Lecture 14 Cellular respiration parts 1-6

cellular respiration

the catabolism of organic molecules to yield energy that is used to regenerate ATP

C6H12O6+6O2 → 6 CO2 + 6 H2O + Energy (heat and ATP)

aerobic respiration

is the most efficient pathway for generating energy to make ATP

– Consumes organic molecules and O2

– Produces CO2 and H2O

fermentation

a partial degradation of sugars that occurs without O2; performed by facultative anaerobes (can use O2); pyruvate enters fermentation pathway when oxygen is low or absent. allows glycolysis to continue to take place when the rest of aerobic respiration can’t due to lack of O2

what is special about fermentation

allows glycolysis to continue in absence of O2 by regenerating NAD+ by oxidizing NADH from glycolysis back into NAD+ during fermentation

alcohol fermentation

regenerates NAD+ by release of co2 and fermenting of 2 ethanol for 2 pyruvate

lactic acid fermentation

regenerates NAD+ by turning 2 pyruvate into 2 lactate

anaerobic respiration

is similar to aerobic respiration but consumes compounds other than O2; performed by strict anaerobes (O2 is toxic to them), use different electron acceptor molecule at the end of ETC

relative levels of ATP production

aerobes>strict anaerobes»fermentation

why can O2 be toxic or dangerous

O2 can lead to the generation of reactive oxygen species (ROS)

ROS

highly reactive molecules (strong oxidants) that remove electrons from other molecules such as phospholipids, proteins, nucleic acids, and damage important cellular structures. mitochondria are the largest contributor to cellular ROS which can lead to cancer, inflammatory and immune responses and metabolism responses

what allows cells to maintain the proper levels of ROS

by using antioxidants which are cellular enzymes that inactivate the ROS (ex, vitamin c) …strict anaerobes lack these enzymes

cell step oxidation of sugar vs just burning sugar

small activation energies overcome by body temperature and small amounts of released energy can be captured by molecules in the cell; whereas burning sugar all free energy is released as heat and none of it is stored and there is a large activation energy overcome by the heat of the fire

what happens to energy captured during oxidation of glucose

it is transferred to the sites of ATP synthesis by electron carrier molecules and the most common one in cellular respiration is NAD

NAD+

oxidized form (gave up electrons)

NADH

reduced form (gained electrons)

glycolysis

breaks down glucose into two molecules of pyruvate and 2 molecules of water through a series of 10 biochemical reactions, occurs outside the mitochondrion in the cytosol of the cell; releases electrons via 2 NADH and 2 ATP via substrate level phosphorylation all without the need for oxygen

substrate level phosphorylation

Transfer of a phosphate group from an organic molecule

(substrate) to ADP to make ATP

pyruvate oxydation

takes the 2 pyruvate made from glycolysis and converts them into 1 acetyl co a, 1 CO2, and 1 NADH (all per pyruvate ultimately yielding two of each after both pyruvate are oxidized) in the mitochondrion of eukaryotes and occur in the cytosol of prokaryotes

what enzymes are stored in the matrix

enzymes for pyruvate oxidation and citric acid cycle

what enzymes are stored in the inner membrane

enzymes for oxidative phosphorylation (ETC proteins and ATP synthase)

where is mitochondrial DNA stored

in the matrix

how does pyruvate get into the matrix

it goes from the cytosol outside the mitochondrion through a voltage gated anion channel in outer membrane and then through an H+/pyruvate symport protein into the matrix

H+/pyruvate symport protein

brings pyruvate across inner membrane into matrix using the proton (H+) gradient

citric acid cycle

completes the breakdown of glucose by taking the acetylcholine co A by feeding the 2 carbon acetyl group into the citric acid cycle and releases electrons via 3NADH and 1FADH in the mitochondrion as well as 1 atp (made by substrate level phosphorylation) released and 2 CO2

acetyl co a structure

acetyl group with a high energy covalent bond to the co A portion which contains a nucleotide

oxidative phosphorylation

accounts for most of the atp synthesis by taking the released electrons from glycolysis and the citric acid cycle and sends them through the etc and chemiosmosis

where does oxidative phosphorylation occur in prokaryotes and eukaryotes

prokayr: cell membrane with the protons being pumped into the periplasm( outside) and the ATP being pumped in the cytoplasm

eukaryote: in the innermitochondrial membrane pumping protons into the inter membrane space and the atp into the matrix

etc in cellular respiration

consists of 4 multi protein complexes embedded in a membrane that accept and donate electrons in a unidirectional manner (series of redox reactions, where electrons drop in free energy as they are passed from protein to protein

how do electrons drop in free energy as they are passed down the etc

The electrons begin in a high energy state and drop to a low energy state. The ETC proteins alternate between reduced and oxidized states as they accept and donate electrons. In complex IV, there is a binding site (active site) for O2. O2 is the final electron acceptor, removing electrons from the ETC

how is H2O gained in cellular respiration

O2 is converted into H2O (O2 +4e- + 4H+→2H2O)

how do ETC proteins accept and donate electrons

They have iron in their

structures that can easily accept

and donate electrons

what path do electrons follow in the ETC

NADH donates its 2 electrons to Complex I

• FADH2 donates its 2 electrons to Complex II

• Both Complex I and II donate their

electrons to Complex III

• Complex III donates its electrons to

Complex IV

• In Complex IV, O2 receives electrons and

reacts with H+, producing H2O molecules.

• O2 is the final electron acceptor of the ETC

electron flow in etc

is exergonic and provides the energy needed for the ETC complexes to pump H+ across the membrane & against their concentration gradient (endergonic)

complexes that pump H+

1 3 and 4

which complex takes electrons from NADP

1 which then turns it into NAD+

which complex takes electrons from FADH2

II and turns it into FAD

where does Q come in

in between I and III to take electrons from I and II to III

where does cytochrome c happen

between complex III and IV as it carries electrons to IV

where does O2 accept electrons and become water

complex 4

chemiosmosis

the energy stored int he H+ gradient is used to drive atp synthesis

what reduces the amount of ATP made by cells doing aerobic respiration

Reduced O2 concentrations in cells

– e.g., restricted blood flow limits O2 delivery to the cells

• When ETC or ATP synthase proteins (enzymes) are inhibited by an inhibitor

– e.g., cyanide, rotenone (insecticide), antimycin A and oligomycin (both are antibiotics

how many ATP is made by oxidative phosphorylation from one glucose molecule

26-28 ATP

maximum atp made per glucose in cellular respiration

30-32

2 types of electron shuttles that span the membrane

one gives electrons to NAD+ in matrix to make NADH

• another gives electrons to FAD in matrix to make FADH2

what can reduce the amount of ATP made per glucose

When products made in glycolysis, pyruvate oxidation and the citric acid cycle are siphoned off for making other biomolecules. When the ETC is “uncoupled” from chemiosmosis (ATP synthesis)

uncoupling agents

chemicals that allow H+ to cross the membrane passively without going through atp synthase (ex 2,4dinitrophenol) they reduce the H+ gradient

uncoupling protiens

some specialized mitochondria have this in their inner membrane that allow H+ to diffuse across the membrane this cane important in thermoregulation

fatty acid oxidation spiral

each cycle shortens a fatty acid by 2 carbon tails. Each cycle (or spiral) generates:

1 acetyl CoA

1 NADH

1 FADH2