Unit 5 IB HL Biology

ATP

Vocabulary:

• ATP hydrolysis -

• Phosphorylation -

• Autotrophs -

• Photoautotrophs -

• Trophic level -

• The name for Adenosine Triphosphate

• ATP is a modified nucleotide

  • Nucleotides are the monomers for DNA and RNA

• ATP is produced by the mitochondria during aerobic respiration

• ATP is required in cells to transfer energy wherever it is needed

• ATP is often referred to as the universal energy currency of cells

Cellular energy

ATP energy is used for cellular processes that require energy, such as:

• Active transport

• Anabolic reactions

• Muscle contractions

• Movement of cells or parts within cells

• etc…

Structure of ATP

ATP has three components:

• Adenine (nitrogenous base - orange rectangle)

• Ribose (pentose sugar - blue pentagon)

• 3 Phosphate groups (Functional group - purple circles)

  

Energy

• The three phosphate groups all have a negative charge

• The negative charges repel each other

  • The phosphate groups don’t want to be next to each other and are constantly trying to break away

ATP storing energy

By creating bonds between the three phosphate groups it is compressing them together like a spring.

Releasing energy

• The energy is released when the third bond is broken

• The process of breaking the bond between the 2nd and 3rd phosphate is called ATP hydrolysis

  • Hydro - water

  • Lysis - breaking

• ATP hydrolysis is an exergonic reaction

  • Exergonic reaction - A spontaneous reaction wherein energy is released into the surrounding environment

• ATP hydrolysis creates:

  • ADP (Adenosine diphosphate)

  • P_i (Phosphate)

    

ATP hydrolysis

• This is an exergonic reaction because the energy is released

• A water molecule is used to break the bond between the phosphate groups

  • The phosphate group that is released often attaches to another molecule

Adenosine diphosphate

ADP contains some energy but not as much as ATP. Since ADP only contains two phosphate groups the repel force is not as strong leading to less energy being created.

ADP phosphorylation

• This is an endergonic reaction because the energy is temporarily stored

• Phosphorylation is an endergonic reaction

  • Endergonic reaction - Non-spontaneous reactions wherein energy is absorbed from the surrounding environment

• ADP can be turned into ATP by adding a phosphate group and removing a water molecule. This is known as phosphorylation

ATP - ADP cycle

Photosynthesis

Vocabulary:

• Photolysis - The splitting of water molecules using light energy during the light-dependent reactions of photosynthesis, releasing oxygen, electrons, and protons

• Photons - The fundamental unit or particle of light. Photons have no mass and travel at the speed of light

• Light-dependent reactions - The initial stages of photosynthesis that occur in the thylakoid membranes of chloroplasts. These reactions utilize light energy to convert ADP and P_i into ATP, and reduced NADP to reduced NADP. They also generate oxygen through the process of photolysis.

• Light-independent reactions - The second stage of photosynthesis. These reactions occur in the stroma of chloroplasts and involve the fixation of carbon dioxide and the production of carbohydrates using the ATP and reduced NADP generated in the light-dependent reactions

• Autotrophs -

• Phototrophs -

• Trophic level -

• Thylakoids - Flattened, membrane-bound sacs in chloroplasts that contain the photosynthetic pigments and proteins necessary for the light-dependent reactions of photosynthesis

• Chloroplasts - Organelles found in some plant cells. They contain chlorophyll and carry out the process of photosynthesis

• Stroma - The space between the inner membrane and thylakoid membranes in chloroplasts containing enzymes and products for the Calvin cycle

• Action spectrum - A graphical representation that shows the effectiveness of different wavelengths of light in driving a specific physiological or biochemical process, such as photosynthesis

• Chlorophyll - A green pigment found in the chloroplasts of plants and algae that plays a central role in photosynthesis by absorbing light energy.

• Accessory Pigments - Additional pigments found in chloroplasts that assist chlorophyll in capturing light energy during photosynthesis. These pigments broaden the absorption spectrum, allowing plants to capture light energy from a wider range of wavelengths

• Absorption spectrum - The wavelengths of light absorbed by a particular substance or pigment

• Light reaction -

• Calvin cycle - A series of biochemical reactions that occur in the stroma of chloroplasts during the light-independent reactions of photosynthesis. The Calvin cycle involves the fixation of carbon dioxide, reduction of carbon compounds, and regulation of RuBP, leading to the production of carbohydrate

• Photosystems - Large protein complexes found in the thylakoid membranes of chloroplasts. They are involved in the light-dependent reactions of photosynthesis and contain pigments, including chlorophyll and accessory pigments, that capture light energy and initiate the electron transport chain

• Reaction Center - A specific protein complex within a photosystem where light energy is converted into chemical energy. It contains specialized chlorophyll molecules that can donate electrons directly to the electron transport chain

• Photoactivation - The activation of a molecule or system through the absorption of light energy. In the context of photosynthesis, it typically refers to the activation of chlorophyll and other pigment, which trigger subsequent biochemical reactions.

• Photophosphorylation - The process of generating ATP using light energy. It occurs during the light-dependent reactions of photosynthesis, where light energy is used to phosphorylate ADP to ATP

• Electron Transport Center - A series of protein complexes in the inner membrane of the mitochondria that transfer electrons and pump protons to create a proton gradient

• Concentration gradient -

• Chemiosmosis - The process by which energy stored in the proton gradient is used to produce ATP.

• ATP synthase -

• Cyclic phosphorylation -

• Non-cyclic phosphorylation -

• Carbon fixation - The conversion of inorganic carbon (carbon dioxide from the atmosphere) to organic carbon by a living organism

• Rubisco - An enzyme that catalyzes the addition of carbon dioxide to RuBP during the Calvin Cycle. It is the most abundant enzyme on Earth and plays a critical role in carbon fixation

• Photorespiration -

Energy cannot be created or destroyed, it can only be transferred and transformed

Photosynthesis transforms light energy (from the sun) and turns it into chemical energy (glucose and other organic molecules).

Photosynthetic organisms

Organisms have developed the ability to absorb this light energy from the sun and convert it into chemical energy in the form of glucose and other carbon compounds, thus providing the energy for almost all ecosystem on the planet

• Autotrophs- organisms that can produce their own chemical energy (organic compounds).

  • Autotrophs are also known as producers.

  • Supply chemical energy to the entire ecosystem

  • Every organism, regardless of its trophic level, relies on the energy from the sun that is converted using photosynthesis.

    • Primary consumers eat the producers and absorb the energy they have stored

    • Secondary consumers then eat the primary consumers and the food chain continues

  • Examples:

    • Plants

    • Algae

    • Cyanobacteria

  • Photoautotrophs- use light to produce their chemical energy (they perform photosynthesis).

    • Producers absorb light and produce glucose and other carbon compounds

Photosynthesis Equation

• Water is used in photosynthesis because a source of hydrogen is required to convert CO into glucose

  • Water is the most accessible source of hydrogen on Earth

• To access the hydrogen it must go through photolysis

  • The energy in photons is used to split water molecules, generate hydrogen ions, electrons, and oxygen

• Photolysis is the process of breaking up molecules using light

  • 2H₂O + photons → 4H⁺ + O₂ + 4e^–

  • Photo = light

  • lysis = break

Chloroplast structure

• Has a double membrane surrounding the organelle

  • Outer membrane

  • Inner membrane

• Thylakoids

  • Flattened, membrane-bound sacs

  • Surrounded by the thylakoid membrane

  • Thylakoid space - the inner region of the thylakoid

  • Because of its size and shape, it has a high SA: V ration

  • Contains chlorophyll

  • Location of light reaction

  • Arranged in stacks called grana to maximize light absorption

• Stroma

  • Fluid-filled space between the inner membrane

  • Containing enzymes and materials for the Calvin Cycle

Thylakoid = stack of pancakes

Stroma = Syrup

Photosynthetic pigments

• Pigments are molecules that absorb light

• Wavelengths that are not absorbed are reflected - this is the color that we perceive

• Major photosynthetic pigment = chlorophyll

• Accessory pigments include xanthophyll and carotenoids

Chlorophyll

• Chlorophyll is the main pigment found in plants

• Chlorophyll a and chlorophyll b reflect green light and absorb most of the other colors of light (wavelengths)

• Causes chloroplast to appear green

Absorption spectrum

• the wavelengths of light absorbed by a particular substance or pigment

• Visualized in a graph

• Peaks in the graph represent high absorption

• Each absorption spectrum line represents one type of pigment

Plants have several different types of pigments, so the overall rate of photosynthesis is a result of a combination of all of the pigments absorbing light

More light absorption by pigments increases the rate of photosynthesis

Paper chromatography

• A lab technique to separate pigments as they move up the paper

• Pigments will dissolve in the solvent and will separate based on their solubility

2 Halves of photosynthesis

• Light-dependent reactions

  • Light reaction

    • Occurs in the thylakoids

    • Utilizes photosynthetic pigments to absorb light

    • Light energy splits H₂O and produces O₂ as a byproduct

    • Creates ATP and NADPH to be used by the Calvin Cycle

• Light-independent Reactions

  • Calvin Cycle

    • Occurs in the stroma

    • Uses ATP and NADPH from the light reaction

    • Carbon fixation of CO₂ from the atmosphere

    • Produces Sugars

Reduction and Oxidation

• Reduction

  • Gaining electrons

  • The charge is “reduced” because it becomes more negative

• Oxidation

  • Losing electrons

Light Reaction

Photosystems

• Integral protein complexes located within the phospholipid bilayer

• In chloroplast: the thylakoid membrane

• In cyanobacteria: the cell membrane

• Photosystems contain chlorophyll that will absorb light energy

Photosynthesis occurs first within the photosystems.

Photosystems - Large protein complexes found in the thylakoid membranes of chloroplasts. They are involved in the light-dependent reactions of photosynthesis and contain pigments, including chlorophyll and accessory pigments, that capture light energy and initiate the electron transport chain.

Reaction Center - A specific protein complex within a photosystem where light energy is converted into chemical energy. It contains specialized chlorophyll molecules that can donate electrons directly to the electron transport chain.

There are two types of photosystems:

• Photosystem 2

  • Sensitive to 680nm of light

• Photosystem 1

  • Sensitive to 700nm of light

The light reaction is all about the flow of electrons.

Photoactivation in photosystems

Photoactivation - The activation of a molecule or system through the absorption of light energy. In the context of photosynthesis, it typically refers to the activation of chlorophyll and other pigments, which triggers subsequent biochemical reactions.

• Photons of light strike the pigment molecules within the photosystem

• Excite the electrons within these molecules

• Excited electrons are transferred between the array of pigments within the photosystem

• Excited electrons finally reach the reaction center - a special chlorophyll A molecule

• At the reaction center, the excited electron will be emitted from the photosystem

• The photosystem has become oxidized (lost an electron)

Photosystem 2

• Photosystem 2 is the first photosystem to undergo photoactivation

• After the electron is emitted from photosystem 2, it is transferred from the reaction center to the first electron transport chain (ETC)

• Now PS2 is missing an electron (it is oxidized) - this is very unstable

Photolysis in Photosystem 2

• Electrons are replaced during the process of photolysis

  • Photolysis is the process of using light energy to break water molecules to replace missing electrons in PS2

  • Equation: 2H₂O → 4H⁺ + O₂ + 4e^-

• Photolysis occurs in the thylakoid space by PS2

• H⁺ (protons) remain in the thylakoid space, beginning to build a concentration gradient

• O₂ diffuses out of the chloroplast →cell →leaf

• e^- (electrons) are transferred to PS2

Electron transport chain (ETC)

• A series of integral protein complexes within the thylakoid membrane

• The first ETC receives excited electrons from PS2

• There are 2 functions of the first ETC:

  • Transfer electrons from PS2 to PS1

  • Harness the extra energy from excited electrons & use it to pump H⁺ (protons) into the thylakoid space - This establishes a proton concentration gradient: high (H⁺) in thylakoid

Proton concentration gradient

High concentration of the H⁺ in the thylakoid space for 3 reasons:

• H⁺ produced in the thylakoid during photolysis

• H⁺ pumped into the thylakoid by the first ETC

• Thylakoids are small spaces so H⁺ accumulates quickly

Chemiosmosis

• The proton concentration gradient allows for passive transport of protons OUT of the thylakoid (down its concentration gradient)

• Can the protons (H⁺) pass through the membrane unassisted via simple diffusion? NO!

• Because of their charge, protons (H⁺) can only exit the thylakoid via transmembrane integral protein

• Chemiosmosis is the diffusion of H⁺ down its concentration gradient

ATP synthase

• Transmembrane integral protein that is also an enzyme (-ase)

• ATP synthase performs phosphorylation to create (synthesize) ATP

• This process requires energy - where is the energy coming from?

Chemiosmosis drives ATP synthesis

• As the H⁺ diffuses through ATP synthase, it causes the enzyme to turn - much like a water wheel creating power

• This provides the energy needed to phosphorylate ADP into ATP

• This process is ultimately driven by light: Phosphorylation

ATP made during phosphorylation will go to power the Calvin Cycle

Photosystem 1

Photoactivation in PS1

• Photoactivation occurs in PS1

• Excited electrons are:

  • Transferred between the pigments & and end up in the reaction center

  • Emitted from the reaction center and are transferred to an enzyme called NADP⁺ reductase

Replacing electrons in PS1

• After the excited electrons are emitted from PS1, they need to be replaced

• Electrons traveling from PS2 via the 1st ETC will replace the missing electrons from PS1

NADP⁺/NADPH

• NADP⁺ (Nicotinamide adenine dinucleotide phosphate) is an electron carrier

• NADP⁺ is the oxidized form (“empty” of electrons)

• When NADP⁺ picks up electrons it becomes reduced (NADPH, “full” of electrons)

Reduction of NADP⁺

• Electrons leave PS1 and are transferred to NADP⁺ reductase

• NADP⁺ reductase is an enzyme that combines the electrons with NADP⁺ to NADPH

• This process reduces NADP⁺ into NADPH

• Occurs on the stroma side of the thylakoid membrane

The NADPH produced (“filled”) during the light reaction will go to the Calvin Cycel to drop off the electrons

Non-cyclic Photophosphorylation

• The process of phosphorylation that was described earlier is non-cyclic photophosphorylation

• Electrons flow from:

  • Water → PSII → 1st ETC → PSI → NADPH

• ATP is generated as a result of the 1st ETC’s function

Cyclic photophosphorylation

• The thylakoid membranes contain thousands of PS2s, PS1s, ETC’s, and ATP synthases

• Sometimes electrons that are emitted from PS1 are transferred back to the 1st ETC (instead of NADP⁺ reductase)

• The electrons travel from:

  • PSI → 1st ETC → PSI

• When this happens ATP is made like normal because the ETC still creates the proton gradient

• What makes this “cyclic” is the pathway that the electrons take: electrons are lost from and return to the same photosystem

Light Reaction Summary

• Pigments harness light energy to excite electrons that will eventually reduce NADP⁺ into NADPH

• ATP is synthesized using photophosphorylation

• O₂ is produced as a byproduct of the photolysis of H₂O

• ATP and NADPH will go into the Calvin Cycle

• The light reaction is also called the light-dependent reaction

Calvin Cycle

• The Calvin Cycle is also called the light-independent reaction

• Occurs in the stroma

• CO₂ is “fixed” from the atmosphere and converted into sugars (organic molecules)

• Utilizes the energy from ATP and electrons from NADPH (both of which were made in the light reaction)

• Cyclical metabolic pathway

• There are three phases

  • Carbon fixation

  • Reduction (synthesis of triose phosphate)

  • Regeneration

Carbon fixation

• The process of attaching a CO₂ to a 5-carbon sugar called ribulose (RuBP)

• 3 CO₂ + 3 RuBP total per “turn”

• Carbon fixation is catalyzed by an enzyme called Rubisco

• Rubisco is the most abundant enzyme on Earth

• After CO₂ has been “fixed” to RuBP, each of the resulting 6 carbon compounds breaks into 2 × 3 carbon compounds called glycerate 3 phosphate (GP)

• This creates a total of 6 x GP

Rubisco

Rubisco is found in really high concentrations in the stroma because:

• Rubisco is a “slow” enzyme and doesn’t work very efficiently

• There is a very high energy requirement for the Calvin Cycle

• Rubisco can mistakenly add an O₂ instead of a CO₂

• That makes Rubisco even less efficient

• If an O₂ is added, the molecule can no longer proceed through the rest of the Calvin Cycle (this is called photorespiration)

• Rubisco works best in high concentrations of CO₂ to reduce the chance of an O₂ being mistakenly added to RuBP

Reduction

• Each GP molecule is converted into a triose phosphate (TP) called Glyceraldehyde 3 phosphate (G3P)

• Each molecule requires:

  • The energy from 1 ATP molecule

  • The electrons from 1 NADPH molecule

• This is a total of:

  • 6 x GP converted into 6 TP (G3P)

  • 6 x ATP used (creates 6 x ADP)

  • 6 x NADPH used (creates 6 x NADP⁺

• It is called reduction because GP gains electrons as it is converted into TP

Leaving the cycle

• At the end of the reduction phase, there are 6 x TP (G3P)

• One triose phosphate (G3P) will exit the cycle

• Five triose phosphate (G3P) will remain in the cycle and go into the 3rd phase: regeneration

Regeneration

• Five triose phosphates (G3P) remain in the cycle (this is a total of 15 carbons)

• The carbons in the 5 x TP will get rearranged into 3 x RuBP

• This requires the energy from 3 x ATP (creates 3 x ADP)

The regeneration phase of the Calvin cycle recreates the CO₂ receptor (RuBP). This allows the cycle to continue in a cyclical manner.

Making Glucose

The triose phosphate (G3P) will get turned into glucose after it exits the Calvin Cycle.

Making other Organic molecules

The triose phosphates that exit the Calvin Cycle can also be used to create any other organic molecule that plants need to synthesize.

Examples:

• Other carbohydrates

• Amino acids

• Nucleotides

Limiting Factors of Photosynthesis

The rate of photosynthesis is limited by:

• Light intensity (brightness)

• CO₂ concentration

• Temperature

The wavelength of light also impacts photosynthesis

Cellular respiration

Vocabulary:

• Exergonic -

• Catabolic -

• Heterotrophs -

• Aerobic respiration -

• Anaerobic respiration -

• Glycolysis -

• Link reaction -

• Kreb cycle -

• Oxidative phosphorylation -

Producing ATP from organic molecules

• All living things must have some way to extract energy out of organic molecules to produce ATP

• Photosynthetic organisms (autotrophs) make the organic molecules first, then they break them down

• Heterotrophs - organisms that must get their energy from other organisms because they cannot produce their own organic molecules

  • Can be prokaryotic or eukaryotic

  • Example:

    • Humans

    • E.coil

    • Fungi

• Breaking down organic molecules is catabolic and exergonic

• The controlled release of energy stored in organic molecules is harnessed to produce ATP

Aerobic vs Anaerobic respiration

• Aerobic respiration: utilizing O₂ while breaking down organic molecules

• Anaerobic respiration: Not utilizing O₂ while breaking down organic molecules

Cellular respiration is used to refer to aerobic respiration

Mitochondrial Structure

• Double membrane

  • Inner membrane

    • Highly folded

    • Cristae are the folds of the inner membrane

  • Outer membrane

• Intermembrane space

  • Space between the two membranes

  • Very small - allows for easy accumulation (high concentrations) of protons

• Mitochondrial matrix

  • Space inside of the inner membrane

  • Separate space with ideal pH and enzymes for specific reactions

Cellular respiration equation

Redox reactions

Cellular respiration is a series of redox reactions

4 Stages of cellular respiration

1. Glycolysis

2. Link reaction

3. Kreb cycle

4. Oxidative phosphorylation (OxPhos)

Stage 1 = aerobic

Stage 2-4 = anaerobic

Glycolysis

• The process of breaking glucose into 2 pyruvate molecules

• Occurs in the cytoplasm of cells

• Prokaryotes and eukaryotes can perform glycolysis

• Thought to be one of the most ancient cellular pathways

• Glycolysis will occur in the presence and absence of oxygen (O₂) - anaerobic

• Glycolysis is a linear metabolic pathway

• Series of 10 reactions each catalyzed by their own enzyme

• Remember: we need a controlled release of energy = lots of small steps/reaction

• There are 4 events of glycolysis

  • Phosphorylation

  • Lysis

  • Oxidation

  • ATP formation

Glycolysis: Energy investment phase

• 2 ATP molecules are used to phosphorylate glucose - this makes the molecule unstable - “phosphorylation”

• The phosphorylated glucose is split into 2 G3P (triose phosphate) molecules “lysis”

Glycolysis: Energy payoff phase

• Electrons and hydrogens are removed from the 2 G3P molecules - “oxidation” and “dehydrogenation”

• The electrons (and hydrogens) are then transferred to 2 NAD⁺ to make 2 NADH

  • NAD⁺/NADH (Nicotinamide Adenine Dinucleotide) is an electron carrier

    • NAD⁺ is the oxidized state (“empty”)

    • NADH is the reduced state (“full”)

• 4 ATP are produced using substrate level phosphorylation - “ATP formation”

  • Substrate level phosphorylation - a metabolic reaction that results in the formation of ATP by the direct transfer of a phosphate group to ADP from another phosphorylated compound

  • The enzyme takes the phosphate group from its substrate and attaches it to ADP to make ATP (phosphorylation)

• During the energy payoff phase, the 2 G3P are converted into 2 pyruvate

Glycolysis: Overall

• Glucose → 2 pyruvate

• Also produced:

  • 2 NADH

  • 4 ATP (net 2 ATP)

After Glycolysis

• If O₂ is present: pyruvate will enter the mitochondria

• After entering the mitochondria, the following stages will occur:

  • Link reaction

  • Kreb cycle

  • OxPhos

Link reaction

• Occurs in the Mitochondrial matrix

• Maintains a low concentration of pyruvate in the Mitochondrial Matrix

• 2 things are removed from pyruvate after it enters the matrix:

  • CO₂ (decarboxylation)

  • Electrons (oxidation)

• “Oxidative decarboxylation”

• After oxidative decarboxylation, Coenzyme A will be added

• produces 1 Acetyl-CoA per pyruvate

Net products (glycolysis + link)

For one glucose molecule we have:

• 2 Acetyl-CoA

• 2 CO₂ (from link reaction)

• 2 ATP (from glycolysis)

• 4 NADH (2 from glycolysis, 2 from link reaction)

Krebs cycle

• Occurs in the mitochondrial matrix in the presence of O₂

• A cyclical metabolic pathway made of 8 reactions each with their own enzyme

• Finishes the breakdown of glucose

• Acetyl-CoA (2C) is combined with oxaloacetate (4C) to release the Coenzyme-A and make citrate (6C)

• The Krebs cycle is also called the Citric ACid cycle after citrate (citric acid)

• Citrate then undergoes oxidative decarboxylation to produce:

  • NADH

  • CO₂

  • 5-Carbon compound

• The 5-Carbon compound undergoes oxidative decarboxylation, producing:

  • NADH + CO₂

  • 4-Carbon compound

• An ATP is also made by substrate level phosphorylation

• Remember: this is a cycle - the starting molecule must be regenerated

• The 4-carbon compound is converted back into oxaloacetate

• Produces NADH and FADH₂ in the process

  • FAD/FADH₂ (Flavin Adenine Dinucleotide) is an electron carrier

    • FAD is the oxidized state (“empty”)

    • FADH₂ is the reduced state (“full”)

  • FADH₂ can carry 1 more hydrogen compared to NADH

Krebs cycle products

• 2 Acetyl-CoA enter to produce:

  • 4 Co₂

  • 6 NADH

  • 2 FADH₂

  • 2 ATP

• Remember: The Krebs cycle finishes the breakdown of glucose (and it “fills” the largest number of electron carries)

Oxidative Phosphorylation (OxPhos)

• OxPhos creates the largest amount of ATP during the cellular respiration process

• Utilizes O₂ - Aerobic

• OxPhos is accomplished by utilizing an electron transport chain and ATP synthase

OxPhos: Electron transport Chain

• The Mitochondrial ETC is made of a series of protein complexes that are embedded in the inner mitochondrial membrane

• Cristae increase the surface area of the inner mitochondrial membrane

• NADH and FADH₂ will drop off their electrons with the ETC creating NAD⁺ and FAD

• As electrons are transferred the ETC pumps H⁺ (protons) into the intermembrane space - creates a proton concentration gradient

• O₂ is the final electron acceptor of the mitochondrial ETC

• O₂ combines with the electrons and will pick up protons (H⁺) from the mitochondrial matrix - this creates H₂O

OxPhos is Aerobis because O₂ is required for the process to happen.

A lack of O₂ would cause a backup of electrons in the ETC and would shut the process down

Mitochondrial proton gradient

• High concentration of H⁺ in the intermembrane space

• Low concentration of H⁺ in the mitochondrial matrix

Intermembrane Space:

• High concentration of H⁺ in the intermembrane space because:

  • ETC pumps H⁺ into the intermembrane space

  • O₂ combines with H⁺ to make water in the matrix, reducing the H⁺ concentration

  • Intermembrane space is small

OxPhos: Chemiosmosis

• The proton concentration gradient allows for passive transport out of the intermembrane space (down its concentration gradient)

• Can the protons (H⁺) pass through the membrane unassisted via simple diffusion?

  • NO!

• Because of their charge, protons (H⁺) can only exit the intermembrane space via a transmembrane integral protein

  • Chemiosmosis is the diffusion of H⁺ down its concentration gradient through ATP synthase

OxPhos: Chemosmosis & ATP Synthase

• Transmembrane integral protein that is also an enzyme (-ase_

• ATP synthase performs ADP phosphorylation to create (synthesize) ATP

  • This process requires energy

OxPhos: Chemiosmosis

• As the H⁺ diffuses through ATP synthase, it causes the enzyme to turn - much like a water wheel creating power

• This provides the energy needed to phosphorylate ADP into ATP

OxPhos:ATP production

• Most of the ATP produced during cellular respiration is produced during the OxPhos step

• A theoretical maximum of 32-34 ATP can be produced during OxPhos

ATP Production Overall

• Glycolysis = 2 ATP (net)

• Link reaction = 0 ATP

• Krebs cycle = 2 ATP

• OxPhos = up to 34 ATP

Fermentation (Anaerobic respiration)

Vocabulary:

• Pyruvate -

• Fermentation -

Generating ATP with O₂

• Glycolysis occurs in the cytoplasm of a cell

• When O₂ is present - pyruvate will enter the mitochondria and the following processes will occur:

  • Link Reaction

  • Krebs Cycle

  • OxPhos

Generating ATP without O₂

• Glycolysis occurs in the cytoplasm

• When there is no O₂ present, pyruvate will stay in the cytoplasm and enter:

  • Alcohol Fermentation

    OR

  • Lactic Acid Fermentation

Glycolysis review

• Converts glucose into 2 pyruvate molecules

• Produces 2 ATP (net) and 2 NADH

Glycolysis requires NAD⁺ and ADP to continue

Making NAD⁺ and ADP available (with O₂)

• When oxygen is present:

  • NADH will drop off their electrons with the ETC: Creating NAD⁺

  • ATP is continually used for various cellular functions: Creates ADP

Without O₂ present, NADH cannot drop off their electrons with the ETC

Without O₂: Glycolysis Couples with fermentation

Fermentation regenerates NAD⁺ in order to allow glycolysis to continue under anaerobic conditions:

• Occurs in the cytoplasm - all cells can do fermentation

• 2 types:

  • Alcohol fermentation

  • Lactic acid fermentation

Glycolysis is how ATP is created in anaerobic conditions (net 2 ATP)

Alcohol fermentation

• 1st Glycolysis:

  • Glucose →
    2 Pyruvate + 2 ATP + 2 NADH

• Then:

  • 2 Pyruvate + 2 NADH →
    2 Ethanol + 2 CO₂ + 2 NAD⁺

• Overall:

  • Glucose →
    2 Ethanol + 2 CO₂ + 2 ATP

• Yeast (ex. Saccharomyces cerevisiae) and zymomonas mobilis (an anaerobic bacterium)

• Uses in industry:

  • Baking bread

  • Alcoholic beverages

Also called alcoholic fermentation or ethanol fermentation

Lactic Acid Fermentation

• 1st Glycolysis:

  • Glucose →
    2 Pyruvate + 2 ATP + 2 NADH

• Then:

  • 2 Pyruvate + 2 NADH →
    2 Lactate + 2 NAD⁺

• Overall:

  • Glucose → 2 Lactate + 2 ATP

• Humans, Animals, and some Bacteria (ex. from the genera Escherichia, and Lactobacillus)

• Uses in industry (not exhaustive):

  • Yogurt

  • Kimchi

  • Cheese

  • Pickles

Lactic Acid Fermentation in Humans

• Humans have large energy (ATP) requirements, so lactic acid fermentation is not a good long-term solution for us because only 2 ATP (net) are produced.

• However, it is effective for generating ATP for short, intense exercises (ex. Sprinting or weightlifting)

Pros and Cons of Anaerobic Respiration

Pros:

• Produces ATP in the absence of O₂

• Faster

• Doesn’t require special structures (ETC/ATP synthase)

Cons:

• Much less ATP than aerobic

Pros and cons of Aerobic respiration

Pros:

• Much more ATP is produced

Cons:

• Requires O₂

• Requires special structures (ETC/ATP synthase)

• Slower

Practice Questions

ATP

1. What is the role of ATP in plants?

2. How is ATP produced in plants?

3. Which cellular processes in plants require ATP?

4. Can plants store ATP for later use?

5. How is ATP used in photosynthesis?

6. What happens to ATP during cellular respiration in plants?

7. Are there any specific enzymes involved in ATP synthesis in plants?

8. How does ATP contribute to plant growth and development?

9. Can plants obtain ATP from sources other than cellular respiration?

10. Are there any factors that can affect ATP production in plants?

1. What is the process of converting ATP to ADP?

2. What enzyme is responsible for the conversion of ATP to ADP?

3. How is the conversion of ATP to ADP related to energy release?

4. Can ADP be converted back to ATP in plants?

5. What role does ADP play in cellular metabolism?

6. Are there any specific cellular processes that require ADP?

7. How does the conversion of ATP to ADP affect plant growth and development?

8. Can plants obtain ADP from external sources?

9. Are there any factors that can affect the conversion of ATP to ADP in plants?

10. How does the ratio of ATP to ADP impact cellular energy levels in plants?