nerve activates contraction - st. johns county school districtwhat is the primary purpose of...

• Living is work.

• To perform their many

tasks, cells must bring in

energy from outside

sources.

• In most ecosystems, energy enters as sunlight.

• Light energy trapped in organic molecules is available to both photosynthetic organisms and others that eat them.

Introduction

Fig. 9.1

• Cellular respiration is similar to the combustion of

gasoline in an automobile engine.

• The overall process is:

• Organic compounds + O2 -> CO2 + H2O + Energy

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

the fuel, but it is traditional to start learning with

glucose as the fuel molecule, because it is the one

most abundantly used.

• C6H12O6 + 6O2 -> 6CO2 + 6H2O + Energy (ATP + heat)

Benchmark Clarifications

Students will explain how the products of photosynthesis are used

as reactants for cellular respiration and vice versa.

Students will explain how photosynthesis stores energy and

cellular respiration releases energy.

Students will identify the reactants, products and/or the basic

function of photosynthesis.

Students will identify the reactants, products and/or the basic

functions of aerobic & anaerobic cellular respiration.

Students will connect the role of ATP to energy transfers within

the cell.

• In cellular respiration, glucose and other fuel

molecules are oxidized, releasing energy.

• Molecules that have an abundance of hydrogen are

excellent fuels because their bonds are a source of

energetic electrons that give off their energy as they

are transferred to oxygen.

• The energy from these electrons will be transferred

to the energy rich bonds of ATP molecules when

they help form these bonds.

4. Electrons “fall” from organic molecules to

oxygen during cellular respiration

• Cellular respiration does not oxidize glucose in a single step that transfers all the hydrogen in the fuel to oxygen at one time.

• Rather, glucose and other fuels are broken down gradually in a series of chemical reaction steps, each catalyzed by a specific enzyme.

• At key steps, hydrogen atoms are stripped from glucose and passed first to a coenzyme, like NAD+

(nicotinamide adenine dinucleotide).

5. The “fall” of electrons during respiration

occurs in small steps

Fig. 9.4

• This changes NAD+, to NADH, which carries the

energy of the electrons.

Part of this involves mitochondria in eukaryotic cells

1. Respiration involves glycolysis, the Krebs

cycle, and electron transport:

an overview

Fig. 9.6

• During glycolysis, glucose, a six carbon-sugar, is split into two, three-carbon sugars, pyruvate. Let’s watch the whole thing. 5 min.

• Each of the ten steps in glycolysis is catalyzed by a specific enzyme, and occurs in the cytoplasm.

• These steps can be divided into two phases: an energy investment phase and an energy payoff phase.

2. Glycolysis breaks down glucose to

pyruvate in 10 small steps:

a closer look

• In the energy investment phase, ATP provides activation energy by phosphorylating glucose.

• This requires 2 ATP per glucose.

• In the energy payoff phase, 4 ATP are produced and NAD+ is reduced to NADH.

• 2 ATP (net) and 2 NADH are produced per glucose.

Fig. 9.8

• The net yield from glycolysis is 2 ATP and 2

NADH per glucose.

• No CO2 is produced during glycolysis.

• Glycolysis occurs whether O2 is present or not.

• If O2 is present, pyruvate moves into the

mitochondria to the Krebs cycle and the

energy stored in NADH can be converted to

ATP by the electron transport chain.

• As pyruvate enters the mitochondrion, a

multienzyme complex modifies pyruvate to acetyl

CoA which enters the Krebs cycle in the matrix.

• A carboxyl group is removed as CO2.

• A pair of electrons is transferred from the remaining

two-carbon fragment to NAD+ to form NADH.

• The 2 carbon acetic

acid combines with

coenzyme A to

form acetyl CoA.

Fig. 9.10

• More than three quarters of the original energy in

glucose is still present in two 2 molecules of

pyruvate.

• If oxygen is present, pyruvate enters the

mitochondrion where enzymes of the Krebs cycle

complete it’s breakdown to carbon dioxide. Let’s

watch it..

3. The Krebs cycle completes the energy-

releasing breakdown of organic

molecules: a closer look

• The Krebs cycle is named after Hans Krebs who

was largely responsible for elucidating its

pathways in the 1930’s.

• This cycle begins when acetic acid from acetyl CoA

(2C) combines with oxaloacetate (4C) to form citrate

• Ultimately, the oxaloacetate is recycled and the acetate

is broken down to CO2.

• Each cycle produces one ATP, three NADH, and one

FADH2 (another electron carrier) per acetyl CoA.

• The Krebs

cycle consists

of eight steps.

Fig. 9.11

• Only 4 of 38 ATP ultimately produced by respiration

of glucose are derived from glycolysis and the Krebs

• The vast majority of the ATP comes from the energy

in the electrons carried by NADH (and FADH2).

• The energy in these electrons is used in the electron

transport system to power ATP synthesis.

4. The inner mitochondrial membrane

couples electron transport to ATP

synthesis: a closer look

• Electrons carried by NADH and FADH are transferred to the molecules in the electron transport chain.

• The electrons continue along the chain, which includes several cytochromeproteins.

Fig. 9.13

Fig. 9.15

• Electrons from NADH or FADH2 ultimately pass to

oxygen, the so-called final electron acceptor, causing this

to be called aerobic respiration.

• The electron transport chain generates no ATP directly.

• The movement of electrons along the chain does contribute

to a process called chemiosmosis, which leads to ATP

synthesis by oxidative phosphorylation (or ox-phos as

it’s referred to in small talk at biologists’ cocktail parties).

• Here’s how it works:http://highered.mcgraw-

hill.com/sites/0072437316/student_view0/chapter9/animati

ons.html

• A proton gradient is produced by the movement

of electrons along the electron transport chain,

because several chain molecules can use the

exergonic flow of electrons to pump H+ from the

matrix to the intermembrane space.

• The gradient produced involves more protons in

the intermembrane space than in the matrix.

• This gradient represents a form of potential energy,

very similar to the one in a flashlight battery.

• A protein complex, ATP synthase, in the cristae actually makes ATP from ADP and Pi.

• The energy of theproton gradient is used as the source of power to do the work of ATP synthesis.

• How about a little animation? http://vcell.ndsu.nodak.edu/animations/atpgradient/movie.htm

Fig. 9.14

• The ATP synthase molecules are the only place that

will allow H+ to diffuse back to the matrix.

• This exergonic flow of H+ through the protein complex

is used by the enzyme to generate ATP.

• This coupling of the redox reactions of the electron

transport chain to ATP synthesis is called

chemiosmosis.

• The energy from glucose electrons was used to move

protons across a membrane (uphill, so to speak), and

when they passively flowed back across the membrane

(downhill), their energy was used to do the work of

making ATP.

• During respiration, most energy flows from glucose -> NADH -> electron transport chain -> ATP.

• Considering the fate of carbon, one six-carbon glucose molecule is oxidized to six CO2 molecules.

• Some ATP is produced during glycolysis and the Krebs cycle, but most comes from the electron transport chain.

5. Cellular respiration generates many ATP

molecules for each sugar molecule it

oxidizes: a review

• Assuming the most energy-efficient

shuttle of NADH from glycolysis, a

maximum yield of 34 ATP is produced by

the ETC from one glucose.

• This plus the 4 ATP from substrate-level

phosphorylation gives a bottom line of 38

ATP per glucose molecule broken down.

• Glycolysis generates 2 ATP whether oxygen is

present (aerobic) or not (anaerobic).

1. Fermentation enables some cells to produce

ATP without the help of oxygen

• Anaerobic catabolism of sugars can occur by fermentation.

• Fermentation can generate ATP from glycolysis as long as there is a supply of NAD+ to accept electrons.

• If the NAD+ pool is exhausted, glycolysis shuts down.

• Under aerobic conditions, NADH transfers its electrons to the electron transfer chain, recycling NAD+.

• Under anaerobic conditions, various fermentation pathways generate ATP by glycolysis and produce fresh NAD+ by transferring electrons from NADH to pyruvate. This, like glycolysis, happens in the cytoplasm, so it can’t help the Krebs Cycle.

• In alcohol fermentation, pyruvate is converted to

ethanol in two steps.

• First, pyruvate is converted to a two-carbon compound,

acetaldehyde, by the removal of CO2.

• Second, acetaldehyde is reduced by NADH to ethanol.

• Alcohol fermentation

by yeast is used in

baking and alcoholic

beverage making.

Fig. 9.17a

• During lactic acid fermentation, pyruvate is

reduced directly by NADH to form lactate (lactic

acid).

• Lactic acid fermentation by some fungi and bacteria is used to make cheese and yogurt.

• Muscle cells switch from aerobic respiration to lactic acid fermentation to generate ATP when O2 is scarce.

• The waste product, lactate, was thought of to be the cause muscle fatigue, but ultimately it is converted back to pyruvate in the liver.

Fig. 9.17b

• Carbohydrates, fats,

and proteins can all be

catabolized through

the same pathways.

We usually learn about

the breakdown of

glucose, but at rest,

most of our ATP’s

actually come from the

breakdown of fatty

acids into 2 carbon

acetyl CoA’s.

Fig. 9.19

Chloroplasts are found in most plant cells but not in

animal cells. Mitochondria are found in animal

cells and most plant cells. Why are mitochondria

found in most plant cells?

What is the primary purpose of cellular

respiration?

a. To store chemical energy in glucose molecules

b. To store chemical energy in carbon dioxide and

water molecules

c. To use chemical energy from glucose molecules

d. To use chemical energy from carbon dioxide and

water molecules

Cellular respiration is a chemical process and can be

represented by a chemical equation. What are the

products in this chemical process?

a. Hydrocarbons and oxygen

b. Hydrocarbons and carbon dioxide

c. Water, carbon dioxide, and energy

d. Water, carbon dioxide, and oxygen

Which equation shows the reactants and

products of cellular respiration?

a. Carbon dioxide + water → sugar + oxygen

b. Carbon dioxide + oxygen → sugar + water

c. Sugar + carbon dioxide →water + oxygen

d. Sugar + oxygen →water + carbon dioxide

All cells need energy. Where does the energy come

from in plants? Briefly trace the energy from the

original source to the “endpoint”.

In animals?

Which of these is required for aerobic

cellular respiration?

• A. oxygen

• B. nitrogen

• C. carbon dioxide

• D. sunlight

In terms of energy, how are cellular respiration

and photosynthesis related?

a. Energy captured in photosynthesis is used to

power cellular respiration

b. The energy transformed in cellular respiration is

used to power photosynthesis

c. Photosynthesis and respiration perform the same

task in terms of energy transformation

d. Energy is not involved in either photosynthesis

or cellular respiration

Photosynthesis and cellular respiration are

interrelated processes. During which biogeochemical

cycle do the biological processes of photosynthesis

and cellular respiration play key roles?

A. carbon cycle

B. hydrogen cycle

C. nitrogen cycle

D. oxygen cycle

nerve activates contraction - st. johns county school districtwhat is the primary purpose of...

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