Unit 1: Human Cells: Chapter 1: Division & differentiation Flashcards
Differentiation
The process by which an unspecialized cell becomes altered and adapted to perform a specialized function as part of a permanent tissue.
Once a cell becomes differentiated it only expresses the genes that produce the proteins characteristic for that type of cell.
Zygote
Egg cell (ovum) which has been fertilized by a sperm cell.
Stem cells
Unspecialized cells that can
- REPRODUCE - (‘self-renew’) themselves by repeated cell division (mitosis) while remaining undifferentiated.
- DIFFERENTIATE - change into specialized cells with specific functions when required to do so by the multicellular organism.
(Human) Blastocyst
Ball of approx 100 undifferentiated stem cells.
Pluripotent
Having the potential for all genes within the cell to be switched on, so the cell is capable of differentiating into almost all of the cell types found within the human body.
(i.e. embryonic stem cell.)
Tissue (adult) stem cells
Partially differentiated stem cells found in ‘stem cell niches’ - skin, bone marrow, teeth, brain, skeletal muscle, heart, gut, peripheral blood & liver. Narrower differentiation potential than embryonic stem cells because many of their genes are already switched off. Able to replenish continuously the supply of certain differentiated cells needed by the human body.
Multipotent
Describes ability of tissue stem cells with potential to replenish all cell types found within a particular tissue type.
Somatic cell
All differentiated cells (except reproductive cells) derived from stem cells.
Epithelium
Composed of cells that unite to form membranes, either single (oesophagus, blood vessels) or multi layered (skin).
Connective tissue
e.g. bone, cartilage & blood. Characterized by large quantity of material present in spaces between cells. Matrix may be solid (bone), fibrous or gelatinous (cartilage) or liquid (plasma in blood).
Bone
Concentric layers of calcified material laid down around blood vessels. Live bone cells receive oxygen & nutrients via tiny canals in contact with blood vessels.
Cartilage
Several forms differing in composition of extracellular material. Can be solid & smooth or slightly flexible with dense fibres embedded in a solid background.
Blood
Classified as a connective tissue because approx 50% of its volume composed of plasma.
Muscle
Cells capable of contraction.
- SKELETAL - striped fibres.
- SMOOTH - spindle shaped cells arranged in sheets e.g. alimentary canal & blood vessels.
- CARDIAC - each cell has one or more branches in contact with adjacent cells.
Nervous tissue
Composed of network of
- NEURONS - to receive & transmit nerve impulses.
- GLIAL - cells to support & maintain neurons
Chromosome
An organized package, thread like structure of DNA found in the nucleus of a cell. Subdivided into genes, mostly in functional pairs.
Diploid
Containing pairs of homologous chromosomes.
Mitosis
Division of a cell nucleus, where genetic material is divided equally between 2 daughter nuclei. Each somatic cell receives an identical copy of full set of 23 paired homologous chromosomes.
Germline cell
A cell that eventually leads to the formation of sex cells (gametes).
Germline cells are set aside from somatic cells early in the course of human development but, like a somatic cell, is diploid, i.e. contains 23 pairs of homologous chromosomes & can undergo mitosis to replicate to form more germline ‘mother’ diploid cells.
Meiosis
Secondary nuclear division of germline cells. Genetic material doubled by replication but divided between 4 nuclei, each receiving single set of 23 chromosomes, and forming 4 haploid gametes.
Mutation
Alteration of genetic material (genome) of a cell, which can be transmitted to descendants if in a germline cell. Mutations in somatic cells are not inheritable.
Ethics
Moral values and rules that govern human conduct
Induced pluripotent stem cells
Differentiated cells (e.g. from human skin) that have been genetically reprogrammed using transcription process to switch some of their turned-off genes back on again. They act as stem cells but can only be used for research, as the viruses used as transcription vectors have been shown to cause cancers in laboratory mice.
Nuclear transfer technique
Introduction of a human cell nucleus into an enucleated animal cell to form a CYTOPLASMIC HYBRID CELL. Some of these cells will divide to produce undifferentiated stem cells. Can only be used for research because of mixed species origin not 100% human.
