(PRELIM) HH L3

Nuclear envelope

Cytoplasm is separated from nucleoplasm by the __________, a double set of membranes with a narrow perinuclear space; the outer membrane binds ribosomes and is continuous with the RER.

Nuclear pore complexes

The nuclear envelope is penetrated by __________, large assemblies of nucleoporins with eightfold symmetry through which proteins and protein–RNA complexes move in both directions.

Lamins

The nuclear envelope is supported internally by a meshwork, the nuclear lamina, composed of intermediate filament subunits called __________.

DNA (deoxyribonucleic acid)

Chromatin is the combination of __________ and its associated proteins.

Euchromatin

Chromatin with DNA that is active in transcription stains lightly and is called __________; inactive chromatin stains more darkly and is called heterochromatin.

Heterochromatin

Chromatin with DNA that is active in transcription stains lightly and is called euchromatin; inactive chromatin stains more darkly and is called __________.

Histones

The DNA molecule initially wraps around complexes of basic proteins called __________ to form nucleosomes, producing a structure resembling beads on a string

Nucleosomes

The DNA molecule initially wraps around complexes of basic proteins called histones to form __________, producing a structure resembling beads on a string

Nonhistone proteins

Additional levels of chromatin fiber condensation are less well understood and involve _________, including scaffolds of large protein complexes

Barr body

The extra X chromosome in cells of female mammals forms facultative heterochromatin and can be seen as the __________.

Nucleolus

The __________ is a very basophilic or electron-dense area of chromatin localized where rRNA transcription and ribosomal subunits assembly occur

rRNA transcription

The nucleolus is a very basophilic or electron-dense area of chromatin localized where __________ and ribosomal subunits assembly occur

Fibrous and granular parts

By TEM, an active nucleolus is seen to have __________ where rRNA forms and ribosomal subunits are assembled, respectively.

Cell cycle

The __________ is the sequence of events that controls cell growth and division.

G1 phase

The __________, the longest part of the cycle, begins immediately after mitosis and includes all preparations for DNA replication.

S phase

The period of DNA (and histone) synthesis is the __________.

G2 phase

In a short __________ the cell prepares for division during mitosis (M).

Cyclins

Cell cycling is controlled by the sequential appearance of key cytoplasmic proteins, the __________, which bind cyclin-dependent kinases (CDKs).

Cyclin-dependent kinases (CDKs)

Cell cycling is controlled by the sequential appearance of key cytoplasmic proteins, the cyclins, which bind __________.

Phosphorylate

Cyclin-dependent kinases (CDKs) __________ and activate the enzymes and transcription factors whose functions characterize each phase of the cell cycle.

G1 restriction point

Progress through the cell cycle stages is monitored at checkpoints, including the ___________; only when each phase’s activities are completed are the cyclins changed to trigger those of the next phase.

Prophase

Stages of mitotic cell divisions include __________, when chromosomes condense, the nuclear envelope disassembles, and the microtubular spindle forms; metaphase, when chromosomes are aligned; anaphase, when they begin to separate toward the two centrosomes; and telophase, when nuclear envelope re-forms around the separated chromosomes.

Metaphase

Stages of mitotic cell divisions include prophase, when chromosomes condense, the nuclear envelope disassembles, and the microtubular spindle forms; ___________, when chromosomes are aligned; anaphase, when they begin to separate toward the two centrosomes; and telophase, when nuclear envelope re-forms around the separated chromosomes.

Anaphase

Stages of mitotic cell divisions include prophase, when chromosomes condense, the nuclear envelope disassembles, and the microtubular spindle forms; metaphase, when chromosomes are aligned; __________, when they begin to separate toward the two centrosomes; and telophase, when nuclear envelope re-forms around the separated chromosomes.

Telophase

Stages of mitotic cell divisions include prophase, when chromosomes condense, the nuclear envelope disassembles, and the microtubular spindle forms; metaphase, when chromosomes are aligned; anaphase, when they begin to separate toward the two centrosomes; and __________, when nuclear envelope re-forms around the separated chromosomes.

Cytokinesis

Telophase ends with __________ or cell cleavage into two daughter cells by a contractile ring of actin filaments and myosin.

Stem cells

__________ occur in all tissues with rapid cell turnover; they divide slowly in an asymmetric manner, with one daughter cell remaining the same way (as __________) and one becoming committed toward differentiation

Asymmetric

Stem cells occur in all tissues with rapid cell turnover; they divide slowly in an __________ manner, with one daughter cell remaining a stem cell and one becoming committed toward differentiation

Transit amplifying or progenitor cells

Cells committed to differentiate (__________) typically divide more rapidly than stem cells before slowing or stopping division to differentiate.

Meiosis

__________ is the process by which two successive cell divisions produce cells called gametes containing half the number of chromosomes found in somatic cells.

Gametes

Meiosis is the process by which two successive cell divisions produce cells called __________ containing half the number of chromosomes found in somatic cells.

Synapsis

Prophase of the first meiotic division is a unique, extended period in which homologous chromosomes pair and undergo genetic recombination during the process called __________.

Synaptic pairs

__________ separate toward two daughter cells at the first meiotic division.

Haploid

The second meiotic division occurs with no intervening S phase and separates the sister chromatids into two final cells that are _________.

Apoptosis

__________ is the process by which redundant or defective cells are rapidly eliminated in a manner that does not provoke a local inflammatory reaction in the tissue

Bcl-2 family of proteins

Apoptosis involves a cascade of events controlled by the __________ regulating the release of death-promoting factors from mitochondria.

Caspases

Cytochrome c from mitochondria activates cytoplasmic proteases called __________, which degrade proteins of the cytosol, cytoskeleton, and cell membrane

Endonucleases

__________ are activated, which degrade all nuclear DNA.

Cell surface

Cell and nuclear volumes shrink rapidly, and the cell membrane changes produce extensive blebbing of the _________.

Apoptotic bodies

Late in apoptosis, the cell breaks into many small __________ that undergo phagocytosis by neighboring cells.

Phagocytosis

Late in apoptosis, the cell breaks into many small apoptotic bodies that undergo __________ by neighboring cells.

Necrosis

Apoptosis occurs rapidly, with little or no release of proteins that would trigger inflammation, unlike the death of injured cells by __________ that typically induces local inflammation.