lec 22 energy production in the cell and mitochondria

Question 1

what are two sources of energy available to organisms:

Answer 1

electromagnetic-light energy

chemical-energy stored in molecules, usually held in electron orbitals

Question 2

the electron orbital energy is stored in the

Answer 2

molecular bonds

Question 3

different bonds store

Answer 3

different amounts of energy

Question 4

breaking and formation of bonds results in…

Answer 4

energy transfers

Question 5

in ATP, energy is stored in the _______ of the molecules and released when the molecules is ________ to form ______ and ______.

Answer 5

structure
cleaved
ADP
Phosphate

Question 6

metabolism

Answer 6

• sum total of all chemical changes that occur in cells
• each reaction is catalyzed by a specific enzyme
• compounds formed in each step along the pathway are metabolites
• pathway leads to an endproduct

Question 7

two broad types of metabolic pathways

Answer 7

catabolic pathways

anabolic pathways

Question 8

catabolic pathways

Answer 8

breaking of chemical bonds in large, complex molecules to form small simple molecules; exergonic (energy releasing)

Question 9

anabolic pathways

Answer 9

synthesis of large molecules by chemically bonding together small molecules; endergonic (energy using)

Question 10

glycolysis

Answer 10

a universal catabolic pathway
breakdown of glucose
ten step reaction sequence (glucose to pyruvate)
occurs in presence of absence of O2
occurs in cytosol
Net yield 2ATP + 2NADH

Question 11

mitochondria is visible by

Answer 11

light microscopy
1500 per liver cell
15-20% of the cell volume
production of ATP

Question 12

mitochondria vary greatly in their ______ and _______

Answer 12

morphology and distribution 
Vary in:
*shape-filamentous to spherical
*size- 0.5 to 7.0 um
*vary in number from a few in spermatozoa to 300,000 in oocytes
*number and shape of their cristae

Question 13

mitochondria are often clustered in certain regions of cells, concentrated where they are needed for ATP production

Answer 13

• in sperm, they are concentrated around the base of the flagellum
• in renal tubular cells, mitochondria are located b/w baso-lateral membrane invaginations, which contain ATPase pumps for establishing concentration gradients

Question 14

mitochondria structure

Answer 14

outer membrane
inner membrane (folded into cristae)
inter -membrane space
matrix

Question 15

mitochondrion outer membrane

Answer 15

-porins- integral proteins that form large, non selective membrane channels

Question 16

inner membrane of mitochondrion

Answer 16

• electron transport chain
• ATP synthase
• folded to provide greater surface area for this machinery

Question 17

matrix of mitochondrion

Answer 17

• TCA cycle
• DNA (genes for 13 polypeptides)
• ribosomes

Question 18

inter-membrane space of mitochondrion

Answer 18

does not contain anything

Question 19

how is mitochondrion similar to bacteria

Answer 19

• some bacteria, like mitochondria have a double membrane
• membrane composition of mitochondria more closely resembles that of bacteria (eg. cardiolipin)
• both divide by fission (independent of host cells divisions)
• both have a circular DNA -encoding some unique rRNAs and tRNAs
• 13 proteins, involved in electron transport chain, most similar to those of bacteria
• the endosymbiosis theory postulate that mitochondria in eukaryotes evolved from aerobic bacteria living within their cells

Question 20

how does the cell use the energy stored in NADH and FAHD2?

Answer 20

Chemiosmotic hypothesis

Question 21

chemiosmotic hypothesis

Answer 21

• peter mitchell proposed this
• the energy of NADH and FADH2 used to create a proton gradient across the mitochondrial membrane
• this energy is used by a reversible proton pump, the ATP synthase to create ATP
• electrons are removed from NADH and FADH2 and passed through an electron transport chain
• the energy is bled off in a series of small steps, which oxidation of one compound is linked to the reduction of another
• as the electrons move through the electron transport chain, this energy is used to pump H+s out of the compartment, forming H+ gradient across membrane
• in a separate reaction, H+s move down their concentration gradient, through an ATP synthase complex

Question 22

overview of mitochondrial function: generation of ATP

Answer 22

a) electrons are transferred to NADH and FADH2 in the TCA cycle
b) a two step process converts NADH and FADH2 into ATP

Question 23

two step process that converts NADH and FADH2 into ATP

Answer 23

step 1: electron transport : electrons are fed into enzyme complexes in the inner mitochondrial membrane (IMM) and end up on an oxygen molecule
-passed through a series of steps in the membrane, causing the transfer of H+ into the inter membrane space, results in electrical/concentration gradient like H+ion gradient
-electrons finally transferred to Oxygen, which also picks up 2 H+ producing water
Step 2: the hydrogen ion gradient is used for ATP production by ATP synthase
NADH transfer H+ ions and electrons into the electron transport system

Question 24

electron carries of respiratory chain:

NADH transfer H+ ions and electrons into the electron transport system

Answer 24

• protons are translocated across the membrane, from the matrix to the inter-membrane space
• electrons are transported along the membrane, through a series of protein carriers
• oxygen is the terminal electron acceptor, combining with the electrons and H+ ions to produce water
• as NADH delivers more H+ and electrons into the ETS, the proton gradient increases, with H+ building up outside the inner mitochondrial membrane, and OH- inside the membrane

Question 25

summary

Answer 25

a. reactions in the mitochondrial matrix produce NADH and FADH2 from pyruvate
b. NADH and FADH2 provide high energy electrons to the electron transport chain, these produce a H+ ion gradient across the inner mitochondrial membrane (lower conc. on matrix side, higher in inter-membrane space)
c. Next, the H+ ion gradient is used to make ATP

Question 26

Hydrogen ion gradient is used to make ATP

Answer 26

• an electrochemical hydrogen ion gradient across the inner mitochondrial membrane
• 20% stored energy is due to concentration difference of H+
• low H+ in matrix, high H+ in inter membrane space
• the membrane is impermeable to hydrogen ions
• 80% of store energy is electrogenic, a voltage generated gradient
• bc the membrane is not permeable to the counter-ions
• protects cytoplasm- pH difference limited to one pH unit

Question 27

ATP formation 4 steps

Answer 27

1. Chemiosmotic mechanism
   - energy stored in proton gradient drives phosphorylation of ADP
2. catalyzed by ATP synthase
3. ATP synthase
   a) F1 headpiece projects into matrix
   b) F0 basepiece embedded in lipid bilayer-contains H+ channel
4. controlled movement of H+ through channel induces:
   a) conformation changes
   b) these drive ATP formation

Question 28

overall products of electron transport chain

Answer 28

ATP: each NADH=3 ATP; each FADH2= 2 ATP
H20: formed by O2 finally accepting electrons

Question 29

nantotechnology

Answer 29

using nanometer sized biological molecules as machines

• ATPase molecules has been engineered to be a microscopic motorized propeller
• proof of concept stage only, but where could it lead?
• using nano sized machines to deliver drugs
• using nano sized machines to manufacture miniaturized components of larger instruments

Question 30

making the molecular rotary motor:

Answer 30

1. the ATP synthase in its natural environment
2. F1 subunit of ATP synthase linked to an actin filament (by recombinant DNA techniques)
3. Add ATP and the motor turns the propeller

Question 31

targeting of proteins to the mitochondria

Answer 31

• uses a signal system (like the nuclear entry) recognized by diff carrier proteins and a mitochondrial receptor
• the signal includes a series of positively charged amino acids in an alpha helix on the N-end of a new protein; termed the pre-sequence
• cytosolic chaperon proteins unfold the protein to let it enter the mitochondrial pore
• mitochondrial proteins refold the protein once inside; pre-sequence is cut off
• most mitochondrial proteins (13 exceptions) are encoded in the nuclear genome
• exceptions are made by the mitochondrial ribosomes in the matrix

Question 32

mitochondria and heat production

Answer 32

• under certain conditions, protons can re-enter the mitochondrial matrix without contributing to ATP synthesis
• this process is known as proton leak or mitochondrial uncoupling and is due to the facilitated diffusion of protons into the matrix, mediated by a proton channel called thermogenin
• this results in the unharnessed potential energy of the proton electrochemical gradient being released as heat
• thermogenin is found in brown adipose tissue (brown in colour due to high levels of mitochondria)
• it is used to generate heat by non shivering thermogenesis.

Question 33

non thermogenesis

Answer 33

primary means of heat generation in newborn of hibernating mammals

Question 34

mitochondria fissions and fusions

Answer 34

• mitochondria are not static organelles- they change shape often
• before cell division, mitochondria divide by fission, similar to bacteria
• young, non-dividing cells may have long, filamentous mitochondria
• a recent study showed the removal dynamin-related protein 1 gene, which encodes a protein needed for mitochondrial fission, greatly extended the life of yeast cells
• we have the same gene-could we extend human life by silencing this gene?

Question 35

mitochondria and cellular aging

Answer 35

mitochondria have multiple chromosomes

• perhaps extra copies of genes allows for removal of damaged DNA and being an oxidative organelle, oxidative damage could result in frequent mutations
• the gradual accumulation of mutations in mtDNA may be a cause of again
• evidence for this hypothesis:
• cells from old people have more mtDNA mutations than young
• a mutator strain of mice endure 3-8x more mtDNA mutations than normal mice and mutator mice age prematurely and die at half the normal age

Question 36

peroxisomes

Answer 36

-membrane bound vesicles, characterized by dense, crystalline core of oxidative enzymes

Question 37

peroxisomes and mitochondria shared features

Answer 37

• both involved in oxidative metabolism
• both import proteins into organelle
• both form by dividing from pre-existing organelles

Question 38

peroxisomes have over 50 oxidative enzymes

Answer 38

-metabolizing fatty acids- ex.in germinating seeds
-urate oxidase and amino acid oxidases
-these enzymes tend to produce hydrogen peroxide as a toxic by-product
-hydrogen peroxide and other powerful oxidants damage membranes and proteins
substrate- H2+O2 -> oxidized substrate + H2O2

Question 39

peroxisomes contain high concentrations of

Answer 39

catalase, which removes the highly reactive peroxide and other oxygen free-radicals (charged molecules of oxygen)
2H2O2 -> O2 + 2H2O

Question 40

fruit-flies and nematodes w/ extra catalase

Answer 40

• fruit flies with extra copies of the catalase gene live longer than normal flies
• nematodes that are induced by drugs to increase catalase activity lived longer than control nematodes - suggests a role for catalase and other anti oxidizing enzymes for prolonged cell functions

Question 41

what do organisms use energy for?

Answer 41

• build complex biological molecules
• maintain their structure
• move