C1.2: Cell Respiration

Adenosine Triphosphate

a molecule that distributes energy within cells

-nucleotide made of central ribose attached to adenine base and three phosphate groups

three covalent, phosphate bonds store potential energy

-adenine and ribose provide sites for enzyme attachment, allowing ATP to behave as a coenzyme

Coenzyme

small, non-protein molecules that bind to and facilitate enzyme reactions

-often function as temporary carriers (hydrogen, energy) that cycle btwn forms

ATP as Coenzyme

ATP provides chemical energy to enzymes, which allow them to meet activation energy threshold

Hydrolyzation of ATP

three covalent bonds bold phosphate together store energy (due to phosphate's negative charges)

when ATP is hydrolyzed to release P, energy is also released

energy is required to produce ATP from ADP

-phosphorylation (adding P) makes the ATP and other molecules more reactive, therefore energy is transferred through phosphorylation and hydrolyzation of P

Digestion of Carbon Compounds

cell respiration is the controlled release of energy from breakdown of carbon compounds to produce ATP

ATP is made from ADP using energy from oxidative reactions that break down food

Molecules in Respiration

main molecule used are carbohydrates (and simple fatty acids)

-preferred over lipids, harder to move/digest

-which are preferred over proteins, can release toxic nitrogenous compounds as byproducts

Carbs vs. Lipids

carbohydrates are the most commonly used respiratory substrates

-can be broken down into monosaccharides (glucose) which is used in glycolysis

Lipids are more difficult to digest, they are long-term energy source (nonpolar therefore less osmotic effect)

-fatty acids are broken down into 2C compounds (for acetyl CoA) that can only be digested aerobically (not glycolysis)

Processes that Involve ATP (3)

anabolism, active transport, movement

Anabolism

to form bonds during synthesis of polymers from monomers

Active Transport

move solutes against concentration gradient

-Na+/K+ pump establish resting potential b4 action potential

-membranes are broken/reformed during endocytosis and exocytosis

Movement

to move both cellular components and entire organism

-segregation of chromosomes during mitosis/meiosis

-shortening of sarcomeres during muscle contractions

Factors that Affect Respiratory Enzymes (4)

temperature, pH, substrate [], inhibitors

Temperature

impacts frequency of enzyme-substrate collisions

-lower temp --> low rxn rate due to insufficient kinetic energy

-higher temp --> disrupts bonds, enzyme denatures (active site loses shape and enzyme loses function)

optimal conditions --> peak activity w/ most collisions (typically body temp 37 C)

pH

impacts the charge/solubility of enzymes

optimal conditions --> peak activity w/ greatest number of collisions (typically pH around 7)

-moving away from this range denatures enzyme and decreases enzyme activity

Substrate []

substrate concentration also impacts frequency of enzyme-substrate collisions

-increase substrate [] --> increase enzyme activity --> increase rxn rate

at some point, rxn rate eventually plateaus since all enzymes become occupied or "saturated"

*other respiratory substrates (fatty acids) will need to be controlled for so as not to slow respiration rate*

Inhibitors

decrease or prevent normal activity of enzymes

either competitive or non-competitive

Competitive Inhibitors

bind to active sites and physically prevent substrates from binding

Non-Competitive Inhibitors

bind to allosteric sites and change the shape of enzymes and thus their active sites

ex. cyanide binds irreversibly to an electron carrier in the ETC

Measuring Cell Respiration

done w/ a respirometer which monitors O2 consumption

living specimen (germinating seeds) are enclosed in sealed container

-O2 consumption is measured as pressure change when alkali (limewater) is added to absorb CO2

-pressure can be detected via data logger or U-tube manometer

**respiration rate of plants must be conducted in darkness to control for production of O2)

Aerobic Respiration

aerobic respiration breaks down organic molecules completely

-by linking steps, energy expenditure is reduced since activation energy can be divided amongst them

-released energy is not lost, it is transferred to carrier molecules via redox rxns

*needs oxygen*

Redox Reactions

paired reactions that involve the reduction of one molecule and oxidation of another, involve transfer of e-, H+, or oxygen

Reduction

gain of e- or H+, or the loss of oxygen (gains energy)

Oxidation

loss of e- or H+, or the gain of oxygen (loses energy)

ATP as a Carrier

ATP is the primary energy carrier and produced directly by substrate-level phosphorylation (or oxidative phosphorylation)

Substrate-Level Phosphorylation

Enzyme uses energy from substrate to attach a phosphate to ADP

Hydrogen Carriers

act as transitional energy carriers and move energy indirectly to form ATP via oxidative phosphorylation

-hydrogen atoms consist of protons and high energy electrons

they carry high energy e- to ETC in mitochondria

-in the presence of O2, energy from e- is used to make ATP

as glucose broken down, it's energy in form of e- is transferred to hydrogen carriers via oxidation

*Carriers are NAD+ or FAD*

NAD+

more common hydrogen carrier, reduced to NADH

NAD+ + 2e + 2H+ ---> NADH + H+

FAD

less common hydrogen carrier, reduced to FADH2

FAD + 2e + 2H+ ---> FADH2

What Do Hydrogen Carrier Do?

carry e- and H+ from various processes to ETC in cristae

-energy in e- is used to make ATP

due to O2 requirement, hydrogen carriers generate more ATP in aerobic respiration

e- flow from:

food --> NADH/FADH2 --> ETC --> O2

Mitochondria Parts (5)

outer membrane, inner membrane, intermembrane space, cristae, matrix

Outer Membrane

contains transport proteins that move key materials (pyruvate) from cytosol

Inner Membrane

allows oxidative phosphorylation, contains ETC and ATP synthase

Cristae

inner membrane folds that increase SA:V ratio

Intermembrane Space

holds high [H+], made by ETC

-volume is very small, allowing a gradient to build rapidly

Matrix

central cavity that contains all enzymes and maintains a suitable pH for krebs cycle

Glycolysis

occurs in cytosol

-one glucose (6C) converted to 2 pyruvates (3C)

-each step catalyzed by a different enzyme

Glycolysis Results

2 NADH via oxidation

net of 2 ATP (4 generated, 2 used)

no oxygen required

Glycolysis Procedure (4)

phosphorylation, lysis, oxidation, ATP formation

Phosphorylation

glucose + 2 ATP become hexoses bisphosphate (6C)

-molecule becomes very unstable (more reactive)

Lysis

6C is split into two triose phosphates, AKA G3P

Oxidation (in Glycolysis)

hydrogens are moved from each triose phosphate to NAD+

-two NADHs are formed

ATP Formation

two net ATPs are generated by substrate level phosphorylation

Types of Cell Respiration (2)

anaerobic and aerobic

Anaerobic Respiration

partial breakdown of glucose in cytosol for small amount of ATP, WITHOUT oxygen

Anaerobic Respiration Process

begins w/ glycolysis

-followed by fermentation (NAD+ regeneration)

glucose is broken down into 2 pyruvate, generates 2 ATP

Reason For Fermentation

fermentation is needed to regenerate NAD+

-converts NADH back to NAD+ so the NAD+ doesn't run out

*glycolysis can only work if NAD+ available*

Animal Fermentation

pyruvate --> lactic acid (or lactate)

Plant/Yeast Fermentation

pyruvate --> ethanol + CO2

Lactic Acid Fermentation

muscle contractions need ATP

-at high intensity, body needs ATP more quickly than O2 can be provided, therefore engages in anaerobic respiration

-produces lactic acid, which leads to muscle fatigue

when intensity stops, O2 increases

-lactic acid is converted back to pyruvate

-reversible reaction

Lactic Acid Fermentation in Bacteria

bacteria also undergo lactic acid fermentation

-modify milk proteins to create yogurt and cheese

Alcohol Fermentation

in yeasts, pyruvate is converted to ethanol + CO2

Ethanol

used to make alcoholic beverages

CO2

causes dough to rise (leavening) while ethanol evaporates during baking

Aerobic Respiration Overview

requires O2 and takes place in mitochondria

-begins w/ glycolysis, although this part is anaerobic

-continues to link rxn, then Krebs Cycle, then oxidative phosphorylation (ETC and chemiosmosis)

Glycolysis breaks down glucose (6C) into pyruvate (3C), which is completely broken down to produce CO2, H2O, and 36-38 ATP

Link Reaction

1st stage of aerobic respiration, links products of glycolysis to aerobic respiration

Link Reaction Process (5)

1. Pyruvate enters matrix from cytosol via carrier proteins on outer membrane

2. undergoes decarboxylation to produce CO2

3. 2C loses hydrogen and becomes an acetyl group

4. NAD+ is reduced to NADH

5. acetyl group + Coenzyme A --> Acetyl CoA

**link rxn occurs twice, producing 2 of everything (2 CO2, 2 NADH, 2 Acetyl CoA)

Acetyl Group

metabolized from carbs and lipids (only glucose or fatty acids)

Krebs Cycle

Second Stage

-occurs in matrix

each cycle converts 1 pyruvate to:

-2 CO2 released via decarboxylation

-3 NADH and 1 FADH2 via reduction

-1 ATP via substrate-level phosphorylation

Krebs Cycle Process

entering acetyl CoA gives its acetyl group to oxaloacetate (4C) to form citrate (6C)

-coenzyme A returns to link rxn to join w/ another acetyl group

Forms products (previous card)

Oxidative Phosphorylation

process where energy from oxidation of hydrogen carriers makes ATP

-consists of ETC and chemiosmosis

Electron Transport Chain

embedded in the inner membrane (cristae increase SA)

-consists of 4 protein complexes that alternate btwn being reduced and oxidized (depending on if they have an electron or not)

NADH drops its pair of e- at Complex I, becomes oxidized to NAD+

FADH2 drops its e- to Complex II (lower energy level), becomes oxidized to FAD

Oxidative Phosphorylation Process (3)

proton motive force, chemiosmosis, reduction of O2

Proton Motive Force

hydrogen carriers releas e- and H+ when oxidized

-e- are dropped into ETC made of 4 carrier protein complexes (protein complexes increase in electronegativity going down the line)

lost energy from e- being passed down is used to pump H+ from matrix to intermembrane space

-accumulation of H+ creates an electrochemical gradient (proton motive force)

Chemiosmosis

generated proton motive force forces H+ to move back down their gradient into matrix

-moves through transmembrane enzyme ATP synthase

flow of H+ rotates the enzyme to make ATP (chemiosmosis)

Reduction of O2

oxygen is the final electron acceptor that removes the de-energized e- from ETC to prevent blockage

-also binds H+ in matrix to form H2O AND maintain the H+ gradient

if O2 is absent, e- cannot be transferred and ATP production stops

Anaerobic Respiration General Process

No oxygen

makes about 2 ATP

uses glucose, glycerol (lipids) and some AA as substrates

makes lactate or ethanol and CO2 as products

occurs in cytosol

Stages: glycolysis, fermentation

Aerobic Respiration General Process

oxygen required

makes about 34-36 ATP

uses pyruvate, fatty acids (lipids) and some AA as substrates

makes CO2 and H2O as products

occurs in mitochondria

Stages: glycolysis, link rxn, Krebs cycle, oxidative phosphorylation

Where does decarboxylation occur?

Glycolysis:

Link Rxn: 2 CO2

Krebs Cycle: 4 CO2

ETC:

Overall: 6 CO2

Where does oxidation occur?

Glycolysis: 2 NADH

Link Rxn: 2 NADH

Krebs Cycle: 6 NADH, 2 FADH2

ETC:

Overall: 10 NADH, 2 FADH2

Where does phosphorylation occur?

Glycolysis: 2 ATP, net (substrate-level)

Link Rxn:

Krebs Cycle: 2 ATP (substrate-level)

ETC: 32-34 ATP (oxidative)

Overall: 36-38 ATP