DNA Replication, Cell Cycle

anaphase

stage of mitosis during which sister chromatids are separated from each other

binary fission

prokaryotic cell division process

cell cycle

ordered series of events involving cell growth and cell division that produces two new daughter cells

cell plate

structure formed during plant cell cytokinesis by Golgi vesicles, forming a temporary structure (phragmoplast) and fusing at the metaphase plate; ultimately leads to the formation of cell walls that separate the two daughter cells

cell-cycle checkpoint

mechanism that monitors the preparedness of a eukaryotic cell to advance through the various cell-cycle stages

centriole

rod-like structure constructed of microtubules at the center of each animal cell centrosome

centromere

region at which sister chromatids are bound together; a constricted area in condensed chromosomes

chromatid

single DNA molecule of two strands of duplicated DNA and associated proteins held together at the centromere

cleavage furrow

constriction formed by an actin ring during cytokinesis in animal cells that leads to cytoplasmic division

condensin

proteins that help sister chromatids coil during prophase

cyclin

one of a group of proteins that act in conjunction with cyclin-dependent kinases to help regulate the cell cycle by phosphorylating key proteins; the concentrations of cyclins fluctuate throughout the cell cycle

cyclin-dependent kinase (Cdk)

one of a group of protein kinases that helps to regulate the cell cycle when bound to cyclin; it functions to phosphorylate other proteins that are either activated or inactivated by phosphorylation

cytokinesis

division of the cytoplasm following mitosis that forms two daughter cells

diploid

cell, nucleus, or organism containing two sets of chromosomes (2n)

FtsZ

tubulin-like protein component of the prokaryotic cytoskeleton that is important in prokaryotic cytokinesis

G0 phase

distinct from the G1 phase of interphase; a cell in G0 is not preparing to divide

G1 phase

first phase of interphase centered on cell growth during mitosis

G2 phase

third phase of interphase during which the cell undergoes final preparations for mitosis

gamete

haploid reproductive cell or sex cell (sperm, pollen grain, or egg)

gene

physical and functional unit of heredity, a sequence of DNA that codes for a protein

genome

total genetic information of a cell or organism

haploid

cell, nucleus, or organism containing one set of chromosomes (n)

histone

one of several similar, highly conserved, low molecular weight, basic proteins found in the chromatin of all eukaryotic cells; associates with DNA to form nucleosomes

homologous chromosomes

chromosomes of the same morphology with genes in the same location; diploid organisms have pairs of homologous chromosomes (homologs), with each homolog derived from a different parent

interphase

period of the cell cycle leading up to mitosis; includes G1, S, and G2 phases (the interim period between two consecutive cell divisions)

karyokinesis

mitotic nuclear division

kinetochore

protein structure associated with the centromere of each sister chromatid that attracts and binds spindle microtubules during prometaphase

locus

position of a gene on a chromosome

metaphase

stage of mitosis during which chromosomes are aligned at the metaphase plate

metaphase plate

equatorial plane midway between the two poles of a cell where the chromosomes align during metaphase

mitosis

period of the cell cycle during which the duplicated chromosomes are separated into identical nuclei; includes prophase, prometaphase, metaphase, anaphase, and telophase

mitotic phase

period of the cell cycle during which duplicated chromosomes are distributed into two nuclei and cytoplasmic contents are divided; includes karyokinesis (mitosis) and cytokinesis

mitotic spindle

apparatus composed of microtubules that orchestrates the movement of chromosomes during mitosis

nucleosome

subunit of chromatin composed of a short length of DNA wrapped around a core of histone proteins

oncogene

mutated version of a normal gene involved in the positive regulation of the cell cycle

origin (ORI)

region of the prokaryotic chromosome where replication begins

p21

cell-cycle regulatory protein that inhibits the cell cycle; its levels are controlled by p53

p53

cell-cycle regulatory protein that regulates cell growth and monitors DNA damage; it halts the progression of the cell cycle in cases of DNA damage and may induce apoptosis

prometaphase

stage of mitosis during which the nuclear membrane breaks down and mitotic spindle fibers attach to kinetochores

prophase

stage of mitosis during which chromosomes condense and the mitotic spindle begins to form

proto-oncogene

normal gene that when mutated becomes an oncogene

quiescent

refers to a cell that is performing normal cell functions and has not initiated preparations for cell division

retinoblastoma protein (Rb)

regulatory molecule that exhibits negative effects on the cell cycle by interacting with a transcription factor (E2F)

S phase

second, or synthesis, stage of interphase during which DNA replication occurs

septum

structure formed in a bacterial cell as a precursor to the separation of the cell into two daughter cells

telophase

stage of mitosis during which chromosomes arrive at opposite poles, decondense, and are surrounded by a new nuclear envelope

tumor suppressor gene

segment of DNA that codes for regulator proteins that prevent the cell from undergoing uncontrolled division

alternation of generations

life-cycle type in which the diploid and haploid stages alternate

chiasmata

the structure that forms at the crossover points after genetic material is exchanged

cohesin

proteins that form a complex that seals sister chromatids together at their centromeres until anaphase II of meiosis

crossover

exchange of genetic material between nonsister chromatids resulting in chromosomes that incorporate genes from both parents of the organism

fertilization

union of two haploid cells from two individual organisms

gametophyte

a multicellular haploid life-cycle stage that produces gametes

germ cells

specialized cell line that produces gametes, such as eggs or sperm

interkinesis

brief period of rest between meiosis I and meiosis II

life cycle

the sequence of events in the development of an organism and the production of cells that produce offspring

meiosis

a nuclear division process that results in four haploid cells

meiosis I

first round of meiotic cell division; referred to as reduction division because the ploidy level is reduced from diploid to haploid

meiosis II

second round of meiotic cell division following meiosis I; sister chromatids are separated into individual chromosomes, and the result is four unique haploid cells

recombination nodules

protein assemblies formed on the synaptonemal complex that mark the points of crossover events and mediate the multistep process of genetic recombination between nonsister chromatids

reduction division

nuclear division that produces daughter nuclei each having one-half as many chromosome sets as the parental nucleus; meiosis I is a reduction division

somatic cell

all the cells of a multicellular organism except the gametes or reproductive cells

spore

haploid cell that can produce a haploid multicellular organism or can fuse with another spore to form a diploid cell

sporophyte

a multicellular diploid life-cycle stage that produces haploid spores by meiosis

synapsis

formation of a close association between homologous chromosomes during prophase I

synaptonemal complex

protein lattice that forms between homologous chromosomes during prophase I, supporting crossover

tetrad

two duplicated homologous chromosomes (four chromatids) bound together by chiasmata during prophase I

electrophoresis

technique used to separate DNA fragments according to size

helicase, during replication

this enzyme helps to open up the DNA helix by breaking the hydrogen bonds

induced mutation

mutation that results from exposure to chemicals or environmental agents

lagging strand

during replication, the strand that is replicated in short fragments and away from the replication fork

leading strand

strand that is synthesized continuously in the 5'-3' direction, which is synthesized in the direction of the replication fork

ligase

enzyme that catalyzes the formation of a phosphodiester linkage between the 3' OH and 5' phosphate ends of the DNA

mismatch repair

type of repair mechanism in which mismatched bases are removed after replication

mutation

variation in the nucleotide sequence of a genome

nucleotide excision repair

type of DNA repair mechanism in which the wrong base, along with a few nucleotides upstream or downstream, are removed

Okazaki fragment

DNA fragment that is synthesized in short stretches on the lagging strand

point mutation

mutation that affects a single base

primase,

enzyme that synthesizes the RNA primer; the primer is needed for DNA pol to start synthesis of a new DNA strand

primer

short stretch of nucleotides that is required to initiate replication; in the case of replication, the primer has RNA nucleotides

proofreading

function of DNA pol in which it reads the newly added base before adding the next one

replication fork

Y-shaped structure formed during initiation of replication

silent mutation

mutation that is not expressed

single-strand binding protein

during replication, protein that binds to the single-stranded DNA; this helps in keeping the two strands of DNA apart so that they may serve as templates

sliding clamp

ring-shaped protein that holds the DNA pol on the DNA strand

spontaneous mutation

mutation that takes place in the cells as a result of chemical reactions taking place naturally without exposure to any external agent

telomerase

enzyme that contains a catalytic part and an inbuilt RNA template; it functions to maintain telomeres at chromosome ends

telomere

DNA at the end of linear chromosomes

topoisomerase

enzyme that causes underwinding or overwinding of DNA when DNA replication is taking place

transformation

process in which external DNA is taken up by a cell

transition substitution

when a purine is replaced with a purine or a pyrimidine is replaced with another pyrimidine

transversion substitution

when a purine is replaced by a pyrimidine or a pyrimidine is replaced by a purine

7-methylguanosine cap

modification added to the 5' end of pre-mRNAs to protect mRNA from degradation and assist translation

aminoacyl tRNA synthetase

enzyme that "charges" tRNA molecules by catalyzing a bond between the tRNA and a corresponding amino acid

anticodon

three-nucleotide sequence in a tRNA molecule that corresponds to an mRNA codon

CAAT box

essential eukaryotic promoter sequence involved in binding transcription factors

central dogma

states that genes specify the sequence of mRNAs, which in turn specify the sequence of proteins

codon

three consecutive nucleotides in mRNA that specify the insertion of an amino acid or the release of a polypeptide chain during translation

colinear

in terms of RNA and protein, three "units" of RNA (nucleotides) specify one "unit" of protein (amino acid) in a consecutive fashion

consensus

DNA sequence that is used by many species to perform the same or similar functions