Cellular RespirationCellular Respiration

Cellular Respiration Overview

Transformation of chemical energy in food into chemical energy cells can use: ATP

These reactions proceed the same way in plants and animals. Process is called cellular respiration

Overall Reaction:– C6H12O6 + 6O2 → 6CO2 + 6H2O

Cellular Respiration Terms

Photoautotrophs – change light energy into chemical energy stored in bonds of glucose and polysaccharides (green plants, cyanobacteria)

Heterotrophs – feed on other organisms for chemical energy

Chemoautotrophs – microorganisms that can obtain energy from inorganic sources (Fe or S compounds in volcanoes, deep sea vents…)

Glucose – primary source of energy for most organisms

Cellular respiration – process by which glucose is broken down and energy stored in bonds is released, can be aerobic or anaerobic

Aerobic – oxygen used as an oxidizing agent (electron acceptor)

Anaerobic – uses a molecule other than oxygen as an oxidizing agent

Cellular Respiration Overview

Purpose of Cellular Respiration:Trap free energy in form of ATPMove H+ electrons from glucose to oxygen

creating 6 H2OBreak bonds between 6C atoms in glucose

creating 6 CO2

Formation of ATP

2 Ways ATP is formed:1. Substrate-level

Phosphorylation ATP formed directly in

enzyme catalyzed reaction

P containing compound transfers P gp to ADP making ATP

4 ATP created this way from 1 molecule glucose

2.Oxidative Phosphorylation ATP formed indirectly in more complex process co-enzyme NAD+ (nicotinamide adenine

dinucleotide) removes 2 H+ atoms and is reduced to NADH+ + H+

another co-enzyme, FAD (flavin adenine dinucleotide) also reduced by 2 H+ to become FADH2

these co-enzymes act as mobile energy carriers in cell, moving energy from one stage of cellular respiration to another where its used to create ATP

4 Stages of Cellular Respiration

Name Details

Stage 1 Glycolysis 10 step process in cytoplasm

Stage 2Pyruvate Oxidation

1 step process in mitochondria

Stage 3 Kreb’s Cycle 8 step cycle in mitochondria

Stage 4Electron Transport Chain

multi-step process in mitochondrial membrane

1. Glycolysis

Series of reactions which break the 6-carbon glucose molecule down into two 3-carbon molecules called pyruvate– Process is an ancient one-all organisms from simple

bacteria to humans perform it the same way– Yields 2 ATP molecules for every one glucose

molecule broken down (creates 4 ATP but uses 2)– Yields 2 NADH per glucose molecule (used later to

create more ATP)– cellResp_main

4 Parts to Glycolysis

1. Glucose activation 2 molecules ATP

transfer P to glucose results in 2 ADP and

F1,6 BP (fructose 1,6 biphosphate)

2. Sugar Splitting F1,6 BP splits into 1

G3P (glyceraldehyde 3-phosphate) and 1 DHAP (dihydroxyacetone)

DHAP is then immediately converted into G3P by enzyme isomearase (result is 2 G3P)

3. Oxidation

• both G3P are oxidized by NAD resulting in 2 NADH.

• this releases energy and 2 ATP produced by substrate level phosphorylation.

• result is 2 molecules of 1,3 BPG (biphosphoglycerate)

4. ATP Formation

• phosphate gps of BPG are transferred to 2 ADP creating 2 ATP by substrate level phosphorylation

• end result is 2 molecules pyruvate

Glucose + 2 ADP + 2 Pi + 2 NAD+

2 pyruvate + 2 ATP + 2 NADH

Aerobic or Anaerobic Respiration?

After glycolysis, life diverges into two forms and two pathways

if O2 is present, pyruvate from glycolysis moves from cytoplasm into mitochondria to start aerobic cellular respiration

if no O2 is present, pyruvate enters anaerobic cellular respiration (aka fermentation)

Aerobic Cellular Respiration

Oxygen required=aerobic 3 more sets of reactions which occur in the

mitochondria– Pyruvate Oxidation– Kreb’s Cycle– Electron Transport Chain

2. Pyruvate Oxidation

3 step reaction:

1. carboxyl gp removed as CO2

2. remaining 2 carbon group is oxidized by NAD+, forming NADH and becomes acetate

3. co-enzyme A attaches to acetate, forming acetyl-coenzyme A

cellResp_main acetyl-co A formed by catabolism of carbs,

proteins, and lipids in eukaryotes if ATP levels are high, acetyl-co A will be directed

into synthesis of fatty acids for long term energy storage

if ATP needed, acetyl-co A is directed to next part of cellular respiration: Kreb’s Cycle

Kreb’s Cycle (Citric Acid Cycle)

Completes the breakdown of glucose– Occurs in matrix of mitochandria– 8 step process, each step catalyzed by a specific

enzyme– Product of 8th reaction (oxaloacetate) is a reactant in

the 1st reaction (cycle)– Takes the pyruvate (3-carbons) and breaks it down, all

6 carbon and oxygen atoms end up in CO2 and H2O

– Hydrogens and electrons are stripped and loaded onto NAD+ and FAD to produce 6 NADH and 2 FADH2 which are transported to the final step

Production of only 2 more ATP (substrate level phosphorylation)

cellResp_main

Electron Transport Chain

NADH & FADH2 loaded with electrons and protons from the Kreb’s cycle move to this chain-like a series of steps (staircase).

made of 4 lg protein molecules and 2 smaller mobile protein carriers proteins are arranged in order of electronegativity, so each one will

be reduced (gain 2e-) then immediately oxidized (lose 2e-) as electrons drop down stairs, energy released to form a total of 32

ATP oxygen waits at bottom of staircase, picks up electrons and protons

and in doing so becomes water

cellResp_main

Steps of ETC

1. NADH gives 2e- to NADH dehydrogenase, first protein in ETC.

2. Electrons (e-) pass through the ETC, releasing energy.

3. Energy is used to pump H+ ions across membrane into intermembrane space.

4. Build up of H+ ions in the space creates an electrochemical gradient.

5. H+ ions want to diffuse back across membrane but are unable to and must use special protein channels called ATPase complex (facilitated diffusion).

6. Pores in the protein channels contain an ATP-synthesizing enzyme called ATP synthase. So as the H+ ions move through the channels, Pi (inorganic phosphate) is joined to ADP to create ATP.

7. Every e- NADH drops off will pump 3 H+ ions across the membrane, therefore producing 3 ATP.

8. FADH2 skips the first protein and drops its e- off further down chain so only 2 H+ ions are pumped across, therefore producing only 2 ATP.

9. When e- from NADH and FADH2 reach last protein in chain called cytochrome oxidase, they have lost energy.

10. Once cytochrome oxidase has 4e-, it gets oxidized by O2 (high electronegativity). O2 takes the e- and combines them with four H+ ions from the matrix to produce 2 H2O molecules.

VCAC: Cellular Processes: Electron Transport Chain: The Movie

Energy Tally

36 ATP for aerobic vs. 2 ATP for anaerobic

– Glycolysis 2 ATP

– Kreb’s 2 ATP

– Electron Transport 32 ATP 36 ATP

Anaerobic organisms can’t be too energetic but are important for global recycling of carbon

Other Catabolic Pathways

Carbohydrates broken into monosaccharide, then broken down for

energy avg. yield of 16 kJ/g of energy

Proteins broken down into amino acids to be used to produce

cell’s proteins amino groups removed in deamination and converted into

ammonia (wastes) rest of a.a. continue through glycolysis or Kreb’s cycle

Lipids

triglycerides broken into glycerol and fatty acids glycerol broken down into glucose or G3P and

goes through glycolysis fatty acids go into matrix of mitochandria and

undergo oxidation – get converted in acetyl groups which combine with co-enzyme A to produce acteyl-coA (used in Kreb’s cycle)

much more ATP formed than from carbs. ex lauric acid (12 C fatty acid) – produces 92 ATP

avg yield is 38kJ/g of energy

Anaerobic Cellular Respiration

Some organisms thrive in environments with little or no oxygen– Marshes, bogs, gut of animals, sewage treatment

ponds No oxygen used= ‘an’aerobic Results in no more ATP if no O2 available to ETC it stops and NADH can’t

drop off H+ ions free NAD+ can’t return to pick up more electrons

and hydrogens in glycolysis, causing it to stop

organisms have alternative methods to get energy

ex. NADH can drop off H+ ions to certain organic molecules instead of ETC (fermentation)

End products such as ethanol and CO2 (single cell fungi (yeast) in beer/bread) or lactic acid (muscle cells)

PhotosynthesisPhotosynthesis

Photosynthesis

Method of converting sun energy into chemical energy usable by cells

done by autotrophs takes place in specialized

structures inside plant cells called chloroplasts

1. Capturing light energy2. Using captured energy to make ATP and NADP+

(energy carrying co-enzyme like NAD. It is reduced by 2 H atoms to NADPH+ + H+)

3. Using ATP and energy from NADPH to synthesize molecules like glucose.

first 2 steps require sunlight (light dependant) and occur in chlorophyll

last step does not necessarily need sunlight (light independent) and takes place in stroma

3 Steps of Photosynthesis

Light-Dependent Phases

occurs in thylakoid membrane light energy converted to chemical energy of

ATP & NADPH (reduced NADP = NADPH) photosystems (highly organized light capturing

complexes) are found in thylakoid membranes and made of 2 parts:

antenna complex – system of chlorophyll molecules and pigments that transfers energy to reaction centre

reaction centre – protein complex containing chlorophyll a that absorbs energy from antenna complex and raises it to high energy level to start photosynthesis

there are 2 kinds of photosytems (I and II) depending on which wavelength of light chlorophyll a absorbs

Steps in Light Dependent Reactions

1. Photoexcitation: Sunlight hits leaf and some energy passes into stroma

then absorbed by antenna complex of photosystem II and passed along to chlorophyll a.

2. Electron Transport: An electon gets boosted to a higher level and passed

along a ETC (like in cellular respiration) in thylakloid membrane.

This energy boost also causes H2O to split which releases H+ ions and O2 which is vital to other living things.

e- passes through several carriers via redox reactions releasing energy as they pass through the proteins. H+ ions are pumped from stroma into intermembrane space which creates electrochemical gradient.

3. Chemiosmosis: H+ ions move through ATPase complex back into stroma

converting ADP to ATP a process called photophosphorylation. It takes 4 H+ to make 1 ATP.

At same time light of a different wavelength is also striking photosystem 1. e- from P1 pass through another ETC, then move to enzyme NADP reductase that reduces NADP to NADPH which moves to Light Independent Phase.

Reactants: H2O, sunlight

Products: ½ O2, NADPH, ATP

YouTube - Light (Dependant) Reactions of Photosynthesis Animation

2. Light Independent Reactions (the Calvin Cycle)

ATP and NADPH generated in light reactions used to fuel the reactions which take CO2 and break it apart, then reassemble the carbons into glucose.

called carbon fixation: taking carbon from an inorganic molecule (atmospheric CO2) and making an organic molecule out of it (glucose)

occur in stroma don’t require light also known as C3 Cycle

Steps in Light Independent Phase:

1. Carbon Fixation CO2 molecule combines with 5C molecule called

RuBisCO (ribulose biphosphate) to produce 2, 3C molecules called 3-PGA (3-phosphoglycerate).

2. Reduction Reactions 3-PGA phorphorylated by ATP then reduced by NADPH

to produce G3P (glycerate 3-phosphate).3. RuBisCO Regeneration G3P phosphorylated by ATP to re-create RuBisCO to

restart the cycle. For every 2 G3P, 1 molecule glucose is removed from cycle, so need 6 CO2 to create 1 glucose.

Other Methods of Carbon Fixation

Type of carbon fixation

Stomata open

Advantages Examples

C3 dayUses fewer

ATPMost plants

C4day Faster

photosynthesisCorn, sugar

cane, grasses…

CAMnight Water

efficiency

Succulents, cacti, orchids, pineapple…