Lecture 3: Intracellular components Flashcards
How much volume does cytosol occupy in a cell?
About half the volume is cytosol in the cell
What is the function of hepatocyte?
Detoxification and it is found in the liver
What is the role of pancreatic exocrine cell?
It secretes digestive enzymes
What are the roles of rough ER and smooth ER?
Rough ER: has membrane bound ribosomes, and are involved in synthesis of soluble proteins and transmembrane proteins of the endomembrane,
the soluble proteins it makes are mostly secreted
Smooth ER: It is involved in phospholipid synthesis and also detoxification.
How much membrane does rough and smooth ER make together?
about 50%
What components of a cell are expected to be more in a hepacyte?
Smooth er cause it helps in detoxification
What components are expected to be more in a pancreatic exocrine cell?
Rough Er cause it makes soluble proteins and excretes them.
What are non membrane organelles also called?
Biomolecular condensates
What are organelles?
Discrete structures or sub compartments of a eukaryotic cell that is specialized to carry out a particular function (most are membrane enclosed)
What is a sorting signal on proteins called?
Signal sequence
What proteins dont have the sorting signal?
Cytosolic proteins
Are sorting signals or sequence signals added on to the protein?
No they are specific aa sequence that are part of the protein
Who recognizes the signal sequences on the proteins?
Sorting receptors recognize them and take them to their destination.
What are the two methods in which proteins are sorted?
1) post-translational sorting: Proteins are nuclear-encoded, and fully synthesized in cytosol before sorting
2) Co-translation sorting: Proteins are nuclear-encoded and have ER signal sequence, they are associated with ER during protein synthesis in the cytosol.
in the post-translation sorting, where do folded proteins go and where do unfolded proteins go?
Folded: Nucleus and Peroxisomes
Unfolded: Mitochondria and Plastids
What are perioxisomes?
They contain enzymes for oxidative reactions, used to detoxify, and break down fatty acid molecules.
The enzymes are imported into peroxisome through a transmembrane protein complex.
what helps to keep the proteins unfolded when they go to mitochondria or chloroplast?
Hsp70 chaperone proteins
What are the characteristics of co-translation sequence sorting?
first the protein gets nuclear encoded and has an ER sorting sequence. now as it is getting translated they get associated with Er during the synthesis in the cytosol.
However the Er signal is specific and hydrophobic.
What are the co-translation steps for SOLUBLE proteins
Ok so co-translation occurs simultaneously in the Er and the ribosomes.
First the Ribosome starts to translate the mRNA. Next it reads the SPECIFIC SEQUENCE SIGNAL that tells it it take the protein to the ER.
This signal is identified by SRP (signal receptor proteins) which then stops the translation process completely.
The SRP then take this SRP-ribosome domain to the SRP receptor which are located in the ER.
Now the SRP is released and passes the protein synthesis to the TRANSLOCON protein, and the translocon protein is usually closed and open only to the ER specific signal.
Now the protein synthesis begins as usual but it keeps transferring the newly synthesized protein into the ER.
Once the end of the protein has been reached, the signal sequence is cleaved off by SIGNAL PEPTIDASE. And the hydrophobic signal sequence is rapidly degraded in the lipid bilayer.
The protein is released into the ER lumen, and translocon closes.
How does co translation occur in transmembrane proteins?
1) NH2 (N-terminal) sequence is identified in the translation protein by the SRP and then it stops the translation.
2) this SRP-Ribosomal complex binds to the SRP-Receptor
3) This is then attached to the TRANSLOCON and translation continues. But the newly translated protein will be pushed into the ER instead of
4) next a stop sequence is read by the TRANSLOCON and it leaves the protein once Signal peptidase cleaves the starting signal sequence and it gets rapidly degraded in the bilipid layer.
5) the transmembrane domain remain between the bilipid layer while the ribosome continues to translate the MRNA.
What happens to the internal ER sequence?
It is the same, as the ER sequence- it is still hydrophobic stretch of amino acids sequence however the signal peptidase does not cleave off the signal. This signal becomes the protein domain along with the end signal sequence and remain as alpha helices in the meme range
What make up the Endomembrane system?
ER, lysosomes, Golgi apparatus, early endosome and late endosome.
How does endocytosis occur?
The contents to be delivered are stored in vesicles and delivered to extra cellular space, and the vesicle membrane becomes part of the plasma membrane
How does endocytosis take place?
The vesicle liminal contents come from extracellular space and the plasma membrane forms the vesicle membrane
What are the two sectretory pathways ?
Constitutive and Regulated exocytosis pathways
How does constitutive exocytosis pathway work?
It is present in ALL EUKARYOTIC cells. It is the continual delivery of proteins (transmembrane and soluble) proteins and lipids to plasma membrane.
It includes CONSTITUTIVE SECRETION of soluble proteins like collagen and ECM
How does regulated exocytosis pathway work?
It is the regulated secretion in specialized cells. These are stored in specialized secretory vesicles.
To release these extracellular signal is required and once the vesicle is fused with PM the contents are released.
For example pancreatic beta cells are released when insulin release with increased blood glucose.
What do you call the closest side of golgi that is closest to the ER
Cis-golgi network
What are the parts of golgi that are not connected to ER?
Under the Golgi network is cis-cisterna
Then medial cisterna
Next is the trans-cisterna and finally the trans Golgi network this is connected though
Where does protein glucosylation take place? (Adding sugar to proteins)
In the ER- a single type of Oligosaccbaride is attached to many proteins
What are the function that occur in protein in detail
Complex oligosaccharide processing occurs in the Golgi apparatus. It is the multi stage processing unit. It has different enzymes in each cisterna.
Glycosylation modification for proteins and lipids take place here
Which side of Golgi does the late endosomes come from?
From the trans Golgi network. And then they mature into lysosomes
What are the types of endosomes?
Early endosomes: contain the endocytosis material, the endocytosis vesicles fuse to early endosomes and get sorted. Now the early endosomes mature into late endosomes.
Late endosomes: these have lysosomal proteins, H+ hydrolases pump and then these mature into lysosomes
Lysosomes: these are membrane bound organelles and contain hydrolytic enzymes to digest worn out proteins organelles and wastes
What are the main sites for intracellualr digestion?
Lysosomes
How many types of hydrolytic enzymes does lysosome contain?
About 40 different types however they work only in acidic conditions. Like proteases, nucleuses, lipases, so these lysosomes are acidified by the H+ pumps (V-type, ATPases) and low PH is maintained.
What protects the inner lining of lysosomes from being digested
Lysosomal membrane proteins are glycosylated for protection from proteases.
What do proteins in the lysomal membrane transfer?
Nucleotides, amino acids and sugars
