Lecture 3: Intracellular components

Question 1

How much volume does cytosol occupy in a cell?

Answer 1

About half the volume is cytosol in the cell

Question 2

What is the function of hepatocyte?

Answer 2

Detoxification and it is found in the liver

Question 3

What is the role of pancreatic exocrine cell?

Answer 3

It secretes digestive enzymes

Question 4

What are the roles of rough ER and smooth ER?

Answer 4

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.

Question 5

How much membrane does rough and smooth ER make together?

Answer 5

about 50%

Question 6

What components of a cell are expected to be more in a hepacyte?

Answer 6

Smooth er cause it helps in detoxification

Question 7

What components are expected to be more in a pancreatic exocrine cell?

Answer 7

Rough Er cause it makes soluble proteins and excretes them.

Question 8

What are non membrane organelles also called?

Answer 8

Biomolecular condensates

Question 9

What are organelles?

Answer 9

Discrete structures or sub compartments of a eukaryotic cell that is specialized to carry out a particular function (most are membrane enclosed)

Question 10

What is a sorting signal on proteins called?

Answer 10

Signal sequence

Question 11

What proteins dont have the sorting signal?

Answer 11

Cytosolic proteins

Question 12

Are sorting signals or sequence signals added on to the protein?

Answer 12

No they are specific aa sequence that are part of the protein

Question 13

Who recognizes the signal sequences on the proteins?

Answer 13

Sorting receptors recognize them and take them to their destination.

Question 14

What are the two methods in which proteins are sorted?

Answer 14

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.

Question 15

in the post-translation sorting, where do folded proteins go and where do unfolded proteins go?

Answer 15

Folded: Nucleus and Peroxisomes

Unfolded: Mitochondria and Plastids

Question 16

What are perioxisomes?

Answer 16

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.

Question 17

what helps to keep the proteins unfolded when they go to mitochondria or chloroplast?

Answer 17

Hsp70 chaperone proteins

Question 18

What are the characteristics of co-translation sequence sorting?

Answer 18

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.

Question 19

What are the co-translation steps for SOLUBLE proteins

Answer 19

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.

Question 20

How does co translation occur in transmembrane proteins?

Answer 20

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.

Question 21

What happens to the internal ER sequence?

Answer 21

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

Question 22

What make up the Endomembrane system?

Answer 22

ER, lysosomes, Golgi apparatus, early endosome and late endosome.

Question 23

How does endocytosis occur?

Answer 23

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

Question 24

How does endocytosis take place?

Answer 24

The vesicle liminal contents come from extracellular space and the plasma membrane forms the vesicle membrane

Question 25

What are the two sectretory pathways ?

Answer 25

Constitutive and Regulated exocytosis pathways

Question 26

How does constitutive exocytosis pathway work?

Answer 26

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

Question 27

How does regulated exocytosis pathway work?

Answer 27

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.

Question 28

What do you call the closest side of golgi that is closest to the ER

Answer 28

Cis-golgi network

Question 29

What are the parts of golgi that are not connected to ER?

Answer 29

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

Question 30

Where does protein glucosylation take place? (Adding sugar to proteins)

Answer 30

In the ER- a single type of Oligosaccbaride is attached to many proteins

Question 31

What are the function that occur in protein in detail

Answer 31

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

Question 32

Which side of Golgi does the late endosomes come from?

Answer 32

From the trans Golgi network. And then they mature into lysosomes

Question 33

What are the types of endosomes?

Answer 33

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

Question 34

What are the main sites for intracellualr digestion?

Answer 34

Lysosomes

Question 35

How many types of hydrolytic enzymes does lysosome contain?

Answer 35

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.

Question 36

What protects the inner lining of lysosomes from being digested

Answer 36

Lysosomal membrane proteins are glycosylated for protection from proteases.

Question 37

What do proteins in the lysomal membrane transfer?

Answer 37

Nucleotides, amino acids and sugars