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University “Goce Delcev”-Stip

Faculty of Medical Sciences

-Pharmacy-

Topic: How Cells Release Chemical Energy

PAPER WORK

Made by Mentor

Dragana Milchevska Dragan Donev

Stip, february 2012 Content

1

Introduction……………………………………………………………..…….….3

Fermentation……………………………………………………........................4

Glucose Breakdown Starts In Cytoplasm………………………….............5

Glycolysis Steps……………………………………………………..................5

Acetyl CoA Formation.................................................................................7

Electron Transfer Phosphorylation...........................................................8

How Aerobic Respiration Ends..................................................................9

How Anaerobic Pathways End..................................................................10

Energy from fats and proteins..................................................................11

Used literature............................................................................................12

2

Introduction

Impacts, Issues:

When Mitochondria Spin Their Wheels

■ More than forty disorders related to defective mitochondria are known (such as

Friedreich’s ataxia); many of those afflicted die young

Overview of Carbohydrate Breakdown Pathways

✓ ATP is the cell’s storage unit for energy

✓ Photoautotrophs make ATP during photosynthesis and use it to

synthesize glucose and other carbohydrates

3

Most organisms, including photoautotrophs, make ATP by breaking down glucose and

other organic compounds.

Main Pathways Of Respiration

Aerobic respiration

Aerobic metabolic pathways (using oxygen) are used by most

eukaryotic cells

Fermentation

Anaerobic metabolic pathways (occur in the absence of oxygen) are used by

prokaryotes and protists in anaerobic habitats.

Aerobic respiration and fermentation both begin with glycolysis, which converts one molecule of glucose into two molecules of pyruvate

✓ After glycolysis, the two pathways diverge

✓ Fermentation is completed in the cytoplasm, yielding 2 ATP per glucose molecule

✓ Aerobic respiration is completed in mitochondria, yielding 36 ATP per glucose

molecule if all processes there go to completion.

Overview Of Aerobic Respiration

■ Three stages

• Glycolysis (carried out in cytoplasm; necessary to set stage for

mitochondrial processes that follow

• Acetyl-CoA formation during Krebs cycle

• Electron transfer phosphorylation (ATP formation)

C6H12O6 (glucose) + O2 (oxygen) → CO2 (carbon dioxide) + H2O (water)

4

• Coenzymes NADH and FADH2 carry electrons and hydrogen

Energy From Carbohydrate Breakdown

Various degradative pathways convert the chemical energy of glucose

and other organic compounds to the chemical energy of ATP

Aerobic respiration yields the most ATP from each glucose molecule in

eukaryotes; it is completed inside the mitochondria

Glucose Breakdown Starts In Cytoplasm

✓ Glycolysis starts and ends in the cytoplasm of all prokaryotic and

eukaryotic cells

✓ An energy investment of ATP starts glycolysis

Glycolysis Steps

✓ Two ATP are used to split glucose and form 2 PGAL, each with one

phosphate group

✓ Enzymes convert 2 PGAL to 2 PGA, forming 2 NADH

5

✓ Four ATP are formed by substrate-level phosphorylation (gives net 2 ATP by process)

Glycolysis – Cytoplasm Only

Glycolysis – Respiration’s First Step

Glycolysis is the first stage of aerobic respiration and of anaerobic

routes such as fermentation pathways

Enzymes of glycolysis convert glucose to pyruvate

Respiration Second Stage

✓ The second stage of aerobic respiration finishes breakdown of glucose

that began in glycolysis

✓ Occurs in mitochondria

6

✓ Includes two stages: acetyl CoA formation and the Krebs cycle (each

occurs twice in the breakdown of one glucose molecule)

Acetyl CoA Formation

✓ In the inner compartment of the mitochondrion, enzymes split pyruvate,

forming acetyl CoA and CO2 (which diffuses out of the cell)

✓ NADH is formed

Krebs Cycle Summary

• A sequence of enzyme-mediated reactions that break down 1 acetyl

CoA into 2 CO2

• Oxaloacetate is used and regenerated

• 3 NADH and 1 FADH2 are formed

• 1 ATP is formed

• All these products set stage for big payoff in ATP storage in next

process of sequence

Inside A Mitochondrion

7

Acetyl CoA Formation

And Krebs Cycle

8

Aerobic Respiration’s Big Energy Payoff

✓ Many ATP are formed during the third and final stage of aerobic

respiration

✓ Electron transfer phosphorylation

• Occurs in mitochondria

• Results in attachment of phosphate to ADP to form ATP

• Results in many times the ATP from glycolysis

Electron Transfer Phosphorylation

✓ Coenzymes NADH and FADH2 donate electrons and H+ to electron

transfer chains

✓ Active transport forms a H+ concentration gradient in the outer

mitochondrial compartment

9

✓ H+ follows its gradient through ATP synthase, which attaches a phosphate

to ADP

✓ Finally, oxygen accepts electrons and combines with H+, forming water

How Aerobic Respiration Ends

The final stages of aerobic respiration break down pyruvate to CO2

Many coenzymes that become reduced deliver electrons and hydrogen

ions to electron transfer chains; energy released by electrons flowing

through the chains is captured in ATP

Oxygen accepts electrons at ends of the chains

Other Energy-Releasing Pathways

✓ Fermentation pathways break down carbohydrates without using oxygen

✓ The final steps in these pathways regenerate NAD+ but do not produce

ATP

✓ Glycolysis is the first stage of fermentation

✓ Forms 2 pyruvate, 2 NADH, and 2 ATP

✓ Pyruvate is converted to other molecules, but is not fully broken down to

CO2 and water

✓ Regenerates NAD+ but doesn’t produce ATP

✓ Provides enough energy for some single-celled anaerobic species

Two Pathways Of Fermentation

Alcoholic fermentation

• Pyruvate is split into acetaldehyde and CO2

10

• Acetaldehyde receives electrons and hydrogen from NADH, forming NAD+

and ethanol

Lactate fermentation

• Pyruvate receives electrons and hydrogen from NADH, forming NAD+ and

lactate

Muscles And Fermentation

✓ Slow-twitch muscle fibers (“red” muscles) make ATP by aerobic respiration

• Have many mitochondria

• Dominate in prolonged activity

✓ Fast-twitch muscle fibers (“white” muscles) make ATP by lactate

fermentation

• Have few mitochondria and no myoglobin

Sustain short bursts of activity

How Anaerobic Pathways End

Fermentation pathways start with glycolysis

Substances other than oxygen accept electrons at the end of the

pathways

Compared with aerobic respiration, the net yield of ATP from fermentation

is very small

Energy Sources In Body

11

✓ Pathways that break down molecules other than carbohydrates also keep

organisms alive

✓ In humans and other mammals, the entrance of glucose and other organic

compounds into an energy-releasing pathway depends on the kinds and

proportions of carbohydrates, fats and proteins in the diet

So What Happens To Glucose At Mealtime And Between Meals

✓ It’s a constant balancing act

✓ When blood glucose concentration rises, the pancreas increases insulin

secretion

• Cells take up glucose faster, more ATP is formed, glycogen and fatty-acid

production increases

✓ When blood glucose concentration falls, the pancreas increases glucagon

secretion

• Stored glycogen is converted to glucose

Energy From Fats

✓ About 78% of an adult’s energy reserves is stored in fat (mostly

triglycerides)

✓ Enzymes cleave fats into glycerol and fatty acids

• Glycerol products enter glycolysis

• Fatty acid products enter the Krebs cycle

• Compared to carbohydrates, fatty acid breakdown yields more ATP per

carbon atom

Energy From Proteins

12

✓ Enzymes split dietary proteins into amino acid subunits, which enter the

bloodstream

• Used to build proteins or other molecules

• Excess amino acids are broken down into ammonia (NH3) and various

products that can enter the Krebs cycle

Other Metabolic Pathways

Molecules other than glucose are common energy sources

Different pathways convert lipids and proteins to substances that may

enter glycolysis or the Krebs cycle

Reflections on Life’s Unity

✓ Life’s diversity and continuity arise from unity at the level of molecules and

energy

• Energy inputs drive the organization of molecules into cells (one-

way flow of energy)

✓ Energy from the sun sustains life’s organization

• Photosynthesizers use energy from the sun to feed themselves and

other forms of life

• Aerobic respiration balances photosynthesis

13

Used literature:

-“Pharmacy and Biology” –by D. Attwood, Alexander Taylor Florence - Chapman and

Hall (1983)

- “Hugo and Russell's Pharmaceutical Microbiology”- by Norman A. Hodges, Sean P. Gorman & others Stephen P. Denyer

http://www.google.com/products/catalog?q=biology+book+for

+pharmacy&hl=en&biw=1366&bih=667&prmd=imvns&um=1&ie=UTF-8&tbm=shop&cid=403011423

6410199401&sa=X&ei=p_k2T7XgA8bbsga666HZDA&ved=0CIsBEPMCMAY

http://www.archive.org/stream/handbookofpharma00elil/handbookofpharma00elil_djvu.txt

14

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