4.6 - Mitochondria and respiration Flashcards
role of mitochondria (2)
- oxidative phosphorylation
- heme biosynthesis
endosymbiotic mitochondria origin theory (2)
- ancestral eukaryote engulfed bacteria that utilises oxidative phosphorylation
- symbiotic relationship provided energy required for eukaryotic and multicellular evolution
oxygen (2)
- critical for aerobic life
- dangerous - free radicals damage proteins/nucleic acids (mitochondria 2x membrane keeps reactions seperate)
mitochondria role in apoptosis
responsible for apoptosis, contents of mitochondria released into cytoplasm (very reactive and contains enzymes)
step by step mitochondria origin theory
gradually over process of evolution more and more complicated structures within cell started to form organelles
how is mitochondrial DNA inherited
only through maternal line (mitochondria in sperm do not enter the egg/destroyed if they do)
role of mitochondrial DNA
codes for its own traits
syndrome associated with mitochondrial DNA
kearns-sayre syndrome:
rare human disorder caused by decreased ability of cells to get energy from food
similarities between mitochondria and bacteria (2)
- use oxygen to break down food (aerobic bacteria) - same biochemical process
- contain membrane proteins that are of bacterial origin (porins)
porins
membrane proteins imbedded in outer mitochondrial membrane, involved in regulation of membrane permeability
what do all mitochondrial genomes have
approximately the same 2% of bacterial genes
what bacteria are chloroplasts most closely related to?
cyanobacteria
mitochondrion division
mitochondrial fission (similar to binary fission)
bacteria and mitochondria chromosomal similarity
both have their own circular chromosome with potential for multiple copies in one mitochondria
evidence against step by step mitochondrial origin theory
no known species with transitional mitochondria/chloroplasts
how can mitochondrial DNA be used in mapping migration of humans? (2)
- mitochondria contain 37 genes only ever inherited down maternal line
- fast mutation rate (10x faster than nuclear DNA)
- helped provide evidence for “out of Africa” model of human evolution
protein import into mitochondria
anything under 5kDa (small) can enter mitochondria via porin channels
protein import into mitochondria (2)
- nuclear encoded proteins must be unfolded to cross mitochondria double membrane
- signal sequence on precursor protein recognised by sequence of receptors and transporters on both membranes (later cleaved off in matrix)
- only a fraction of mitochondrial proteins made using mtDNA
chaperone proteins
number of proteins that help with protein import into mitochondria (require some energy)
where are mitochondria located? (2)
near sites of high ATP utilisation such as:
1. sperm tail
2. close to contractile apparatus in cardiac muscle
why are mitochondria located near sites of high ATP utilisation?
enables supply of ATP by oxidative phosphorylation to energy hungry tissues
stages of respiration (3)
- glycolysis
- citric acid cycle
- electron transport chain
glycolysis
occurs in cytosol (liquid component of cytoplasm): breakdown of glucose into pyruvate
citric acid cycle
occurs in mitochondrial matrix: pyruvate further broken down producing electron carriers NADH, FADH2
electron transport chain
occurs in inner mitochondrial membrane: uses electron carriers to produce ATP through oxidative phosphorylation
how are electron transport mechanisms used in mitochondria and chloroplast (2)
- mitochondria - proton gradient used to generate ATP from oxidative phosphorylation
- chloroplast - energy from sunlight used to make ATP (via proton gradient)
what % potential energy of glucose does oxidative phosphorylation allow to be converted into useful chemical energy (ATP)
50%
oxidative phosphorylation
energy released by oxidation of NADH to NAD+ harnessed through energy conversion processes to drive the phosphorylation of ADP -> ATP
(smaller amount of ATP similarly generated from oxidation of FADH2 -> FAD)
link reaction
pyruvate enters mitochondria and is converted to acetylCoA
why do mitochondria have 4 separate compartments?
- each compartment contains a unique set of proteins:
1. enabling it to fulfil its distinct function
2. keeping reactions separate
3. allowing generation of chemical gradients across membranes
generation of ATP in mitochondria by chemiosmosis
protons ejected into inter-membrane space by electron transport chain establish proton gradient used to synthesise ATP via ATP synthase (imbedded in inner mitochondrial membrane)
cristae
numerous infolds in inner membrane maximising surface area
chemiosmosis
membrane bound mechanism of utilising both concentration gradient and electromotive force of pumping protons outside membrane to generate ATP
proton gradient driven transport? (2)
- pyruvate and Pi moved into matrix along with protons as the protons move down their electrochemical gradient
- ADP pumped into matrix and ATP pumped out by antiport process - uses voltage gradient across membrane to drive the exchange
- outer mitochondrial membrane freely permeable to components due to porins
(proton flow across membrane also drives bacterial flagella rotation)
ATP synthase (2)
- acts like motor to convert energy of protons flowing down electrochemical gradient to chemical bound energy (ATP)
- also capable of reverse reaction (hydrolysing ATP to ADP to pump protons against concentration gradient)
evolution of ATP synthesis (3)
- evolution of ATPase that pumped protons out of cell using energy of ATP hydrolysis (to reduce acidity)
- evolution of a different proton pump (driven by electron transport chain)
- linked 2 systems together to generate primitive ATP synthase (used protons pumped by electron transport chain to synthesise ATP)
- early bacterium with final system had selective advantage
deep sea archaea chemiosmosis
methanococcus:
use the H2 gas bubbles from deep sea vents as source of reducing power to generate energy via chemiosmotic coupling
