Mitochondria and peroxisomes Flashcards
Mitochondrial replacement therapy [2 marks]
- Healthy ovum is enucelated first
- Nucleus of healthy ovum replaced by nucleus of mother (with defective mitochondria)
Structure of mitochondria [5 marks]
- Double membrane
- Gel-like, viscous matrix (due to reduced water content)
- Inner membrane folds to form cristae
- Inner membrane is impermeable to passage of ions and small molecules
- Outer membrane contains porins
Where does the citric acid cycle occur? [1 mark]
Mitochondrial matrix
Purpose of cirstae
- Increases surface area for enzymes involved in ATP synthesis
- Sites of oxidative phsophorylation
Why do mitochondria associate with microtubules? [1 marks]
Allow even distribution of mitochondria across the cell
Why do mitochondria change their morphology? [1 marks]
To suit a cell’s need
How do mitochondria change their morphology? [3 marks]
- Fuse together
- Form elongated, dynamic tubular networks
- Networks are evenly distributed across the cytoplasm
When do mitochondria change their morphology? [4 marks]
- During apoptosis (due to proteins released from them)
- Calcium transfer
- Cell cycle
- Starvation
What happens to mitochondria during starvation? [2 marks]
- They become stretched out (due to fusion)
- May protect against autophagy
Nuclear pathway (of protein synthesis) [4 marks]
Genomic DNA → RNA → precursor protein → imported protein
Mitochondrial pathway (of protein synthesis) [3 marks]
Organelle DNA → RNA → Protein synthesised in organelle
Where are mitochondrial DNA (mtDNA) present and how do they arise? [2 marks]
- Present in matrix
- Inherited cytoplasmically from the mother
mtDNA structure [3 marks]
- Circular chromosomes
- Has almost 17,000 base pairs
Mitochondrial stop codon [2 marks]
- AGA/AGG
- In the nucleus, this forms arginine
Mitochondria functions [5 marks]
- Breakdown of fatty acids to acetyl CoA (in the matrix)
- Decarboxylation of pyruvate (in matrix)
- Oxidation phosphorylation
- Thermogenesis
- Important in apoptosis
Causes of beriberi disease [2 marks]
- Caused by a deficiency of thiamine (vitamin B1)
- Thiamine pyrophosphate is a prosthetic group for pyruvate dehydrogenase and α-ketoglutarate dehydrogenase
Effects of beriberi [4 marks]
- High serum levels of substrates
- DUE TO LACK OF ATP: damage to peripheral nervous system, limb pain, muscle weakness, distorted skin sensations
- Enlarged heart (for compensation)
- Insufficient cardiac output
Peroxisome structure [4 marks]
- Single membrane
- Crystalloid core (due to high concentration of proteins)
- Rich in concentrated enzymes
- Have no DNA or ribosomes
Where do peroxisome come from? [1 mark]
From precursor vesicles that pinch off from ER
How are proteins made for the peroxisomes made and imported? [3 marks]
- Encoded in the nucleus
- Translated in the cytoplasm
- Imported into the peroxisomes
How do peroxisomes replicate? [1 mark]
Fission
What do enzymes for peroxisomes do? [2 marks]
- Break down purines (AMP, GMP) into uric acid
- oxidise substrates and form H2O2
What are peroxisomes important for? [1 mark]
Important for the synthesis of some lipids
What happens to hydrogen peroxide? [1 mark]
Broken down by catalase to form water and oxygen
