Cellular Level (235 #3, 230 #2) Flashcards Preview

Physiology & Anatomy > Cellular Level (235 #3, 230 #2) > Flashcards

Flashcards in Cellular Level (235 #3, 230 #2) Deck (97):
1

plasma membrane

forms the cell's flexible outer shell, separating the internal environment from the external environment - selective barrier that regulates flow of materials in/out of cell. Plays key role in communication among cells and between cells and external environment.

2

cytoplasm

cellular contents between plasma membrane and nucleus - cytosol and organelles

3

cytosol

Composed of water, solutes, suspended particles, lipid droplets, and glycogen granules. Within the cytoplasm is the cytoskeleton, a network of microfilaments, intermediate filaments, and microtubules. - Fluid in which many of cell's metabolic reactions occur. Maintains shape and general organization of cellular contents; responsible for cellular movements.

4

organelles

little organs - specific shape and function - cytoskeleton, ribosomes, endoplasmic reticulum, Golgi complex, lysosomes, peroxisomes and mitochondria

5

nucleus

large organism that houses most of a cell's DNA.

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chromosome

a single molecule of DNA associated with several proteins containing thousands of hereditary units called GENES that controls most aspects of cellular structure & function.

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fluid mosaic model

a continually moving sea of fluid lipids that contains a mosaic of different proteins - some float freely while others are anchored. Membrane lipids allow passage of lipid-soluble molecules, but act as a barrier to charged or polar substances.

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lipid bilayer

two back-to-back layers made up of three types of lipids - phospolipids (75%), cholesterol (20%) and glycolipids (5%). Phospholipid heads (hydrophilic) face the outside, tails face inside. Glycolipids are in membrane layer facing extracellular fluid, cholesterol are among other lipids in both membranes.

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integral proteins

extend into or through the lipid bilayer among fatty acid tails and are firmly embedded. Most are TRANSMEMBRANE, protruding into both cytosol and extracellular fluid. AMPHIPATHIC

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peripheral proteins

attached to polar heads of membrane lipids, or to integral proteins at the inner or outer surface of the membrane.

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cholesterol

AMPHIPATHIC and are inspersed amonth the other lipids in both layers of the membrane

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glycolipids

appear only in the membrane layer that faces the extracellular fluid which is why the bilayer is asymmetric.

13

glycoproteins

proteins with carb groups attached to the ends that protrude from into ECF. They are coated with glycocalyx (sugary coat) that varies from one cell to another - molecular signature for cell recognition. Also enables cells to adhere to one another and protects cells from being digested by enzymes in ECF. Hydrophilic properties allow a film of fluid to attach to somes (makes RBCs slippery).

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Ion Channels

allow specific ions to pass through water-filled pores - selective! Integral! Small-diameter (0.8 nm) may be open or closed to its specific ion as a result of changes in channel shape in response to a controlling mechanism.

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Carriers/Transporters

transports specific substances across membranes by changing shapes (polar substances or ions) - integral!

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Receptors

recognizes specific 'ligands' and alters cells' function in some way - cellular recognition sites - integral!

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Enzyme

catalyzes reaction inside or outside cell depending on side it faces. integral or peripheral

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Linker - Cell Adhesion Molecules (CAMs)

anchors filaments inside and outside the plasma membrane, providing structural stability and shape of the cell. may also participate in movement of cell or link two cells together - integral and peripheral. Form loops or hooks that the cells use to grip each other and grasp connective tissue fibres between cells.
CADHERINS - on the surface of adjacent cells interlock in zipper fashion
INTEGRINS - span the plasma membrane, connecting inner membrane surfaces to intracellular cytoskeltal scaffolding. Also 'signalling molecules'

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Cell Identity Marker - Glycoprotein

distinguishes your cells from anyone else's. Allow cells to recognize others of the same type during tissue formation or recognize and respond to potentially dangerous foreign cells.

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membrane fluidity

membrane lipids and many membrane proteins easily rotate and move sideways in their own half of the lipid bilayer. Depends on the number of double bonds in the fatty acid tails (more kinks mean more fluidity) and on the amount of cholesterol present. Cholesterol fills space between tails and makes it stronger at normal body temp, lower temps it increases fluidity.

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selective fluidity

allowing some substances to pass more readily through the membrane than others. Permeable to nonpolar uncharged particles (O2, CO2, steriods) but impermeable to large uncharged polar molecules and ions. Slightly permeable to H2O, urea.

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concentration gradient

difference in the concentration of a chemical from one place to another. 'Down' the gradient is going to the lower concentration, 'Up' is going towards higher concentration (requires energy)

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electrical gradient

the difference in electric charges between two areas. Across the plasma membrane, this is known as the membrane potential.

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electrochemical gradient

the combined influence of concentration and electrical gradients on movement of a particular ion

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passive transport processes

substance moves DOWN concentration or electrical gradient to cross the membrane using only kinetic energy - no input of energy from the cell.

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active transport processes

cellular energy is used to drive the substance UP it's concentration or electrical gradient, usually in the form of ATP.

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diffusion

a passive process in which the random mixing of particles in a solution occurs because of the particles' kinetic energy. affected by 1)steepness of gradient, 2) temp, 3) mass of diffusing substance, 4) surface area, 5) diffusion distance

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simple diffusion

passive movement of substance DOWN its concentration gradient without any help of membrane tx proteins

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facilitated diffusion

passive movement of a substance down its concentration gradient through the bilayer by transmembrane proteins that function as channels or carriers TXS= polar or charged solutes, glucose, fructose, galactose, some vits, ions

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osmosis

passive movement of H2O across selectively permeable membrane from higher to lower water conc. until equilibrium. txs = water

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tonicity

a measure of the solution's ability to change the volume of cells by altering H2O content - isotonic = the concentration of solutes are the same on either side of the membrane. hypotonic = the solution has lower concentration of solute, so H2O enter cells faster than they leave (cells swell, hemolysis/lysis
), hypertonic = solution has higher conc of solute, so H2O leaves cells (crenation).

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active transport

active processes in which a cell expends energy to move a substance across the membrane against its conc. gradient by transmembrane proteins that function as carriers. txs = polar or charged solutes.

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primary active transport

active process in which a substance moves across the membrane UP its conc. gradient by pumps (carriers) that use energy supplied by ATP hydrolysis. Na+, K+, Ca2+, H+, I-, Cl-

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Na+/K+ ATPase

primary active transport mechanism expels Na+ from cells and bring K+ into cells. a part of the sodium-potassium pump acts as an ATPase (enzyme that hydrolizes ATP) - maintains low conc. of Na+ in the cytosol, by pumping Na+ into ECF while bringing in K+. Work non-stop, thousands in each cell's plasma membrane. Crucial form maintaining cell volume and for cells to generate electrical signals (action potentials). Maintain normal tonicity on each side of membrane so cells neither shrink or swell.

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secondary active transport

coupled active transport of two substances across the membrane using energy supplied by Na+ or H+ conc. gradient maintained by primary active transport pumps. Antiporters move Na+ (or H+) and another substance in opposite directions, Symporters move them in the same direction. Anti = Ca2+ and H+ out of cells. Sym = glucose, amino acids

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transport in vesicles

active process in which substances move into or out of cells in vesicles that bud from plasma membrane, requires energy from ATP

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endocytosis

movement of substances INTO a cell in vesicles

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receptor-mediated endocytosis

ligand-receptor complexes trigger infolding of a clathrin-coated pit that forms a vesicle containing ligands. Ligands: transferrin, LDLs, some vits, hormones and antibodies.

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phagocytosis

cell-eating. movement of a solid particle into a cell after pseudopods engulf it to form a phagosome. TXs= bacteria, viruses, and aged or dead cells

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bulk-phase endocytosis / pinocytosis

cell-drinking. movement of ECF into a cell by infolding of plasma membrane to form a vesicle. TXs = solutes in ECF.

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Exocytosis

movement of substances OUT of a cell in secretory vesicles that fuse with the plasma membrane and release their contents into the ECF. TX = neurotransmitters, hormones and digestive enzymes.

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transcytosis

movement of a substance through a cell as a result of endocytosis on one side and exocytosis on the opp side. TX = antibodies across endothelial cells. common route for substances to pass between blood plasma and interstitial fluid.

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Centrosome

Pair of centrioles plus pericentriolar material.

The pericentriolar material contains tubulins, which are used for growth of the mitotic spindle and microtubule formation.

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Cilia and flagella

Motile cell surface projections that contain 20 microtubules and a basal body. (9 groups of 2 tubules with 2 tubules in the centre) Inside the 'nine plus two' arrangement are 'arms' of Dynein which allow the tubules to slide past each other to allow the projection to bend.

Cilia: move fluids over cell's surface; flagella: move entire cell.

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Ribosome

Composed of two subunits containing ribosomal RNA and proteins; may be free in cytosol or attached to rough ER.

Protein synthesis.

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Endoplasmic reticulum (ER)

Membranous network of flattened sacs or tubules. Rough ER is covered by ribosomes and is attached to the nuclear envelope; smooth ER lacks ribosomes.

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Rough ER

synthesizes glycoproteins and phospholipids that are transferred to cellular organelles, inserted into plasma membrane, or secreted during exocytosis

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smooth ER

synthesizes fatty acids and steroids, inactivates or detoxifies drugs, removes phosphate group from glucose‐6‐phosphate, and stores and releases calcium ions in muscle cells.

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Golgi complex

Consists of 3–20 flattened membranous sacs called cisternae; structurally and functionally divided into entry (cis) face, medial cisternae, and exit (trans) face.

Entry (cis) face accepts proteins from rough ER; medial cisternae form glycoproteins, glycolipids, and lipoproteins; exit (trans) face modifies molecules further, then sorts and packages them for transport to their destinations.

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Lysosome

Vesicle formed from Golgi complex; contains digestive enzymes.

Fuses with and digests contents of endosomes, pinocytic vesicles, and phagosomes and transports final products of digestion into cytosol; digests worn‐out organelles (autophagy), entire cells (autolysis), and extracellular materials.

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Peroxisome

Vesicle containing oxidases (oxidative enzymes) and catalase (decomposes hydrogen peroxide); new peroxisomes bud from preexisting ones.

Oxidizes amino acids and fatty acids; detoxifies harmful substances, such as hydrogen peroxide and associated free radicals.

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Proteasome

Tiny barrel‐shaped structure that contains proteases (proteolytic enzymes).

Degrades unneeded, damaged, or faulty proteins by cutting them into small peptides.

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Mitochondrion

Consists of an outer and an inner mitochondrial membrane, cristae, and matrix; new mitochondria form from preexisting ones.

Site of aerobic cellular respiration reactions that produce most of a cell's ATP. Plays an important early role in apoptosis.

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NUCLEUS

Consists of a nuclear envelope with pores, nucleoli, and chromosomes, which exist as a tangled mass of chromatin in interphase cells.

Nuclear pores control the movement of substances between the nucleus and cytoplasm, nucleoli produce ribosomes, and chromosomes consist of genes that control cellular structure and direct cellular functions.

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cytoskeleton

network of protein filaments that extends throughout the cytosol - Three types of filamentous proteins: microfilaments, intermediate filaments, and microtubules.
1.
Serves as a scaffold that helps to determine a cell's shape and to organize the cellular contents.
2.
Aids movement of organelles within the cell, of chromosomes during cell division, and of whole cells such as phagocytes.

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microvilli

nonmotile, microscopic fingerlike projections of the plasma membrane. Within each microvillus is a core of parallel microfilaments that supports it. Because they greatly increase the surface area of the cell, microvilli are abundant on cells involved in absorption, such as the epithelial cells that line the small intestine.

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intermediate filaments

found in parts of cells subject to mechanical stress; they help stabilize the position of organelles such as the nucleus and help attach cells to one another. neurofilaments strengthen and stabilize elongated cell axons. Skin cells contain networks of keratin filaments to tie cells together which gives the skin strength. when surface cells die, the keratin persists to form protective waterproof layer.

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Microtubules

largest of the cytoskeletal components and are long, unbranched hollow tubes composed mainly of the protein tubulin. The assembly of microtubules begins in an organelle called the centrosome - Microtubules help determine cell shape. They also function in the movement of organelles such as secretory vesicles, of chromosomes during cell division, and of specialized cell projections, such as cilia and flagella.

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gene expression

a gene's DNA is used as a template for synthesis of a specific protein via transcription and translation.

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Transcription

the info encoded in a specific region of DNA is copied to produce a specific molecule of RNA. Occurs in the nucleus - three types of RNA are made from the DNA template:

1.
Messenger RNA (mRNA) directs the synthesis of a protein. functional molecule that passes out of the nuclear envelope through a pore, into the cytoplasm for translation.
2.
Ribosomal RNA (rRNA) joins with ribosomal proteins to make ribosomes in the cytoplasm.
3.
Transfer RNA (tRNA) binds to an amino acid and holds it in place on a ribosome until it is incorporated into a protein during translation. One end of the tRNA carries a specific amino acid, and the opposite end consists of a triplet of nucleotides called an anticodon. By pairing between complementary bases, the tRNA anticodon attaches to the mRNA codon. Each of the more than 20 different types of tRNA binds to only one of the 20 different amino acids.

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RNA Polymerase

catalyzes transcription of DNA. Attaches at the 'promoter' at the beginning of the gene, finishes at a 'terminator' which specifies the end of the gene.

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translation

the nucleotide sequence in an mRNA molecule specifies the amino acid sequence of a protein. Ribosomes in the cytoplasm carry out translation.
1.
An mRNA molecule binds to the small ribosomal subunit at the mRNA binding site. A special tRNA, called initiator tRNA, binds to the start codon (AUG) on mRNA, where translation begins. The tRNA anticodon (UAC) attaches to the mRNA codon (AUG) by pairing between the complementary bases. Besides being the start codon, AUG is also the codon for the amino acid methionine. Thus, methionine is always the first amino acid in a growing polypeptide.
2.
Next, the large ribosomal subunit attaches to the small ribosomal subunit–mRNA complex, creating a functional ribosome. The initiator tRNA, with its amino acid (methionine), fits into the P site of the ribosome.
3.
The anticodon of another tRNA with its attached amino acid pairs with the second mRNA codon at the A site of the ribosome.
4.
A component of the large ribosomal subunit catalyzes the formation of a peptide bond between methionine, which separates from its tRNA at the P site, and the amino acid carried by the tRNA at the A site.
5.
After peptide bond formation, the tRNA at the P site detaches from the ribosome, and the ribosome shifts the mRNA strand by one codon. The tRNA in the A site bearing the two‐peptide protein shifts into the P site, allowing another tRNA with its amino acid to bind to a newly exposed codon at the A site. Steps 3 through 5 occur repeatedly, and the protein lengthens progressively.
6.
Protein synthesis ends when the ribosome reaches a stop codon, which causes the completed protein to detach from the final tRNA. When the tRNA vacates the ribosome, the ribosome splits into its large and small subunits.

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polyribosome

As the ribosome moves along the mRNA and before it completes synthesis of the whole protein, another ribosome may attach behind it and begin translation of the same mRNA strand. The simultaneous movement of several ribosomes along the same mRNA molecule permits the translation of one mRNA into several identical proteins at the same time.

64

somatic cell division

cell undergoes a nuclear division called mitosis (mī‐TŌ‐sis; mitos = thread) and a cytoplasmic division called cytokinesis (sī‐tō‐ki‐NĒ‐sis; cyto‐ = cell; ‐kinesis = movement) to produce two genetically identical cells, each with the same number and kind of chromosomes as the original cell. Somatic cell division replaces dead or injured cells and adds new ones during tissue growth.

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Reproductive cell division

produces gametes, the cells needed to form the next generation of sexually reproducing organisms. This process consists of a special two‐step division called meiosis, in which the number of chromosomes in the nucleus is reduced by half.

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homologous chromosomes

Two chromosomes that belong to a pair. Also called homologs.

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sex chromosomes

designated X and Y. In females the homologous pair of sex chromosomes consists of two large X chromosomes; in males the pair consists of an X and a much smaller Y chromosome.

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interphase

the cell replicates its DNA, also produces additional organelles and cytosolic components in anticipation of cell division. Interphase is a state of high metabolic activity; it is during this time that the cell does most of its growing. Interphase consists of three phases: G1, S, and G2

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S phase (Synthesis)

lasts about 8 hours. During the S phase, DNA replication occurs. As a result of DNA replication, the two identical cells formed during cell division later in the cell cycle will have the same genetic material. Once a cell enters the S phase, however, it is committed to go through the rest of the cell cycle.

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G1 phase

the cell is metabolically active; it replicates most of its organelles and cytosolic components but not its DNA. Replication of centrosomes also begins in the G1 phase. Virtually all the cellular activities described in this chapter happen during G1. For a cell with a total cell cycle time of 24 hours, G1 lasts 8 to 10 hours. However, the duration of this phase is quite variable. It is very short in many embryonic cells or cancer cells. Cells that remain in G1 for a very long time, perhaps destined never to divide again, are said to be in the G0 phase. Most nerve cells are in the G0 phase.

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G2 phase

asts 4 to 6 hours. During G2, cell growth continues, enzymes and other proteins are synthesized in preparation for cell division, and replication of centrosomes is completed.

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mitotic (M) phase

results in the formation of two identical cells, consists of a nuclear division (mitosis) and a cytoplasmic division (cytokinesis) to form two identical cells. The events that occur during mitosis and cytokinesis are plainly visible under a microscope because chromatin condenses into discrete chromosomes.

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Prophase

The first stage of mitosis during which chromatid pairs are formed and aggregate around the metaphase plate of the cell.

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mitotic spindle

Collective term for a football‐shaped assembly of microtubules (nonkinetochore, kinetochore, and aster) that is responsible for the movement of chromosomes during cell division.

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Metaphase

The second stage of mitosis, in which chromatid pairs line up on the metaphase plate of the cell.

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Anaphase

The third stage of mitosis in which the chromatids that have separated at the centromeres move to opposite poles of the cell.

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Telophase

Nuclear envelopes and nucleoli reappear; chromosomes resume chromatin form; mitotic spindle disappears.

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cytokinesis

Cytoplasmic division; contractile ring forms cleavage furrow around center of cell, dividing cytoplasm into separate and equal portions.

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haploid (n) cells

Having half the number of chromosomes characteristically found in the somatic cells of an organism; characteristic of mature gametes. Symbolized n.

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diploid cells

Having the number of chromosomes characteristically found in the somatic cells of an organism; having two haploid sets of chromosomes, one each from the mother and father. Symbolized 2n.

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Meiosis

the reproductive cell division that occurs in the gonads (ovaries and testes), produces gametes in which the number of chromosomes is reduced by half.

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synapsis

The pairing of homologous chromosomes during prophase I of meiosis. The resulting four chromatids form a structure called a tetrad. Second, parts of the chromatids of two homologous chromosomes may be exchanged with one another. Such an exchange between parts of nonsister (genetically different) chromatids is called crossing‐over. This process, among others, permits an exchange of genes between chromatids of homologous chromosomes.

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meiosis I

begins with a diploid starting cell and ends with two cells, each with the haploid number of chromosomes.

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meiosis II

each of the two haploid cells formed during meiosis I divides; the net result is four haploid gametes that are genetically different from the original diploid starting cell.

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Cancer

a group of diseases characterized by uncontrolled or abnormal cell division.

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3 functions of cytosol

1) enzymatic regulation of intermediary metabolism (degradation, synthesis and tx of molecules), 2) ribosomal protein synthesis, 3) storage of fat, carbs and secretory vesicles.

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3 functions of microtubules

maintain assymetric shape and coordinate complex cell movements: 1) tx of secretory vesicles or materials around cell, 2) mvmnt of specialized cell projections (cilia/flagella), 3) dist of chromosomes during cell division through mitotic spindle.

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molecular motor

protein that attaches to a particle and uses energy from ATP to walk along a microtubule. Kinesin 'walks' along a microtubule by binding with the tubulin to tx specific chemicals in nervous tissue along the axons. Debris is tx'ed with Dynein, back to the lysosomes for degradation. This reverse highway is also the way that some viruses can travel long nerve cells (herpes, rabies, poliomyelits).

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microfilaments

made of actin & myosin - play a vital role in various cell contractile systems, 2) act as mechanical stiffeners for several specific cell projections. ACTIN - muscle contraction, cell division and locomotion (amoeboid movement). White blood cells, fibroblasts (responsible for scar formation), skin cells (restore skin surface after cut).

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microtribecular lattice

interlinked filaments extending through the cytoplasm and connecting to the inner layer of the plasma membrane. 'skeleton'

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Docking-Marker Acceptor

peripheral membrane protein that binds lock and key style with the docking markers of secretory vesicles, so they can interact between the matching labels and empty their contents via exocytosis.

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extracellular matrix ECM

intricate meshwork of fibrous proteins in watery gel-like substance made of complex carbohydrates. 'Biological Glue' or interstitial fluid. Secreted by 'fibroblasts in the ECM are three major types of proteins:
ELASTIN: rubbery, used for stretch & recoil (found in skin and blood vessel walls and lungs)
COLLAGEN: forms sheets or cable-like fibres that provide tensile strength (bones, tendons, ligaments)
FIBRONECTIN: promotes cell adhesion and holds cells in position
RETICULAR: composed of collagen and glycoprotein, found around fat cells, nerve fibres and skeletal/smooth muscle cells.

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Desmosomes

Adhering junction. 'spot rivets' that anchor together two adjacent but non-touching cells. dense button-like cytoplasmic thickenings (plaque) on the inner cell surface with glycoprotein filaments (CAMs - cadherins) extending across the space, attaching to intermediate filaments (keratin) in the cytoskeleton. Found in tissue subject to considerable stretching (heart, uterus, skin)

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Tight Junctions

adjacent cells firmly bound at contact points (kiss sites) to seal off passageway between. Primarily in sheets of epithelial tissue - highly selective barriers between compartments with very different chemical compositions.

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Gap Junctions

gap exists between adjacent cells, connected by small connecting tunnels (connexons - 6 protein subunits in a hollow tube-like structure). Connexons extend from each cell and meet - small water-soluble particles can pass between cells without entering ECF. Cardiac & smooth muscle, transmits electrical activity through entire muscle mass for synchronized contraction. Also in developing egg cell from cells around the egg to allow it to store glucose, amino acids and nutrients.

96

Adherens Junctions

contain plaque - dense layer of proteins on the inside of the plasma membrane that attaches to membrane proteins and microfilaments of the cytoskeleton. Cadherins (transmembrane glycoprotein) cross into the plaque of the adjacent cell. Often form extensive zones called adhesion belts.

97

Hemidesmosomes

resemble desmosomes, but don't link adjacent cells, instead link to basement membrane laminin with transmembrane proteins called integrins.