Lecture 11- Organelles I

Question 1

Three mechanisms of protein import into organelles

Answer 1

Transport via nuclear pores
Transport via protein translocators
Transport via vesicles

Question 2

Signal sequences

Answer 2

Directs proteins to the correct organelle

3-60 aa

Question 3

Mitochondrial matrix space

Answer 3

Internal space
High concentration of enzymes (including those that break down fatty acids and involved in citric acid cycle)
Location of the mitochondrial DNA genome and machinery necessary for expression of mitochondrial genes

Question 4

Mitochondrial inner membrane

Answer 4

Encloses matrix space
Infoldings called cristae, increase surface area
Contains proteins of ETC and ATP synthase (both necessary for oxidative phosphorylation)
Contains transport proteins regulating passage into and out of matrix
Electrochemical gradient drives ATP synthesis

Question 5

Mitochondrial outer membrane

Answer 5

Separate mitochondrion from the cytosol

Contains porin molecules

Question 6

Mitochondrial intermembrane space

Answer 6

Contains cytochrome c (released during apoptosis, involved in ETC)

Question 7

Conversion of fatty acids and pyruvate to ATP

Answer 7

• Pyruvates and fatty acids selectively transported into matrix and converted to acetyl coA
• Acetyl CoA enters the citric acid cycle and is converted to CO2 and high energy electrons held by NADH and FADH2
• High energy electrons transported down the ETC in inner membrane and release energy used to pump protons out of matrix creating a gradient, at end electrons transfered to O2 to produce H2O
• Protons flow down gradient through ATP synthase complex which creates ATP

Question 8

Apoptosis

Answer 8

• Programmed cell death
• Release of cytochrome C from the intermembrane space of the mitochondria triggers activation of the caspase cascade which is a proteolytic cascade responsible for cleaving key cellular proteins

Question 9

Transport of proteins into mitochondria

Answer 9

• Have a signal sequence (n term)
• Occurs post translationally
• Precursor protein binds to a receptor associated with TOM via signal sequence
• Tom complex diffuses laterally until encountering a TIM
• Precursor protein translocated across both membranes (chaperone proteins help)
• Signal sequence cleaved by mitochondrial signal peptidase
• Final folding

Energy requirements- ATP hydrolysis and EC gradient across inner membrane

Question 10

Mitochondrial genome

Answer 10

• Very small
• Encodes 2 rRNAs, 22 tRNAs, 13 mRNAs
• Little regulatory sequences and no introns
• Slightly different genetic code
• 10-20 copies per mitochondria

Question 11

Replication of mitochondrial DNA

Answer 11

Occurs at any time (not just during S phase)

Most proteins for replication imported in

Question 12

Mitochondrial DNA transcription

Answer 12

Single promoter region on each strand
Produces two giant RNA molecules each containing a full-length transcript of one DNA strand
Later cleaved

Question 13

Mitochondrial DNA translation

Answer 13

Produces only 13 polypeptides involved in ETC and oxidative phosphorylation

Question 14

Peroxisomes

Answer 14

• In all eukaryotic cells
• Major site of oxygen utilization in the cell
• Oxidative degradation
• Beta oxidation (break down of fatty acids)
• Synthesis of cholesterol, bile, acids, and some lipids

Question 15

Disorders of peroxisome biogenesis

Answer 15

Loss of perox function due to defects in proteins required for biogenesis, lack of enzymes, or no peroxisomes at all

Zellweger syndrome–empty peroxisomes (fatal)

Question 16

Deficiency of a single peroxisomal enzyme

Answer 16

Less severe
Partially functional peroxs
X-linked adrenoleukodystrophy–missing an enzyme to break down long chain fatty acids, nervous system problems

Question 17

Treatment of ALD

Answer 17

Allogeneic hematopoietic stem cell transplantation (HCT)

Gene therapy