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