Respiration and Digestion (Cellular Respiration) and Fermentation

chloroplasts

found in plants and algae, are the site of photosynthesis, a metabolic process that uses the energy from sunlight to fix carbon (from CO₂) and uses it to generate energy-rich organic molecules such as glucose

mitochondria

are the site of cellular respiration, a metabolic process that uses oxygen to generate ATP

• smooth outer membrane and inner membrane folded into cristae

• inner membrane creates two soluble compartments: intermembrane space and mitochondrial matrix

What are some characteristics of mitochondria?

catabolic pathways breakdown organic molecules

What metabolic process is used to produce ATP?

• consumes organic molecules of O₂ and yields ATP

• carbohydrates, fats, and proteins from our diet are all consumed as fuel; but cellular respiration is usually traced with the sugar glucose

What is aerobic respiration?

C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy (ATP + heat)

What is the equation for aerobic respiration?

True; cellular respiration involves many reactions in which electrons are passed from one molecule to another

(T/F) Respiration is a redox reaction.

redox reactions (oxidation-reduction reactions)

reactions involving electron transfers

oxidative phosphorylation

• the process that generates most of the ATP, powered by redox reactions

  • it accounts for almost 90% of the ATP generated by cellular respiration

For each molecule of glucose broken down to CO₂ and water by respiration, the cell makes up to 32 ATP

How much ATP is created from cellular respiration?

• glycolysis

• pyruvate oxydation

• Krebs cycle (citric acid cycle)

• electron transport chain

What are the phases of cellular respiration?

• breaks down glucose into two molecules of pyruvate

  • occurs in cytosol

  • 10-step pathway that’s broken in two phases

    • energy investment phase (1st 5 steps)

    • energy payoff phase (last 5 steps)

  • occurs whether or not O₂ is present

What happens in glycolysis?

anaerobic → no oxygen consumed

Glycolysis is an (anaerobic/aerobic) process.

1. the investment phase → energy is consumed, glucose is split into two

2. the payoff phase → ATP is one of the products

What are the two main phases of glycolysis?

• glucose is prepared for the next two phases by the addition of two phosphate groups

  • produces fructose 1,6 - bisphosphate

  • requires an input of energy in the form of two molecules of ATP (substrate-level phosphorylation)

• phosphorylation of glucose traps the molecule inside the cell and destablilizes it so that it is ready for next phase

Describe how the energy investment phase of glycolysis works.

substrate level phosphorylation

a metabolic reaction that creates ATP or GTP by transferring a phosphate group from a high-energy compound to ADP or GDP

• fructose 1, 6-bisphosphate is unstable and cleaved into two molecules

  • glyceraldehyde 3-phosphaste (G3P) and its isomer,

  • dihydroxyacetone phosphate (DHAP)

• DHAP is converted into another molecule of G3P

  • resulting in two molecules of G3P at the end of phase 1

What happens when glucose is split in glycolysis?

• during the payoff phase of glycolysis

  • two molecules of pyruvate are formed

  • two molecules of the electron carrier NADH are produced

  • four molecules of ATP are produced

What happens in energy payoff?

• carries electrons from one reaction to another

• co-enzyme utilized in both cellular respiration and photosynthesis

• NAD+ is oxidizing agent

  • electron acceptor

• NAADH is the reducing agent

  • electron donor

How does nicotinamide adenine dinucleotide (NAD+) work?

• net gain of two ATP

  • energy payoff produced four ATP, but two were “invested” earlier

• production of two NADH

  • used in the last reaction of cellular respiration

• two molecules of pyruvate

  • these will be used in the next part of respiration

What are the products of glycolysis?

• links glycolysis and the citric acid cycle

• three reactions

  • pyruvates’s carboxyl group (-COO-) removed (produces CO₂)

    • remaining 2-C molecule oxidized to form acetate (CH₃COO-)

  • NAD+ reduced to NADH

  • coenzyme A (CoA) attached to acetate forming acetyl CoA

    • high potential energy

What is pyruvate oxidation?

• a closed loop

  • starts with and re-creates oxaloacetate

  • completes the oxidation of glucose into CO₂

• each turn of the citric acid cycle generates

  • 1 ATP

  • 3 NADH

  • 1 FADH₂

  • 1 CO₂

• central driver of respiration

What is the citric acid cycle?

• oxidation of acetyl-CoA produces the carbon dioxide we exhale

• chemical potential energy that was stored in acetyl-CoA is then stored in NADH and FADH₂

• production of GTP is the result of substrate-level phosphorylation

What happens when acetyl-CoA is oxydized?

flaven adenine dinucleotide (FAD)

• co-enzyme during step 6 of citric acid cycle

• shuttles two electrons

• spins twice for every molecule of glucose that enters cellular respiration

• one spin

  • 1 ATP

  • 3 NADH (6 electrons)

  • 1 FADH₂ (2 electrons)

• for each molecule of glucose it produces

  • 2 ATP

  • 6 NADH (12 electrons)

  • 2 FADH₂ (4 electrons)

What does the citric acid cycle generate?

• electron transport chain

  • during glycolysis, pyruvate oxidation and the citric acid cycle, most of the energy extracted form organic molecules is transferred to NADH and FADH₂

Where do the products of the citric acid cycle go?

• the overall energy drop (ΔG) for electrons traveling through the chain is 221.8 kJ/mol

  • the “fall” is broken up into a series of smaller steps

• electrons passed down chain through a series of electrons carriers

  • breaks the large free-energy drop from NADH ana FADH₂ into smaller steps

  • electrons release energy at each step in chain

  • some energy from fall used to pump H⁺ out of matriz into intermembrane space

How does the chain in the ETC work?

• electrons are donated to split oxygen and form water

  • four electrons required to reduce each molecule of O₂

  • two water molecules generated in the process

How are electrons used to actively pump H⁺?

• use of energy in a H⁺ gradient to drive cellular work

• H⁺ pumped against concentration gradient

• H⁺ then flow down their concentration gradient backa cross the inner membrane, through ATP synthase

• ATP synthase uses the exergonic flow of H⁺ to drive phosphorylation of ADP to form ATP

What is chemiosmosis?

• glucose → NADH/FADH₂ → electron transport chain → H⁺ gradient → ATP

• 34% of energy in a glucose molecule is transferred to ATP via cellular respiration

  • Makes ~ 30-32 ATP

How does energy flow during cellular respiration?

metabolic integration

processes of cellular respiration use or produce many of the same molecules, making their rates interdependent

• citric acid cycle uses NAD⁺ and produces NADH

• ETC uses NADH and produces NAD⁺

How is NAD⁺ and NADH used?

if ETC slows down, it produces less NAD⁺, which reduces the rate of the citric acid cycle

What is the effect of the ETC on the citric acid cycle?

• primary producers

  • autotrophs

• primary consumers

  • herbivores

• secondary consumers

  • primary carnivores

• tertiary consumers

  • secondary carnivores

What are the different trophic levels?

• ingestion

  • mechanical digestion

• digestion

  • chemical digestion (enzymatic hydrolysis)

• absorption

  • nutrient molecules enter body cells

• elimination

  • undigested material

What are the stages of food processing?

• catabolic pathways funnel electrons from organic molecules into cellular respiration

  • carbs accepted in glycolysis

  • proteins digested to amino acids; amino groups can feed glycolysis or citric acid cycle

  • fats digested to glycerol (used in glycolysis) and fatty acids are broken down to produce acetyl CoA

What is the catabolism for different molecules of food?

• in the absence of oxygen, pyruvate produced from glycolysis can be reduced to lactic acid

• enables NAD⁺ regeneration

• the NAD⁺ can then be reduced in glycolysis, and ATP is still synthesized in small amounts for use by the cell

Glucose + 2 ADP + 2 P_i → 2 lactic acid + 2 ATP + 2 H₂O

What happens to pyruvate when O₂ is absent?

• ethanol fermentation occurs in plants and fungi

• pyruvate releases carbon dioxide and the acetaldehyde produced is reduced to form ethanol

• regenerates NAD⁺ so than ATP can be generated during glycolysis

Glucose + 2 ADP + 2 P_i → 2 ethanol + 2 ATP + 2 H₂O

What happens during ethanol fermentation?

obligate anaerobes

carry out fermentation or anaerobic respiration and cannot survive in the presence of CO₂

facultative anaerobes

yeast and bacteria; they can survive using either fermentation or cellular respiration

• pyruvate is a fork in the metabolic road, leading to alternative catabolic routes