

A pair of chromosomes of the same length, centromere position, and staining pattern that possess genes for the same characters at corresponding loci. One homologous chromosome is inherited from the organism’s male parent, the other from the female parent. Also called a homologous pair

DNA

A nucleic acid molecule, usually a double-stranded helix, in which each polynucleotide strand consists of nucleotide monomers with a deoxyribose sugar and the nitrogenous bases adenine (A), cytosine (C), guanine (G), and thymine (T); capable of being replicated and determining the inherited structure of a cell’s proteins

replication

The process by which a DNA molecule is copied; also called DNA synthesis

somatic cell

Any cell in a multicellular organism except a sperm or egg or their precursors

gamete

A haploid reproductive cell, such as an egg or sperm, that is formed by meiosis or is the descendant of cells formed by meiosis.

haploid

cell containing only one set of chromosomes (n)

diploid

A cell containing two sets of chromosomes (2n), one set inherited from each parent

mitosis

A process of nuclear division in eukaryotic cells conventionally divided into five stages: prophase, prometaphase, metaphase, anaphase, and telophase. Mitosis conserves chromosome number by allocating replicated chromosomes equally to each of the daughter nuclei

centrosome

A structure present in the cytoplasm of animal cells that functions as a microtubule-organizing center and is important during cell division. A centrosome has two centrioles

centriole

A structure in the centrosome of an animal cell composed of a cylinder of microtubule triplets arranged in a “9 plus 0” pattern. A centrosome has a pair of centrioles

spindle

An assemblage of microtubules and associated proteins that is involved in the movement of chromosomes during mitosis

microtubule

A hollow rod composed of tubulin proteins that makes up part of the cytoskeleton in all eukaryotic cells and is found in cilia and flagella

histone

A small protein with a high proportion of positively charged amino acids that binds to the negatively charged DNA and plays a key role in chromatin structure

kinetochore

A structure of proteins attached to the centromere that links each sister chromatid to the mitotic spindle

spindle apparatus

the whole structure of spindle fibers, centrioles, and fibers

s phase

The synthesis phase of the cell cycle; the portion of interphase during which DNA is replicated

meiosis

A modified type of cell division in sexually reproducing organisms consisting of two rounds of cell division but only one round of DNA replication. It results in cells with half the number of chromosome sets as the original cell

crossing over

The reciprocal exchange of genetic material between nonsister chromatids during prophase I of meiosis

nondisjunction

An error in meiosis or mitosis in which members of a pair of homologous chromosomes or a pair of sister chromatids fail to separate properly from each other

zygote

The diploid cell produced by the union of haploid gametes during fertilization; a fertilized egg

karyotype

A display of the chromosome pairs of a cell arranged by size and shape