1-29 Organelles and Protein Sorting

Question 1

targeting of newly synthesized enzymes to mitrochondria involves which transport mechanisms?

Answer 1

transmembrane transport

Question 2

proteins encoded by the mitochondrial genome (synthesized where)? carry out functions in which compartment of the mitrochondria?

Answer 2

synthesized in matrix, transported to inner membrane. they are all components of the ETC or ATP synthase complex (both localized in inner membrane)

Question 3

the mitochondrial genome encodes

Answer 3

rRNAs, tRNA,s and mRNAs

Question 4

where is the mito genome located?

Answer 4

in the mito matrix

Question 5

how many copies of mito genome are in each mitro?

Answer 5

several copies

Question 6

mito uses a ____________ than the nuclear genome

Answer 6

slightly different genetic code

Question 7

What is synthesized in the mito?

Answer 7

ATP (atp synthatase), DNA (during replication), RNA (when transcribed into 2 giant strands), Proteins (13 are synthesized within mito)

Question 8

what is NOT synthesized in mito?

Answer 8

oligosaccharides. they are synthesized in the ER and Golgi

Question 9

ETC occurs in which compartment?

Answer 9

the inner membrane

Question 10

proteins are imported into the mito matrix _______

Answer 10

post-translationally

Question 11

What effect does maternal inheritance of mito genes have on mutation frequency?

Answer 11

no effect.

Question 12

synthesis of mtDNA encoded proteins occurs in the

Answer 12

mitochondrial matrix

Question 13

x-linked adrenoleukodystrophy is caused by defects in

Answer 13

the fatty acid transporter in peroxisomal membranes.

a defect leads to a build up of long fatty acids in cytoplasm - toxic- leads to demyelination of neurons.

Question 14

golgi

Answer 14

proteins synthesized in the ER are modified here

Question 15

worn out organelles are digested in the

Answer 15

lysosomes

Question 16

where are mitochondria located?

Answer 16

either in areas that need lots of ATP or around the cell along microtubules

Question 17

structure of mitochondria from outside to inside

Answer 17

Outer membrane, intermembrane space, matrix, inner membrane

Question 18

Matrix space

Answer 18

large internal space

lots of enzymes for breaking down fatty acids and citric acid cycle

contains mito genome with machinery

Question 19

inner membrane

Answer 19

encloses matrix

convoluted cristae to increase SA for ETC and ATP synthetase (both necessary for oxid phosp)

Electrochemical gradient that powers ATP syntehsis is established across the membrane by the ETC

Question 20

outer membrane

Answer 20

separates the mito from cytosol

contains porins across lipid bilayer, permeable to small molecules

Question 21

intermembrane space

Answer 21

small space between inner/outer membrane

contains cytocrome C component of ETC, also gets released signaling apoptosis

Question 22

final destination of proteins depends on

Answer 22

amino acid sequences which may contain sorting signals, directing them to an organelle

no sorting signal - stay in cytosol

Question 23

three mechanisms of protein transport

Answer 23

nuclear pores (GAF/GEF), protein translocators (co-translation or translationally, and vesicles (ER to Golgi to PM/extracellular space/lysosomes

Question 24

three mechanisms of protein transport

Answer 24

nuclear pores (GAF/GEF)

protein translocators (co-translation or translationally

vesicles (ER to Golgi to PM/extracellular space/lysosomes

Question 25

SRP

Answer 25

signal recognition particle - recognizes the signal sequence, directs it to correct organelle

Question 26

process of importing proteins to mitochondria

Answer 26

Transport mediated by two protein translocators (TOM & TIM complexes) located in outer and inner membranes

1. Precursor protein binds its recept sequence to receptor on TOM
2. Precursor protein and TOM move laterally across outer membrane until encouters TIM complex
3. Unfolded precursor protein translocates across both membranes, signal sequecne first. Chaperone proteins in matrix help pull the protein across the two membranes
4. Signal sequence cut off by microchondrial signal peptidase - protein unfolds to active confirmation with help for other chaperone proteins

Question 27

structure of peroxisomes

Answer 27

small multifucntional organelles found in all eukaryotic cells.

Major site of oxygen utilization, contains high concentrations of oxidatize enzymes used in reactions that break down molecules includig toxins, alcohol, and fatty acids, also synthesize special phospholipids.

Cells have hundreds

Question 28

3 functions of peroxisomes

Answer 28

Oxidative degradation - remove hydrogen atoms from organic substrates to produce hydrogen peroxide. Catalase uses h2o2 to oxidize/detox molecules

Beta oxidation (break down of fatty acids)

Synthesis of cholestrol, bile acids, some lipids - essential for making the plasmologens of myelin sheaths

Question 29

describe the mitochondrial genome

Answer 29

i. Very small circular ds DNA
ii. 37 genes for 2 rRNAs, 22 tRNAs, and 13 polypeptides
iii. Very little non-coding (junk) sequences
iv. No introns
v. Genetic code varies slightly from nuclear

Each mito contains 10-20 copies of the genome. Each cell therefor has thousands of copies

Question 30

Mitochondrial replication

Answer 30

a. Replication - occurs throughout cell cycle, on average the total number of mtDNA molecules doubles with each cell cycle

Question 31

mitochondrial transcription

Answer 31

both strands of mtDNA transcribed from single promoter region on each strand. Produces 2 giant rna molecules, each cleaved to give 2 rnas, 22 trnas, and 13 mRNA’s.

Question 32

mitochondrial translation

Answer 32

occuring in matrix using tRNAs and rRNAS encoded by mito genome. Produces only 13 pp, all of which involved in eT and oxidative phos

Question 33

basic principles of mito genetics and inheritance

Answer 33

maternal inheritance

heteroplasmy/threshold effect - homoplasmy penetrance can decrease due to environmental factors

mtDNA has high mutation rate

Question 34

mutation rate of mtDNA?

Answer 34

much higher than normal

• no introns = all mutations are within a coding sequence
• no protective histones
• inefficient repair
• mtDNA is exposed to oxygen free radicals

Question 35

describe mito disorders

Answer 35

often late onset due to increasing mutations over time. Broad range of tissues but usually those that require most oxidative phosphorylation - neuropathies, myopathies, etc..

Question 36

release of cytochrome c

Answer 36

triggers a caspase cascade creating lots of proteolytic enzymes that cause apoptosis

Question 37

catlase

Answer 37

uses hydrogen peroxide to oxidize substrates. Important in detoxifying areas of teh body like kidney and liver cells.

Question 38

synthesis of mtDNA encoded proteins occurs in the..

Answer 38

mitochondrial matrix

Question 39

What is the role of the mitochondria in the intrinsic pathway of apoptosis?

Answer 39

Releases cytochrome c from the intermembrane space into the cytosol which triggers activation of the caspase cascade

Question 40

What is the caspase cascade?

Answer 40

Triggered by the release of cytochrome c from the intermembrane of the mitochondria into the cytosol, the caspase cascade is an intracellular proteolytic cascade responsible for cleaving key cellular proteins

Question 41

What are TOM/TIM and what do they do?

Answer 41

TOM-protein Translocator located in Outer Membrane
TIM-protein Translocator located in Inner Membrane

Precursor protein binds to a receptor associated with TOM (must reach outer membrane first), via signal sequence. This complex will diffuse laterally until they reach TIM…protein is in folded state at this point, then chaperone proteins in the matrix pull protein through two membranes

Question 42

What do chaperone proteins do?

Answer 42

located in the mito matrix, they pull the protein being translocated through TOM/TIM into the matrix…where the mito signal sequence is cleaved off by mito signal peptidase and protein re-folds into its final conformation

Question 43

if you destroy the electrochemical gradient across the inner membrane, what happens to protein transport?

Answer 43

It stops.

Question 44

DNA replication is limited to the S phase in both nuclear DNA and mito DNA replication

Answer 44

False…mito DNA replication occurs throughout cell cycle

Question 45

Where does translation of mito proteins occur? How many polypeptides are made and where do they go after translation?

Answer 45

Occurs in mito matrix, synthesizes 13 polypeptides that all go to the inner membrane to function in the ETC and oxidative phosphorylation

Question 46

What is heteroplasmy and the threshold effect?

Answer 46

Heteroplasmy is when mutant and WT mtDNA both express in cells at different percentages…resulting in variable espressivity…differences in severity of disease. A phenotype will not be apparent until a threshold is reached…known as the threshold effect.

Question 47

What is homoplasmic?

Answer 47

Homoplasmic is when all of a woman’s mtDNAs carry a particular mutation…in this case, all of her children will inherit the mutation and any disease associated with with it

Question 48

What is N-linked glycosylation and where does this occur?

Answer 48

N-linked glycosylation is a protein modification that occurs in the ER. A preformed oligosaccharide (sugar) of 14 sugars is attached to a.a. residues during translocation (co-translationally).

N-linked glycosylation modification begins in the ER, but continues in the golgi