Intro to Cytology HANDOUT Flashcards
Describe eukaryotic cells organelles and particles
contain a number of membranes that form barriers between the cell and external enironment (pm) and also subdivide the cell into compartments
what are organelles
membrane bound compartments within the cell
what do membranes allow
each type of organelle to maintain novel ionic and enzymatic interior environments, which are different from the surrounding cytoplasm.
what are membranes composed of
lipids, proteins, carbs
membranes and visualization
cannot be visualised in a light microscope bc they are too thing (7nm) and do not stain with standard histological dyes (H&E), but can be seen in an electron microscope when stained with osmium tetroxide
Membrane lipid types
phospholipids, cholesterol, glycolipids
polarity of membrane lipids
ampipathic - they have uncharged hydrophobic (dont like water) tails and polar hydrophilic heads .
what does the ampipathic nature of membrane lipids cause
them to spontaeously form a lipid bilayer with the hydrophobic tails facing each other and the hydrophilic heads facing towards the aqueous environment
what is the key to the organization of the membrane
the presence of the hydrophobic center, which acts as an anchor to membrane proteins that can move within the lipid bilayer - FLUID MOSAIC MODEL
Permeability of the membrane
highly permeable for small, uncharged molecules that cross the membrane by simple diffusion. All other molecules such as ions and large molecules require membrane transport proteins to provide them with passage across the membrane.
how can membrane proteins be classified
based on their structure and based on their function
how do you divide structurally membrane proteins
integral and peripheral
describe integral membrane proteins
they have a hydrophobic region which is embedded into the hydrophobic core of the membrane.
what are transmembrane proteins
integral membrane proteins that extend all the way through the membrane
describe peripheral membrane proteins
they are not embedded within the lipid bilayer and attach either to integral proteins or to the hydrophilic heads of the membrane lipids.
How can membrane proteins be divided functionally
into transport proteins, receptors, and structural proteins
transport proteins description
the lipid bilayer forms a barrier which is impassible for charged and polar molecules. Transport proteins selectively allow such molecules to cross the membranes. There are several classes of transport proteins: Channel, carrier, pumps
channel proteins
form “pores”, which allow passage of small molecules across the membrane via passive diffusion. Channels are ion-selective.
Carrier proteins
drag other molecules through the membrane by hiding them in a cleft in the protein
Pumps
use ATP energy to pump ions actively though the membrane
Receptors
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 evironment
Structural or anchoring proteins serve to
attach cell to its surroundings. They use their cytoplasmic domains to link to the elements of the cytoskeleton, and their extracellular domains to link to the extracellular proteins
Carbohydrates description
mostly oligosaccharides, are often attached to the extracellular domains of membrane proteins and lipids to form glycoproteins and glycolipids.
What is the glycocalyx
a fuzzy coating on the external surface of a cell due to the large amount of carbohydrates attached to proteins and lipids. This can be seen on an electron microscope
What are particles and inclusions for
synthesis and storage.
2 main types of particles and inclusions
ribosomes and glycogen particles
What are ribosomes
RNA/protein particles that catalyze protein synthesis. They bring together mRNA and tRNA to synthesis a polypeptide
Structure of ribosomes
15-25nm 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
How do ribosomes in eukaryotic cells exist
either as free ribosomes, mitochondrial ribosomes, or ribosomes bound to rough ER
Where are the majority of cellular proteins synthesized
on free ribosomes, except those in the Golgi apparatus, lysozomes, secretory granules, and plasma membrane, which are synthesized on RER ribosomes
how much of mitochondrial proteins are synthesized on mitochondrial ribosomes
20%. The rest are on free ribosomes int he cytoplasm
Describe Polysomes
During protein synthesis, many ribosomes attach to a single mRNA molecule. This string of ribosomes connected to mRNA is known as a polysome.
Glycogen particles
a storage form of polysaccharides
Endoplasmic Reticulum consists of
series of membrane-formed anastomosing tubules and cisternae
what is cisternae
flattened, pancake like vesicles
what is the ER subdivided into
smooth and rough ER
what part of the ER has a large amount of ribosomes bound to it
the cytoplasmic side of the rough ER
Smooth ER description
does not have ribosomes bound to its surface and it also has a more tubular appearance than the rough ER.
functions of the SER
- Lipid and steroid metabolism. - Phospholipids for all cells membranes are produced here so the SER is involved in membrane synthesis and recycling.
- Detoxifcation of noxious substances
- Glycogen metabolism
- Storage and transport of Ca2+ (in muscle tissue SER)
where does SER become prominent
in steroid secreting cells
where is SER very well developed
in liver cells and contains enzymes that can modify and detoxify such toxins like carcinogens, pesticides, etc.
SER in muscle tissue is called
sarcoplasmic reticulum - here is is involved in storage and transport of Ca2+, which regulates the contractions of muscle cell.
Rough ER description
has ribosomes bound to its surface, which creates its rough look.
What is RER mainly formed of
cisternae
Where is RER prominent
in cells specialized for protein secretion, so it is the principle site of synthesis of proteins destined for export out of the cell. Proteins found in the GA, lysosomes, and the PM are also synthesized in the RER
Golgi Apparatus consists of
series of stacked, flattened, membrane limited cisternae and tubular extensions.
What does GA receive
proteins synthesized in the RER
describe the stack of GA cisternae
polarized.
sides of the GA
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
how does the GA function
in the post translational modification, sorting, ang packaging of proteins
Describe the modification of protein process in the GA
(such as adding or removing sugar residues, sulfate or phosphate groups). 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
Sorting and packaging of proteins into transport vesicles in the Golgi location
mainly in the trans Golgi network. From here, there are 3 main destinations for the proteins
what happens after proteins leave the Golgi
most leave with specific signal sequences, which direct them to their destination
Secretory vesicles description
where many cells (pancreatic acinar cells) store proteins and other products.
maturation process of secretory vesicles
the 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.
Lysosomes description
spherical organelles of variable size produced by the Golgi. They are often involved in digesting the material taken up from outside the cell and in degradation of senescent organelles.
How are lysosomes characterized
by low pH and presence of hydrolytic enzymes.
Principle sorting signal which directs proteins from the trans Golgi network to the lysosome
mannose-6-phosphate
what happens if one of the enzymes that creates mannose 6 phosphate is mutated
it causes the lysosomal protein to be secreted into the intercellular space -> resulting in I-cell disease (mucolipidosis), which is one of the lysosomal storage diseases.
How can lysosomes be classified
- Primary lysosomes
- Secondary lysosomes
- Lipofuscin granules
Primary lysosomes
lysosomes which have not yet received substrates for digestion
Secondary Lysosomes
results from the fusion of primary lysos with their target
Lipofuscin grranules
or residual bodies are senescent lysosomes with undigestible material
Constitutive pathway
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 pm, where the vesicle fuses with the pm. Integral membrane proteins and proteins that are secreted continuously into the extracellular space (collagen) reach the plasma membrane by this route.
Peroxisomes description
small (0.5um) membrane bound organelles containing oxidative enzymes, particularly catalase.
what are peroxisomes used for
to oxidize a wide range of organic substances including very long chain fatty acids and to converse ethanol to acetaldehyde
what do oxidative enzymes produce and why
produce hydrogen peroxide, which is a toxic substance.
what does abnormal functioning of peroxisomes cause
severe disorders
Zellweger Syndrome
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. 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 months of age.
Adrenoleukodystrophy
Caused by oxidation of very long chain fatty acids. It is inherited X-linked disorder that results in progressive brain damage, failure of he adrenal glands, and eventually death. The symptoms are caused by the accumulation of lipids in the brain and adrenals.
What are mitochondria involve din
the production of ATP through the oxidation of pyruvate and fatty acids.
where are mitochondria present
virtually all cells (except RBC and terminal keratinocytes), but are most numerous in cells that use large amounts of energy.
What can mitochondria do that is unique
they can change their location and 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 evolution
believed to have evolved from aerobic bacteria (symbiotic prok) that were engulfed by eukaryotic cells and differ from the organelles discussed above in several ways.
- mitochondria contain their own separate genome
- possess 2 membranes
- increase their number by division
Mitochondria sizes and shapes
vary (1-5um). Including spheres, rods, elongated filaments, and even spirals. But all have 2 membranes with an intermembrane space between them.
What is the space enclosed within the inner membrane of the mitochondria
the mitochondrial matrix
Outer mitochondrial membrane
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 5000 daltons), ions, and metabolites
Inner mitochondrial membrane
thinner than the outer membrane and highly folded into the cristae. The inner membrane contains many of the enzymes involved in energy production
describe cristae in mitochondri
project into the matrix and greatly increase the inner membrane surface
Cristae in steroid producing cells
may have tubulovesicular appearance.
pH and ionic composition of the intermembrane space
similar to the cytoplasm
protein composition of intermembrane space
is unique in containing enzymes that use ATP generated in the inner membrane.
Cytochrome C
located in intermembrane space. Important factor in initiating apoptosis.
what are mitochondria sensors of
cell health and if the cell is no viable mitochondria release Cytochrome C, which triggers the intrinsic pathway of programmed cell death.
describe the matrix of the mitochondria
enclosed within the inner mitochondrial membrane and contains soluble enzymes including those for the Krebs Cycle, DNA transcription, etc.
What does the mitochondrial matrix contain
mitochondrial DNA, mito ribosomes, rRNA, mRNA, tRNA, and electron dense granules
electron dense granules do what
store Ca2+ so mitochondria can also regulate concentration of certain ions in the cytoplasm
SER and mitochondrial shared role is
regulation of certain ions in the cytoplasm
how much of the proteins involved in oxidative phosphorylation are encoded by mitochondrial DNA
1/5
What are mutations in both nuclear and mitochondrial genes caused by
the so called mitochondrial myopathis
mitochondrial myopathies are
Diseases that involve the mitochondrial DNA. They show maternal inheritance since only the oocyte contributes mitochondria to the embryo.
Presentation of mitochondrial disesases
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 neurological symptoms, lactic acidosis, and cardiomyopathy.
Nucleus description
a large (5-10um) membrane limited organelle that contains the genome in euk cells in the form of DNA bound to proteins, which is known as chromatin. The nucleus also contains machinery for DNA replication and RNA transcription and processing and one or more nucleoli.
what is the nucleus surrounded by
double membrane called the nuclear envelope
nuclear envelope
consists of 2 membranes (inner and outer), perinuclear space between them, nuclear lamina, and nuclear pores
outer nuclear membrane
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
Perinuclear space
continuous with the lumen of the RER
Inner nuclear membran
distinct from the endoplasmic reticulum in its ability to bind chromatins and lamins. It is supported by a rigid network of intermediate filaments.
Nuclear lamina
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
how are lamins distinct from other intermediate filaments
they disassemble during mitosis and reassemble when mitosis ends. Lamin filaments are cross linked into orthogonal lattice, which is attached to the inner nuclear membrane.
Nuclear pores
70-80nm openings through the envelope, which allow communication between the cytopolasm 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 (9nm or less) particles.
How do larger particles (proteins, RNA protein complexes) get out of the nucleus
must be actively transported out
Chromatin contains
DNA associated with roughly an equal mass of various nuclear proteins such as histones.
chromatin in the nucleus of a non-dividing cell
2 types. More densely packed heterochromatin and less densely packed euchromatin
Euchromatin
contains transcriptionally active DNA, which is more loosely packed as a result appears to be lightly stained in both light and electron microscope.
what does euchromatin indicate
active chromatin, or the chromatin that is stretched out so that the DNA can be read and transcribed
where is euchromatin prominent
in metabolically active cells such as neurons
Heterochromatin predominates in
metabolically inactive cells
heterochromatin contains
transcriptionally inactive DNA, which is densely packed. As a result, heterochromatin stains more intensely than euchromatin.
Nucleolus
small area within the nucleus in which ribosomal RNA is processed and assembled into ribosomal subunits.
what does the nucleolus contain
3 morphologically distinct regions when vied with TEM: Fibrillar centers, dense fibrillar component, and granular component
Fibrillar centers
contain DNA loops with rRNA genes and transcription factors
Dense fibrillar component
(pars fibrosa) contains ribosomal genes that are being translated and large amounts of RNA
granular component
(pars granulosa) is the site for ribosome assembly and is made of densely packed clusters of pre-ribosomal particles
Cytoskeleton determines
the shape of cells, provides structural support for its organelles and plays a major role in cell motility (included mitosis and cytokinesis).
Cytoskeleton composition
consists of 2 major types of filaments: actin filaments, microtubules, and intermediate filaments
Actin cytoskeleton role
cell movement, cell shape, and organelle transport
forms of actin
G-actin and F-acting
G-actin
soluble monomeric globular protein. It can polymerize into a double stranded helical filament which is called F-actin.
polymerization of G-action
to make F-action. Occurs from head to tail so the actin filaments have polarity.
other name for F-actin filaments
thin filaments
functions of thin filaments
- 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
- Interacts with myosin to generate force and movement
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
myosin is the
motor associated with thin filaments.
Microtubules
cytoskeletal elements present in all cells except erythrocytes
Functions of microtubules
- organelle and vesicle movement (sometimes over rather long distances like across the axon of a neuron)
- Formation of the mitotic spindle and chromosome movement during mitosis and meiosis
- beating of cilia and flagella
Structure of microtubules
They are stiff, non branching, cylindrical polymers made of 1 polymerized globular proteins (alpha and beta tubulin)
how are tubulin molecules polymerized
side to side and head to tail so microtubules have a plus and minus end.
Plus and v minus end of microtubule
Plus grows faster. Plus is cell periphery and minus associated with the microtubule-organizing center/centriole.
motor proteins associated with microtubules
2 types - Dyneins and Kinesins
energy used in Dynein and Kinesin
ATP energy to generate force that moves the motor and materials attached to it along the microtubule.
Dyneins description
group of motor proteins that move towards the minus end of a microtubules. They are involved in the beating of cilia and flagella.
Kinesins description
group of motor proteins that move towards the plus end of a microtubule
Higher order structures
Microtubules in euk cells are organized into several higher order structures, including cilia, flagella, centrioles, and microtubules-organizing centers
Axoneme
forms the core of cilia and flagella. Composed if 9 doublets and a central pair of microtubules. Dynein arms attached to the A-tubules of each of the doublets interacts with the neighboring B-tubules of the next doublet and by walking along it cases the bending of the axoneme. The axoneme generates force for the movement of cilia and flagella
what is at the base of each cilium or flagellum
centriole, or a basal body, also composed of microtubules arranged into 9 triplets without the central pair
most human cells except neurons and RBCs contain
a microtubule-organizing center (MTOC)
MTOC consists of
2 centrioles. Virtually all cellular microtubules arise from the MTOC
Intermediate filaments description
they are intermediate in thickness between actin filaments and microtubules. They are 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
classes of intermediate filaments
several major classes that have certain distribution in different types of tissues.
- Lamins
- Keratins
- Vimentin
- Desmin
- Glial fibrillary acidic protein
- Neurofilaments
Lamins location and function
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
Keratins location
principally in epithelial cells
Vimentin primary location
fibroblasts of the connective tissue
Desmin location
muscle cells
GFAP location
in the support cells of the nervous system, called glial cells
neurofilaments location
neurons
what do cytoplasmic intermediate filaments form
bundles between the pm and the nucleus. They spread tensile forces, maintain cell architecture and act as a cocoon when the cell is damaged. Intermediate filaments anchor ion channel proteins.
Colors of most tissues
colorless - this is why we need dye
components of most dyes used
basophilic and acidophilic components
most commonly used combo of dyes
Hematoxylin and eosin (H&E).
Hematoxylin
a basic dye as it stains structures, which have acids in their composition, such as nucleic acids or glucosaminoglycans blue.
Eosin
acid dye - it stains basic cell components.
Nucleus staining with H&E dye
Dark blue/purple
Cytoplasm staining with H&E dye
Pink
Mitochondria staining with H&E dye
Pink
RER/Ribosomes staining with H&E dye
Blue
Membranes, GA, SER staining with H&E dye
Do not stain
Collagen staining with H&E dye
Pink
Glucosaminoglycans staining with H&E dye
Blue
