Vet histology lectures 3 & 4
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What are the four types of RNA's? What do they do?
- mRNA - encodes proteins
- tRNA - Transfer amino acids to ribosomes
- rRNA - Structural component of ribosomes
- miRNA - non coding RNA's for regulating gene expression
Explain more in depth of what miRNA does.
It attaches to mRNA and chews it up to stop production of that specific protein when it is no longer needed
Darker spots on the nucleus likely signify RNA transcription or mRNA post processing
How can you distinguish the large unit of the ribosome in a picture?
Has the handle on it
What does the large part of ribosome do? Small part?
- Transfers AA from 1 side to the other
- Has reading frame
What is a poly ribosome?
Many ribosomes working on the same mRNA strand
Proteins being made for the cell to keep are made in the
What is a polyribosome
Multiple ribosomes on a single mRNA
A cell that is making lots of proteins for export would have a larger (Rough ER or Polyribosome population)
What happens in the Golgi?
Final packaging and sorting
If a protein is made in the cytosol and needs to be exported how does it happen?
- In proteins meant for export there is a beginning code called the signal peptide (tag) which is et by the signal recognition particle (SRP) which has a docking station onto the ER protein goes through but TAG is cut off on its way in.
- From ER goes to Golgi via vesicles where Golgi takes care of it
Where does folding and extra peptide addition occur? in the Golgi or ER?
All in the ER, we know how important this is because the function of a protein lies in its 3D structure not linnear
Are polyribosomes possible on the rER surface?
Yes they are contrary to what thought before (see page 2 slide 3 of lecture 3 for nice illustration)
Can smooth and rough ER interchange according to need?
Yes they can even though they use different enzymes
What are annulate lamellae
- structures identical to cell membranes, occurring singly or stacked in groups, in the cellular cytoplasm. Their function is unknown
- Possible left over RER membrane leftover from mitosis
What are 3 good functions of smooth ER and what kind of cells would you expect to find sER in?
- work with cholesterol and make sex hormones
- store Ca
- Liver cells, sexual organ cells etc etc
How can you differentiate rER and sER under a microscope?
rER looks like sheets with bumps and dots on them, sER resemble small holes or tubes
Describe the cis face of the golgi
- Receives from the ER
- convex face
Describe the trans face of the golgi
- Exports vessicles
- Concave face
What is inbetween the trans and cis face of the Golgi?
The medial cisternae
Why is the Golgi often hard to see under stain?
High phospholipid content so does not always stain very well
What happens if something reaches the Golgi and is not folded or made right?
It has the amazing ability to sort through find these mistakes and send them back to the ER
Where does RNA and ribosomal subunit synthesis occur?
Another name for Golgi complex?
Trans Golgi network
Are ribosomes and rER basophilic or acidophilic?
What are the three pathways found in the Golgi? describe them each
- Constitutive secretory pathway - constantly secreting after production, regardless of stimulus
- Regulated secretory pathway (receptor mediated release) - only secreted upon stimulation often seen when big amounts are needed at once
- Lysosomal packaging - packaging of lysosomes specifically for digestion
Differentiate between nucleosomes and a nucleolus
- nucleolus is a denser area of action in the nucleus where the ribosomes are being made
- nucleosomes are a level of folding found on chromatin
What is the opposite of a sex chromosome
What are porins
Transmembrane proteins spanning the membrane, essentially channels allowing difficult particles through
So if most folding happens in rER are proteins found in the cytoplasm not as complex?
No the cytoplasm has its own folding proteins and chaperones etc etc
3 types of vesicles a lysosome could fuse with?
After a lysosome fuses with its target and digests what are 2 paths it could take?
It ends up as a residual body or being exocytosed
What is the pH of an early endosome? Late endosome? Lysosome? What is the function of the intermediate endosome? Why do endosomes pump in H+?
- Not really sure
- Because lysosomal enzymes work better at these lower pH's
What are some examples of the enzymes found in lysosomes?
M-6-P is what?
- Mannose 6 phosphate is a tag often added to proteins in the Golgi
- Added to rptoeins destined for lysosomes
Which face of the Golgi adds M-6-P
While a primary lysosome is homologous a secondary lysosome is
Heterogenous as it has fused with an endosome of some sort
What are 3 end products (options) of lysosomal digestion
- Lamella body
- Dense body
- Lipofuscin body
Where are you most likely to find a peroxisome?
Inside liver and kidney cells
The oxalate crystals seen on some peroxisomes are not always the most useful to us, why?
Cant always see them under H&E
Do peroxisomes digest?
No they remove oxygen from components such as ethanol and H2O2
4 things that make up the cytoskeleton?
- Intermediate filaments
- Associated interconnecting proteins
microfilaments are also known as? What do they both look like under microscope?
- Actin and myosin
- Actin tiny little pin prick, myosit big black dot
WHat is used in peroxisomes to break down H2O2
Actin has 2 ends differentiate them, which end is being added to ?
- positive and negative end
- positive end is where more is added
Are intermediate filaments all the same?
No it is a general group they will differ strongly depending on the cell
What kind of intermediate filament would you expect to find in a epithelial cell? Connective tissue? Neurons?
What is useful clinically about the fact that different cells have different intermediate filaments
Can identify origin of cancer cells
Differentiate between G actin and F actin
G is amonomer that makes up F the polymer
Many cells have actin and myosin, so what makes muscle cells able to contract?
The fact they are organized in a coordinated fashion
Microtubules function as? And are made up of? Which has which two ends?
- alpha, and beta
What are the two transport proteins found on microtubules? Which direction do they travel? Do they require energy input?
- Dynein - away from nucleus
- Kinesin - toward nucleus
Where do all microtubules start?
At a centriole
What is a centrosome?
What is a centrosome important for?
- Cells with flagella and cillia
- cell division
Do cellular inclusions partake in metabolism?
Give 3 examples of cellular inclusions
- Lipid droplets
Will we see glycogen inclusions under our microscopes? What do they look like?
- No too fragile we need to be more careful
- Dots, essentially glycogen granules
Lipid droplets can be distinguished by their? Do they have a membrane?
- Homogenous stain and perfectly round appearence
- No just accumulation of stuff surrounding it
Do we often see lipids under the microscope in reality?
Nope usually the place where they were that's why its so homogenous, during the slide making process, alchohol washes most lipid away
Where do we see more melanin in peoples skin?
Closer to the equator
What cell produces melanin? How does it spread? Skin cells are short lived what about melanocytes?
- Melanocytes, they inject it into neighbouring cells
- Nope long lived
Describe lipofuscin as a pigment
- Essentially aging pigment, leftover in long lived cells from cellular digestion, basically residual bodies
- Often black and strangely shaped
Micro filaments are used for contraction, microtubules for transport, what are intermediate filaments used for?
Tensile strength and reinforcement
Describe intracellular digestion from pinocytosis vs phagocytosis
Pinocytosis-early endosome-late endosome-lysosome-exocytosis or residual body
Phagosome-late endosome-lysosome-exocytosis or residual body
Essentially phagocytosis skips early endosome
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