Bio Exam 1

Chromatin

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.

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.

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.

Nucleosome

The basic, bead-like unit of DNA packing in eukaryotes, consisting of a segment of DNA wound around a protein core composed of two copies of each of four types of histone.

Ribosome

A complex of rRNA and protein molecules that functions as a site of protein synthesis in the cytoplasm; consists of a large and a small subunit. In eukaryotic cells, each subunit is assembled in the nucleolus. See also nucleolus.

Capsule

(1) In many prokaryotes, a dense and well-defined layer of polysaccharide or protein that surrounds the cell wall and is sticky, protecting the cell and enabling it to adhere to substrates or other cells. (2) The sporangium of a bryophyte (moss, liverwort, or hornwort).

Flagellum

a slender threadlike structure, especially a microscopic appendage that enables many protozoa, bacteria, spermatozoa, etc. to swim.

Pili

In bacteria, a structure that links one cell to another at the start of conjugation; also called a sex pilus or conjugation pilus.

Extremophile

An organism that lives in environmental conditions so extreme that few other species can survive there. Extremophiles include extreme halophiles (“salt lovers”) and extreme thermophiles (“heat lovers”).

Biofilm

A surface-coating colony of one or more species of unicellular organisms that engage in metabolic cooperation; most known biofilms are formed by prokaryotes.

Quorum sensing

the process of cell-to-cell communication that allows bacteria to detect and respond to cell population density by gene regulation, typically as a means of acclimating to environmental disadvantages.

Nuclear envelope

In a eukaryotic cell, the double membrane that surrounds the nucleus, perforated with pores that regulate traffic with the cytoplasm. The outer membrane is continuous with the endoplasmic reticulum.

Nucleoplasm

a type of protoplasm that is found in nucleus of eukaryotic cells, including both plant and animal cell. This jelly-like substance, resembling the cytoplasm is also known as karyoplasm, karyolymph, or nucleus sap. It remains completely enclosed within the nuclear membrane or nuclear envelope. The primary function of nucleoplasm is to suspend other nuclear structures within it.

Nucleolus

A specialized structure in the nucleus, consisting of chromosomal regions containing ribosomal RNA (rRNA) genes along with ribosomal proteins imported from the cytoplasm; site of rRNA synthesis and ribosomal subunit assembly. See also ribosome.

Endomembrane system

The collection of membranes inside and surrounding a eukaryotic cell, related either through direct physical contact or by the transfer of membranous vesicles; includes the plasma membrane, the nuclear envelope, the smooth and rough endoplasmic reticulum, the Golgi apparatus, lysosomes, vesicles, and vacuoles.

Vesicle

A membrane-bound sac in or outside a cell.

Phagocytosis

A type of endocytosis in which large particulate substances or small organisms are taken up by a cell. It is carried out by some protists and by certain immune cells of animals (in mammals, mainly macrophages, neutrophils, and dendritic cells).

Autophagy

destruction of damaged or redundant cellular components occurring in vacuoles within the cell.

Endosymbiosis

A relationship between two species in which one organism lives inside the cell or cells of another organism; The theory that mitochondria and plastids originated as prokaryotic cells engulfed by a host cell. The engulfed cell and its host cell then evolved into a single organism.

Motor protein

A protein that interacts with cytoskeletal elements and other cell components, producing movement of the whole cell or parts of the cell.

Pseudopodia

A cellular extension of amoeboid cells used in moving and feeding.

Primary cell wall

In plants, a relatively thin and flexible layer that surrounds the plasma membrane of a young cell.

Secondary cell wall

In plant cells, a strong and durable matrix that is often deposited in several laminated layers around the plasma membrane and provides protection and support.

Lignin

A strong polymer embedded in the cellulose matrix of the secondary cell walls of vascular plants that provides structural support in terrestrial species.

Cuticle

Protective outer covering. Typically on outside of plants. Shine

Extracellular matrix

The meshwork surrounding animal cells, consisting of glycoproteins, polysaccharides, and proteoglycans synthesized and secreted by cells.

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. Gametes unite during sexual reproduction to produce a diploid zygote.

Germ Cell

a cell containing half the number of chromosomes of a somatic cell and able to unite with one from the opposite sex to form a new individual; a gamete.

Stem cell

Any relatively unspecialized cell that can produce, during a single division, two identical daughter cells or two more specialized daughter cells that can undergo further differentiation, or one cell of each type.

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.

karyokinesis

division of a cell nucleus during mitosis

Cytokinesis

The division of the cytoplasm to form two separate daughter cells immediately after mitosis, meiosis I, or meiosis II.

Binary Fission

A method of asexual reproduction in single-celled organisms in which the cell grows to roughly double its size and then divides into two cells. In prokaryotes, binary fission does not involve mitosis, but in single-celled eukaryotes that undergo binary fission, mitosis is part of the process.

G1

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

G0

A nondividing state occupied by cells that have left the cell cycle, sometimes reversibly.

S

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

Chromatid

each of the two threadlike strands into which a chromosome divides longitudinally during cell division. Each contains a double helix of DNA.

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.

G2

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

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.

Spindle

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

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.

Kinetochore

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

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.

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.)

Metaphase Plate

An imaginary structure located at a plane midway between the two poles of a cell in metaphase on which the centromeres of all the duplicated chromosomes are located.

Contractile Ring

generates the constricting force to separate one cell into two cells in cytokinesis

Cell Plate

A membrane-bounded, flattened sac located at the midline of a dividing plant cell, inside which the new cell wall forms during cytokinesis.

Tumor

A membrane-bounded, flattened sac located at the midline of a dividing plant cell, inside which the new cell wall forms during cytokinesis.

tumor-a swelling of a part of the body, generally without inflammation, caused by an abnormal growth of tissue, whether benign or malignant:

A cancerous tumor containing cells that have significant genetic and cellular changes and are capable of invading and surviving in new sites. Malignant tumors can impair the functions of one or more organs.

Apoptosis

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

Asexual reproduction

The generation of offspring from a single parent that occurs without the fusion of gametes. In most cases, the offspring are genetically identical to the parent.

Sexual reproduction

Reproduction arising from fusion of two gametes.

Parthenogenesis

A form of asexual reproduction in which females produce offspring from unfertilized eggs.

Diplontic

(of an alga or other lower plant) having a life cycle in which the main form, except for the gametes, is diploid. start haploid-diploid

Alternation of generations

A life cycle in which there is both a multicellular diploid form, the sporophyte, and a multicellular haploid form, the gametophyte; characteristic of plants and some algae.

Haplontic

(of an alga or other lower plant) having a life cycle in which the main form is haploid, with a diploid zygote being formed only briefly.

Haploid

A cell containing only one set of chromosomes (n).

Diploid

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

Tetrad (Bivalent)

a group or set of four:

Crossing over

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

Chiasmata

The X-shaped, microscopically visible region where crossing over has occurred earlier in prophase I between homologous nonsister chromatids. Chiasmata become visible after synapsis ends, with the two homologs remaining associated due to sister chromatid cohesion.

Fertilization

the action or process of fertilizing an egg, female animal, or plant, involving the fusion of male and female gametes to form a zygote.

Zygote

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

Spermatogenesis

The continuous and prolific production of mature sperm in the testis.

Oogenesis

The process in the ovary that results in the production of female gametes.

Polar body

each of the small cells which bud off from an oocyte at the two meiotic divisions and do not develop into ova.