Visual Anatomy & Physiology First Edition Martini & Ober Chapter 22 (Sections 22.1-22.4) Metabolism...

Visual Anatomy & PhysiologyFirst Edition

Martini & Ober

Chapter 22(Sections 22.1-22.4)

Metabolism & Cellular RespirationLecture 8

2

Lecture Overview

• Enzymes and control of metabolic reactions• Energy and metabolic reactions• Cellular respiration

– Overview– ATP as the biological energy carrier– Oxidation/Reduction– Steps in Cellular Respiration

• Glycolysis• The Citric Acid (Krebs) Cycle • The Electron Transport Chain

• Relationship of anabolism to catabolism

3

Enzymes and Metabolic Reactions

Enzymes – Biological catalysts

• control rates of metabolic reactions• lower activation energy needed to start reactions• globular proteins with specific shapes• not consumed in chemical reactions

• substrate specific

• shape of active site determines which substrate(s) the enzyme can act on

Figure from: Hole’s Human A&P, 12th edition, 2010

5

Enzymes Lower Activation Energy

Enzymes lower the barriers that block chemical reactions, i.e., they lower the activation energy needed to begin energetically favorable reactions

6

Control of Metabolic ReactionsMetabolic pathways

• series of enzyme-controlled reactions leading to formation of a product• each new substrate is the product of the previous reaction

Factors that alter activity of enzymes

• heat• radiation• substrate concentration• required cofactors• changes in pH

Enzyme names commonly• reflect the substrate• have the suffix – ase• sucrase, lactase, protease, lipase, hydrolase, oxidase

7

Cofactors and CoenzymesCofactors

• make some enzymes active• ions or coenzymes

Coenzymes• complex organic molecules that act as cofactors (so coenzymes ARE cofactors)• vitamins• NAD+

Vitamins are essential organic substances that human cells cannot synthesize, i.e., they must come from the diet

- required in very small amounts

- examples - B vitamins: Thiamine (B1), niacin

The protein parts of enzymes that need a nonprotein part (coenzymes, cofactors) to work are called apoenzymes

8

Overview of Cellular Metabolism

Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001

Metabolism – All the chemical reactions that occur in an organism

KEEP THIS OVERALL SCHEME IN MIND AS WE GO INTO DETAILS!!

ETS

9

Overview of Glucose Breakdown


11

Overview of Catabolism

Figure from: Martini, Visual Anatomy & Physiology, Pearson, 2011

12

A Closer Look at Mitochondria

Strategically placed in cell where ATP demand is high

Concentration of enzymes in the matrix is so high that there is virtually no hydrating water. Enzyme-linked reactions and pathways are so crowded that normal rules of diffusion do not apply!


(Impermeable to charged or polar molecules)

13

Carbohydrate Metabolism

• Most cells generate ATP and other energy-yielding compounds via the catabolism of carbohydrate (and fats)

General Reaction sequence in carbohydrate catabolism

C6H12O6 + 6 O2 6 CO2 + 6 H2O + ENERGY

If the above reaction happened all at once, all the chemical energy contained in the carbohydrate would be DISSIPATED AS HEAT.

How does the body harness the energy from carbohydrates?

14

Harnessing Energy - Stepwise Breakdown of Carbohydrates

Figure from: Alberts et al., Essential Cell Biology, Garland Press, 1998

15

Energy for Metabolic Reactions

Energy• ability to do work or change something (potential, kinetic)• heat, light, sound, electricity, mechanical energy, chemical energy• changed from one form to another, but NEVER destroyed (law of conservation of energy)• involved in all metabolic reactions

Release of chemical energy• most metabolic processes depend on chemical energy• oxidation of glucose generates chemical energy• cellular respiration releases chemical energy slowly from molecules and makes it available for cellular use

16

Oxidation and Reduction Revisited

Oxidation• gain of O2

• loss of e-

• loss of H (since a H carries an electron with it) • increase in oxidation number, e.g., Fe2+ -> Fe3+

Oxidation Is Loss of electrons; Reduction Is Gain of electrons

“OIL RIG”

Reduction • loss of O2

• gain of e-

• gain of H • decrease in oxidation number, e.g., Fe3+ -> Fe2+

17

Energy of Organic Molecules• Carbohydrates like glucose store a great deal

of chemical energy (as H·)• As carbohydrates (C6H12O6) are oxidized to

CO2 they liberate their energy and lose electrons and H (H·)

• But there must be molecules to accept these electrons, i.e., some molecules must be reduced.

• In cellular respiration, O2 becomes the final electron (H·) acceptor and is reduced to H2O

18

Harnessing Energy from Carbohydrates

General Reaction sequence in carbohydrate catabolism

C6H12O6 + 6 O2 6 CO2 + 6 H2O + ENERGY

OXIDATION

REDUCTION

Electrons (H·) “fall” in energy from organic molecules to oxygen during cellular respiration.

That is, e- LOSE potential energy during this process and this energy is captured to make ATP

However, electrons CANNOT be transferred directly from glucose to the electron transport chain. There are intermediates – activated carrier molecules

19

Activated Carrier Molecules


Some activated carriers: ATP, NADH, FADH2, GTP, NADPH

20

ATP – An Activated Carrier Molecule

• each ATP molecule has three parts:• an adenine molecule• a ribose molecule• three phosphate molecules in a chain

• ATP carries its energy in the form or P (phosphate)

• ATP is a readily interchangeable form of energy for cellular reactions (“common currency”)

These two components together are called a ?

High-energy bonds


21

NAD(H) – An Activated Carrier Molecule

NAD (and NADP) are specialized to carry high-energy e- and H atoms


A “packet” of energy = H·

These packets of energy will be passed to oxygen in the electron transport chain, and their energy used to drive the synthesis of ATP

Important carriers of e- in catabolism: NADH, FADH2

NAD+

NADH + H+

NAD+ NADH

22

Overview of Cellular Respiration


Cellular respiration

(aerobic)

Anaerobic

23

Overview of Glucose BreakdownFigure from: Hole’s Human A&P, 12th edition, 2010

24

Overview of Glucose BreakdownOccurs in three major of reaction series…

1. Glycolysis (glucose to pyruvate; in cytoplasm) 2. Citric acid cycle (finishes oxidation begun in glycolysis;

in the matrix of mitochondria)3. Electron transport chain (uses e- transfer to make

ATP; on inner membranes of mitochondria)

Produces• carbon dioxide• water• ATP (chemical energy)• heat (energy has changed form from chemical)

Includes• anaerobic reactions (without O2) - produce little ATP• aerobic reactions (requires O2) - produce most ATP

25

Glycolysis• series of ten reactions

• breaks down glucose (6C) into 2 molecules of pyruvic acid (pyruvate) (3C)

• occurs in cytosol

• anaerobic phase of cellular respiration (that is, it can continue to work with OR without O2)

• yields 2 ATP and 2 NADH molecules per glucose

Glucose (6C) 2 Pyruvate (3C)NAD+ NADH

ADP + Pi ATP

26

Overview of Glycolysis

glucose (6C) → 2 pyruvate (3C)

Products of glycolysis

- ATP

- NADH

- Pyruvate

NOTE what happens with and without O2 being available…


27

Metabolism of Pyruvate Without O2

• process of forming lactate from glucose is anerobic glycolysis

• important for regenerating NAD+ so glycolysis can continue to generate ATP for the cell

Glucose (6C) 2 Pyruvate (3C)

NAD+ NADH + H+

ADP + Pi ATP

Pyruvic acid (pyruvate)NADH + H+ NAD+

Lactic acid (lactate)

O2

28

Overview of Aerobic Reactions

If oxygen is available – • pyruvic acid is used to produce acetyl CoA• citric acid (Krebs) cycle begins• electron transport chain functions• carbon dioxide and water are formed• maximum of 36 molecules of ATP produced per glucose molecule


29

Citric Acid Cycle

What happens…

- Acetyl CoA enters cycle - Citric Acid is converted to various intermediates - Several important products are produced in these interconversions of citric acid…

• ATP is produced•NAD+ is reduced to NADH and FAD is reduced to FADH2

• CO2 produced

In mitochondria…Figure from: Hole’s Human A&P, 12th edition, 2010

30

Source of e- for the Electron Transport Chain

Notice the flow of electrons to the Electron Transport Chain


31

Electron Transport Chain• NADH and FADH2 carry electrons to the ETC• ETC series of electron carriers located in cristae of mitochondria• energy from electrons transferred to ATP synthase• ATP synthase catalyzes the oxidative phosphorylation of ADP to ATP• water is formed

*Chemiosmosis


32

Oxidative Phosphorylation


Chemiosmosis, Chemiosmotic coupling, or Chemiosmotic phosphorylation

33

Summary of Cellular Respiration


34

Is This All the Metabolism There Is?

Definitely NOT!

Notice how many lines connect pyruvate and Acetyl CoA to the rest of metabolism

35

Intermediates of Metabolism

Acetyl CoA (2C) and Pyruvate (3C) are important:

Allow interconversion of different types of molecules so cell’s needs can be met

Figure from: Martini, Visual Anatomy & Physiology, Pearson, 2011

36

Summary of Catabolism of Proteins, Carbohydrates, and Fats

Acetyl CoA is a common intermediate in the breakdown of most fuels.

Acetyl CoA can be generated by carbohydrates, fats, or amino acids

Acetyl CoA can be converted into fatty acids


37

Pyruvate is a Key Junction in Metabolism


Pyruvate is used to synthesize amino acids and Acetyl CoA

Pyruvate can also be used to synthesize glucose via gluconeogenesis.

*

Lipolysis

Lipo-

genesis

GlycogenesisGlycogenolysis

38

Carbohydrate StorageExcess glucose can be

• stored as glycogen by glycogenesis (liver and muscle cells) • stored as fat by lipogenesis• converted to amino acids


39

Terms to Know…

• Glycolysis – metabolism of glucose to pyruvate• Gluconeogenesis – metabolism of pyruvate to

glucose (making CHO from non-CHO source)• Glycogenesis – metabolism of glucose to

glycogen• Glycogenolysis – metabolism of glycogen to

glucose• Lipolysis – breakdown of triglyceride into

glycerol and fatty acids• Lipogenesis – creation of new triglyceride (fat)

-olysis breakdown of -neo new-genesis creation of

40

Review

• Enzymes are biological catalysts– Highly specific for their substrate– Lower activation energy needed to start a reaction– Are not consumed during reaction– May require cofactors/coenzymes– Effectiveness is greatly affected by temperature,

pH, and the presence of required cofactors

• The goal of metabolism is to provide the cell with energy (catabolism) and materials for the manufacture of cellular components (anabolism)

41

Review

• Cells derive energy mainly from carbon compounds like carbohydrates and fats– These substances contain a great deal of energy

stored in their chemical bonds– This energy must be liberated in stepwise

fashion– Activated carriers serve as intermediates to

capture the energy liberated at each step

• Energy is the ability to do work– May be potential or kinetic– Changes form– Is never destroyed (only converted to another

form)

44

Review

• Anabolism is intimately tied to catabolism– Energy derived from catabolism is used to drive anabolic

reactions– Some molecules are important junctions between

catabolism and anabolism – Acetyl CoA

• Generated from pyruvate, fatty acids, and amino acids• Can be used to synthesize fatty acids and other molecules• CANNOT be used to generate pyruvate

– Pyruvate • Can be synthesized from glucose and amino acids• can be used to synthesize amino acids, glucose and acetyl CoA

– NOTE, however, that in humans fatty acids cannot be converted to glucose

Visual Anatomy & Physiology First Edition Martini & Ober Chapter 22 (Sections 22.1-22.4) Metabolism...

Documents

Transcript of Visual Anatomy & Physiology First Edition Martini & Ober Chapter 22 (Sections 22.1-22.4) Metabolism...