Chapter 3 part 2: Cell dynamics

Membrane transport: Diffusion, osmosis, active transport

Cellular respiration

Lecture outline

• ATP and cell energy• Cell membrane dynamics

– Diffusion– Osmosis– Active transport

• Cell respiration

ATPThe Energy Currency of the Cell(Text review: Chapter 2, pg. 34)

ATP is the energy currency of all living things

Phosphate groups

Ribose

Adenine

ATP: Adenosine Triphosphate

ATP belongs in which category of molecule?

1. Carbohydrates2. Lipids3. Proteins4. Nucleic Acids5. None of these

How ATP works• ATP ADP + P + energy• Energy from ATP can do

work in the cell• When we eat food, we

use its energy to re-convert:

• ADP + P + energy ATP• Humans use food to

make ATP by the process of Aerobic Respiration

LE 8-9

Adenosine triphosphate (ATP)

Energy

P P P

PPP i

Adenosine diphosphate (ADP)Inorganic phosphate

H2O

+ +

How ATP Performs Work• When ATP breaks, the P can be added to a protein• The recipient protein then changes shape, and behaves

differently

When proteins change shape, work can get done

Pi

ADP

Energy for cellular work(endergonic, energy-consuming processes)

Energy from catabolism(exergonic, energy-yielding processes)

ATP

+

Energy from food Regenerates ATP

Your body breaks down and re-builds your own weight in ATP each day

Cell membranes

Cell Membrane review

• What is the cell membrane made out of?• What is the purpose of the cell membrane?

One way in, one way out

Everything which enters or exits a cell must pass through the cell membraneThe cell membrane must therefore:-Keep things the cell needs-Get things it wants from its environment-Get rid of wastes without losing desirable substances-All parts of the cell membrane work to these tasks

Parts of the cell membrane

• Phospholipid bilayer• Cholesterol (animal cells only)• Membrane proteins• Some carbohydrates

Cell membranes are made of a phosphlipid bilayer

Phospholipids are amphipathic• Similar in structure to

triglycerides• Phosphate is polar• Lipids are nonpolar• Degree of saturation

influences shape and fluidity

Fatty acid saturation influences fluidity of cell membranes

Saturated fatty acids pack into membranes more easily, making

membranes tighter (and less fluid)

Cholesterol can stabilize the fluidity of animal cell membranes

• Higher temperature also influences fluidity of membranes

Proteins comprise ~50% of cell membranes

The membrane is a fluid mosaicThe membrane is Selectively permeable

Proteins assist in allowing things to pass in and out

Transmembrane proteins serve a variety of functions

Some things can pass through easily, others require help

• Substances which can pass without help:– Water– Small nonpolar

molecules

• Substances that require help:– Ions– Polar small molecules – Large molecules

Membrane dynamics:Ways things can enter or leave the

cellDiffusion, Osmosis, and Active

Transport

Things can enter the cell in three ways

• Diffusion (Can be Passive or facilitated)

• Osmosis• Active transport

Diffusion: the movement of a substance from a high concentration to a low concentration

• Simple diffusion• Facilitated diffusion

Diffusion is the movement of a substance from a high concentration

to a low concentration

What happens next?

Membranes can change the way diffusion works

What determines the rate of diffusion here?On what properties of the dye and membrane does the diffusion depend?

Figure 5.12

The cell membrane can’t control simple

diffusion

Small, nonpolar molecules can pass easily through the phospholipid bilayer:-Oxygen-Carbon dioxide-Alcohol-Steroids-gasoline(Water is polar but very small- it can pass the membrane at low rates )

Facilitated diffusion allows passage of desirable molecules

Membrane proteins allow ions and small polar molecules to pass in and out

-Potassium ions (K+), other things

-Sugars and other nutrients

Diffusion

• Diffusion is the movement of substances from a high concentration to a low concentration

• Liquids and gasses diffuse spontaneously

Osmosis: the diffusion of water across a selectively permeable membrane

Osmosis is the diffusion of water

What can we infer about the permeability of this membrane?

Osmosis

• The diffusion of water• Requires no energy• Water moves from a

high concentration to a low concentration

• Water can pass through membranes

Osmosis can do work

When only water can

pass, Osmosis

can cause a cell to

shrivel, or to swell

The bag losesmore water thanit gains and shrivels.

The bag gainsmore water thanit loses and swells.

98% water2% sugar

(a) HypertonicSolution

(90% water10% sugar)

(b) Isotonicsolution

(98% water2% sugar)

(c) Hypotonicsolution

(100% water,distilled)

The bag gains andloses the same amountof water and maintainsits shape.

Figure 5.14

Isotonic- equal concentrations of solutes inside and out

• Water flows equally into and out of cells

• Necessary for animal cells

• A wilted state in plant cells

Hypotonic- A low concentration of solutes outside the cell

• Water flows in• This keeps plants in

proper shape• This can lyse an animal

cell

Hypertonic- A greater concentration of solutes outside the cell

• Water flows from a high concentration (inside the cell) to a low concentration (outside the cell)

What kind of solution are these plants in?

Active Transport

• Substances are moved by the cell from low concentration to high

• Spending cellular energy to move substances against a concentration gradient

Membrane proteins can do Active Transport to bring needed items into the cell

Figure 3.10

What kind of substances might a cell wish to bring into the cell in this way?

ATP can be used to power Active Transport

Active transport for very large things

• When substances are too big to be brought in through a channel, the cell can do endocytosis

• Substances can be shipped out of the cell by exocytosis

• Both are forms of active transport

Endocytosis and Exocytosis

• When things are too big to fit through the membrane, they can be brought in by endocytosis

• …or released by exocytosis

Endocytosis

• The vesicle then travels into the cell and through the cytoplasm

• Two types– Phagocytosis (cell eating) – large particles or

bacteria– Pinocytosis (cell drinking) – droplets of fluid

Endocytosis

Figure 3.11a

Endocytosis

Figure 3.11b

Exocytosis- a vesicle fuses

with the membrane, freeing the contents

Figure 3.12

Figure 5.17

Figure 5.18

Membrane transport review

The “powerhouse of the cell” is the_________.

1. Nucleus.2. Mitochondrion.3. Golgi complex.4. Ribosome.5. None of these

Mitochondrial structure review

Cellular respiration provides us with the energy we use

Slow-twitch muscles have more mitochondria than fast-twitch

Cellular Respiration

All Living Things Require and Consume Energy

• Ultimate source of energy for all life on earth is the sun

• We get our energy from food

C6H12O6(s) + 6O2(g) 6CO2(g)+ 6H2O(l)

This is a combustion reaction

Aerobic respiration of glucose is the most basic means for cells to acquire energy

Respiration at the cellular level necessitates our breathing

The more our cells respire, the more oxygen (& food) we need

The Stages of Cellular Respiration

• Cellular respiration has three stages:– Glycolysis– The citric acid cycle (a.k.a. the Krebs cycle)– The electron transport chain

LE 9-6_1

Mitochondrion

Glycolysis

PyruvateGlucose

Cytosol

ATP

Substrate-levelphosphorylation

LE 9-6_2

Mitochondrion

Glycolysis

PyruvateGlucose

Cytosol

ATP

Substrate-levelphosphorylation

ATP

Substrate-levelphosphorylation

Citricacidcycle

LE 9-6_3

Mitochondrion

Glycolysis

PyruvateGlucose

Cytosol

ATP

Substrate-levelphosphorylation

ATP

Substrate-levelphosphorylation

Citricacidcycle

ATPOxidative

phosphorylation

Oxidativephosphorylation:

electron transportand

chemiosmosis

Electronscarried

via NADH

Electrons carriedvia NADH and

FADH2

Overview of respiration

• Glycolysis: Glucose is split, 2 pyruvates are formed, a little ATP is gained ( 2 ATP/ glucose)

• The Citric Acid Cycle: Pyruvates are brokent into CO2, Redox molecules NAD+ and FAD are charged up, a little ATP is gained (2 ATP/ glucose)

• Electron transport: Lots of ATP is made by ATP synthase (~32 ATP/ glucose)

Step 1: Glycolysis

In: 1 glucose, 2 NAD+Out: 2 ATP (net), 2NADH, 2

pyruvate

Glycolysis converts glucose to pyruvate

• Glycolysis (“breaking of sugar”) breaks down glucose into two molecules of pyruvate

• Glycolysis occurs in the cytoplasm and has two major phases:– Energy investment phase– Energy payoff phase

Overview of Glycolysis

• Actually a 10- step process• Glucose (6C) 2 Pyruvate ( 3 C ea.)• 2 ATPs net profit• 2 NAD+’s are charged

LE 9-9a_2

Glucose

ATP

ADP

Hexokinase

ATP ATP ATP

Glycolysis Oxidationphosphorylation

Citricacidcycle

Glucose-6-phosphate

Phosphoglucoisomerase

Phosphofructokinase

Fructose-6-phosphate

ATP

ADP

Fructose-1, 6-bisphosphate

Aldolase

Isomerase

Dihydroxyacetonephosphate

Glyceraldehyde-3-phosphate

LE 9-9b_2

2 NAD+

Triose phosphatedehydrogenase

+ 2 H+

NADH2

1, 3-Bisphosphoglycerate

2 ADP

2 ATPPhosphoglycerokinase

Phosphoglyceromutase

2-Phosphoglycerate

3-Phosphoglycerate

2 ADP

2 ATPPyruvate kinase

2 H2OEnolase

Phosphoenolpyruvate

Pyruvate

Step 2: The Krebs Cycle

Bonds in pyruvate are stripped of their energy

The Krebs cycle strips all the electrons off of glucose’s carbon

atoms, forming CO2

The electrons are used to charge up electron carriers NAD+ ( NADH) and FAD ( FADH2)

Step 3: Electron transport

In which the electron transport chain generates a proton gradient, and ATP synthase makes tons of ATP

The electron transport chain uses electrons to generate a proton gradient

Intermembranespace

Innermitochondrialmembrane

Mitochondrialmatrix

Proteincomplex Electron

carrier

Electronflow

NADH NAD

FADFADH2

H

H

HH

H2O

H

H

ATPsynthase

2O212

H

PADP ATP

Electron Transport Chain Chemiosmosis

OXIDATIVE PHOSPHORYLATION

H

H

H

H

H

H

H

Some poisons can disrupt e- transport, creating a lethal e- traffic jam

Oxygen is the final e- resting place in the chain

• ATP synthase uses the potential energy in the proton gradient to generate ATP

LE 9-14

INTERMEMBRANE SPACE

H+ H+

H+H+

H+

H+

H+

H+

ATP

MITOCHONDRAL MATRIX

ADP+

P i

A rotor within the membrane spins as shown when H+ flows past it down the H+ gradient.

A stator anchored in the membrane holds the knob stationary.

A rod (or “stalk”) extending into the knob also spins, activating catalytic sites in the knob.

Three catalytic sites in the stationary knob join inorganic phosphate to ADP to make ATP.

ATP BookkeepingCYTOSOL Electron shuttles

span membrane 2 NADHor

2 FADH2

MITOCHONDRION

Oxidativephosphorylation:

electron transportand

chemiosmosis

2 FADH22 NADH 6 NADH

Citricacidcycle

2Acetyl

CoA

2 NADH

Glycolysis

Glucose2

Pyruvate

+ 2 ATP

by substrate-levelphosphorylation

+ 2 ATP

by substrate-levelphosphorylation

+ about 32 or 34 ATP

by oxidation phosphorylation, dependingon which shuttle transports electronsform NADH in cytosol

About36 or 38 ATPMaximum per glucose:

Review of Cellular Respiration

STEP Key Players ATPGlycolysis Glucose, pyruvate 2/glucoseKrebs NAD+/NADH, CO2 2/glucosee- transport e- transport chain,

ATP synthase32-34/glucose

The portion of aerobic respiration which generates the most ATP is

1. Glycolysis2. The Citric Acid/Krebs cycle3. Electron transport4. All of these make the same amount of ATP5. None of these make ATP

Review of Cellular Respiration

Oxygen is the final acceptor in the electron transport chain

Review of Cellular Respiration

STEP Key Players ATPGlycolysis Glucose, pyruvate 2/glucoseKrebs NAD+/NADH, CO2 2/glucosee- transport e- transport chain,

ATP synthase32-34/glucose

Human cells can do glycolysis faster than human lungs can take in oxygen

Q: What happens if there is not enough oxygen?

A: It depends on what kind of creature you are…

Without O2, yeast make alcohol, and CO2 is a waste product

This is alcohol fermentation

Humans make lactic acid instead of ethanol

This is lactic acid fermentation

Lactic Acid in muscles creates a burning sensation

• Overworked muscles can become anoxic

• In low oxygen environments, pyruvate is converted to lactate to regenerate NAD+

• Lactic acid causes great suffering

Where is aerobic

respiration here?

Metabolism can build up, or break down

The Versatility of Catabolism• Catabolic pathways funnel electrons from many kinds

of organic molecules into cellular respiration• Glucose- 4 calories/gram• Proteins- 4 calories/gram• Fats- 9 calories/gram

Anabolic process are fueled with

ATP

Which of the following produces the most ATP per glucose?

A) aerobic respiration B) anaerobic respiration C) alcoholic fermentation D) lactic acid fermentation E) All produce approximately the same amount

of ATP per molecule of glucose