Cell Physio

Study guide 1

Gamete

A haploid cell specialized for sexual reproduction

Ovum

(pl. ova) Egg, female gamete

Sperm

male gamete

Zygote

the cell resulting from fusion of gametes (the zygote last only until it divides)

Oocyte

NOT the same as egg, the oocyte is the cell that will become the egg after competing meiosis

Spermatocyte

NOT the same as sperm, cell that will become sperm

Maturation

develop, mature (includes meiosis- makes ooctyle into egg, etc.)

Egg

Mature oocyte (after completing meiosis), ovum, female gamete (in some animals fertilization occurs in this stage- urchins, cnidarians)

*Isn’t just for eggs.

Zygote

the diplood cell resulting from fusion of gamete (last only until it divides). Zygote is the fertilized eggs, but isn’t a zygote until oocyte meiosis is complete and pronuclei have gotten together

Acrosome

The acrosomal vescile located at the anterior end of sperm head is derived from the Golgi apparatus and contains enzymes which digestive proteins and complex sugars in the egg coats, enabling sperm entry during fertilization. Fuses with sperm plasma membrane in the acrosome reaction when the sperm binds the egg. the event is associated with assembly or extension of an acrosomal filament in many species

Acrosomal vesicle

specialized, membrane- bound organelle located in the anterior head of sperm cell, derived from golgi appartus- during spermatogensis

Golgi apparatus

organelle found in most eukaryotic cells that acts as “post office”- modifying, sorting, and packaging proteins and lipids into vesicles for specific destinations

Acrosomal reaction

critical, calcium-dependent exocytotic process in sperm that release enzymes to digest egg coating

Acrosomal filament

actin-based structure that extends from the sperm head during fertilization, enabling it to penetrate the eggs jelly coat

Cytoskeleton

roughly, a set of protein filaments that give shape and structure to living cytoplasm

Actin

a protein which exists in unpolymerized (globular: G-actin) or polymerized (filamentous: F-actin) state in animal cells. Actin is a central agent inc ell shape change and contractility and is among the most abundant of cellular proteins in most eukaryotes. In the electron microscopically literature F-actin is often called microfilaments. Actin filaments can be several microns long and form bundles and networks of all sorts with the help of diverse actin-binding proteins. Actin filaments are of the most fundamental bases of the exoskeleton

barbed end, pointed end

actin filaments are polar, and generally assemble more rapidly at the barbed end. The names are derived from a classic technique in which the heads of the motor protein myosin are used to decorate microfilaments in electron microscope preps.

ATPase

Any enzyme that hydrolyzes ATP (adenosine triphosphate; the cell's main energetic currency) for whatever reason. Actin is an ATPase, although strictly speaking it's not a very good one. A Common Theme which will recur almost ad nauseam: very many biological mechanisms use nucleotide hydrolysis not for energy but for biasing state transitions; in this context, we usually find enzymes that, by conventional standards, are poor and inefficient catalysts of their nominal reaction.

Fertilization

union of egg and sperm, which leads to the formation of a new organism.

Plasma membrane

the outermost boundary surrounding living protoplasm, consisting of a bilayer lipid film in which is dissolved a high concentration of protein. A largely-obsolete synonym is plasmalemma, which you will see in older papers.

Cell cortex

as much an idea as an observation, there is a specialized film of cytoplasm associated with the plasma membrane in which organelles are scarce (compared to bulk cytoplasm) and the cytoskeleton, especially actin, is enriched.

Cortical granule

one of the numerous exocytotic vesicles in the cortex of unfertilized egg, which contain hyalin, enzymes and mucopolysaccharides. Cortical granules are an instance of secretory vesicles that are derived from the Golgi apparatus, transported to the plasma membrane, and docked, awaiting a signal to fuse with the plasma membrane and void their contents outside the cell. They are in this respect equivalent to synaptic vesicles that contain neurotransmitters awaiting release or numerous other instances of the regulated secretory pathway.

Vesicle

small, membrane-bound, fluid-filled sacs in cells that transport, store, or digest substance

Regulated secretory pathways

a cellular process in specialized cells (e.g., neurons, endocrine cells) that packages specific proteins, such as hormones or neurotransmitters, into dense-core vesicles

Cortical reaction

a process, normally triggered by fusion of sperm and egg plasma membranes during fertilization, in which the cortical granules abruptly fuse with the egg plasma membrane, releasing their contents into the space between the plasma membrane and vitelline envelope. The fusion of cortical granules with the membrane is an instance of exocytosis …which just means "out (of) cell process". No, really. Hey, guess what endocytosis means!

Exocytosis

an active transport process where cells move materials (proteins, neurotransmitters, waste) from the cytoplasm to the extracellular space

Endocytosis

an active transport process where eukaryotic cells ingest extracellular material by enveloping it in a segment of the plasma membrane, which then pinches off to form an internal vesicle

Polyspermy

a condition in which more than one sperm enter the egg (which results in abnormal development in most animals)

Hyalin

a protein released from the cortical granules into the space between the egg plasma membrane and the vitelline envelope in the process of fertilization. It forms a coat around the egg and helps to hold blastomeres together during early development (before embryonic cells figure out how to hold on to each other with tight junctions)

Vitelline (envelope/membrane)

an extracellular coat which contains glycoproteins and is bound to the egg plasma membrane. It is important in species-specific interactions with the sperm.

Fertilization envelope

a noticeable membrane which surrounds a fertilized egg of a sea urchin. It is the product of the vitelline envelope, cleaved off and raised from the surface of the egg and then hardened enzymatically as a result of the cortical reaction.

Pronucleus

his term distinguishes the haploid gamete-derived nuclei from the diploid zygote nucleus.

Haploid

having a single set of unpaired chromosomes.

Diploid

containing two complete sets of chromosomes, one from each parent.

Microtubule

a tubular protein polymer; the second major eukaryotic cytoskeletal filament (the first being F-actin). Compared to actin filaments, microtubules are larger and stiffer and often longer.

Tubulin

the building block of microtubules is a dimer of alpha- and beta-tubulin. Tubulin is a GTPase, but – like actin – not a very good one. Microtubules are hollow bundles of 13 nearly-straight protofilaments of tubulin dimers stacked one atop the next. They are polar filaments and have a plus end and a minus end characterized by dramatically different growth rates. These are analogous to the barbed and pointed ends of actin filaments.

Protofilaments

linear, longitudinal rows of polymerized globular proteins—typically alpha and beta-tubulin dimers—that associate laterally to form the cylindrical wall of a microtubule. Generally, 13 protofilaments assemble into the hollow tube that serves as a core component of the cytoskeleton

Plus end

the fast-growing, dynamic distal end of a microtubule filament, typically radiating toward the cell periphery

Minus end

the slower-growing, polarized end of a microtubule, characterized by exposed -tubulin, often anchored at the centrosome (MTOC) near the nucleus.

GTP cap

the plus end of a growing microtubule is thought to consist entirely or mostly of tubulin bound to GTP (GTP-tubulin, that is). Some time after adding into the microtubule, tubulin hydrolyzes its GTP, becoming GDP-tubulin. Microtubules composed of GTP-tubulin are stable and tend to add more subunits (most rapidly at the plus end). Microtubules composed of GDP-tubulin are unstable and tend to disassemble rapidly.

Dynamic instability

a characteristic behavior epitomized by individual microtubules, conferred by the coupling of assembly to GTP hydrolysis. In brief: a microtubule whose plus end has a GTP cap continues to assemble as long as GTP-tubulin is available; if growth slows, GTP hydrolysis can catch up to the plus end, obliterating the GTP cap; when this happens it is a catastrophe! - meaning, the now-unstable end starts to rapidly disassemble; but a shrinking microtubule can be rescued and grow again. Hence, the life of a microtubule begins with nucleation and consists thereafter of an indefinite sequence of growth, catastrophe, disassembly, and rescue, until the last comes too late.

Catastrophe

a mechanism of cell death or senescence that occurs when a cell attempts to divide (mitosis) with damaged DNA or improper mitotic spindle formation

Rescue

experimental procedures that reverse or correct a genetic defect or dysfunctional phenotype, restoring normal function to a cell

Treadmilling

under some conditions, protein filaments (including F-actin and microtubules) may assemble from the preferred end (barbed; plus) while disassembling from the other (pointed; minus). From a point of view fixed to filament position, subunits would therefore appear to flow through the filament like the band on a treadmill

Nucleation

pure actin plus ATP will assemble into filaments. So will tubulin plus GTP. But the rate-limiting step is getting enough subunits together in the right configuration to start growth; this special configuration constitutes a nucleus for the new polymer. For actin, the nucleus means just three monomers. For tubulin it is almost certainly more. In most living contexts, microtubule nucleation is a high enough barrier that most microtubules arise from nucleating complexes assembled by other proteins. Even for actin, nucleation is often prompted by specific protein complexes (about which more later). This is a key element of the cell's control over its own structure

Centrosome

microtubule nucleation is indeed very tightly controlled in most eukaryotic cells, and is localized tightly to microtubule-organizing centers (MTOC). The best-known MTOC is the centrosome, so called because animal cells tend to have just one of them which appears to define the cell center. The centrosome is a nebulous cloud of material at the heart of which is the

Microtubules organizing centers (MTOC)

specialized eukaryotic cellular structure that nucleates, anchors, and organizes microtubules, essential for cell shape, division, and transport.

Centriole

a highly-structured microtubule-containing structure that seems to organize the centrosome. How's that for a circular definition? Really: a huge amount of ink and energy has been spilled on the relationship between the centriole, centrosome, MTOCs in general, and the

Basal body

here we go again. It's a body, and it's basal because it's at the base… of the ciliary axoneme, that is (more on that later). The same structure that we call a centriole when it's at the center of the centrosome is called a basal body when it serves as the template and anchor for the microtubules that form the core of the cilium. But we will leave cilia for another week in the hope of ending this vocabulary list soon

Chromosome,chromatin, chromatid

you all know what a chromosome is, right? A big long DNA molecule that behaves as a faithfully-copied and -segregated subset of the genome. And chromatin is the stuff of chromosomes, i.e., the DNA and all the associated proteins. A chromatid is a copy of a chromosome while it is still stuck to the other copy by its

Centromere

a chromosome region, whether defined by sequence or epigenetically, that controls the assortment of chromosomes during division by nucleating assembly of the…

Kinetochore

a large-scale protein complex that assembles around the centromeric chromatin on each replicated chromosome during mitosis, which serves as the attachment point for microtubules of the mitotic apparatus. The set of microtubules that attach the kinetochore to one spindle pole is called a kinetochore fiber or K-fiber.

Kinetochore fiber

Bundles of microtubules that connect chromosomes to the spindle poles during cell division, specifically attaching to the kinetochore protein complex on chromosomes.

Mitotic appartus

the chromosome-sorting machine that ensures daughter cells get one copy of each chromosome during cell division. The structure of the mitotic apparatus differs from one to the next branch of the eukaryotic tree but is universally based on microtubules. In animal cells it is normally bipolar and generally consists of a spindle (the densest bit with the chromosomes attached to K- fibers), two spindle poles (which are basically the centrosomes, plus a bunch of mitosis-specific stuff added), and asters, which are radial arrays of microtubules that extend in every direction through the cytoplasm. Astral microtubules are not directly visible in the transmitted light microscope, but astral rays are, because microtubules organize cytoplasm wherever they go

Spindle

elongated, thin cells found in both normal tissue (like fibroblasts in connective tissue) and various tumors

Spindle pole

the microtubule organizing center (MTOC) in fungi and certain lower eukaryotes, serving as the functional equivalent of the animal cell centrosome

Astral microtubules

a dynamic subpopulation of microtubules that radiate from centrosomes toward the cell cortex during cell division (mitosis/meiosis).

Mitosis

the normal way that eukaryotic cells divide: DNA replicates, condenses, aligns on the mitotic apparatus and then partitions into two daughter cells. Mitosis consists of: prophase (chromosomes condensing, nucleus still intact); prometaphase (nucleus broken down, chromosomes not yet aligned); metaphase (chromosomes aligned at future division plane); anaphase (sister chromatids separating along the spindle); and telophase (chromosomes far apart, reforming nuclei). Oh, and of course, there's interphase, when none of this is happening. (Note that prometaphase is obviously a late addition to the vocabulary; animal cells have an open mitosis, meaning the nuclear envelope breaks down, and a possibly extended period in which chromosomes move back and forth before settling into position.

Cytokinesis

usually coupled to mitosis (in telophase) is the physical partitioning of the cytoplasm, in which the cell pinches itself in two. In animal cells, cytokinesis takes the form of constriction of the cleavage furrow around the cell equator (as defined by the mitotic apparatus). Ingression of the furrow is caused by the action of a contractile ring composed of actin filaments, myosin and other proteins. Because no one really knows how the contractile ring works, many refer instead to the cytokinetic apparatus to include the actin-rich ring, the furrow, and associated regulatory physiology.

Cleavage furrow

a groove that forms on the surface of animal and some fungal cells during cytokinesis, marking the beginning of the cell's physical separation into two daughter cells

Contractile ring

a dynamic, equatorial structure made of actin filaments, myosin II, and regulatory proteins that drives cytokinesis (cell division) in animal cells

Cytokinetic apparatus

a transient, dynamic structure responsible for physically separating a mother cell into two daughter cells during cytokinesis.

Cleavage

a series of mitotic cell divisions whereby the volume of egg cytoplasm is divided into numerous progressively smaller cells

Blastomere

a cleavage-stage cell. Get enough of 'em and you have a blastula.

Blastula

an animal embryo at the early stage of development when it is a hollow ball of cells