Anaerobic/Aerobic Respiration 1

Describe the structure of mitochondria.

1-10um in size

• Mitochondria have a double-membrane structure with an outer smooth membrane and a highly folded inner membrane forming cristae, which increases surface area for ATP production. These membranes enclose the intermembrane space and the inner matrix, a gel-filled space containing enzymes, ribosomes (For protein synthesis), and mitochondrial DNA, essential for cellular respiration.

What are mitochondrial networks?

Mitochondrial networks are complex, dynamic, interconnected structures formed by mitochondria constantly fusing and dividing within a cell, acting as central hubs for energy production, metabolism, and cell signaling.

Describe the differences between Nuclear DNA vs. Mitochondrial DNA.

Nuclear DNA

• Double helix, large

• Encodes 20,000 protein coding genes

• Located inside the nucleus

Mitochondrial DNA

• Circular, double-stranded DNA, extracellular source of DNA, found within the mitochondria

• mtDNA contains 37 total genes, not all protein-coding

• 13 protein-coding genes

  • Components of the oxidative phosphorylation (Ox Phos) system

• 22 tRNA genes

• 2 rRNA genes

Explain the Endosymbiosis Theory.

The endosymbiosis theory says that mitochondria were once free-living bacteria that were swallowed by a larger cell and eventually became a permanent part of it.

Step-by-step, very simply:

1. A large primitive cell engulfed a small aerobic bacterium.

2. The bacterium was not digested.

3. Instead, it:

   • Made ATP (energy) for the host cell

   • Got protection and nutrients from the host

4. Over time, the bacterium lost independence and became the mitochondrion.

Why scientists believe this:

Mitochondria still look like bacteria because they:

• Have circular DNA

• Have their own ribosomes

• Divide by binary fission - similar to bacteria

• Have a double membrane - similar to bacteria

How is mitochondrial DNA inherited?

Mitochondrial DNA is inherited only from the mother.

Why?

• The egg contains many mitochondria

• The sperm contributes almost none (and those are destroyed after fertilization)

So:

• All offspring get their mitochondrial DNA from their mother

• Both males and females inherit it, but only females pass it on

Why is paternal mtDNA eliminated

Maternal mitochondrial DNA that enters with the sperm during fertilization is destroyed and not passed on.

What actually happens:

• Sperm do carry a few mitochondria in the midpiece

• After fertilization:

  • These paternal mitochondria are tagged

  • They are broken down and eliminated inside the embryo

What structures does the mitochondrial membrane have allowing transport within the structrure?

1. Porins

• Channel proteins in the outer mitochondrial membrane (OMM)

• Form large, water-filled pores

What they do:

• Allow small molecules and ions (≤ ~5 kDa) to freely pass, passively.

• Examples:

  • ATP, ADP

  • Pyruvate

  • Ions

TOM = Translocase of the Outer Membrane

• Located in the outer mitochondrial membrane

TIM = Translocase of the Inner Membrane

• Located in the inner mitochondrial membrane

Both actively import nuclear-encoded proteins across the outer and inner mitochondrial membranes into the matrix, respectively.

What occurs in the inner mitochondria membrane?

Site of oxidative phosphorylation (ATP production)

How do mitochondria reflect the energetic needs of particular tissues?

Low metabolic rates = adipose tissue, skin, resting muscle, brain

High metabolic rates = contracting muscle, heart at heavy exercise

• Reflects the number of mitochondria

What does it mean in saying “mitochondria are dynamic” (Aka mitochondrial dynamics)?

Mitochondrial dynamics refers to the fact that mitochondria are not static—they are constantly changing shape, size, and number to meet the cell’s needs.

It involves two opposite but coordinated processes:

• Fusion → mitochondria join together

• Fission → mitochondria split apart

These processes help with:

• Energy efficiency

• Quality control

• Adaptation to stress

• Cell survival and apoptosis

What is mitochondrial fussion and why does it happen?

Mitochondrial fusion is when two mitochondria merge into one.

What happens:

• Outer membranes fuse

• Inner membranes fuse

• Contents (proteins, mtDNA, metabolites) mix

Why fusion is important:

• Helps dilute damaged components

• Allows sharing of mtDNA

• Improves ATP production

• Supports cell survival during stress

Why it happens:

Mitochondrial fusion occurs to maintain mitochondrial function by mixing contents, improving ATP production, and protecting against cellular stress.

What is an example of diseases which affect mitochondrial fusion?

MFN2 mutations and Charcot-Marie-Tooth Disease

• Most common inherited neuromuscular disorder. No current drug therapy

• In humans: muscle weakness, muscle wasting, hammer toes/fingers

• In dogs: Mini snauzzers: mega-esophagus: can get regurgitations, inspiratory dyspnea

What are some of the ways that mitochondria are dynamic?

Cellular migration, fusion, fission, turnover

• Can also respond to damage by mitophagy

Respond to energetic requirements: Exercise, hypoxia

Where are mitochondria found within the muscle fiber?

Periphery - to reduce diffusion distance of nutrients and oxygen for cotracting muscles

How does exercise training change mitochondrial health?

Exercise training

• Mitochondrial density increased with exercise (OXPHOS increased), you can produce more ATP

• Number of capillaries increased

• Diffusion index decreased

Correlation between mitochondrial density and max. O₂ consumption VO₂ max

Correlation between mitochondrial density and run time (treadmill), longer time to exhaustion = greater mitochondrial density

What is the primary function of the mitochondria?

Powerhouse of the cell - generating ATP

Net production = 38mol A TP/mol glucose

Glycolysis in the cytosol produces 2 ATP/mol glucose

• Within mitochondria:

  • Krebs / Citric Acid Cyle

  • Beta-Oxidation - fatty acids into Acetyl CoA

  • Formation of components of sex hormones

  • Formation of components of heme

  • Calcium homeostasis

What occurs within glycolysis?

• Happens in the cytoplasm

• Does not require oxygen

• Breaks one glucose into two pyruvate

• Makes a small amount of ATP (energy) and NADH

Glycolysis is the cytoplasmic pathway that converts glucose into pyruvate, producing ATP.

Why is glycolysis called substrate-level phosphorylation?

Glycolysis - substrate level phosphorylation

ATP is made by directly transferring a phosphate group from a substrate molecule to ADP.

Breaking that down simply:

• A substrate = an energy-rich molecule made during metabolism

• That substrate already has a phosphate attached

• The phosphate is directly passed to ADP

• This makes ATP, without any membranes or oxygen

What and how does anaerobic metabolism occur?

When oxygen is limited, cells rely on glycolysis in the cytoplasm to produce ATP. Glucose is converted to pyruvate, generating 2 ATP per glucose. Because mitochondria cannot use pyruvate without oxygen, lactate dehydrogenase converts pyruvate to lactate, regenerating NAD⁺ so glycolysis can continue. Lactate accumulates in muscles, causing temporary fatigue, and can later be transported to the liver to be converted back to glucose via the Cori cycle.

• More rapid then aerobic metabolism

• Used in fight or flight

How do lactate concentrations change with training?

Increasing exercise and work increases level of lactate

• But more training produces less lactate over time

What is Type A Lactic Acidosis?

Build-up of (typically) L-lactate in blood leading to excessively low pH

Leading to:

• Tissue hypoperfusion and hypoxia

  • Oxygen consumption/delivery mismatch leading to anaerobic metabolism

• Associated with:

  • Hypovolemia - blood loss

  • Cardiac failure

  • Sepsis

  • Cardiac arrest

What is Type B Lactic Acidosis?

Occurs under normoxia, with no evidence of organ hypoperfusion

• Usually drug or toxin interference of cellular metabolism

  • For Instance:

  • Cyanide poisoning/alcoholism

  • Metformin - common drug used to treat diabetes, affects complex I within mitochondria

  • Mitochondrial disease

  • Excessive exercise to exhuastion

What is another way Type B Lactic acidosis may manifest within cattle?

Sudden, unaccustomed ingestion of CH-rich feeds in ruminants Grain or concentrates usually (Highly fermentable, lots of sugars, increase the VFAs which alter bacterial growth rates, increasing bacterial which produce lactic acid - leading to a decrease in pH, get dying off of other microbes, increasing lactic acid more).

• Leads to:

• Colic

  Tooth grinding - common sign of pain

  Cattle weak and may fall

  Laminitis

  Profuse diarrhoea

  Recumbency

  May die in 24-48hrs

What dietary deficiencies may cause lactic acidosis?

Thiamine (Vitamin B₁) Deficiency

• Pyruvate dehydrogenase complex - is a multi-enzyme mitochondrial matrix complex which catalyzes conversion of pyruvate into acetyl-CoA

• Deficiency in B₁ can reduce ability of Thiamine pyrophosphate (TPP) which is a cofactor for PDC, which is critical for movement of pyruvate from cytosol into the mitochondria

  • Can therefore reduce ability of transport protein to get pyruvate into cell, so aerobic metabolism not possible

  • Causing:

    • Lactic acidosis, anorexia, cardiac hypertrophy, muscle weakness, convulsions, Opithotonos (star gazing)

How is lactic acid distinct from metabolic acidosis?

In metabolic acidosis, a metabolic processes that produce/manage acids break down is impacted

Example: Antifreeze (Ethylene glycol) ingestion

• Is a competitive inhibitor of Alcohol dehydrogenase

  • Sweet tasting, toxic even if feet/coat contaminated

• Breakdown of antifreeze metabolites highly toxic

  • Glycolic and oxalic acid

• Calcium oxalate crystals within the kidney- renal failure

• Treatment- ethanol or 4-MP (Fomepizole)

  • ‹ 3hrs for cats

  • ‹ 8-12 hrs for dogs

Summarize the processes of aerobic and anaerobic metabolism and when each occurs.

1. Why aerobic metabolism occurs

Aerobic metabolism is the main way cells make ATP when oxygen is available.

Key points:

• Location: mitochondria

• Starting molecule: glucose → pyruvate

• Process: Pyruvate enters mitochondria → converted to acetyl-CoA → Krebs cycle → NADH/FADH₂ → electron transport chain → oxidative phosphorylation

• Oxygen’s role: Final electron acceptor in the ETC (O₂ + e⁻ → H₂O)

• ATP yield: ~30–32 ATP per glucose (much higher than glycolysis alone)

Summary:

Aerobic metabolism efficiently converts glucose to ATP because oxygen allows pyruvate to enter the mitochondria and fully oxidize into CO₂ and H₂O.

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2. When anaerobic metabolism takes over

Anaerobic metabolism occurs when:

• Oxygen is limited (e.g., intense exercise, hypoxia, ischemia)

• Mitochondria cannot use pyruvate in the Krebs cycle/ETC

Result: Cells rely on glycolysis alone to generate ATP.

• Glucose → 2 pyruvate (glycolysis, 2 ATP)

• Problem: Glycolysis uses NAD⁺ → must be regenerated

• Solution: Pyruvate → lactate (via lactate dehydrogenase), regenerating NAD⁺ so glycolysis can continue

ATP yield: 2 ATP per glucose (much less than aerobic)

Describe the Krebs Cycle.

Occurs within Mitochondrial Matrix

• Pyruvate (Glycolysis) from CHO, fats, protein

  • transformed to Acetyl CoA

  • Acetyl group oxidised in Krebs cycle

Produces high energy electron donors- 3 NADH, 1 FADH2 (For ETC in oxidative phosphorylation)

Describe the features of ATP.

Adenosine triphosphate

Nucleoside phosphate- ~45 atoms (Small)

• Highly unstable molecule - cannot be stored in this form, has to store: ADP+Pi- (ATP synthase) → ATP and H₂O

• ATP hydrolysed to ADP+Pi (Hydrolization is what produces release of energy)

1. Location

• Occurs in the inner mitochondrial membrane

• Complexes I–IV are embedded in this membrane

• ATP synthase (Complex V) uses the proton gradient produced by the ETS

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2. Main purpose

• The complexes transfer electrons from NADH and FADH₂ to oxygen

• Pump protons (H⁺) into the intermembrane space → creates a proton gradient (proton motive force), pass through complex V

• This proton gradient is then used by ATP synthase to produce ATP (oxidative phosphorylation)

• Taking ADP → ATP