Lecture 22 - Cell Energetics & Mitochondria (22) Flashcards
what do organisms use E for?
build complex molecules
maintain their structure
move
what are the 2 sources of E available to organisms?
electromagnetic - light E
chemical - E of molecules & eletrons
glycolysis chemical formula
glucose –> 2 pyruvate + 2 ATP + 2 NADH
why does glycolysis not require?
oxygen
where does glycolysis occur?
cytoplasm
where does the citric acid cycle occur?
mitochondria
chemical formula of the citric acid cycle & TCA
Pyruvate –> acetyl CoA (+NADH) –> 3 NADH + FADH2 + CO2 + GTP `
what does the ETC use to generate ATP?
NADH & FADH2
what is the net gain of ATP from TCA + ETC?
36 ATP
what is the main function of mitochondria?
production of ATP
structure of mitochondria
Outer membrane: impermeable, contains porins forming non-selective membrane channels, porins don’t require a mitochondria localization signal
Intermembrane space
Inner membrane:
ETC
ATP synthase
Contain cristae which are highly folded to increase the SA for ATP machinery
Matrix:
TCA
DNA
Ribosomes
what does the mitochondria vary in?
shape: filamentous to spherical
number: oocytes have more than spermatozoa
number & shape of cristae
how many mitochondria do oocytes have?
300,000
why do oocytes have more mitochondria than spermatozoa?
undergoes division without gaining size, require the production of many daughter cells prior to growing
undergo many cell divisions
what cell type has the greatest amount of mitochondria?
egg
where do mitochondria cluster in sperm cells?
around the base of the flagellum
where do mitochondria cluster in renal tubular cells?
b/w basolateral membrane invaginations at the periphery which contain ATPase pumps for establishing gradients
how are mitochondria similar to bacteria?
Double membrane
Membrane composition (ex: cardiolipin –> a gene sequence only found in the mitochondria membrane)
Divide by fission, independent of the host
Circular DNA encoding unique rRNAs & tRNAs
13 PROs in the ETC are similar to bacteria PROs
Endosymbiotic theory
mitochondria in eukaryotes evolved from aerobic bacteria living within their cells
symbiotic relationship
where does ETC occur?
inner membrane of the mitochondrial
steps of ATP production
TCA cycle: NAD+ & FADH –> NADH & FADH2
Electrons are fed into enzyme complexes & end up on an oxygen molecule
H+ move to the intermembrane space creating the H+ electrical/concentration gradient
Electrons are transferred to an oxygen which also picks up 2H+ –> H2O
No consumption of ATP, conformational changes are caused
Electron will be received by H –> H-
H+ ions are returned to the mitochondrial matrix by ATP synthase for ATP production
movement of H+ in ETC
from the matrix to the intermembrane space
what is the terminal electron acceptor in the ETC?
oxygen
how much E in the ETC is stored due to the concentration diff of H+?
20%
How much of E stored is electrogenic in the ETC? & why is this?
80%
the membrane isn’t permeable to the counter-ions –> protects cytoplasm from being too acidic
if too many H+s are pumped out, what can happen?
they can leak through the proins & cause the cytoplasm to become acidic
that is why it is important for ATP synthase to bring them back
structure of ATP synthase?
F1 headpiece projects into matrix, responsible for ADP phosphorylation
F0 base piece is embedded in the lipid bilayer, contains the H+ ion channel
what does the movement through the H+ channel induce?
conformational changes & drives ATP formation
each NADH produces how many ATP molecules?
3
each FADH2 produces how many ATP molecules?
2
how does the movement of H+ produce ATP?
H+ flow through the channel causes a rotation of the F0 rotator
this spin causes a conformational change in the F1 headpiece
Change of shape enables the phosphorylation of ADP
kinetic E (of the F0 rotator) is used to create chemical E
how is ATP synthase being utilized in nanotechnology?
Production of a microscopic motorized propeller: F0 + actin filament
Feed an ATP solution through the propeller & rotation occurred
This could lead to the production of nano-bots, which would be sent throughout the body carrying out various functions
Ex: delivery of medication
how do PROs enter mitochondria?
through a signal system which includes carrier PROs & a mitochondrial receptor
PROs require a presequence (target sequence), directs PRO to mitochondria
cytosolic chaperone PROs on the outer membrane recruit & unfold the PRO enabling it to enter through the pore
once the PRO enters the mitochondria matrix, the sequence is cut off & the PROs refold
(pass through the outer membrane & inner membrane)
where are most mitochondrial PROs encoded?
nuclear genome (except 13)
proton leak or mitochondrial uncoupling & what is the result?
protons re-enter the mitochondrial matrix without contributing to ATP synthesis, this is accomplished by facilitated diffusion through a proton channel called thermogenin
potential E of the H+ gradient is released as heat
where is thermogenin located?
brown adipose tissue (in newborns)
non-shivering thermogenesis
primary means of heat generation in newborns & hibernating mammals
production of heat, but no ATP
ATP synthase is blocked
what causes mitochondrial DNA damage
oxygen molecules become superoxide ions if they aren’t coupled with H quickly in the ETC
Why do mitochondria have multiple c’some copies?
Divide by fission, require DNA copies to share with daughter cells
Highly metabolic organelle requires a high amount of PRO production
Enables removal of damaged DNA copies, damage occurs frequently since it is an oxidative organelle
how do mitochondria contribute to aging? & what is the evidence?
Gradual accumulation of mutations in mitochondrial DNA may be the cause of aging
Old people have more mutated mtDNA than young
Mutator strain of mice have 3-8x more mtDNA mutations than normal mice age prematurely & die at half the normal age
peroxisomes
membrane-bound vesicles with a core of oxidative enzymes
what are 3 similarities b/w mitochondria & peroxisomes?
oxidative metabolism
import PROs
Formed from pre-existing organelles
what are peroxisomes involved in metabolizing?
FAs
what are the enzymes in peroxisomes?
urate oxidase & AA oxidase
what is the by-product of peroxisomes?
hydrogen peroxide (toxic) causes damage to membranes & PROs
how many oxidative enzymes do peroxisomes have?
over 50
catalase location
peroxisomes & mitochondria
catalase
removes highly reactive peroxide & other oxygen free-radicals
what evidence is there that suggests that catalase prevents aging?
Fruit flies with extra copies of catalase genes live longer than normal flies
Nematodes that are induced by drugs to increase catalase activity lived longer than control nematodes
