Cellular Respiration(Electron Transport Chains)

Introduction

The energy from the sun trapped by plants is obtained

by other organisms such as animals.

The plants and animals carry out the chemical energy of

food molecules that is released and partially captured in

the form of ATP (Adenosine Triphosphate).

Carbohydrates, fats, and proteins can all be used as fuels

in cellular respiration, but glucose is most commonly

used as an example to examine the reactions and

pathways involved.

Living cells require

energy to perform

different tasks. The

chloroplast of the plants

can collect the energy

from the sun through

photosynthesis and store

it in the chemical bonds

of carbohydrate

molecules.

What is Cellular Respiration?

Photosynthesis

What is Cellular Respiration?

However, other types of organisms such as fungi,

protozoa, and a large portion of bacteria, are unable to

perform photosynthesis. Thus, these organisms rely on

the carbohydrates formed in plants for their metabolic

processes. The process of converting carbohydrates from

food produced by plants into energy is known as cellular

respiration.

Cellular RespirationTherefore, cellular respiration can be defined as a long complicated process that breaks down the food molecules to release energy.

RELEASE ENERGYEating Food = Eating Glucose

• Food molecules are glucose specifically.

• We also need oxygen to oxidize thoroughly.

• Cell respiration also enables us to breathe out

carbon dioxide and the water that has made off to

the side.

• But the adenosine triphosphate is what we are

concerned about.

C6 H12 O6 + SUNLIGHT6O2 6CO2 + 6H2O + ATP

Oxygen acts as oxidizing agent because it accepts electrons to form water, the waste product of cellular respiration.

Cellular Respiration Processes

ETC

Krebs

Cycle

Glycolysis

We can divide cellular respiration into three metabolic processes: glycolysis,

the Krebs cycle, and electron transport chain. Each of these occurs

in a specific region of the cell:

1. Glycolysis occurs in the cytoplasm.

2. The Krebs cycle takes place in the matrix of the mitochondria.

3. Electron Transport Chain is carried out on the inner

mitochondrial membrane.

In the absence of oxygen, respiration consists of two metabolic pathways: glycolysis and fermentation. Both of

these occur in the cytoplasm.

Glycolysis

Glycolysis literally means "splitting sugars." Glucose, a six

carbon sugar, is split into two molecules of a three

carbon sugar. In the process, two molecules of ATP, two

molecules of pyruvic acid and two "high energy" electron

carrying molecules of NADH are produced. Glycolysis can

occur with or without oxygen. In the presence of oxygen,

glycolysis is the first stage of cellular respiration. Without

oxygen, glycolysis allows cells to make small amounts of

ATP. This process is called fermentation.

Krebs Cycle/ Citric Acid Cycle

The Krebs Cycle begins after the two molecules of the three carbon sugar produced in glycolysis are converted to a slightly different compound (acetyl CoA). Through a series of intermediate steps, several compounds capable of storing "high energy" electrons are produced along with two ATP molecules. These compounds, known as nicotinamide adenine dinucleotide (NAD) and flavinadenine dinucleotide (FAD), are reduced in the process. These reduced forms carry the "high energy" electrons to the next stage. The Citric Acid Cycle occurs only when oxygen is present but it doesn't use oxygen directly.

Electron Transport Chain (ETC)

Electron Transport requires oxygen directly. The electron

transport "chain" is a series of electron carriers in the

membrane of the mitochondria in eukaryotic cells.

Through a series of reactions, the "high energy" electrons

are passed to oxygen. The energy used in the electron

transport change pumps protons and the process of

pumping of protons is known as chemiosmosis. In the

said process, a hydrogen concentration gradient is

formed, and through phosphorylation ATP is ultimately

produced.

Metabolic Pathways

Glycolysis – it is the process that involves the

catabolism of glucose into two molecules of pyruvic

acid. There are several metabolic fates of a pyruvate.

In aerobic metabolism, the pyruvic acid is converted

to acetyl CoA which enters the Krebs Cycle. Pyruvic

acid in anaerobic metabolism is reduced to lactic acid.

Anaerobic Respiration

It is used by some microorganisms in which neither oxygen (aerobic respiration) nor pyruvate derivatives (fermentation) is the final electron acceptor. Rather, an inorganic acceptor such as sulfate or nitrate is used. Pyruvates were converted to lactate and this lactate remains in cytoplasm which could either be converted again to lactic acid as a waste product or enter the Cori Cycle. Below is the net equation for lactic acid fermentation.

Glucose + 2 ADP + 2 Pi 2 Lactate + 2 ATP

Cori CycleThis involves the utilization of lactate produced from

glucose by anaerobic glycolysis (lactic acid fermentation)

in the muscle cells and red blood cells. The lactate is

moved to the liver, re-oxidized to pyruvate and turned

back to glucose through gluconeogenesis. Then, it is

returned to the muscle or other peripheral tissues.

Aerobic Respiration

It requires oxygen in order to generate ATP.

Although carbohydrates, fats, and proteins can all be

processed and consumed as reactants, it is the preferred

method of pyruvate breakdown in glycolysis and requires

that pyruvate enter the mitochondrion in order to be fully

oxidized by the Krebs Cycle. The products of this process

are carbon dioxide and water, but the energy transferred

is used to break strong bonds in ADP as the third

phosphate group is added to form ATP,

NADH and FADH2.

Steps in Glycolysis

There are two major stages of glycolysis: preparatory

phase and pay off phase. In the first stage, the glucose is

prepared for its catabolism by its phosphorylation and

then cleaved to form three-carbon sugar. In this stage, 2

ATP molecules are expended. The second phase involves

the production of 4 molecules of ATP.

Preparatory Phase

Stage 1: Glucose

Phosphorylation

Stage 2: Isomerization

Stage 3: Second

Phosphorylation

Stage 4: Cleavage to

two triose phosphates

Stage 5: Isomerization

Preparatory Phase

Stage 6: Generation of

1,3-biphosphoglycerate

Stage 7: Substrate-level

phosphorylation

Stage 8: Phosphate

transfer

Stage 9: Synthesis of

phosphoenolpyruvate

Stage 10: Substrate-

levek phosphorylation

Overall Reaction of Glycolysis

C6 H12 O6 + 2 NAD+ + 2 ADP + 2 P 2 pyruvic acid

+ 2 ATP + 2 NADH + 2 H+

The reaction above is considered as exergonic due to

the production of 2 molecules of ATP.