Discussion - Chapters 5-8

Malik333

Brooker_Biology_5ed_Ch07_lecture_ppt_edit.pdf

Home >Biology homework help >Discussion - Chapters 5-8

Because learning changes everything.®

Chapter 7

Lecture Outline

See separate PowerPoint slides for all

figures and tables pre-inserted into

PowerPoint without notes and animations.

No reproduction or further distribution permitted without the prior written consent of McGraw-Hill Education.

Chapter 7

Cellular Respiration and Fermentation

Key Concepts: • Overview of Cellular Respiration

• Glycolysis

• Breakdown of Pyruvate

• Citric Acid Cycle

• Oxidative Phosphorylation

• A Closer Look at ATP Synthase

• Connections Among Carbohydrate, Protein, and Fat Metabolism

• Anaerobic Respiration and Fermentation

Overview of Cellular Respiration

Process by which living cells obtain energy from organic molecules

Primary aim to make ATP and NADH

Aerobic respiration uses oxygen

• O2 consumed and CO2 released

Primarily use glucose but other organic molecules also used

Glucose metabolism

Four metabolic pathways:

• Glycolysis

• Breakdown of pyruvate

• Citric acid cycle

• Oxidative phosphorylation

Figure 7.1

Glycolysis

Stage 1 of cellular respiration

Glycolysis can occur with or without oxygen

Steps in glycolysis nearly identical in all living species

Ten steps in three phases:

• Energy investment

• Cleavage

• Energy liberation

Three phases of glycolysis

Energy investment

• Steps 1 to 3 • 2 ATP hydrolyzed to create fructose-1,6 bisphosphate

Cleavage

• Steps 4 to 5 • 6 carbon molecules broken into two 3 carbon molecules of

glyceraldehyde-3-phosphate

Energy liberation

• Steps 6 to 10 • Two glyceraldehyde-3-phosphate molecules broken down into two

pyruvate molecules – produces 2 NADH and 4 ATP (net yield = 2 ATP)

Figure 7.2: Energy Investment Phase

Access the text alternative for slide images.

Figure 7.2: Cleavage and Energy Liberation Phases

Access the text alternative for slide images.

Figure 7.2

Steps of glycolysis in greater detail

Access the text alternative for slide images.

Figure 7.3 steps 6 through 10

Access the text alternative for slide images.

Cancer Cells Usually Exhibit

High Levels of Glycolysis

• Many disease associated with alterations in carbohydrate metabolism

• Warburg effect – cancer cells preferentially use glycolysis while decreasing oxidative phosphorylation

• Used to diagnose cancers in PET scans

• Glycolytic enzymes overexpressed in 80% of all types of cancers

• May be due to low oxygen levels inside tumors, with overexpression of glycolysis genes in response

Figure 7.4

©Steven Needell/Science Source

Breakdown of Pyruvate

• Stage 2 of cellular respiration

• In eukaryotes, pyruvate is transported into the mitochondrial matrix

• Broken down by pyruvate dehydrogenase

• Molecule of CO2 removed from each pyruvate

• Remaining acetyl group attached to CoA to make acetyl CoA

• Yield = 1 NADH for each pyruvate

Figure 7.5

Pyruvate is made in the cytosol by glycolysis. It travels through a channel in the outer membrane and an H pyruvate symporter in the inner membrane to reach the mitochondrial matrix.

Pyruvate is oxidized via pyruvate dehydrogenase to an acetyl group and CO2. NADH is made. During this process, the acetyl group is transferred to coenzyme A (CoA) and is later removed and enters the citric acid cycle.

Citric Acid Cycle

Stage 3 of cellular respiration

Metabolic cycle

• Some molecules enter while others leave

• Series of organic molecules regenerated in each cycle

Acetyl is removed from Acetyl CoA and attached to oxaloacetate to form citrate (aka citric acid)

Series of steps releases 2 CO2, 1 ATP, 3 NADH, and 1 FADH2

Oxaloacetate is regenerated to start the cycle again

Figure 7.6

Details of the citric acid cycle

Access the text alternative for slide images.

Oxidative Phosphorylation

• Stage 4 of cellular respiration

• High energy electrons removed from NADH and FADH2 to make ATP

• Typically requires oxygen

• Oxidative process involves electron transport chain

• Phosphorylation occurs by ATP synthase

Oxidation by the Electron Transport Chain (ETC)

• Protein complexes and small organic molecules embedded in the inner mitochondrial membrane

• Accept and donate electrons in a linear manner in a series of redox reactions

• Movement of electrons generates an

H  electrochemical gradient (proton-motive force)

• This provides energy for the next step –synthesizing ATP

Figure 7.8

Access the text alternative for slide images.

Phosphorylation by ATP synthase

• Lipid bilayer of inner mitochondrial membrane is relatively impermeable to H



• Protons can only pass through ATP synthase

• Harnesses free energy to synthesize ATP from ADP

• Chemiosmosis – chemical synthesis of ATP as a result of pushing H across a membrane

Figure 7.9

Access the text alternative for slide images.

NADH oxidation makes most of the cell’s ATP

NADH oxidation creates the H electrochemical gradient used to synthesize ATP

Yield = up to 30 to 34 ATP molecules / glucose

But rarely achieve maximal amount because:

• NADH also used in anabolic pathways • H

 gradient used for other purposes

ATP synthase

• ATP synthase captures free energy as H ions flow through

• The enzyme converts energy from the proton motive force

of the H  gradient to

chemical bond energy in ATP

• Racker and Stoeckenius confirmed ATP uses an H

 electrochemical gradient

1. ATP synthase and bacteriorhodopsin were incorporated into membrane vesicles.

2. ADP and iP were added on the outside of the vesicles.

3a One sample was kept in the dark. No ATP was made.

3b One sample was exposed to light. ATP was made.

ATP Synthase consists of subunits

The nonmembrane- embedded portion consists of 1ε , 1 γ , 1δ , 3 α , and 3 β subunits. Movement of H

between a c subunit and the a subunit causes the γ subunit to rotate. The rotation, in 120 increments, causes the β subunits to progress through a series of 3 conformational changes that lead to the synthesis of ATP from ADP and

i P .

The membrane-embedded portion consists of a ring of 9 to 12 c subunits, 1 a subunit, and 2 b subunits. H

 move

between the c and a subunits.

Figure 7.12

• ATP synthase is a rotary machine

• Conformational changes produce ATP

Access the text alternative for slide images.

Yoshida and Kinosita demonstrated that the gamma subunit of the ATP synthase spins

Masasuke Yoshida, Kazuhiko Kinosita, and colleagues set out to visualize the rotary nature of the ATP synthase

They released membrane embedded portion and adhered it to a slide

Revealed γ subunit using fluorescence

Added ATP to make reaction run backward

Rotated counterclockwise to hydrolyze ATP

• So it must rotate clockwise to synthesize ATP

Figure 7.13 1 HYPOTHESIS ATP synthase is a rotary machine.

KEY MATERIALS Purified complex containing 1γ , 3 α , and 3 β subunits.

1. Adhere the purified 3 3γα β complex to a glass

slide so the base of the γ subunit

is protruding upward.

2. Add linker proteins and fluorescently labeled actin filaments. The linker protein recognizes sites on both the γ subunit and the actin filament.

3. Add ATP. As a control, do not add ATP.

4. Observe under a fluorescence microscope. The method of fluorescence microscopy is described in Figure 4.6.

Figure 7.13 2 HYPOTHESIS ATP synthase is a rotary machine.

KEY MATERIALS Purified complex containing 1 γ, 3 α, and 3 β subunits.

5. THE DATA

Results from step 4:

ATP Rotation

No ATP added No rotation observed.

ATP added Rotation was observed as shown below. This is a time-lapse view of the rotation in action.

6. CONCLUSION The γ subunit rotates counterclockwise when ATP is hydrolyzed. It would be expected to rotate clockwise when ATP is synthesized.

7. SOURCE Noji, H., Yoshida, M. 2001. The rotary machine in the cell, ATP synthase. Journal of Biological Chemistry 276: 1665 to 1668.

Connections Among Carbohydrate,

Protein, and Fat Metabolism

• Besides glucose, other molecules also used for energy: carbohydrates, proteins, fats

• Enter into glycolysis or citric acid cycle at different points

• Utilizing the same pathways for breakdown increases efficiency

• Metabolism can also be used to make molecules (anabolism)

Figure 7.14

Anaerobic Respiration and

Fermentation

For environments that lack oxygen or during oxygen deficient times

Two strategies:

• Use substance other than O2 as final electron acceptor in electron transport chain

• Produce ATP only via substrate-level phosphorylation

Other acceptors

• E. coli uses nitrate

 3NO 

under anaerobic conditions

• Also makes ATP via chemiosmosis even under aerobic conditions

Fermentation

• Fermentation is the breakdown of organic molecules without net oxidation

• Many organisms can only use O2 as final electron acceptor, so under anaerobic conditions, they need a different way to produce ATP, like using glycolysis

• But glycolysis uses up NAD and makes too much NADH under anaerobic conditions (dangerous situation)

• Muscle cells solve problem by reducing pyruvate into lactate

• Yeast solve problem by making ethanol

• Fermentation produces far less ATP than oxidative phosphorylation

Figure 7.16

a) Production of lactic acid

Glucose is oxidized to 2 pyruvate molecules. Two pyruvates are reduced to 2 lactate molecules.

b) Production of ethanol

Glucose is oxidized to 2 pyruvate molecules. Two acetaldehyde molecules are reduced to 2 ethanol molecules.

No reproduction or further distribution permitted without the prior written consent of McGraw-Hill Education.

End of Main Content

Because learning changes everything. ®

www.mheducation.com

http://www.mheducation.com/