Part 6: Metabolism & Cellular RespirationChapter 8 (8.3) & 9

Date:10/18/16

AP Bio Vocabulary of the Day(Stems, Prefixes, and Suffixes…Oh my!)

10/22:

crypt- hidden; covered

Example: cryptographer (someone who deciphers messages/breaks codes)

Fabulous Fact

Our eyes are always the same size from birth, but our nose and ears never stop growing.

What You Need To Know:

• The key role of ATP in energy coupling.

• The summary equation of cellular respiration.

• The difference between fermentation and cellular respiration.

• The role of glycolysis in oxidizing glucose to two molecules of pyruvate.

• The process that brings pyruvate from the cytosol into the mitochondria and introduces it into the citric acid cycle.

• How the process of chemiosmosis utilizes the electrons from NADH and FADH2 to produce ATP.

Energy = capacity to do work

• Kinetic energy (KE): energy associated with

motion

– Heat (thermal energy) is KE associated with

random movement of atoms or molecules

• Potential energy (PE): stored energy as a result of

its position or structure

– Chemical energy is PE available for release in a

chemical reaction

• Energy can be converted from one form to another

– Eg. chemical mechanical electrical

• A cell does three main kinds of work:

–Mechanical

–Transport

–Chemical

• Cells manage energy resources to do work by energy coupling: using an exergonic process to drive an endergonic one

• ATP (adenosine triphosphate) is the cell’s main energy source in energy coupling

• ATP = adenine + ribose + 3 phosphates

When the bonds between the phosphate groups are broken by hydrolysis energy is released

This release of energy comes from the chemical change to a state of lower free energy, not in the phosphate bonds themselves

How ATP Performs Work

• Exergonic release of Pi is used to do the endergonicwork of cell

• When ATP is hydrolyzed, it becomes ADP (adenosine diphosphate)

NH2

Glu

P i

Pi

P i

P i

GluNH3

P

P

P

ATP

ADP

Motor protein

Mechanical work: ATP phosphorylates motor proteins

Protein moved

Membrane

protein

Solute

Transport work: ATP phosphorylates transport proteins

Solute transported

Chemical work: ATP phosphorylates key reactants

Reactants: Glutamic acidand ammonia

Product (glutamine)made

+ +

+

Chapter 9: Respiration

Cellular Respiration• A review of redox (oxidation-reduction) reactions…

•Cellular respiration is a redox reaction

•Redox reactions release energy

• If all energy was released at once, it couldn’t be harnessed

• Instead, cellular respiration is a series of steps to break down glucose

Overview of Cellular Respiration – 3 Stage Process

Who Performs Cellular Respiration???Everyone!!! (Well…sort of)

Stage One: Glycolysis• Summary: the breakdown of glucose to two pyruvate molecules in the

cytosol

Details:

• Glucose is split into two 3 carbon sugars using 2 ATP

• The sugars are rearranged into two pyruvate molecules

• 2 NADH are made (NAD+ is an electron acceptor that is reduced)

• 4 ATP are made via substrate-level phosphorylation- ATP synthesis that transfers a phosphate group from a substrate instead of inorganic phosphate

NAD+ as an electron shuttle

Glycolysis

• “sugar splitting”

• Believed to be ancient (early prokaryotes -no O2 available)

• Occurs in cytosol

• Partially oxidizes glucose (6C) to 2 pyruvates (3C)

• Net gain: 2 ATP + 2NADH

• Also makes 2H2O

• No O2 required!

Stage 1: Glycolysis in a “nutshell”

Glycolysis Detailed Steps

Glycolysis (Summary)

glucose

2 pyruvate

P ADP

2 ATP

2 NAD+

2 NADH + 2H+

(3-C)C3H6O3

2H2O

Stage 2: Pyruvate Oxidation + Citric Acid Cycle

Cellular Respiration

Stage Two Part I: Pyruvate Oxidation

• Summary (Part I and II): Pyruvate is broken down into CO2generating energy

Part I Details:

• Pyruvate enters the mitochondrion via active transport

• Pyruvate is converted to acetyl CoA

• CO2 is released

• Electrons extracted are stored in NADH

Part 1

Part 2

Pyruvate Oxidation

• PyruvateAcetyl CoA (used to make citrate)

• CO2 and NADH produced

Stage Two Part II: Citric Acid (aka Krebs) Cycle

Details:

• Acetyl CoA is broken down in a series of steps into CO2

• The cycle happens twice (two pyruvates, 2 acetyl CoA molecules have been generated)

• Each cycle generates 1 ATP (substrate level phosphorylation), 3 NADH, and 1 FADH2

• In many animals, GTP is made and converted to ATP

• Net yield: 6 CO2 (from Part I and II), 2 ATP, 8 NADH, 2 FADH2

Citric Acid Cycle in Detail – necessary if you major in biochemistry!

Summary of Citric Acid Cycle

BioVisions at Harvard:The Mitochondria

http://multimedia.mcb.harvard.edu/anim_mitochondria.html

http://multimedia.mcb.harvard.edu/anim_mitochondria.html

Stage 3: Oxidative Phosphorylation

Cellular Respiration

Stage Three: Oxidative Phosphorylation

• Summary: ATP synthesis occurs, powered by the redox reactions of the Electron Transport Chain (ETC)

Details:

• Inner membrane of mitochondria is folded- creates surface area for ETC

• Membrane contains ATP Synthase- enzyme that makes ATP from ADP + Pi by moving H

+ ions against the gradient

Stage Three: Oxidative PhosphorylationDetails (cont.):

• NADH and FADH2 are split and donate electrons that go down the ETC

• O2 serves as an electron acceptor forming H2O

• Exergonic energy from splitting causes H+ to be pumped across the membrane

• This allows for chemiosmosis- using energy stored in H+

gradient to drive cellular work

• H+ moves back through membrane via ATP Synthase driving phosphorylation of ADP (adding inorganic phosphate)

Overall Summary: Cellular respiration uses glucose and 6O2produces 6CO2, 6H2O and approx. 30-32 ATP (this is a NEW number)

Why isn’t it exact?

• Redox and phosphorylation are not directly coupled

• The shuttle used to transport electrons to the mitochondria changes ATP yield

• The cell uses proton-motive force for other kinds of work too

• Some energy from glucose is lost as heat

Alternatives to Oxidative Cellular Respiration

• All living organisms need to make cellular energy BUT not all organisms complete oxidative cellular respiration

I. Anaerobic Respiration with new electron acceptor

• Organism uses an ETC but O2 is not the electron acceptor

• Example: Sulfate-reducing marine bacteria generate H2S instead of H2O

–This explains the rotten egg smell in marine environments

II. Fermentation

• Fermentation: Anaerobic respiration (no oxygen used) that breaks down glucose to yield 2 ATP- occurs in the cytoplasm

• In both, NAD+ must be regenerated

Two Types:

1. Alcoholic Fermentation

• Glucose is converted to pyruvate

• Pyruvate is broken down in two steps and CO2 is produced

• Reaction produces 2 ATP, carbon dioxide and ethanol (alcohol)

• Example: Yeast

–Bakers use yeast to make dough rise; brewers use yeast to make beer carbonated and alcoholic, wine makers use grapes and yeast to make wine (alcohol poisons and kills the yeast )

2. Lactic Acid Fermentation

• Performed by humans and other animals when not enough oxygen is available

• Breaks down glucose to produce 2 ATP and lactate

• Fermentation gives you energy quickly, but you run out quickly- can’t sustain you long-term

• Once oxygen is available the lactic acid enters the Citric Acid cycle (in the mitochondria) and is broken down, and aerobic respiration continues.

• Example: used in muscle cells during rapid exercise

–Lactic acid makes muscles burn and cramp- can make you sore later

Glycolysis

Fermentation

• Keep glycolysis going by regenerating NAD+

• Occurs in cytosol

• No oxygen needed

• Creates ethanol [+ CO2] or lactate

• 2 ATP (from glycolysis)

Respiration

• Release E from breakdown of food with O2

• Occurs in mitochondria

• O2 required (final electron acceptor)

• Produces CO2, H2O and up to 32 ATP

O2 presentWithout O2

Types of FermentationAlcohol fermentation

• Pyruvate Ethanol + CO2

• Ex. bacteria, yeast

• Used in brewing, winemaking, baking

Lactic acid fermentation

• Pyruvate Lactate

• Ex. fungi, bacteria, human muscle cells

• Used to make cheese, yogurt, acetone, methanol

• Note: Lactate build-up does NOT causes muscle fatigue and pain (old idea)

Various sources of fuel

• Carbohydrates, fats and proteins can ALL be used as fuel for cellular respiration

• Monomers enter glycolysis or citric acid cycle at different points

Respiration: Big Picture

pyruvateoxidation

ENERGY

glycolysis(cytosol)

ethanol + CO2

(yeast, some bacteria)

anaerobic

(without O2)

aerobic cellular

respiration

(with O2)

lactic acid(animals)

ETC

chemiosmosis

oxidative phosphorylation

citric acid cycle

mitochondria Fermentation(cytosol)

Glycolysis & Citric Acid Cycle

Now…a biology song!!! • https://www.youtube.com/watch?v=jJvAL-iiLnQ