2. Respiration

General Concepts

• goal : to extract as many high potential e- as possible from the substrate & use that energy to create ATP
• the oxidation of a source of energy by removal of e- & donation to an inorganic external terminal e- acceptor
• substrate often has all available e- removed; is fully oxidized
• prod of respiration tend to be highly oxidized
• involves a membrane bound system that creates a H⁺ gradient
• H⁺ gradient can do work & is used to make ATP
• ATP is generated by ETLP

Substrates for aerobic respiration include:

• Organic molecules - Sugars, aa, nucleotides, organic acids, fats
• Organics are most often oxidized to CO₂

Differences between respiration in euks & bacteria

1.In Eukaryotes:

• ETS located in inner mitochondrial membrane
• H⁺ gradient develops across inner mitochondrial membrane
• very efficient at generating proton gradient
• w/ NADH as e- donor, 3 ATP/NADH
• w/ FADH as e- donor, 2 ATP/NADH
• overall efficiency of glc oxidation is ~ 40%

2.In Bacteria:

• ETS located in cytoplasmic membrane
• H⁺ gradient develops across cytoplasmic membrane
• Bacteria are not as efficient because ETS chains are shorter
• w/NADH as e- donor - only ~2 ATP
• overall efficiency of glc oxidation is ~ 28%

Catabolism of Glucose

*e- donated to NADH don't end up reducing the substrate, but are given to the ETS

end product of glycolysis was pyruvate

pyruvate dehydrogenase

The TCA cycle can be broken into 3 phases

6 C

5 C

4 C

Net yield: Acetyl-CoA + 3 NAD⁺ + FAD --> 2 CO₂ + 3 NADH + FADH₂ + ATP

Energy Generation Using a Membrane

Q. What does a cell do w/ high energy e-?

A. Convert them to usable energy - more ATP

Electron Transport Level Phosphorylation (ETLP)

Picture of ETS

ETS in Action

Overview

2 major questions of interest:

1.How is e- flow down the respiratory chain of e- carriers coupled to H⁺ pumping?

2.How does H⁺ movement thru ATPase cause ATP to be synth?

Proton pumping

1. NADH donates it's e- to NADH reductase

2. NADH reductase transfers H⁺ & e^- to a flavoprotein

3. flavoprotein reduces a non-heme iron protein (NH-Fe)

4. NH-Fe accepts e^-, not H⁺, H⁺ are released outside

• the arrangement of proteins in the membrane dictates the path that H+ & e- follow & where H+ eventually end up
• 6 H+ are pumped across for every NADH
• H⁺ move from inside to outside & OH^- accumulate in cytoplasm
• neither H⁺ nor OH^- can pass thru the membrane to establish equilibrium
• pH & a charge gradient

ATP synthesis

• H⁺ outside of membrane are allowed entry to inside by falling thru ATPase
• as ATPase moves H⁺ into cell, ATP is synth from ADP & P_i

ATPase structure

Picture - The structure of ATPase

2 two major regions

ATPase function

• F1 contains 3 b subunits that catalyze synth of ATP
• active site on b subunit can exist in 3 states: loose, tight & open
• each b subunit on F1 is in a different state

Putting it all together

• high potential e- on NADH & FADH are passed into the ETS
• energy of the e- is used to pump H+ from inside to outside
• this creates a H+ gradient or pmf & that is converted to ATP by ATPase

Anaerobic respiration

• most common in bacteria
• use of external e- acceptors other than O₂
• most alternative e- acceptors are inorganic molecules, but some organic molecules can serve
• uses ETS, H⁺ gradient, & ATP synthase

Examples of anaerobic respiration:

Terminal e- acceptors

1.Nitrate (NO₃^-)

Process can have several steps, proceed in 2 different directions:

Ex. Pseudomonas

2. Sulfate (SO₄^2-)

Catabolism of substrates other than glc

1.carbohydrates

2.lipids

3.proteins

NH₂ - RCH - COOH

• remove amino group (deamination)