Mitochondria & peroxisomes Flashcards
What is the primary function of mitochondria
primary function: energy production (ATP)
also in apoptosis
Describe how mitochondria produce energy
- Glycolysis → breakdown of glucose to pyruvate in cytoplasm
- Pyruvate enters the mitochondria - Co2 removed from pyruvate.
- Rest of molecule enters Krebs cycle - 1 function to produce H+ gradient across inner mito membrane → drives ATPase
Describe the outer membrane of a mitochondria and its function
encloses organelle:
Perforated with large channels (Porins)
Allow entry of molecules < 5000 kDa
Contains enzymes involved in mitochondrial lipid synthesis
Describe the inner membrane of a mitochondria and its function
Highly folded (cristae) → high SA
Contains enzymes responsible for energy production
Contains REDOX performing proteins of the ETC
Contains proteins for ATP synthesis
Transport proteins to move molecules in and out of the matrix
Describe the intermembrane space of a mitochondria and its function
Contains enzymes that use ATP to phosphorylate other nucleotides
H+ pumped into this space (to create proton gradient to drive Oxidative phosphorylation)
Describe the matrix of a mitochondria and its function
Internal space containing enzymes of the Krebs cycle
Contains:
Mitochondrial DNA
Ribosomes
tRNAs
Enzymes (Krebs, b-oxidation)
Metabolites (e.g Kreb urea cycle, Ca++, K+, Mg++)
Describe mitochonrial genes
Mitochondria contain their own genetic material
Circular chromosomes (double stranded)
Approx 15-17kbps (average bacterial plasmid is 80kb)
Encodes 37 genes
Mitochondrial DNA is inherited from the mother
Describe how proteins enter the mitochondrial matrix
- Protein precursor with a signal sequence on it
- Not cotranslated = not with ribosome
- Binds to receptor protein in TOM complex
- Binding triggers conformational changes
- Peptide chain is inserted into TOM complex → fed through to TIM23
- Fed into mitochondrial matrix
- Signal peptide is cleaved off
- Trapped as a mature protein in the matrix space
Describe why mitochondrial precursor proteins are imported as unfolded polypeptides
→ Proteins are fully synthesised before translocating into the mitochondria (have tertiary struc)
In order to go through the complexes, the proteins need to be unfolded:
Need to stop precursor protein from folding in the cytosol
You bind interacting proteins to the newly synthesised chain e.g chaperones
Why does getting proteins into the mitochondrial matrix require energy?
- Directional process
- Chaperones need ATP to dissociate from the polypeptide chain
What are the major proteins of the outer mitochondrial membrane (OMM)
Porins
- Beta-barrel proteins
How are proteins inserted into the outer mitochondrial membrane?
- Enters in intermembrane space, kept unfolded by chaperones
- Docks with SAM complex, can then insert into the outer membrane
= Fully folded protein
Describe the most common route of getting proteins into the inner mitochondrial membrane and space
Inner membrane → TOM and TIM23
Describe the less common route of getting proteins into the inner mitochondrial membrane and space
Protein completely enters matrix space (via TOM and TIM23)
Signal sequence cleavage unmasks 2nd signal = causes insertion into OXA complex
OXA = same complex that inserts mitochondrially translated proteins
Protein ends up in intermembrane space
If you want a soluble protein in the intermembrane space you just _____ after membrane insertion
cleave
