Chapter 2 Flashcards
glycocalyx
cell coat of many animal cells over the plasma membrane, consisting of glycoproteins and polysaccharides
provides biochemical identity at the surface of cells, and the components of the coat that establish cellular identity are under genetic control
receptor molecules
recognition sites that transfer specific chemical signals across the cell membrane into the cell
nucleus
membrane-bound cytoplasmic organelle of eukaryotic cells that contain chromosomes and nucleolus
nucleolus
the nuclear site of ribosome biosynthesis and assembly, associated with or formed in association with the DNA compromising the nucleolar organizer region
where ribosomal RNA (rRNA) is synthesized and where the initial stages of ribosomal assembly occur
nucleolus organizer region (NOR)
The portions of DNA that encode rRNA
nucleoid
the DNA-containing region within the cytoplasm in bacterial cells
genetic material is present here as a long, circular DNA molecule that is compacted
cytoplasm
The remainder of the eukaryotic cell within the plasma membrane
includes a variety of extranuclear cellular organelles
cytosol
In the cytoplasm, a nonparticulate, colloidal material
surrounds and encompasses the cellular organelles
microtubules
fibers composed of tubulin, bunches of which are part of the structural framework of the cytoplasm (the cytoskeleton) and also which compose spindle fibers that facilitate chromosome migration during mitosis and meiosis
tubulin
protein making up microtubules
microfilaments
actin-containing microfibers that are a part of the structural framework of the cytoplasm
derived of the protein actin
endoplasmic reticulum
a membranous organelle system in the cytoplasm of eukaryotic cells
synthesizes proteins (rough ER) or fatty acids and phospholipids (smooth ER)
ribosomes
a ribonucleoprotein organelle consisting of two subunits, each containing RNA and protein molecules
Ribosomes are the site of translation of mRNA codons into the amino acid sequence of a polypeptide chain
Mitochondria
Self-reproducing, DNA-containing, cytoplasmic organelles in eukaryotes involved in generating the high-energy compound ATP. They are the so-called powerhouse of the cell.
Chloroplasts
organelles found within plant and algae cells that are responsible for photosynthesis,
centrioles
A cytoplasmic organelle composed of nine groups of microtubules, generally arranged in triplets
function in the generation of cilia and flagella and serve as foci for the spindles in cell division
centrosome
The specialized heterochromatic chromosomal region at which sister chromatids remain attached after replication, and the site to which spindle fibers attach to the chromosome during cell division
The location of the centromere determines the shape of the chromosome during the anaphase portion of cell division
spindle fibers
Cytoplasmic fibrils formed during cell division that attach to and are involved with separation of chromatids at the anaphase stage of mitosis and meiosis as well as their movement toward opposite poles in the cell.
karyotype
The chromosome complement of a cell or an individual. An arrangement of metaphase chromosomes in a sequence according to length and centromere position.
haploid number
The number of homologous chromosome pairs characteristic of an organism or species.
genome
The set of hereditary information encoded in the DNA of an organism, including both the protein-coding and non–protein-coding sequences.
Homologous chromosomes
they contain identical gene sites along their lengths; each site is called a locus
locus
The place on a chromosome where a particular gene is located.
biparental inheritance
inheritance from two parents
alleles
One of the possible alternative forms of a gene, often distinguished from other alleles by phenotypic effects.
During the formation of gametes or spores, meiosis converts the _____ number of chromosomes to the _____ number
diploid, haploid
As a result, haploid gametes or spores contain precisely one member of each homologous pair of chromosomes—that is, one complete haploid set.
Following fusion of two gametes at fertilization, the _______ number is reestablished; that is, the zygote contains two complete _______ sets of chromosomes
diploid, haploid
sex-determining chromosomes differences
these chromosomes are not often homologous in size, centromere placement, arm ratio, or genetic content.
zygotes
The diploid cell produced by the fusion of haploid gametic nuclei
karyokinesis
The end result is the production of two daughter nuclei, each with a chromosome composition identical to that of the parent cell
cytokinesis
the final stage of cell division where the cytoplasm of a single cell physically divides into two separate daughter cells
cell cycle
The sequence of growth phases in a cell; divided into G0, G1 (gap I), S (DNA synthesis), G2 (gap II), and M (mitosis)
A cell may temporarily or permanently withdraw from the cell cycle, in which case it is said to enter the G0 stage.
interphase
In the cell cycle, the interval between divisions.
G1 (gap I) and G2 (gap II)
G1: The phase during the cell cycle between G0 and the S phase, during which the cell develops and grows.
G2: The phase during the cell cycle following the S phase, during which the cell, having replicated its DNA, prepares for mitosis.
G0 stage
A nondividing but metabolically active state (G-zero) that cells may enter from the G1 phase of the cell cycle
prophase
The initial stage of cell division (mitosis and meiosis) during which the nuclear envelope breaks down, the nucleolus disintegrates, centrioles are formed and migrate to opposite ends of the cell, cytoplasmic microtubules are organized into spindle fibers, and diffuse chromatin fibers begin to condense into chromosomes.
sister chromatids
A pair of identical chromatids visible during mitosis and meiosis that are formed following replication of DNA of one member of a homologous chromosome pair
cohesin
A protein complex that holds sister chromatids together during mitosis and meiosis and facilitates attachments of spindle fibers to kinetochores
prometaphase
Stage of cell division (mitosis and meiosis) during which the spindle fibers are assembled and attach to the centromeres of chromosomes, which begin their migration to the equatorial plate
metaphase
The stage of cell division (mitosis and meiosis) in which condensed chromosomes lie in a central plane between the two poles of the cell and during which the chromosomes become attached to the spindle fibers
kinetochore
A protein structure that assembles on the centromere during mitosis and meiosis. It is the site of microtubule attachment during cell division
separase
a protease enzyme that breaks down cohesin, a protein complex that holds sister chromatids together
shugoshin (from the Japanese meaning “guardian spirit”)
proteins that prevent precocious dissociation of cohesin from centromeres
kinetochore microtubules
have one end near the centrosome region (at one of the poles of the cell) and the other end anchored to the kinetochore
anaphase
The stage of cell division (mitosis and meiosis) in which chromosomes begin moving to opposite poles of the cell
disjunction
The separation of chromosomes during the anaphase stage of cell division.
daughter chromosome
each migrating chromatid in anaphase now separated to different cells
molecular motors
Specialized proteins that facilitate the movement of cellular components.
Telophase
The stage of cell division (mitosis and meiosis) in which the daughter chromosomes have reached the opposite poles of the cell and reverse the stages characteristic of prophase, re-forming the nuclear envelopes and uncoiling the chromosomes
cell plate
a structure that forms in plant cells during mitosis to separate dividing cells
middle lamella
The cell plate laid down during telophase becomes a new structure
Subsequently, the primary and secondary layers of the cell wall are deposited between the cell membrane and middle lamella in each of the resulting daughter cells
cell furrow
a groove in a cell’s surface that forms during cell division to separate the cell into two daughter cells
kinases
A broad class of enzymes that phosphorylate a substrate molecule such as a protein, nucleic acid, carbohydrate, or lipid
cyclins
In eukaryotic cells, a class of proteins that are synthesized and degraded in synchrony with the cell cycle and regulate passage through stages of the cycle
cell-cycle checkpoints
Regulated transitions from one stage to another during the cell cycle
meiosis
The process of cell division in gametogenesis or sporogenesis during which the diploid number of chromosomes is reduced to the haploid number
crossing over
The exchange of chromosomal material (parts of chromosomal arms) between homologous chromosomes by breakage and reunion.
The exchange of material between nonsister chromatids during meiosis is the basis of genetic recombination.
Meiosis: Prophase I
once the chromatin characterizing interphase has condensed into visible structures, the homologous chromosomes are not autonomous but are instead seen to be paired up
synapsis
The pairing of homologous chromosomes at meiosis.
bivalent
Synapsed homologous chromosomes in the first prophase of meiosis
tetrad
The four chromatids that make up paired homologs in the prophase of the first meiotic division
In eukaryotes with a predominant haploid stage (some algae and fungi), a tetrad denotes the four haploid cells produced by a single meiotic division
chiasma
The crossed strands of nonsister chromatids seen in the first meiotic division.
Regarded as the cytological evidence for exchange of chromosomal material, or crossing over.
nonsister chromatids
Non-identical chromatids visible during mitosis and meiosis where each chromatid represents one or the other of the two members of a homologous pair of chromosomes
metaphase I
chromosomes have maximally shortened and thickened
the terminal chiasmata of each tetrad are visible and appear to be the major factor holding the nonsister chromatids together
anaphase I
cohesin is degraded between sister chromatids, except at the centromere region, which, as in mitosis, is protected by a shugoshin complex
one-half of each tetrad (a dyad) is pulled toward each pole of the dividing cell
nondisjunction
A cell division error in which homologous chromosomes (in meiosis) or the sister chromatids (in mitosis) fail to separate and migrate to opposite poles; responsible for defects such as monosomy and trisomy
telophase I
a nuclear membrane forming around the dyads
meiosis II
the second and final stage of meiosis, a process that creates gametes for sexual reproduction
each gamete or spore is to receive only one chromatid from each original tetrad
prophase II
each dyad is composed of one pair of sister chromatids attached by the common centromeric region
metaphase II
the centromeres are positioned on the equatorial plate
When the shugoshin complex is degraded, the centromeres separate
anaphase II
sister chromatids of each dyad are pulled to opposite poles
telophase II
reveals one member of each pair of homologous chromosomes present at each pole
Each chromosome is now a monad
our haploid gametes may result from a single meiotic event
