Chapter 4

Copyright © 2009 Pearson Education, Inc.

© 2013 Pearson Education, Inc.

PowerPoint Lecture prepared byJill Feinstein

Richland Community College

Fourth Edition

BIOLOGYScience for Life | with Physiology

Colleen Belk • Virginia Borden Maier

ChapterChapter 4 4Operating a Cell:

Enzymes, Metabolism, and Cellular Respiration


Enzymes and Metabolism Enzymes

Proteins that catalyze (speed up) chemical reactions in a cell

the enzyme speeds up the reaction BUT IS NOT CONSUMED IN THE REACTION

Metabolism: all chemical reactions occurring in the body

organized into distinct metabolic pathways

Enzyme 1 Enzyme 2 Enzyme 3

Reaction 1 Reaction 2 Reaction 3ProductStarting

molecule

A B C D


Enzymes and Metabolism Enzymes

Enzymes work by lowering the activation energy needed for a reaction

activation energy – initial energy you need to put into the system to start the reaction


Enzymes and Metabolism Substrates are the substances being catalyzed by the enzyme enzymes bind a substrate at the active site

active site has a unique shape – fits the substrate specifically now know that the binding of the substrate to the active site

causes a shape change to the active site called induced fit

Specificity of the enzyme to the substrate is based on enzyme shape and active site


Animation: EnzymesClick “Go to Animation” / Click “Play”


Metabolism Types of metabolic reactions

reactions in which the potential energy of the products is lower than that of the reactants are called exergonic

these reactions release energy into the system

those exergonic reactions release some of their energy in the form of heat = exothermic reaction

those reactions in which the potential energy of the products is greater than that of the reactants are called endergonic

these reactions require energy input

those reactions that require the input of heat = endothermic

your metabolism is a combination of exothermic and endothermic reactions

are coupled together

i.e. the exothermic reactions provide the energy to drive the endothermic reactions

Endergonic reaction: energy required, nonspontaneous

ReactantsEnergy

Products

Amount of energy

required

Progress of the reaction

Fre

e en

erg

y

Exergonic reaction: energy released, spontaneous

Reactants

EnergyProducts

Progress of the reaction

Amount of energy

released

Fre

e e

ner

gy


ATP running all of your metabolic pathways takes energy

usually in the form of ATP

ATP = ribose sugar + adenine base + 3 phosphate groups

the breaking of one phosphate bond between 2 phosphate groups releases potential energy into the system

used by the cell to power the endergonic reactions of metabolism

as we breakdown food – use the potential energy in food chemicals to produce ATP

e.g. breakdown glucose to make ATP

160 kg of ATP per day!

phosphate bonds

ATP ADP + Pi + energy


ATP

the energy released from breaking down ATP can power different kinds of work in the cell


Metabolism

we need a way of quantifying the energy required to drive metabolism (i.e. to perform cellular work) calorie

a calorie is the amount of energy required to raise the temperature of 1 gram of water by 1C.

1000 calories 1 kilocalorie or Calorie

the breaking of one phosphate bond between 2 phosphate groups of ATP releases 7300 calories (7.3 kcal) of energy into the system


Metabolism

kilocalorie (kcal) or Calorie:

unit of energy represented on food labels

“Calories are consumed by cells to do work”

cell uses the potential energy in found to do work – by making ATP

we quantify that potential energy as calories

Extra calories can be stored as fat

3,555 Calories = 1 pound of fat

Metabolic rate: the rate at which the body uses energy


Enzymes and Metabolism

metabolic rate = rate at which your body uses energy

can be measured as the number of calories it takes to power your metabolism

Basal Metabolic Rate or BMR = represents the resting energy of a awake, resting but alert person

energy used to power the vital organs – 70% of our total energy needs

70 Calories/hour or 1680 Calories/day for an average male

Metabolic rate is influenced by many factors:

Body weight, sex, exercise, genetic makeup, age, and nutritional status

numerous equations can be used to calculate BMR and the number of Calories to be taken in per day


Cellular Respiration

Cellular respiration is a series of enzymatic reactions that converts energy from food into energy stored in ATP. ATP synthesis is performed in the cytoplasm = fermentation also takes place in the mitochondria = aerobic respiration


Cellular Respiration

when a phosphate group is transferred from ATP to another molecule (phosphorylation) - energy is transferred and ADP is produced.


Cellular Respiration as ATP is used in the cell it must be replenished by cellular

respiration.

Aerobic cellular respiration occurs in the mitochondria and requires the presence of oxygen.

C6H12O6 + 6O2 6CO2 + 6H2O + 36 ATP


Animation: Glucose MetabolismClick “Go to Animation” / Click “Play”


Aerobic Respiration

occurs in four complex steps starting in the cytosol of the cell and completing in the mitochondria.

1. Glycolysis – cytosol 2. Transition step – mitochondria 3. Kreb’s cycle 4. Electron Transport Chain (ETC) & ATP synthesis


Step 1: Glycolysis

6-carbon glucose molecule is broken down into two 3-carbon pyruvic acid molecules (i.e. pyruvate)

Takes place in the cytosol and doesn’t require oxygen and produces 2 ATP two molecules of an electron acceptor called NAD+ are used

these pick up the electrons and hydrogen ions released during glycolysis to become NADH

NADH carries 2 electrons and 2 protons NADH with its electrons will enter into mitochondria

End result:2 ATP2 NADH2 pyruvates


Step 2: Transition Step

pyruvate is brought into the mitochondria and chemically converted – IF O2 IS PRESENT mitochondria composition

a. outer membrane b. inner membrane folded into cristae c. center of the mitochondria = matrix

2 pyruvates are converted into 2 molecules of acetyl coA by the enzymes of the mitochondrial matrix matrix: 2 pyruvate 2 acetyl coA + 2 CO2 + 2NADH

make 2 more molecules of NADH Pyruvate

NAD

NADH

+ HAcetyl CoA

CO2

CoA

CoA

x2

End result:2 CO22 NADH2 acetyl coA


Step 3: Citric Acid Cycle Citric acid cycle: series of chemical reactions catalyzed by 8 different enzymes in the

mitochondrial matrix named this because one product in this cycle is citric acid

also called the Kreb’s cycle cycle runs twice – once for each molecule of acetyl coA made the result is the generation of 2 ATP, 6 NADH, 2 FADH2 and the release of 4 molecules

of carbon dioxide Acetyl CoA

CoA

2 CO2

ADP + P i

FADH2

FAD

ATP

3 NADH

3 NAD

Citricacidcycle

+ 3 H

x2 End result:2 ATP6 NADH2 FADH24 CO2


Step 4: Electron Transport and ATP Synthesis Electron transport chain acts like a conveyor belt, moving electrons through a series of

proteins

three protein complexes in the cristae of the mitochondria

NADH and FADH2 drop off their electrons and hydrogen ions to these complexes

the protein carriers move the electrons through the chain: 1 2 3

turns these complexes into proton pumps

pump the hydrogen into the space between the inner and outer membranes (intermembrane space)

the concentration of H+ ions increases within the intermembrane space H+ GRADIENT


Step 4: Electron Transport Chain and ATP Synthesis

H+ ions are charged, and can’t simply diffuse back across the membrane into the matrix

they must pass through a protein channel called ATP synthase – generating ATP as they do

as H+ ions diffuse through ATP synthase = ADP + P ATP the ETC generates 34 ATP molecules for every pair of pyruvate that enters the

mitochondria add this to the 2 ATP made from cytosolic glycolysis = 36 ATP per glucose

at the end of the chain, the electrons combine with oxygen to produce water.

Ultimate electron acceptor = oxygen

End result:34 ATP made from NADH and FADH2


BioFlix: Cellular Respiration


Cellular Respiration - Metabolism of Other Nutrients

Proteins and fats can also provide energy when carbohydrates are unavailable.

They are broken down and their subunits feed into aerobic cellular respiration.


Anaerobic respiration: uses something other than O2 to accept electrons

done by bacteria

Fermentation takes place in the cytosol and does not require O2 to make ATP

first series of reactions in aerobic respiration

produces CO2 and lactic acid – done by bacteria, yeast and also in animal cells (e.g. muscle in humans)

C6H12O6 2 pyruvate + 2 ATP lactate (lactic acid)

if O2 is present – don’t make lactic acid – pyruvate is brought into the mitochondria to finish aerobic respiration

Cellular Respiration - Metabolism Without Oxygen: Anaerobic Respiration and Fermentation


Cellular Respiration - Metabolism Without Oxygen: Anaerobic Respiration and Fermentation

Bacteria in yogurt also use fermentation to make lactic acid.

Yeast cells use fermentation to convert glucose to ethanol.


Body Fat and Health

Difficult to define “overweight” precisely

Women need more body fat to maintain fertility than men do

Average healthy body fat percentages:

Women: 22% and Men: 14%

Body Mass Index (BMI): correlates amount of body fat with risk of illness and death, using both height and weight

Healthy range of BMI = 20-25

Obesity: BMI of 30 or higher


Body Fat and Health


Body Fat and Health

Risk of obesity is influenced by both lifestyle (diet, exercise) and genetics

Obesity increases risks of:

Diabetes

Hypertension

Heart disease

Stroke

Joint problems

Chapter 4

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