Cell Signalling And Protein Sorting Flashcards Preview

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Flashcards in Cell Signalling And Protein Sorting Deck (161)
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1

How many cells are in the body

10^13

2

How thick is the plasma membrane

2 molecules thick

3

How do lipophilic substances pass across the plasma membrane (PM)

They dissolve in the PM and so can pass through it

4

How do channels work

Allow materials to flow downhill into or out of a cell

5

What does it mean for production if chemical signals are lipophilic

They must be made on demand as they cannot be retained

6

What do transporters do

Export chemical signals from cytosol across PM

7

Give 3 ways for cells to receive a signal (ie get across the PM)

Lipophilic pass through the PM to reach intracellular targets

Extracellular messenger may be recognised by a binding site in a channel (to open or close it) and the flux of ions across PM changes

Allosteric PM-spanning protein (where intracellular side of protein changes shape)

8

3 ways to send our cellular information

Diffusion across PM

transporters

Vesicles

9

How is the nucleus separated from the cytosol

By a double membrane penetrates by nuclear pores

10

What is the ER and what does it contain

Endoplasmic reticulum

A lumen where proteins mature and Ca2+ is stored

The ER also contributes to lipid and steroid synthesis

11

Why is rough ER rough

It is studded with ribosomes

12

Describe the Golgi apparatus

Stacks of tubules linked to the ER
it has an important role in maturation/ glycosylation of proteins and their dispatch

13

What are almost all proteins encoded by

What is the exception

Nuclear genes

Those encoded by the small mitochondrial genome

14

What is the overall process of making proteins

Their DNA is transcribed into mRNA which is processed in the nucleus before export through the nuclear pores. Within the cytosol, mRNA provides the template for synthesis of proteins by ribosomes

15

How many genes are mitochondrial

37

16

How can disease caused by defects in mitochondrial genes be avoided

Use an enucleated egg from a surrogate with normal mitochondria to serve as the host for parent’s DNA/nucleus

17

Where do most proteins begin there life

Then what happens

On a cytosolic ribosome

Address labels in the primary structure dispatch proteins to different destinations

18

How do fully folded proteins re-enter the nucleoplasm

Nuclear localisation signals allow them to move Through nuclear pores

19

If the protein does not stay in the cytosol or go to the nucleoplasm, what happens to them

They must cross a membrane and therefore must stay unfolded

20

What is post translation targeting and where does it occur

When the protein has been fully translated but doesn’t fully fold until it has crossed the membrane

Mitochondria and peroxisomes

21

What is co-translational targeting

When proteins destined for the ER are dispatched before translation is complete

22

What is a NLS

A nuclear localisation signal: a stretch of 6 +/ve residues anywhere in the primary sequence, recognised by importin

23

How can nuclear translocation be regulated

By unmasking a NLS

24

How do proteins reach the peroxisome

When does this go wrong

The C terminal sequence (Serine-Lysine-Leucine) is recognised by PTS1 receptors and guides it to peroxisome membrane

In Zellweger Syndrome, when the PTS1 is non functional

25

Why is mitochondrial targeting complex

There are 4 destinations:
Inner and outer membranes, intermembrane space, and matrix

26

How do cells target for mitochondrial matrix proteins

N-terminal amphipathic helix is recognised by a chaperone protein

27

Is targeting for peroxisomes and mitochondria reversible

No
It is irreversible

28

How is co-translational targeting used for proteins to the ER

A hydrophobic signal sequence at the N terminal (for luminal proteins) or internally (for integral membrane proteins) is recognised by a large protein-RNA complex

29

What are ER proteins from co translational targeting recognised by

Signal Recognition Particle (SRP)

30

What happens when SRP recognises a protein

The protein’s translation stops so SRP-nascent peptide chain can associate with the SRP receptor on the ER membrane