Molecular trafficking lecture 2

Question 1

What is the main function of the cytosol?

Answer 1

contains many metabolic pathways; protein synthesis; the cytoskeleton

Question 2

What is the main function of the nucleus(double membrane)?

Answer 2

contains main genome
DNA and RNA synthesis

Question 3

What is the main function of the ER?

Answer 3

synthesis of most lipids
synthesis of proteins for distribution to many organelles and to the plasma membrane

Question 4

What is the main function of Lysosomes?

Answer 4

Intracellular degradation

Question 5

What is the main function of the golgi apparatus?

Answer 5

modification, sorting, and packaging of proteins and lipids for either secretion or delivery to another organelle

Question 6

What is the main function of the endosome?

Answer 6

sorting of endocytosed material

Question 7

What is the main function of mitochondria(double membrane)?

Answer 7

ATP synthesis by oxidative phosphorylation

Question 8

What is the main function of chloroplasts(plant cells)?

Answer 8

ATP synthesis and carbon fixation by photosynthesis

Question 9

What is the main function of the peroxisome?

Answer 9

oxidative breakdown of toxic molecules, e.g. toxins, alcohol, fatty acids (produce hydrogen peroxide or H2O2).

Question 10

Why is directing newly made proteins to the correct organelle vital?

Answer 10

So a cell can grow and divide effectively and so it can function properly.

Question 11

Where does synthesis of most proteins begin?

Answer 11

Free ribosomes in the cytosol.

Question 12

What does the final location of proteins synthesised in the cytosol depend on?

Answer 12

The amino acid sequence(sorting signal).

Question 13

What are the 3 mechanisms that proteins are transported into organelles by?

Answer 13

1. Through nuclear pores
2. Transport across membranes
3. Transport by vesicles

Question 14

What are the two pathways of delivery for proteins into organelles?

Answer 14

Secretory and non-secretory.

Question 15

Which organelles receive non-secretory delivery of proteins?

Answer 15

Mitochondria, chloroplasts,peroxisomes and the interior of the nucleus

ALL FROM THE CYTOSOL.

Question 16

Which organelles receive secretory delivery of proteins?

Answer 16

Golgi apparatus, lysosomes, endosomes, nuclear and plasma membranes.

INDIRECTLY VIA THE ER.

Question 17

How long is the amino acid chain for sorting signal sequences?

Answer 17

15-60 amino acids long.

Question 18

Are sorting signal sequences removed?

Answer 18

Often removed after a protein has arrived at its destination.

Question 19

When is a sorting signal retained?

Answer 19

Nuclear proteins are retained(important during cell division).

Question 20

Nuclear pores ________ the nuclear envelope

Answer 20

perforate

Question 21

What type of molecules can pass freely and non-selectively through the pore?

Answer 21

Small, water-soluble molecules.

Question 22

How are proteins destined for the nucleus directed there?

Answer 22

Nuclear localisation signal(sequence containing several positively charged lysines or arginines).
It is recognised by cytosolic proteins called nuclear import receptors.

Question 23

What does Ran(GTPase)-GTP do?

Answer 23

Displaces nuclear proteins from their receptors ensuring one-way entry into the nucleus.

Question 24

Signal sequences are recognised by ________ _______proteins which, together with ___________ in the inner and outer membrane, translocate proteins across _____ membranes

[fill in the blanks]

Answer 24

import receptor
translocators
both

Question 25

What happens to proteins as they are transported to the mitochondria?

Answer 25

They unfold.

Question 26

What are N-terminal sequences cleaved by once translocation is complete?

Answer 26

Cleaved by a signal peptidase.

Question 27

What is the function of chaperone proteins?

Answer 27

Proteins help to pull proteins across the membranes and assist with protein refolding.

Question 28

Describe the features of the ER?

Answer 28

Membranous system of interconnected tubules and flattened sacs (cisternae) Continuous with the outer nuclear membrane.

Question 29

What is the difference between RER and SER?

Answer 29

In RER the ribosomes attach to the cytosolic side(site of protein synthesis). The SER lacks ribosomes. Functions in storage of Calcium ions and lipid synthesis, e.g. steroids, new membrane phospholipids.