Unit 3: Lecture 14

Define cellular respiration.

Define cellular respiration.

The process in which fuel (like glucose) are converted into usable energy (ATP)

Where does the citric acid cycle (Krebs cycle) take place?

The mitochondrial matrix

What type of cells is the mitochondria present in?

Only eukaryotic cells

Label the mitochondria.

A. Mitochondrion

B. Intermembrane space

C. Outer membrane

D. Inner membrane

E. Cristae

F. Matrix

G. Mitochondrial DNA

H. Free ribosomes in the mitochondrial matrix

What are the two membranes of the mitochondria?

Inner membrane (from the OG prokaryotic cell); outer membrane (from the larger cell that engulfed it)

What is the matrix?

The space inside of the inner membrane

What is the intermembrane space?

The space between the two membranes (inter= between)

What is the third stage of cellular respiration?

The Citric Acid Cycle; AKA Krebs Cycle

What is the starting carbon molecule that enters the citric acid cycle?

Acetyl-CoA (came from previous stage; a two carbon molecule)

What happens in the first step of the citric acid cycle?

1. Acetyl-CoA (2 carbons) combines with oxaloacetate C4 (a 4 carbon molecule)

2. CoA group is released

3. Forms Citrate C6 (a 6 carbon molecule), the very first intermediate of the cycle

What are intermediates?

Molecules that stay within the cycle

How many steps does the citric acid cycle have?

Eight steps; each catalyzed by a specific enzyme

What happens in the second and third step of the citric acid cycle?

1. Citrate C6 turns into C5 (a 5 carbon molecule)

2. 6th carbon is released as CO2 (occurs because a substrate was oxidized)

3. NAD+ is reduced to NADH and released (the H comes from the OG glucose molecule)

What happens in the fourth step of the citric acid cycle?

1. NAD+ reduced to NADH and released

2. C5 turns into C4

3. 5th carbon is released as CO2 (b/c a substrate was oxidized)

What happens in the fifth step of the citric acid cycle?

ADP becomes GTP/ATP

How does ADP become ATP in the fifth step of the citric acid cycle?

A high-energy phosphate is removed from a substrate and transfers to ADP

What happens in the sixth step of the citric acid cycle?

1. A substrate is oxidized

2. FAD is reduced to FADH2 (H comes from OG glucose molecule and will be carried to the final stage of cellular respiration)

What happens in the last step of the citric acid cycle? (Prof. doesn't mention the 7th step)

1. A substrate is oxidized

2. NAD+ is reduced to NADH

What are reduced electron carriers also known as?

A source of potential energy

What has happened to all of the carbons from the OG glucose molecule by the end of the citric acid cycle?

Expelled as CO2

How many ATP has been made from one glucose molecule?

1. Glycolysis: 2 Net ATP (2 ATP used [energy investment phase] and 4 ATP made)

2. Kreb's Cycle: 2 ATP

Why is 2 ATP made from the citric acid cycle when the steps say only 1 ATP was made?

OG glucose was split releasing 2 Acetyl CoAs; Krebs cycle happens twice (doubling the output)

What are the inputs and outputs of the citric acid cycle per glucose?

Inputs: 2 Acetyl CoA, 6 NAD+, 2 FAD (oxidized)

Outputs: 4 CO2, 6 NADH, 2 FADH2 (reduced), 2 ATP

What is the fourth stage of cellular respiration?

Electron transport chain

What does the fourth stage result in?

ETC- results in proton gradient with much potential energy. Does not generate ATP

What is the electron transport chain made of?

A series of membrane proteins in the mitochondrial membrane; some proteins are transmembrane proteins and some are integral proteins (partially embedded in membrane)

Where is the electron transport chain located?

Inner mitochondrial membrane

What occurs in the electron transport chain?

Electron carriers alternate between reduced and oxidized states, accepting and donating electrons

What is the electron transport chain's primary role in cellular respiration?

To create a proton gradient

How is a proton gradient created?

The electrons carried by the electron carriers open up the transmembrane proteins, allowing it to pump protons from the matrix out to the intermembrane space

How do the electrons of the electron carrier travel through the ETC?

1. Reduced electron carriers travel through the ETC where its hydrogen is stripped off

2. The electron (after H+ is off) will cause the first transmembrane protein of the chain to open b/c of its potential energy

3. The electron moves to the next member of the chain (not a transmembrane protein) which carries it to the next transmembrane protein

4. Steps 2 & 3 repeated twice

What are the four stages of electron transfer in cellular respiration?

1. Electrons from the H atoms of the glucose molecule

2. H added to the electron carrier (e.g. NADH=reduced form)

3. H delivered to ETC where H atoms are split into H+ and e--> e- stays in the chain and activates it-> chain creates proton gradient

4. ETC+ chemiosmosis=Oxidative phosphorylation

What is chemiosmosis?

Energy-coupling mechanism of exergonic and endergonic rxns; in the ATP synthase protons fall down their concentration gradient (exergonic); in the synthase the bottom part turns in the opposite direction of the rotor by using the energy from the concentration gradient to suck in reactants (ADP and Pi)-> creation of ATP w/ a bond (endergonic)

What is ATP synthase?

A transmembrane protein (embedded in inner membrane) that is an enzyme that synthesizes ATP; protons fall down onto the rotor (top part that turns); bottom part of the ATP synthase turns in the opposite direction

What is the final byproduct of cellular respiration?

H2O; H+ (from conc. gradient) and e- (from chain) end up in the matrix to recombine, forming the H atom; H atom combines with oxygen to create water

What would happen if oxygen was not present to be the final electron acceptor?

H+ and e- would build up in the matrix destroying the proton gradient

Why do we breathe?

To get oxygen

Which stages of cellular respiration use substrate-level phosphorylation?

Glycolysis (2 ATP) and Citric acid cycle (2 ATP)

Oxidative phosphorylation accounts for almost ___% of the ATP generated by cellular respiration.

90

What powers oxidative phosphorylation?

Redox reactions (transfer of electrons)

How much ATP does oxidative phosphorylation create?

26-28 ATP

How much ATP is produced per glucose molecule?

30-32 ATP

What is the input and output for Oxidative Phosphorylation?

Input: 10 NADH (reduced carriers), 2 FADH2, Oxygen (O2)

Output: 10 NAD+, 2 FAD, H2O, 26-28 ATP

How are the electron carriers from glycolysis shuttled over to the mitochondria?

Electron shuttles (cytoplasm-> mitochondria)

How is cellular respiration controlled?

Feedback inhibition: most common mechanism for control of ATP production; when ATP or Citrate is high it will inhibit PFK to shut down glycolysis; AMP build up= no more ATP-> stimulates PFK

What is PFK?

Phosphofructokinase; one of the first enzymes used in glycolysis; allosteric regulation w/ receptor sites for inhibitors and activators

What are the three different types of cellular respiration?

1. Aerobic cellular respiration (use 4 stages, final e- acceptor: oxygen)

2. Anaerobic cellular respiration (use 4 stages, final e- acceptor: anything other than oxygen)

3. Fermentation

What is the oldest metabolic pathway on Earth?

Glycolysis:

-evolved early in living organisms before oxygen was present

-used by all types of cellular respiration and almost all organisms

-universal energy-harvesting process of life

-its location within the cell also implies antiquity

What is the only stage of cellular respiration that is not dependent on oxygen?

Glycolysis

What cellular respiration is common among prokaryotes?

Anaerobic cellular respiration

What are the limitations of anaerobic cellular respiration?

Less efficient (only makes around half of the ATP aerobic cellular respiration does)

What happens to aerobic cellular respiration if no oxygen is available?

Cell uses fermentation (occurs in cytoplasm): a series of rxns convert NADH (from glycolysis) back into NAD+ allowing glycolysis to keep producing a small amount of ATP; fermentation does not generate ATP

What organism/ molecule builds up in the mitochondrion?

Pyruvate and NADH (products build up-> shuts down glycolysis)

What is a key juncture in catabolism of glucose?

Pyruvate

What are the two major types of fermentation?

1. Alcohol fermentation (Input: 2 pyruvate, 2 NADH-> Output: 2 ethanol, 2 NAD+)

2. Lactic acid fermentation (Input: 2 pyruvate, 2 NADH-> Output: 2 Lactate, 2 NAD+)

What organisms perform alcoholic fermentation?

Yeast and some bacteria/fungi

What organisms perform lactic acid fermentation?

Bacteria and humans (when muscles are strained and cannot bring in enough oxygen, fermentation is used to survive this circumstance)

What is lactobacillus?

A species of bacteria that performs lactic acid fermentation; gives yogurt a sour taste

Describe the pathway that carries lactate.

Too much lactate is harmful; lactate is carried by the blood to the liver, where it is converted back to pyruvate and oxidized in the mitochondria of liver cells

What are the pros of fermentation?

-allows the organism to survive circumstances when low in oxygen

-quick process

What are the cons of fermentation?

-Ineffeciency (not a lot of ATP produced)

-Creates toxic byproducts (waste products are more difficult to remove than waste from aerobic cellular respiration)

-Not good enough for the brain

Why is fermentation not good enough for the brain?

Does not provide enough ATP for the brain role's: regulating heart rate, keeping your heart beating, keeping the blood flowing thru your vasculature, making you breathe in oxygen and exhale CO2 rapidly enough

What is catabolic interconversion?

Metabolic routes for carbs, fats, and proteins as fuel for cell respiration

Define lipolysis.

Breakdown of lipids into its building blocks

Triglycerides broken down to ___________ and _____________

Glycerol; 3 fatty acids

What happens to triglycerides after lipolysis?

They are further broken down and used in glycolysis; they enter the citric acid cycle as Acetyl-CoA

Where does fatty acid catabolism take place in the cell?

Peroxisome

Fatty acids are ______________.

Highly reduced (making it the best source of fuel; one fatty acid has more potential energy than any other single molecule consumed and it can yield more ATP than four glucose molecules)

What is beta-oxidation?

Breakdown of fatty acids (break a fatty acid two carbons at a time); Each step creates: 1 NADH, 1 FADH2, 1 Acetyl-CoA

How many acetic acids can be made from a 20 carbon long fatty acid?

10 acetic acids

How much ATP does 1 Acetyl-CoA result in?

15 ATP (Fatty acids-> Acetyl CoA-> Citric acid cycle (turn once)-> Oxidative phosphorylation; b/c glucose tends to make 30 ATP and since acetyl CoA turns once it will make half the amount-> 15 ATP)

How much ATP would a 18 carbon fatty acid result in?

135 ATPs (9 acetyl CoA * 15 ATP)

What is the first step of amino acid metabolism?

Deamination- remove the amino group which create ammonium (highly toxic)

What is the urea cycle?

A cycle that takes place in the liver and kidneys to help get rid of ammonium; requires energy; urea is fairly harmless and water soluble

What happens to the central carbon and the carboxyl group of a deaminated amino acid?

It creates two carbon Acetyl CoA, which can enter the Krebs cycle

What is most likely to be used by the cell (for cellular respiration)?

1. Glucose

2. Fatty Acids (Oxygen must be present)

3. Amino acids (only in cases of starvation/ extreme stress-> not efficient and creates toxic byproduct)