The Cell Cycle: Growth, Death, and Differentiation

adult stem cells

undifferentiated cells obtained from various sources and capable of differentiating into related cell types; also known as somatic stem cells

anaphase

stage of mitosis during which sister chromatids separate and move to opposite poles of the spindle fibre within a cell

apoptosis

the programmed death of cells that occurs as a normal and controlled part of an organism's growth or development

apoptosome

a large protein formed during apoptosis; its formation triggers a series of events that leads to apoptosis

apoptotic body

vesicle containing parts of a dying cell

asexual reproduction

that only requires one parent, leading to the production of a clone

binary fission

process of cell multiplication in bacteria and other unicellular organisms in which there is no formation of spindle fibres and no chromosomal condensation

blebs

bulges of the cell membrane created as the cytoskeleton of the cell breaks down; these break off to form apoptotic bodies

cancer

a disease in which cells divide in an uncontrolled manner, forming an abnormal mass of cells called a tumour

caspases

protease enzymes that break down proteins during apoptosis

caspase cascade

a group of proteins that are sequentially activated to bring about apoptosis

cell-based therapies

the use of stem cells in the treatment of human disorders or conditions to repair the mechanisms of disease initiation or progression

cell cycle

the series of events of cell growth and reproduction that results in two daughter cells

cell division

division of a cell into two genetically identical daughter cells

cell elongation

any permanent increase in size of a cell

centrioles

a pair of small cylindrical organelles, used in spindle development in animal cells during cell division

centromere

the position where the chromatids are held together in a chromosome

chromatid

one of two identical threads in a replicated DNA molecule

chromatin

a mass of genetic material composed of DNA and proteins that condense to form chromosomes during eukaryotic cell division

chromosome

a thread-like structure composed of DNA and protein

crypts

tube-like depressions of the mucosa located in the intestine and the site of glandular cells

cytochrome c

a protein that has a role in the formation of ATP in mitochondria; its leakage from the mitochondria leads to apoptosis

cytokinesis

division of the cytoplasm occurring after mitosis

death receptor

receptors on the surface of the cell that, when activated, lead to apoptosis of the cell

dermis

underlying part of the skin

differentiation

the process by which cells, tissues and organs acquire specialised features

ectoderm

the most external primary germ or cell layer that differentiates into epithelial tissue, which covers the outer surfaces of the body

embryo

early stage of a developing organism; in humans this includes the first eight weeks of development

embryonic stem cell (ESC)

an undifferentiated cell obtained from early embryonic tissue that is capable of differentiating into many cell types

endoderm

the innermost primary germ layer that differentiates into digestive lining and organs like the lungs

epicormic shoot

growth occurring from dormant buds under the bark after crown foliage is destroyed

epidermis

the outer layer of cells; in human skin it consists of three layers (outer region of dead cells, layers of living keratinocytes, and a basal layer of melanocytes and constantly dividing stem cells)

ethical issue

a problem or situation that requires a person or organisation to choose between alternatives that must be evaluated as right (ethical) or wrong (unethical)

exponential growth

population growth that follows a J-shaped curve but cannot continue indefinitely

extrinsic

coming from outside

fungal spore

microscopic biological particle that allows fungi to reproduce asexually

G1 checkpoint

a check that occurs during G1 of interphase that makes sure the DNA is not damaged and is ready to undergo replication

G1

stage of interphase the first stage of interphase in the cell cycle where the cell grows, increasing the amount of cell cytosol

G2 checkpoint

a check that occurs during G2 of interphase where the replicated DNA of the cell is checked for completeness and lack of damage; if the cell passes this checkpoint, it can then advance to mitosis

G2 stage of interphase

the third stage of interphase where proteins are synthesised and the cell continues to grow in preparation for division

growth

the process of increasing in size

hyphae

long, branching, filamentous structures of a fungus that make up mycelium; singular = hypha

induced pluripotent stem cell (IPSC)

a stem cell that has been genetically reprogrammed to return to an undifferentiated embryonic state

interphase

a stage in the cell cycle that is a period of cell growth and DNA synthesis

intrinsic

coming from inside

kinetochore

a special attachment site of a chromatid by which it links to a spindle fibre

ligand

a substance that forms a complex with a biomolecule to serve a biological purpose, such as the production of a signal upon binding to a signal

M checkpoint

a check that occurs during mitosis where the connection between chromatid and spindle fibres is checked and corrected

melanocytes

the pigment-producing cells in the basal layer of the epidermis

melanoma

cancer derived from the pigment-producing cells (melanocytes)

meristem

plant tissue found in tips of roots and shoots and made of unspecialised cells that can reproduce by mitosis

meristematic tissue

plant tissue found in tips of roots and shoots that is made of unspecialised cells that can reproduce by mitosis

mesoderm

the middle primary germ layer that differentiates into various tissues and organs, including the heart

metaphase

stage of mitosis during which chromosomes align around the equator of a cell

metastasis

a process where malignant tumours spread throughout the body

migrate

to move from one part of something to another

mitosis

process involved in the production of new cells genetically identical with the original cell; an essential process in asexual reproduction

multipotent

a cell that can differentiate into a number of closely related cell types

oligopotent

a cell that has the ability to differentiate into a few different cell types

oncogene

a gene that signals cells to continue dividing

p53

a protein that is coded for by a gene of the same name and regulates the cell cycle, hence functioning as a tumour suppressor

parthenote

potential source of embryonic stem cells, derived from unfertilised human eggs that are artificially stimulated to begin development

pluripotent

a cell that can differentiate into many different cell types

procreation

the production of offspring

prophase

stage of mitosis in which the chromosomes contract and become visible, the nuclear membrane begins to disintegrate and the spindle forms

proto-oncogene

a gene that leads to the production of proteins which initiate the cell cycle

psoriasis

chronic autoimmune condition in which skin cells are overproduced, resulting in raised patches of red, inflamed skin, often covered in a crust of small silvery scales

regenerative medicine

an experimental field of research involving stem cells in medicine that raises promise for the treatment of degenerative conditions and severe trauma injuries

repair

to restore something damaged or faulty to a good condition

replication

copying or reproducing something

rhizoids

fine, root-like structures present in some plants, such as mosses

S stage of interphase

the stage where the parent cell replicates its DNA; at the end of the S stage the parent cell contains two identical copies of its original DNA

septum

a wall, dividing a cavity or structure into smaller ones

somatic stem cells

undifferentiated cells obtained from various sources and capable of differentiating into related cell types; also known as adult stem cells

specialisation

the adaptation of something for a specific function

spindle

fine protein fibres that form between the poles of a cell during mitosis and to which chromosomes become attached

spindle fibres

clusters of microtubules, composed of the contractile protein actin, that grow out from the centrioles at opposite ends of a spindle

telophase

stage of mitosis in which new nuclear membranes form around the separated groups of chromosomes

therapeutic cloning

cloning carried out to create an embryo from which stem cells can be harvested

totipotent

a cell that is able to give rise to all different cell types

tumour-suppressor gene

a type of gene that produces a protein that signals for cells to stop dividing

unipotent

a cell that has the ability to produce only cells of their own type