Ch 9

advertisement

BEST ORGANELLE EVER…?

BEST ORGANELLE EVER…?

4/13/2020

Ch 9

Cell Respiration

3

4/13/2020 4

Cell Respiration = catabolic, makes ATP, exergonic (ΔG -686 kcal/mol)

C

6

H

12

O

6

+ 6 O

2

→ 6 CO

2

+ 6 H

2

O + energy

 ATP is made and used for energy, recycled, ATP ↔ ADP

ADP + P = phosphorylation (common)

P-bond is very energetic

4/13/2020 5

 Redox reaction = transfer of electrons from reactants to products, energy released

 oxidation = loss of e , reduction = gain of e -

4/13/2020 6

Figure 9.UN01

becomes oxidized

(loses electron) becomes reduced

(gains electron)

Figure 9.UN03

becomes oxidized becomes reduced

Overview

Electrons are passed “downhill” from: glucose  NADH  electron transport chain

 oxygen

In a series of redox reactions

Releases energy, therefore is exergonic

The Key Players

 In resp., transfer of e uses NAD + and electron transport chain

 NAD + = an electron shuttle, is coenzyme and e- acceptor, converts to NADH, gains 2 eand 1 p+, p165

4/13/2020 11

4/13/2020

WHAT IS ROLE OF OXYGEN IN THESE EXAMPLES?

12

Electron transport chain

 Video

 Made of e- carrier molecules in the mitochondrial membrane

 electrons slowly get passed down to oxygen

(final electron acceptor) and energy is given off, p165

 Why slow?

4/13/2020 13

OXIDATION

 Oxygen is HIGHLY electronegative

(6 valence electrons)

 Final electron acceptor in respiration

Ultimately results as water, also picking up H+ ions

 Once a molecule has been oxidized, it has very little free energy

Process of Cell Respiration in detail

4/13/2020 15

Phase 1) Glycolysis

(what does the word mean?)

 catabolic, glucose is broken into two 3carbon parts, which are converted into two pyruvate molecules, easy, video

Where: cytosol

 anaerobic uses 2 ATP to start, 4 are released by substrate level

phosphorylation

: 2 ATP

NET

2 NAD + converted (reduced) to 2 NADH

Exergonic: ΔG = -140 kcal/mol

4/13/2020 16

•Substrate Level Phosphorylation, is about 10% of the ATP.

• 90% occurs as result of oxidative phosphyrlation

• occurs during glycolysis and the citric acid cycle

4/13/2020 17

4/13/2020 18

 Options → If O

2 is available – pyruvate moves to a mitochondrion and the citric acid cycle (a.k.a. the

Krebs cycle) to complete oxidation, if not then fermentation occurs (we’ll do later)

In Mitochondria

Pyruvate is converted into acetyl CoA, (3-C into a 2-

C molecule), makes it reactive, p170

2 NADH’s made (1 per pyruvate)

4/13/2020 19

During part 1 of phase 2 (pyruvate oxidation) pyruvate is oxidized and becomes acetyl coenzyme A, or acetyl CoA

4/13/2020 20

Phase 2) Krebs Cycle, p.170

 (citric acid, TCA cycle) – catabolic, in mitochondrial matrix

The CoA on acetyl CoA is removed and the acetyl group is added to oxaloacetate to create citrate energy released, 8 step cycle

For every acetyl CoA (2 per glucose) 

3 NADH, 1 FADH

2

, 2 CO

2

, 1 ATP made (SLP) most energy is hidden in the electron carriers

 ? GTP and GDP

4/13/2020 21

4/13/2020 22

4/13/2020 23

3) Oxidative Phosphorylation

Electron Transport Chain (ETC)

Where: inner mitochondria

Problem – we have many e- carriers

 electronegativity increases down the chain so e are pulled

“downhill” towards oxygen, the final acceptor

4/13/2020 24

What is the ultimate purpose of the electron transport chain? Of the electrons?

4/13/2020 25

 most carriers are metals or cytochromes

 ATP production powered by [H + ] gradient, p174

ATP Synthase 

4/13/2020 26

Chemiosmosis

Flow of H+ (osmos = “pushing” H+)

 = coupling of rxns to make ATP, p173,

(diffusion & pumps)

 e- move down ETC, H + pumped out into intermembrane space creating a protonmotive force, H + diffuse into matrix through ATP synthase to make ATP

 process is enhanced by cristae (folds) in mitochondria

4/13/2020 27

4/13/2020 28

Process

Glycolysis

ATP by SLP CoEnzyme ATP by ETC Total

Net 2

2 NADH 4-6 6-8

Oxidation of pyruvates

2 NADH 6 6 krebs 2 6 NADH

2 FADH

2

18

4

TOTAL =

24

36-38

- range 36-38 because of rounding p176-177

4/13/2020 29

4/13/2020 30

 Resp. is very efficient – 40%

7.3 kcal/mol ATP x 38 ATP/mol

686 kcal/mol glucose

4/13/2020 31

Fermentation

 anaerobic, makes only 2 ATP, starts after glycolysis if no oxygen, 2 types

1) alcoholic- 2 pyruvates broken down into 2 CO

2 and ethanol, 2 NADH oxidized to 2 NAD + , replenishes NAD +

 many yeast, and bacteria, do

4/13/2020 32

 2) lactic acid – 2 pyruvates broken down into lactate

 occurs in muscles when O

2 is low

4/13/2020 33

Fermentation vs Respiration

 both break down pyruvate and use NADH in ferm. – final electron acceptor is pyruvate, in resp. it is O

2 more energy from respiration, 18 x more ATP

 respiration needs O

2

4/13/2020 34

 some organisms are facultative anaerobes= they can switch back and forth from aerobic to anaerobic

What evolved first, aerobes or anaerobes?

other energy molecules

(ex. fats) can be broken into parts to go into glycolysis, p180

4/13/2020 35

Where does the energy come from to run a race?

• 1 st few seconds:

– An aerobic (no oxygen)

– Using stored ATP

• 2 nd 90 seconds:

– An aerobic

– Lactic acid fermentation allowing glycolysis to continue

• Cause muscles to burn

• Need to deliver oxygen to muscle cells to get rid of lactic acid buildup

• 3 rd : 90 seconds to 17 minutes:

– A erobic (need oxygen)

– Cellular respiration using sugar

• 4 th 17 minutes  ?:

– A erobic (need oxygen)

– Cellular respiration using fats stored in the body

The gist of what you should know

Regulation

 Control of cell respiration is done by feedback inhibition – too much product inhibits rxn

 control at certain enzymes in glycolysis and krebs

 key control enzyme for citric acid cycle (in glycolysis) is phosphofructokinase

 sensitive to ratios of ATP:ADP:AMP

 citrate and ATP are allosteric inhibitors of pfk

ADP and AMP are allosteric activators of pfk

4/13/2020 39

4/13/2020 40

Review with Bioflix on

MasteringBiology.com

How can sunlight, seen here as a spectrum of colors in a rainbow, power the synthesis of organic substances?

Fun Fact:

 Photosynthesis creates 160 billion metric tons of carbohydrates per year (or 17 stacks of our AP text reaching all the way to the sun)

4/13/2020

Ch 10

Photosynthesis

Start with BioFlix on Masteringbiology.com

44

Figure 10.2

(a) Plants

(b) Multicellular alga

(c) Unicellular protists

10

 m

(e) Purple sulfur bacteria

1

 m

(d) Cyanobacteria

40

 m

Photosynthesis

 = converts light energy trapped by chloroplasts into chemical energy stored as sugar uses CO

2 to as carbon source

Endergonic

Anabolic

WAYS OF ENERGY AQUISITION

 Autotroph = organism that makes its own food for energy

Photoautotroph= uses light, ex. algae

Chemoautotroph= uses chemicals, ex. bacteria

Heterotroph = organism that acquires (eats) its food for energy, ex. us

4/13/2020 46

4/13/2020 47

4/13/2020

Let’s see this in action with

Bioflix

48

Chloropast

where photosynthesis occurs

 contains chlorophyll = green pigment, absorbs light mostly in mesophyll of leaves gas exchange through pores (stomata)

Anatomy of chloroplast:

1) intermembrane space- separates double membrane

2) thylakoid space- inside the thylakoid membrane

- thylakoids (sacs in the chloroplast) and stacks called grana

3) Stroma = fluid-filled space outside the thylakoids, where sugar is made, only in eukaryotes

4/13/2020 49

Does CO

2

or H

2

O get split to give oxygen?

Van Neil: gave bacteria H

2

S instead of water the rxn gave sulfur as a byproduct, so…

 splits H

2

O to give O

2

, later done with radioactivity water is split and the electrons are transferred from water to carbon dioxide, reducing it to sugar resp. was exergonic, photosynthesis is endergonic, energy required is light

4/13/2020 50

Photosynthesis Rxn

6 CO

2

+ 6 H

2

O + light energy → C

6

H

12

O

6

+ 6 O

2

4/13/2020 51

Phase 1)

Light Reactions

(including the Electron Transport Chain)

 1 st stage in photosynthesis, convert light energy to chemical energy as ATP &

NADPH, p188

 Light = electromagnetic energy

 distance it travels = wavelength, ranges from 380 to 750 nm (visible spectrum)

 plants absorb blue and red light best, reflect green

4/13/2020 52

1)Light Reactions/Electron Transport

Chain

4/13/2020

What is water’s chief purpose?

53

 Pigments = substances that absorb light,

 each has a specific wavelength it can absorb = absorption spectrum

4/13/2020 54

4/13/2020 55

 measured with a spectrophotometer

 graph wavelength vs. rate of photosynthesis

= action spectrum, p192

 main pigments are chlorophyll a,b, carotenoids (yellow)

4/13/2020

Structure of chlorphyll

56

Tangent:

 Why does magnesium deficiency

Cause light leaves?

4/13/2020 57

RESEARCH METHOD: Determining an Absorption Spectrum

TECHNIQUE

Chlorophyll solution

White light

Refracting prism

Photoelectric tube

Galvanometer

Slit moves to pass light of selected wavelength.

Green light

High transmittance

(low absorption):

Chlorophyll absorbs very little green light.

Blue light

Low transmittance

(high absorption):

Chlorophyll absorbs most blue light.

 Linear electron flow- passes electrons from water to

NADP + to make NADPH, uses P680 and P700

4/13/2020 59

Photons bump electrons’ to orbital of higher energy level

(photoexcitation). This is unstable and the electrons want to drop back down, immediately

When e- drops back down releases heat (think of your car’s hood)

Some pigments delay in their giving off photons as electrons settle back down…this is fluorescence.

 What color of light would a fluorescing flask of chlorophyll give off?

 Redorange… why ?

4/13/2020 61

4/13/2020

• photosystem I (P700), and II(P680), video

62

 Alternate means of generating ATP:

Cyclic electron flow – simpler, only involves P 700, makes ATP but no NADPH, nor oxygen

More common in primitive bacteria groups * p195

4/13/2020 63

vs.

4/13/2020 64

ETC in respiration vs. photosynthesis

 e- source is organic molecules (sugar) vs. water

 H+ reservoir in intermembrane space vs. into the thylakoid space

4/13/2020

Let’s review

electrons from water go to NADP + , NADPH is made to reduce CO

2 to sugar

ATP made, O

2 is byproduct pH gradient of 5 inside to 8 in stroma

(1000x H+ inside)

66

Phase 2) Calvin Cycle

2 nd stage of photosynthesis, also called dark rxns., light not directly used here

Where: stroma carbon source is CO

2 sugar and is ultimately reduced to

 produces 3-C sugar G3P (1/2 a sucrose) powered by ATP made from light reaction, uses

NADPH as reducing agent to add electrons to Ccpds, which ultimately become sugar

 p 198*

4/13/2020 67

4/13/2020 68

(Like citric acid cycle in reverse)

JUST LIKE

RESPIRATION

69

Steps

 a) Carbon fixation = CO

2 is attached to a 5-C molecule (RuBP), catalyzed by rubisco (fun fact: most abundant protein on earth ), later the new 6-C molecule is broken in two b) Reduction –coupled rxns: 6 ATP to 6 ADP, used to convert 3PG to G3P, 6 NADPH to 6

NADP +

 c) Regeneration of RuBP - uses ATP to make

RuBP

4/13/2020 70

QUICK

REVIEW

4/13/2020 71

Similarities of Photo. and resp.

4/13/2020 72

Similarities of Photo. and resp.

 a) both use ETC via a membrane

 b) both make ATP by diffusion of H + over a gradient

 c) similar electron carriers

 d) both are involved in energy conversion

 for mitochondria → chemical energy from food to ATP for chloroplast → light energy into chemical energy

4/13/2020 73

Differences between Photo. and resp.

4/13/2020 74

Other types of carbon fixation, p200-201

1) Photorespiration - uses O

2

, makes no ATP, so it reduces photosynthetic output by wasting C

 occurs when O

2 is higher in leaf than CO

2 evolutionary relic?

favored on hot, dry days

4/13/2020 75

2) C

4 plants - 4 carbon intermediate formed at

Calvin cycle

 C

3 plants make 3 carbon intermediate, ex. rice, wheat

C

4 ex. corn, sugarcane enhances carbon fixation by minimizing photorespiration

 PEP carboxylase can fix carbon efficiently when

Rubisco cannot

 important in hot regions

4/13/2020 76

 3) CAM plants - only open stomata during the night, opposite of usual

 reduces water loss in hot areas, also keeps

CO

2 out during the day ex. cacti, pineapple

4/13/2020 77

4/13/2020 78

Photosynthesis Free-Response Q,

outline only in 12 min.

A controlled experiment was conducted to analyze the effects of darkness and boiling on the photosynthetic rate of incubated chloroplast suspensions. The dye reduction technique was used.

Each chloroplast suspension was mixed with DPIP, an electron acceptor that changes from blue to clear when it is reduced. Each sample was placed individually in a spectrophotometer and the percent transmittance was recorded. The three samples used were prepared as follows.

• Sample 1 – chloroplast suspension + DPIP

• Sample 2 – chloroplast suspension surrounded by foil wrap to provide a dark environment +

DPIP

• Sample 3 – chloroplast suspension that has been boiled + DPIP a) On the graph provided, construct and label a graph showing the results for the three samples.

b) Identify and explain the control or controls for this experiment.

c) The differences in the curves of the graphed data indicate that there were differences in the number of electrons produced in the three samples during the experiment. Discuss how electrons are generated in photosynthesis and why the three samples gave different transmittance results.

4/13/2020 79

Download