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*Histology > Cytology > Flashcards

Cytology Flashcards

1
Q

Integral membrane proteins

A

have a hydrophobic region which is embedded into the hydrophobic core of the membrane

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2
Q

Transmembrane proteins

A

are integral membrane proteins that extend all the way through the membrane.

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3
Q

Peripheral Membrane Proteins

A

are not embedded within the lipid bilayer and attach either to integral proteins or to the hydrophilic heads of the membrane lipids.

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4
Q

Transport proteins

A

The lipid bilayer forms a barrier which is impassible for charged and polar molecules. Transport proteins selectively allow such molecules to cross the membranes

channel/carrier/pump

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5
Q

Channel proteins

A

form “pores”, which allow passage of small molecules across the membrane via passive diffusion. Channels are ion-selective.

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6
Q

Carrier proteins

A

“drag” other molecules through the membrane by hiding them in a cleft in the protein

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7
Q

Pumps

A

use ATP energy to pump ions actively through the membrane

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8
Q

Receptors

A

Some transmembrane proteins bind to specific molecules in the extracellular matrix. This specific binding can result in a conformational change in the transmembrane protein that can serve as a signal that allows the cell to adapt to its environment

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9
Q

Structural or anchoring proteins

A

serve to attach cell to its surroundings. These transmembrane proteins use their cytoplasmic domains to link to the elements of the cytoskeleton, and their extracellular domains to link to the extracellular proteins

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10
Q

Carbohydrates

A

mostly oligosaccharides are often attached to the extracellular domains of membrane proteins and lipids to form glycoproteins and glycolipids. Because of the large amount of carbohydrates attached to proteins and lipids on the external surface many cells exhibit a “fuzzy” coating called the glycocalyx, which can be visualized in an electron microscope.

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11
Q

Particles and inclusions

A

used for synthesis and storage. The two main types are ribosomes and glycogen particles.

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12
Q

Ribosomes

A

are RNA/protein particles that catalyze protein synthesis. They bring together mRNA and tRNA to synthesize a polypeptide.

a. Ribosomes are 15-25 nm in size and consist of a small subunit and a large subunit. Each subunit consists of one or more ribosomal RNA (rRNA) and many specialized proteins.
b. Ribosomes in eukaryotic cells exist as either free ribosomes, mitochondrial ribosomes, or ribosomes bound to rough endoplasmic reticulum (RER). The majority of cellular proteins are synthesized on free ribosomes, except those in Golgi apparatus, lysosomes, secretory granules, and plasma membrane, which are synthesized on RER ribosomes. 20 % of mitochondrial proteins are synthesized on mitochondrial ribosomes, the rest are synthesized on free ribosomes in the cytoplasm.
c. Polysomes. During protein synthesis many ribosomes attach to a single mRNA molecule. This string of ribosomes connected to mRNA is known as a polysome.

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13
Q

Glycogen particles

A

are a storage form of polysaccharides

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14
Q

Endoplasmic reticulum (ER)

A

consists of series of membrane-formed anastomosing tubules and cisternae (flattened, pancake-like vesicles). The ER is subdivided into smooth and rough endoplasmic reticulum. The cytoplasmic side of the rough ER has a large number of ribosomes bound to it.

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15
Q

Smooth endoplasmic reticulum (SER)

A

does not have ribosomes bound to its surface and it also has a more tubular appearance than the rough ER. SER has several functions:

a. One of the most important functions of SER is lipid and steroid metabolism. Phospholipids for all cell’s membranes are produced here, so the SER is involved in membrane synthesis and recycling. SER is rather inconspicuous in most cells, but becomes prominent in steroid-secreting cells.
b. SER plays an important role in detoxification of noxious substances. It is very well-developed in liver cells and contains enzymes that can modify and detoxify such toxins as carcinogens, pesticides, etc.
c. SER is involved in glycogen metabolism.

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16
Q

Rough endoplasmic reticulum (RER)

A

has ribosomes bound to its surface, which creates its “roughened” appearance. RER is formed mostly of cisternae. RER is prominent in cells specialized for protein secretion, so it is the principal site of synthesis of proteins destined for export out of the cell. Proteins found in the Golgi apparatus, lysosomes, and in the plasma membrane are also synthesized in the RER.

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17
Q

Golgi apparatus

A

consists of series of stacked, flattened, membrane-limited cisternae and tubular extensions. Golgi receives proteins synthesized in the RER. The stack of Golgi cisternae is polarized. The side receiving vesicles from the RER is cis Golgi. The middle cisternae form the medial Golgi, and the cisternae from which the mature proteins are transported form the trans Golgi. The Golgi apparatus functions in the posttranslational modification, sorting, and packaging of proteins.

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18
Q

Functions of Golgi

A
  1. The modification of proteins, such as adding or removing sugar residues, sulfate or phosphate groups, occurs in the Golgi apparatus. The early stages of this process occur in the cis Golgi, intermediate steps occur in the medial Golgi, and the final modifications are made in the trans Golgi.
  2. Sorting and packaging of proteins into transport vesicles is another important function of the Golgi apparatus that occurs mainly in the trans Golgi network. From here there are three main destinations for the proteins. Most proteins coming from the Golgi apparatus bear specific signal sequences, which direct them to their destination.
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19
Q

3 destinations of golgi

A

secretory vesicles

lysosomes

constitutive pathway

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20
Q

Secretory vesicles

A

Many cells, e.g. pancreatic acinar cells, store proteins and other products in secretory vesicles. These vesicles undergo a maturation process in which secretory proteins are retained within the vesicle. Mature secretory vesicles eventually fuse with the plasma membrane to release the secretory product into the extracellular space in response to a certain signal.

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21
Q

Lysosomes

A

are spherical organelles of variable size produced by the Golgi. Lysosomes are involved in digesting the material taken up from outside the cell and in degradation of senescent organelles. They are characterized by a low pH and presence of hydrolytic enzymes. The principal sorting signal which directs proteins from the trans Golgi network to the lysosome is mannose-6-phosphate.

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22
Q

Mannose-6-Phosphate deficiency

A

Mutation of one of the enzymes that creates this signal causes the lysosomal proteins to be secreted into the intercellular space. The resulting condition is the so-called I-cell disease (or mucolipidosis), which is one of the lysosomal storage diseases.

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23
Q

Primary Lysosomes

A

are lysosomes which have not yet received substrates for digestion.

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24
Q

Secondary Lysosomes

A

result from the fusion of primary lysosomes with their target.

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25
Q

Lipofuscin Granules

A

or residual bodies are senescent lysosomes with undigestible material.

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26
Q

Constitutive pathway

A

Proteins in the trans Golgi, which are not destined for either lysosomes or secretory granules are sorted into small vesicles, which are transported directly to the plasma membrane, where the vesicle fuses with the plasma membrane. Integral membrane proteins and proteins that are secreted continuously into the extracellular space (e.g. collagen) reach the plasma membrane by this route

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27
Q

Peroxisomes

A

are small (0.5 μm), membrane-bound organelles containing oxidative enzymes, particularly catalase. These enzymes are used to oxidize a wide range of organic substances including very long chain fatty acids and to converse ethanol to acetaldehyde. Oxidative enzymes produce hydrogen peroxide as a product of oxidation reaction. Catalase is important in degrading hydrogen peroxide, which is a toxic substance. Abnormal functioning of peroxisomes causes severe disorders

28
Q

Zellweger Syndrome

A

a congenital disease which is caused by mutations in the proteins that are responsible for the proper transport of peroxisomal enzymes from the cytoplasm, where they are synthesized on free ribosomes, to peroxisomes. As a result, peroxisomes lack the necessary enzymes and do not function properly. This affects brain development through the improper formation of the myelin sheath. There is no cure, or a standard course of treatment, and patients usually die before 6 month of age.

29
Q

adrenoleukodystrophy

A

Disruptions in oxidation of very long chain fatty acids cause an inherited X-linked disorder that results in progressive brain damage, failure of the adrenal glands, and eventually death. The symptoms are caused by the accumulation of lipid in the brain and adrenals

30
Q

Mitochondria

A

involved in the production of ATP through the oxidation of pyruvate and fatty acids. Mitochondria are present in virtually all cells (except red blood cells and terminal keratinocytes), but are most numerous in cells that use large amounts of energy. Mitochondria can change their location and even shape and can be compared with mobile power generators as they migrate from one area of the cell to another to supply the energy where needed. Mitochondria are believed to have evolved from aerobic bacteria that were engulfed by eukaryotic cells and differ from the organelles discussed above in several ways. The facts that mitochondria contain their own separate genome, possess two membranes, and increase their number by division support the hypothesis that mitochondria evolved from a symbiotic prokaryote. Mitochondria display a variety of sizes (1 – 5 μm) and shapes, including spheres, rods, elongated filaments, and even spirals, but all have two membranes with an intermembrane space between them. The space enclosed within the inner membrane is called the mitochondrial matrix.

31
Q

Outer mitochondrial membrane

A

contacts the cytoplasm on the outer side and the intermembrane space on the inner side. It contains numerous pores (anion channels), which allow passage of small molecules (up to 5,000 dalton), ions, and metabolites.

32
Q

Inner mitochondrial membrane

A

is thinner than the outer membrane and highly folded into cristae, which project into the matrix and greatly increase inner membrane surface. In steroid-producing cells the cristae may have tubulovesicular appearance. The inner membrane contains many of the enzymes involved in energy production.

33
Q

intermembrane space

A

The pH and ionic composition of intermembrane space is similar to that of the cytoplasm, but the protein composition is unique in containing enzymes that use ATP generated in the inner membrane. Cytochrome C located here is an important factor in initiating apoptosis, or programmed cell death. Mitochondria are “sensors” of cell health and if the cell is not viable mitochondria release cytochrome C, which triggers the intrinsic pathway of programmed cell death.

34
Q

Matrix

A

enclosed within the inner mitochondrial membrane and contains soluble enzymes including those for the Krebs cycle, DNA transcription, etc. The matrix contains mitochondrial DNA, mitochondrial ribosomes, rRNA, mRNA, and tRNA. The matrix contains electron-dense granules that store Ca2+, so mitochondria also regulate concentration of certain ions in the cytoplasm, the role they share with SER.

35
Q

How much of the proteins are involved in OxPhos

A

Approximately one fifth of the proteins involved in oxidative phosphorylation are encoded by the mitochondrial DNA. The rest of the mitochondrial enzyme complexes is encoded in the nuclear genome.

36
Q

mitochondrial myopathies.

A

Mutations in both nuclear and mitochondrial genes cause mitochondrial myopathies. Diseases that involve the mitochondrial DNA show maternal inheritance, since only the oocyte contributes mitochondria to the embryo. The mitochondrial diseases may present in young adulthood and manifest with proximal muscle weakness, sometimes affecting the extraocular muscles involved in eye movements. The weakness may be accompanied by other neurologic symptoms, lactic acidosis, and cardiomyopathy.

37
Q

Nucleus

A

a large (5-10 μm) membrane-limited organelle that contains the genome in eukaryotic cells in the form of DNA bound to proteins, which is known as the chromatin. The nucleus also contains machinery for DNA replication and RNA transcription and processing and one or more nucleoli. The nucleus is surrounded by a double membrane called the nuclear envelope.

38
Q

Nuclear envelope

A

consists of two membranes, perinuclear space between them, nuclear lamina, and nuclear pores.

39
Q

Outer nuclear membrane

A

closely resembles the membrane of the RER and is continuous with the latter. Ribosomes are commonly attached to the cytoplasmic surface of the outer nuclear membrane in a manner identical to the rest of the RER.

40
Q

Perinuclear space

A

continuous with the lumen of the RER

41
Q

Inner nuclear membrane

A

is distinct from the endoplasmic reticulum in its ability to bind chromatin and lamins. It is supported by a rigid network of intermediate filaments.

42
Q

Nuclear lamina

A

a thin, protein-dense layer attached to the inner nuclear membrane, which represents the “skeleton” of the nucleus formed by specialized intermediate filament proteins called lamins (2.c.i). Lamins are distinct from other intermediate filaments in the fact that they disassemble during mitosis and reassemble when mitosis ends. Lamin filaments are cross-linked into an orthogonal lettuce, which is attached to the inner nuclear membrane.

43
Q

Nuclear pores

A

are 70-80 nm openings through the envelope, which allow communication between the cytoplasm and the nucleus. The pores have a rather complex structure with protein “spokes” projecting into the lumen of the pore to the central “plug.” The pores allow free passage for small (<9 nm) particles. The larger particles (proteins, RNA-protein complexes) must be actively transported through the membrane.

44
Q

Chromatin

A

contains DNA associated with roughly an equal mass of various nuclear proteins, such as histones. In the nucleus of a non-dividing cell there are two types of chromatin, more densely-packed heterochromatin and less densely packed euchromatin.

45
Q

Euchromatin

A

contains transcriptionally active DNA, which is more loosely packed and as a result appears to be lightly stained in both light and electron microscope. Euchromatin indicates active chromatin, or the chromatin that is stretched out so that the DNA can be read and transcribed. Euchromatin is prominent in metabolically active cells such as neurons.

46
Q

Heterochromatin

A

predominates in metabolically inactive cells. It contains transcriptionally inactive DNA, which is densely packed. As a result heterochromatin stains more intensely than euchromatin

47
Q

Nucleolus

A

a small area within the nucleus in which ribosomal RNA is processed and assembled into ribosomal subunits. The nucleolus contains three morphologically distinct regions when vied with TEM.

48
Q

Fibrillar centers

A

DNA loops with rRNA genes and transcription factors.

49
Q

Dense fibrillar component

A

(pars fibrosa) contains ribosomal genes that are being translated and large amounts of RNA.

50
Q

Granular component (pars granulosa)

A

the site for ribosome assembly and is made of densely packed clusters of pre-ribosomal particles.

51
Q

Cytoskeleton

A

determines the shape of cells, provides structural support for its organelles, and plays a major role in cell motility (including mitosis and cytokinesis). The cytoskeleton consists of three major types of filaments: actin filaments, microtubules, and intermediate filaments.

52
Q

Actin cytoskeleton

A

plays an important role in cell movement, cell shape, and organelle transport. Actin exists in two forms: G-actin and F-actin.

53
Q

G-actin

A

a soluble monomeric globular protein. can polymerize into a double-stranded helical filament, which is called F-actin. Polymerization occurs head-to-tail, so the actin filaments have polarity. F-actin filaments are also known as thin filaments. Thin filaments have several important functions.

Actin interacts with myosin to generate force and movement, so myosin is the motor associated with thin filaments. The mechanism of this interaction will be discussed in the muscle tissue lectures.

54
Q

cortex

A

Actin (thin) filaments form a thin sheath beneath the cytoplasm called the cortex. Cross-lined actin filaments resist cell deformation, transmit forces, and restrict the movement of organelles. The cortex also reinforces the plasma membrane and restricts lateral motion of some integral membrane proteins.

55
Q

Microtubules

A

cytoskeletal elements present in all cells except erythrocytes

Functions: organelle and vesicle movement, mitotic spindles/chromosome movement, beating of cilia/flagella

Structure: stiff, nonbranching polymers, made of a/b tubulin. Tubulins have +/- ends. + grows faster and - is associated with MTOC.

56
Q

Motor Proteins:

Dyenins and Kinesins

A

These motors use ATP energy to generate force that moves the motor and materials attached to it along the microtubule.

a. Dyneins are a group of motor proteins that move towards the minus end of a microtubule. Dyneins are also involved in the beating of cilia and flagella.
b. Kinesins are a group of motor proteins that move towards the plus end of a microtubule.

57
Q

axoneme

A

composed of 9 doublets and a central pair of microtubules. Dynein arms attached to the A-tubule of each of the doublets interacts with the neighboring B-tubule of the next doublet and by “walking” along it causes the bending of the axoneme. The axoneme generates force for the movement of cilia and flagella.

58
Q

At the base of each cilium or flagellum

A

there is a centriole or a basal body, also composed of microtubules arranged into 9 triplets without the central pair.

59
Q

microtubule-organizing center (MTOC)

A

Most human cells except neurons and red blood cells contain a microtubule-organizing center (MTOC), which consists of two centrioles. Virtually all cellular microtubules arise from the MTOC.

60
Q

Intermediate filaments

A

strong, but flexible polymers that provide mechanical support for cells. Intermediate filaments do not have polarity and there are no motor proteins associated with them.

61
Q

Lamins

A

form a meshwork of filaments on the inner side of the nuclear envelope, where they form the nuclear lamina and provide structural support for the nucleus.

62
Q

Keratins

A

epithelial cells

63
Q

Vimentin

A

found principally in the fibroblasts of the connective tissue

64
Q

Desmin

A

muscle cells

65
Q

Glial fibrillary acidic protein

A

found in the support cells of the nervous system, called glial cells.

66
Q

Neurofilaments

A

found in neurons

67
Q

Cytoplasmic intermediate filaments

A

form bundles between the plasma membrane and the nucleus. They spread tensile forces, maintain cell architecture, and act as a cocoon when cell is damaged. Intermediate filaments anchor ion channel proteins

*Histology (11 decks)

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