Translocation into the Nucleus, Mitochondria, and Peroxisomes- Lecture 36

Question 1

What distinguishes transport into the nucleus, mitochondria, and preoxisomes from the secretory pathway?

Answer 1

proteins entering these organelles do so after translation in the cytosol

Question 2

What is the main function of the mitochondria?

Answer 2

generation of ATP (which can be used for cellular energy)

Question 3

MItochondria have their own genome that encodes _____ proteins and RNA components of _______.

Answer 3

13

mitochondrial ribosomes

Question 4

Describe how liver mitochondria differ in appearance from skeletal muscle mitochondria.

Answer 4

liver have fewer cristae than skeletal

Question 5

What are the reactions that are completed in the matrix?

Answer 5

oxidation reactions
oxidation of fatty acids
enzymes of urea cycle

Question 6

What creates a membrane potential across the inner membrane?

Answer 6

the movement of protons

Question 7

Where is the mitochondrial genome contained?

Answer 7

in the matrix

Question 8

What are the differences in coding between the mitochondrial genome and universal genome?

Answer 8

AUG is universally a STOP codon, but codes for Tryptophan in mitochondria
AGG is universally an Arginine but becomes a STOP codon in mitochondria

Question 9

Describe the human mitochondrial genome.

Answer 9

circular

16,569 bp

Question 10

How does mitochondria replicate?

Answer 10

divides into two from one existing mitochondria via fission reaction
divide asynchronously

Question 11

Describe the types of nuclear encoded mitochondrial genes contained in target sequences.

Answer 11

15-35 residue N-terminal sequence comprising basic amino acids that are cleaved in the matrix by an endoprotease
non-cleaved internal sequence

Question 12

Describe how a protein is translocated into the mitochondria.

Answer 12

Hsc70 molecular chaperones bind target sequence of protein as it emerges from ribosome –> brings it closer to a specific receptor on the OMM –> proximity to TOM complex allows for the protein to translocate across the outer membrane (still not folded) –> protein is translocated actross the IMM by TIM channels (positive charge in IMS opens the TIM and draws the protein into the channel, where they can be guided further by their Hsc70
once in the matrix, protein folds with help from Hsc60 and Hsc70 and the targeting sequence is cleaved

Question 13

Provide an example of mitochondrial disease/

Answer 13

Leer’s hereditary optic neuropathy(LHON)by missense mutation in subunit 4 of NADH-coQ reductase
results in midlife sudden onset blindness

Question 14

What is the main role of peroxisomes?

Answer 14

fatty acid beta-oxidation resulting in hydrogen peroxide as a biproduct which is metabolized by catalase to water an d oxygen

Question 15

Describe the structure of peroxisomes.

Answer 15

single walled

Question 16

How do proteins enter the peroxisome?

Answer 16

targeting sequence (SKL on the C terminus) is recognized by PGX5 (a soluble receptor) which transports the folded protein into the peroxisome via channel
after entering, the receptor releases and is transported back out

Question 17

The nucleus houses the genetic material to separate it from the cytosol, thereby separating ________ from _______.

Answer 17

Transcription

translation

Question 18

What activities occur in the nucleus?

Answer 18

transcription, mRNA splicing, DNA replication, and ribosome biosynthesis

Question 19

Describe the structure of the nucleus.

Answer 19

surrounded by a double lipid bilayer with the outer one being continuous with the rough ER
perinuclear space between the membranes is contiguous with the lumen of the ER
inner surface is lined with nuclear lamina and punctuated with nuclear pores
a secondary structure inside is called the nucleolus

Question 20

Describe the pathway of genetic material that codes for ribosomes.

Answer 20

ribosomal protein genes are transcribed by RNA pol II –> exit the nucleus to be translated by cytoplasmic ribosomes –> proteins reenter the nucleus and bind cytoplasmic ribosomes –> complex reenters the nucleus and is transported to the nucleolus –> assemble rRNA –> pre-ribosomal particles are delivered to the cytosol

Question 21

An ____ is typically ____ amino acids, rich in ____ and ____ and usually contains ____.

Answer 21

nuclear localization sequence (NLS)
4-8
Arg, Lys
Pro

Question 22

Describe the nuclear pore complex.

Answer 22

eight fold symmetry
contains a central aqueous channel of 9nm diameter and 15 nm length
composed of several ring assemblies that occupy the cytoplasmic face, inner core, and nucleoplasmic face of the structure
filamentous assemblies radiate out from both sides

Question 23

Describe the process of nuclear transport.

Answer 23

karyopherins recognize NLS or NES sequences and bind –> complex travels into nucleus via NPC complex –> Ran-GTP binds the karyopherin –> protein dissociates from complex which is exported into the cytosol –> RanGTP is hydrolized to RanGDP by a GAP and re-enters the nucleus via another NPC