EXAM 2 Learning Objectives (11-14)

Describe fluid mosaic model and chemical composition of membranes

The fluid mosaic model describes the structure of cell membranes as a dynamic and flexible arrangement of various proteins embedded in a fluid phospholipid bilayer.

lipids: (50% ~ phospholipids, glycolipids, steroids) Phospholipids form the bilayer. Cholesterol helps regulate its physical properties, and glycolipids help with protection and recognition

proteins: (50 % ~ integral and peripheral) carry out transport, signaling, anchoring, and enzymatic reactions

Carbohydrates: attach to lipids or proteins (5-10% ~ glycolipids, glycoproteins, proteoglycans) GLYCOCALYX ON EXTRACELLULAR FACE (carb layer of EC face)

cell surface carbs

GLYCOCALYX: carb layer of extracellular surface

protect against chemical and mechanical damage (lubrication)

cell-cell recognition: ligands for lectins (proteins that bind oligosaccharide chains) → lectin binding recruits WBC’s to sites of infection

identify if each of the following are amphipathic, hydrophobic, or hydrophillic: glycerol, fatty acid, triacylglycerol, phospholipid

glycerol = hydrophillic

fatty acid = amphipathic

triacylglycerol = hydrophobic

phospholipids = amphipathic

Explain three types of lipid motions and their importance

lateral diffusion - movement within its same leaflet → allows membrane components to redistribute and interact

Rotation - rotates around its axis → contributes to membranes dynamic behavior

Flip-flop - lipid moves from one leaflet to other → allows redistribution between leaflets (rare since polar heads have to cross the hydrophobic membrane)

Explain the behavior of lipids in water and how phospholipids form the bilayer

They assmeble differently: Micelle or bilayer liposome

Micelle: spherical, phospholipid with ONE fatty acid tail or detergent → cross section area of head > tail area

Bilayer Liposome: phospholipid with TWO fatty acid tails

cross section area of head = tail

Describe membrane properties (Fluidity, asymmetry) and role of membrane lipids and proteins

Fluidity: allows for rapid protein diffusion and interactions, protein movement, even distribution of membrane between daughter cells during cell division, pinching or fusion of membranes (endocytosis/exocytosis), and rapid sealing after membrane damage

→ affected by temperature, cholesterol content, and chain length and saturation of fatty acids.

• Increase fluidity: higher temp, shorter fatty acid tails, cis double bond-unsaturated tails

• decrease fluidity: lower temp, longer fatty acid tails, saturated tails

• cholesterol stiffens bilayer

Asymmetry: the distribution of carbs, lipids, and proteins is uneven between leaflets → important for structural and functional compatibility with their environments

Be able to follow a phospholipid after synthesis from ER to target membranes. Know which side of the membrane contains newly synthesized phospholipids

1. membrane synthesized in ER by adding phospholipids on cytosolic face

2. scramblase randomly flips phospholipids from one face of the membrane to the other in ER

3. symmetric growth of both halves of the bilayer in ER

4. membrane travels to golgi, where asymmetry is established. flippase moves specific phospholipids from the lumen face to the cytosolic face in golgi

5. floppases move specific phospholipids in the opposite direction (cytosol to lumen)

Explain the role of a phospholipid scramblases and flippases / floppases

scramblase: redistributes lipids and reduces asymmetry (no ATP)

flippase: moves selected lipids from lumen face to cytosol face (ATP required)

floppase: moves selected lipids from cytosolic face to lumen face (ATP required)

Compare/ contrast how membrane proteins associate with lipid bilayes

1. transmembrane : crosses the entire lipid bilayer through one or more alpha helices or a beta barrel

2. monolayer-associated: inserts into one leaflet, often through an amphipathic alpha helix

3. lipid-anchored: attaches covalently to a lipid that sits in the bilayer

→ 1-3 are integral membrane proteins: require detergents for extraction

1. peripheral/protein-attached: associates noncovalently with another membrane protein or the membrane surface

→ peripheral membrane protein: can be removed by changing salt concentration or pH

Describe the location and role of membrane-associated carbohydrates

carbs attach to proteins as glycoproteins (proteins with short, covalently attached oligosaccharides) and to lipids as glycolipids (lipid with covalently attached oligosaccharide). Together with surface proteoglycans (protein with 1 or more long oligosaccharides), they form the glycocalyx: the carbohydrate coating outside the cell

role: lubrication—protection from chemical and mechanical damage, cell-cell recognition

Explain how cells restrict the movement of membrane proteins

Not all proteins are mobile, some are restricted to membrane domains

cells can restrict proteins by:

tethered to cell cortex

tethered to EC matrix

cell-cell adhesion (through proteins)

tight junctions (proteins)

diffusion across a synthetic lipid bilayer

• LIMITED

• molecules tend to diffuse from H → L concentration (downhill)

• across a synthetic bilayer, diffusion occurs based on size and solubility (in lipid)

• charged molecules rarely diffuse across lipid bilayer no matter their size

Explain how the amino acid composition on the surface of a protein determines whether it is an integral membrane protein

protein region contacting the membranes hydrophobic interior needs nonpolar, hydrophobic side chains on its exposed surface

→ The protein surface must match its surroundings: hydrophobic toward lipid tails and hydrophilic toward water.

Explain how detergent molecules “break up” lipid vesicles

detergent molecules = aphipathic

• Their hydrophobic regions insert among lipid tails.

• They disrupt the interactions holding the bilayer together.

• At sufficient concentration, the membrane breaks into mixed micelles containing detergent and membrane lipids.

• Detergents surround exposed hydrophobic regions of membrane proteins, allowing those proteins to remain dispersed in water.

integral membrane proteins: can be removed from membranes only by using detergents

peripheral membrane proteins: can be removed by more gentle extraction methods

Detergents: amphipathic and form micelles in water

• disrupt hydrophobic associations and disintegrate lipid bilayer

Able to explain the importance and broad mechanism of transport across membranes

membrane transport allows cells to take in nutrients, remove wastes, regulate water balance, and maintain ion concentrations needed for signaling

selective permeability: some molecules pass directly through membrane, others require channels or carriers, transport down a gradient is passive, transport against a gradient is active (requires ATP)

compare/contrast simple diffusion, facilitated diffusion and active transport

Simple diffusion: travel directly through lipid bilayer down the gradient, no energy required

Facilitated diffusion: travel through a channel or carrier down the gradient, no energy required

active transport: travel through a pump or coupled carrier against the gradient, ATP required

determine whether a molecule can passively diffuse through a membrane based on its physical and chemical characteristics

small, nonpolar: crosses readily

small, uncharged polar: crosses slowly

large, uncharged polar: crosses very poorly

charged: crosses poorly regardless of size

explain the differences between channel and transporter (carrier)

Channel proteins form pores that allow specific ions or molecules to pass through; allows rapid movement when open; always proved passive transport, ion channels/aquaporins

Transporter proteins change shape to move substances across the membrane; move solutes through repeated binding and conformational change; selectively depends on the solute-binding site; can provide passive or active transport

explain why some molecules require energy for transport across a membrane, while others do not

Molecules require energy for transport across a membrane when they are moving against their concentration gradient, which necessitates active transport mechanisms like pumps. In contrast, molecules that move down their concentration gradient can do so passively without the need for energy.

Passive transport: simple diffusion vs facilitated diffusion

simple: downhill the electrochemical gradient

facilitated: involves membrane proteins (channels and transporters/carriers), downhill the electrochemical gradient

active transport: primary vs secondary

primary: ATP or Light energy, PUMPS, ATP-driven pump, light-driven pump, against a concentration gradient

secondary: gradient-driven pump, couples uphill transport with downhill transport, symporter: same direction of uphill and downhill transports, antiporter: opposite directions of uphill and downhill transports

explain ATP and gradient-driven active transport mechanisms and describe examples illustrating both mechanisms

ATP-driven. or primary active transport → direct ATP hydrolysis → example: Na+/K+ -ATPase

Gradient-driven, or secondary active transport → one solute moving downhill drives another uphill → example: Na+/glucose symporter

pump usually creates the gradient first:

• symporter: moves coupled solutes in the same direction

• antiporter: moves coupled solutes in opposite directions

Describe the Na+/K+ - ATPase cycle

1. Three Na⁺ bind on the cytosolic side.

2. ATP phosphorylates the pump.

3. The pump changes shape and releases the three Na⁺ outside.

4. Two K⁺ bind from outside.

5. The phosphate is released.

6. The pump returns to its original shape and releases the two K⁺ inside.

Per cycle: 3 Na⁺ out, 2 K⁺ in, 1 ATP used.

Both ions move against their electrochemical gradients. The pump maintains high Na⁺ outside and high K⁺ inside. Because it exports one net positive charge per cycle, it also contributes to a negative interior.

Describe how glucose is transported into a gut epithelial cell and transported out of a gut epithelial cell into the blood stream

• The basolateral Na⁺/K⁺ pump exports Na⁺, keeping intracellular Na⁺ low.

• An apical Na⁺–glucose symporter brings Na⁺ and glucose from the intestinal lumen into the cell. Na⁺ moving downhill drives glucose uptake uphill.

• Glucose exits through a basolateral GLUT carrier by facilitated diffusion toward the blood.

Describe how membrane potential is generated in neuron (electrochemical gradient, nernst equation, GHK equation)

It develops because cells have unequal ion concentrations and selective permeability to those ions.

The membrane potential is influenced by the distribution of ions, primarily Na⁺ and K⁺, across the membrane, creating an electrochemical gradient. The Nernst equation calculates the equilibrium potential for a specific ion, while the GHK equation predicts the membrane potential based on multiple ions and their relative permeability.

Draw and describe basic components of nerve cells and their function in signal transmission

dendrites: receive signals

soma: integrates signals

axon hillock: generates action potentials axon: transmits signals axon terminals: release neurotransmitters

Depolarization: Na+ enters the cell

Repolarization: K+ exits the cell

Hyperpolarization: K+ channels remain open briefly, allowing more K+ to exit, making the inside of cell super negative (-90 mV)

Peak of action potential: occurs when Na+ channels are inactive and K+ channels are open. (+40 mV)

RMP: -70 mV

describe how nerve cells generate action potential

1. Incoming signals depolarize the membrane toward threshold.

2. At threshold, voltage-gated Na⁺ channels open.

3. Na⁺ enters, causing further depolarization and opening more Na⁺ channels.

4. Na⁺ channels inactivate, while delayed voltage-gated K⁺ channels open.

5. K⁺ leaves, repolarizing the membrane.

6. Continued K⁺ movement briefly causes hyperpolarization.

7. K⁺ channels close, and the membrane returns toward its resting potential.

Action potentials are all-or-none: reaching threshold produces a full action potential. Stronger stimulation generally increases firing frequency rather than action-potential size.

Describe the mechanisms of depolarization, hyperpolarization, and repolarization, and the role of ion channels and the pump (Na+, K+, ATPase)

Depolarization occurs when Na⁺ channels open, allowing Na⁺ to flow into the cell, making the inside more positive.

Hyperpolarization happens when K⁺ channels open, allowing K⁺ to exit the cell, making the interior more negative.

Repolarization is the process of returning to the resting membrane potential after depolarization, primarily through the action of K⁺ channels and the Na⁺/K⁺ ATPase pump, which maintains the ion gradients.

The Na⁺/K⁺ pump continuously maintains and restores ion gradients over time. The rapid falling phase of an individual action potential comes mainly from K⁺ movement through channels.

Describe how action potential spreads along axon

Action potential spreads along the axon through a process called saltatory conduction, where the action potential jumps between nodes of Ranvier. This occurs as voltage-gated Na⁺ channels open at each node, allowing Na⁺ influx, which propagates the electrical signal rapidly down the length of the axon.

in unmyelinated axons: regeneration occurs along successive regions of membrane

Describe synaptic communication and types of synapses

Synaptic communication is the process by which neurons transmit signals to each other at synapses.

_____ carry the chemical signal across the synaptic cleft and it binds to the receptors on the ________?

neurotransmitters; postsynaptic cell

Describe broad overview of catabolism in the cells

• Break large molecules, generate building blocks, generate energy

• Negative delta G

• Release energy by oxidation of organic molecules

• Addition of oxygen to organic molecules = energetically favorable

• Hydrogenation (gain of electrons) = reduction

• Dehydrogenation (loss of electrons) = oxidation

• Oxidation of organic molecules is promoted in small steps (with enzymes) to harvest useful energy -> prevents loss of energy as heat

• Ex: energy released in stepwise oxidation is stored in activated carriers by cells

• 3 steps involving the breakdown (catabolism) and oxidation of food

  • Extracellular: breakdown of large molecules into smaller ones

  • Intracellular/cytoplasm: breakdown of small molecules into intermediates (pyruvate/acetyl CoA)

  • Intracellular/mitochondria: complete oxidation and energy harvesting

• Key: big molecules in the presence of oxygen get broken down into H2O and CO2

identify the cellular location for glycolysis, fermentation, pyruvate oxidation, citric acid cycle and oxidative phosphorylation

glycolysis: cytosol

fermentation: cytosol

Pyruvate oxidation: mitochondrial matrix

citric acid cycle: mitochondrial matrix

oxidative phosphorylation: inner mitochondrial membrane

key steps in energy investment phase of glycolysis: step 1 and 3

step 1: “glucose trapping”

glucose is phosphorylated by ATP and Hexokinase to glucose-6-phosphate

Step 3: Fructose-6-phosphate is phosphorylated by ATP and phosphofructokinase to fructose-1,6-bisphosphate.

key steps in cleavage step in glycolysis: step 4

Step 4: Fructose-1,6-bisphosphate is cleaved by aldolase into two three-carbon molecules: dihydroxyacetone phosphate and glyceraldehyde-3-phosphate (G3P).

key steps in energy generation step of glycolysis: step 10

“second level phosphorylation + pyruvate formation” Phosphoenolpyruvate is converted to pyruvate by pyruvate kinase, producing ATP through substrate-level phosphorylation.

describe the major steps of glycolysis and role for enzymes (hexokinase, phosphofructokinase, aldolase and pyruvate kinase)

Glycolysis is a ten-step metabolic pathway occurring in the cytosol that breaks down glucose into pyruvate, generating ATP and NADH.

Investment of 2 ATP → produce 4 ATP => net yield 2 ATP

Phase 1: Energy investment (1-3)

• uses 2 ATP

• phosphorylates glucose

• rearranges the molecule in preparation for cleavage

Phase 2: Cleavage (4-5

• 6-carbon sugar is split into two 3-carbon molecules

• both are ultimately converted into glyceraldehyde-3-phosphate (2 G3P)

Phase 3: Energy generation (6-10)

• produces 4 ATP

• produces 2 NADH

• forms 2 pyruvate molecules

Hexokinase: phosphorylates glucose to glucose-6-phosphate using ATP, trapping glucose inside the cell

Phosphofructokinase (step 3): converts fructose-6-phosphate to frutose-1,6-biphosphate using ATP. MAJOR regulatory gatekeeper and commitment step.

Aldolase (step 4): cleaves the six-carbon fructose-1,6-biphosphate into two three-carbon molecules

pyruvate kinase (step 10): transfers a phosphate from phosphoenolpyruvate to ADP to form ATP and pyruvate.

ATP production in steps 7 and 10 occurs through ______ phosphorylation, meaning a phosphate is transferred directly from a high-energy intermediate to ADP.

substrate-level

explain how feedback regulation regulates glycolysis

feedback inhibition of PFK by ATP stops fructose-1,6-bisphosphate formation (stopping new product formation) → glycolysis slows down

fructose-1, 6-biphosphatease hydrolyzes fructose 1, 6-biphosphate producing fructose 6-phosphate (depleting already formed product)

describe the role of activated carriers during glycolysis and their relative energy yield

activated carriers temporarily capture and transfer energy released from glucose oxidation

ATP: immediately usable chemical energy → 2 ATP per 2 glucose

NADH: carriers high-energy electrons for later ATP generation → 2 NADH per 2 glucose

NAD+: accepts electrons during oxidation, becoming NADH → 2 NAD+ reduced per 2 glucose

NADH vs NADPH

Both are coenzymes involved in redox reactions; NADH is primarily used in catabolism and ATP production, while NADPH is utilized in anabolic reactions and biosynthesis.

explain the fate of pyruvate under anaerobic conditions (fermentation)

cells can use fermentation to generate NAD+ from NADH to allow glycolysis to continue, producing lactate or ethanol and CO2 as byproducts.

1. Lactic acid fermentation: muscle cells and certain bacteria

   1. pyruvate is reducted to lactate

   2. NADh is oxidized to NAD+

   3. lactate dehydrogenase

   4. Cori cycle: lactate travels from muscle cells to the liver, where it can be converted back into pyruvate and glucose

2. Ethanol fermentation: yeast

   1. pyruvate is converted to acetaldehyde, releasing CO2

   2. acetaldehyde is reduced to ethanol

   3. NADH is oxidized, regenerating NAD+

**** fermentation doesn’t generate additional ATP beyond glycolysis. Its main purpose is to regenerate NAD+ so glycolysis can continue producing ATP

pyruvate is converted into acetyl-coA under ____ conditions

aerobic

Develop the big picture of fate of end products of glycolysis

2 pyruvate, 2 net ATP, 2 NADH

Pyruvate:

• Aerobic: enters mito and is converted into acetyl-CoA

• anaerobic: converted into lactate or ethanol

NADH:

• aerobic: electrons transferred into mito through shuttle system

• anaerobic: used to regenerate NAD+ during fermentation

ATP:

• aerobic/anaerobic: available for cellular work

explain the transport and metabolism of pyruvate in mitochondria

transport:

• actively transported by mitochondrial pyruvate carrier (MPC) into the MITO MATRIX!!!!

Metabolism: matrix

• pyruvate is converted into acetyl-CoA by the pyruvate dehydrogenase complex (PDC), linking glycolysis to the Krebs cycle (oxidation)

• first 2 carbons from glucose are completely oxidized by pyruvate dehydrogenase complex

explain why pyruvate and acetyl CoA are central to energy generation pathways

pyruvate is a key product of glycolysis, serving as a substrate for acetyl-CoA formation, which enters the Krebs cycle. This process leads to the production of high-energy molecules such as NADH and FADH2, essential for ATP synthesis in cellular respiration.

Describe the key outcome of the key steps of citric acid cycle

Eukaryothes = Mitochondrial Matrix

Doesn’t use O2 directly, but requires O2 to regenerate NAD+ in oxidative phosphorylation

8 enzymatic steps but only 6 key steps = 6 key outcomes

Step 1: formation of 6C citrate and release of CoA

Step 3: High energy yield (NADH) + CO2 reease

Step 4: High energy yield (NADH) + CoA bonding + CO2 release

Step 5: High energy yield (GTP) + CoA release

Step 6: High energy yield (FADH2)

Step 8: High energy yield (NADH) and restart of cycle

One turn of cycle produces: 3 NADH, 1 GTP, 1 FADH2, releases 2 CO2

Describe the mechanisms of citric acid cycle regulation

allosteric inhibition and activation

The main idea is that the citric acid cycle speeds up when the cell needs energy and slows down when energy is plentiful.

NADH and ATP act as allosteric inhibitors, while ADP, AMP, and NAD+ act as allosteric activators

2 mechanisms:

1. conversion of pyruvate to acetyl-CoA (PDH Complex controls the conversion)

2. Entry of acetyl-CoA into the cycle (Citrate synthase controls entry)

describe activated carriers involved in citric acid cycle

GTP: readily converted into ATP (GTP + ADP ↔ GDP + ATP) through nucleoside diphosphokinase

NADH/NADPH: are electron carriers that transport high-energy electrons to the electron transport chain

FADH2: also carries 2 high-energy electrons; the electrons have slightly lower energy than those held by NADH

**Activated carriers transfer electrons to ETC

overview of energy generation and ETC in mitochondria

energy conversion takes place in the INNER MITOCHONDRIAL MEMBRANE

Activated carriers produced by glycolysis and the citric acid cycle power ATP production in the mitochondria. Major ATP production occurs by oxidative phosphorylation in the inner mito memb.

energy from electron transfer is used to pump H+ from the matrix into the intermembrane space, creating an ETC

H+ flows bacl down its gradient through ATP synthase → enzyme converts the energy of proton flow into chemical-bond energy in ATP

explain the mechanism of electron transport in terms of electron bonding affinity and redox potential

The electron transport mechanism involves the transfer of electrons through a series of protein complexes, where electrons move from carriers with lower bonding affinity to those with higher bonding affinity.

Redox Potential is a measure of electron affinity (redox pairs)

Electrons are transferred through the electron transport chain (ETC), driven by differences in redox potential, resulting in ATP production.

electrons are transferred from a molecule with low electron affinity to a molecule with high electron affinity (neg delta G)

electron affinity in redox rxns

Redox Pairs:

NAD+/NADH

FAD+/FADH2

two forms of same compound that can interconvert by gaining or losing electrons

explain the role of NADH dehydrogenase and cytochrome reductase and cytochrome oxidase

cytochrome oxidase catalyzes O2 reduction. This is the only step in respiration where oxygen plays a direct role.

NADH dehydrogenase: contains iron-sulfur centers that transfer electrons

Cytochrome reductase: contain iron in heme groups that serve as electron acceptors

ubiquinone: electrons are transferred from FADH2 to ubiquinone (entry point); it’s a membrane-diffusible electron carrier that transfers electrons between ETC enzyme complex.

How are electrons transported along ETC? What makes them to move?

How are H+ pumped into the intermembrane space?

How does pumped H+ come back to the matrix to generate ATP?

Through chemiosmotic coupling. This process occurs via ATP synthase, which uses the flow of H+ ions down their concentration gradient to convert ADP and inorganic phosphate into ATP.

proton motive force

• intermembrane space is more positive than the matrix (-150 to -180 mV)

• H+ is attracted to negative matrix

• intermembrane space has a lower pH since it has a lot of H+

• H+ moves from H to L concentration

• Together, this electrical and chemical force makes the proton motive force

how does proton electrochemical gradient also drive coupled transport?

pH gradient drives pyruvate and phosphate import

voltage gradient drives ADP-ATP exchange

identify the electron donor and electron acceptor in the mitochondrial ETC. Describe the role of oxygen as electron acceptor.

donors: NADH and FADH2 → supply electrons to the ETC, which are passed through successive electron acceptors until they reach oxygen

acceptors: oxygen → acts as final electron acceptor, allowing electron transport to continue

→ if O2 is unavailable: electron transport can’t continue normally, NAD+ regeneration through the ETC is prevented, oxidative phosphorylation stops

what happens if proton gradient is dissipated?

ATP synthesis through oxidative phosphorylation stops because ATP synthase no longer has the electrochemical gradient needed to drive ATP production

Role of an uncoupler: an uncoupler disrupts the proton gradient by allowing protons to flow back into the matrix without passing through ATP synthase, thus stopping ATP production while continuing electron transport.

uncoupler → proton gradient dissipates → ATP synthase loses its driving force → oxidative phosphorylation no longer produces ATP efficiently

A

REDOX

Order: NADH Dehydrogenase (-300 mV) < Ubiquinone (45 mV) < Cytochrome C (254 mV)

Best e- donor: NADH dehydrogenase bc its the most negative so it’s ready to give up e-

Transfer with high energy release: NADH Dehydrogenase and Cytochrome C

Able to relate proton pumping, electrochemical gradient, and proton reentry via ATP synthase in production of ATP

all 3 processes are connected through chemiosmotic coupling (the coupling of ATP synthesis with the diffusion of protons down their gradient).

energy is released as electrons move through the ETC → H+ is pumped from the matrix into the intermembrane space (proton pumping) → a difference in proton concentration and electrical potential is established (electrochemical gradient) → H+ flows back into the matrix through ATP synthase (proton reentry) → ATP synthase converts proton-flow energy into chemical bond energy in ATP

Explain how oxidation of glucose yields 30 ATP

glycolysis: produces ATP and NADH

citric acid cycle: generates activated electron carriers and GTP

oxidative phosphorylation: uses electrons from NADH and FADH2 to establish a proton gradient that drives ATP production

**much of the energy released during glucose oxidation is captured in activated electron carriers before being used for ATP generation through ETC and ATP synthase

1 glucose ~ 30 ATP

predict the outcome of oxidative phosphorylation if the mitochondrial inner membrane is disrupted and explain why.

oxidative phosphorylation cannot produce ATP normally because…

• inner mmebrane is required to maintain separation between the matrix and intermembrane space

• disruption prevents the electrochemical proton gradient from being maintained

• H+ can no longer provide the necessary gradient energy for ATP synthase

• ATP production through oxidative phosphorylation is therefore disrupted

uncouplers dissipate the proton gradient, separating proton-gradient formation from ATP synthesis

Structure of a chloroplast

Chroplast: organelle

• outer membrane

• intermembrane space

• inner membrane

• thylakoid membrane: contains PS II and PS I

• thylakoid space

Grana: stack of thylakoids

Thylakoid space: lumen of thylakoid

Stroma: fluid outside the thylakoid space

Chlorophyll

green, primary light-absorbing pigment found in chloroplasts and photosystems that captures light energy for photosynthesis.

• chlorophyll molecules get excited when photon is absorbed leading to excitatory jumping to higher energy levels

overview of photosynthesis and comparison with cellular respiration

Photosynthesis: Light energy + CO2 +H2O → sugars + O2 + Heat energy (30 ATP)

• light energy to chemical energy

• consumes CO2 and H2O

• releases O2 and sugars

• energetically expensive

• generates and consumes ATP

• 2 stages: light and dark (calvin cycle)

Cellular respiration: Glucose (C6H12O6) + O2 → CO2 + H2O + Energy (30 ATP)

• breaks down sugars in the presence of oxygen to release energy

• releases energy from sugars (30 ATP/ glucose)

• consumes sugar and O2

• produces Co2, H2O, and ATP

identify the locations of processes/enzymes of photosynthesis

photosynthesis: chloroplast

PS I and PS II: thylakoid membrane

H+ accumulation: thylakoid space

calvin cycle: stroma

Locations of major processes and enzymes:

• Light reactions: Thylakoid membrane.

• Photosystems I and II: Thylakoid membrane.

• ATP synthase: Thylakoid membrane.

• Calvin cycle (carbon fixation): Stroma.

• Rubisco: Functions during carbon fixation in the stroma.

identify the electron donor and acceptor in chloroplasts

• Initial electron donor: H₂O (water).

• Terminal electron acceptor: NADP⁺.

• Final reduced electron carrier: NADPH.

• NADP⁺ is the terminal electron acceptor in chloroplasts, whereas O₂ is the terminal electron acceptor in mitochondria.

explain how the light-harvesting complex converts light energy into useful molecules

1. Chlorophyll absorbs light energy in the antenna complex.

2. Light energy excites electrons in the reaction center.

3. High-energy electrons enter an electron transport pathway.

4. Electron transport contributes to proton-gradient formation and ATP production, while electron transfer to NADP⁺ produces NADPH.

The useful molecules generated by the light reactions are ATP and NADPH.

Describe two photosystems and two stages of photosynthesis

• 2 Stages: Light reactions and dark reactions (calvin cycle/ carbon fixation)

  • Stage 1: Light energy captured → photons power electron transport from H2O to ETC → O2 is generated → NADPH and proton gradient generate ATP

    • PS II: H+ gradient established (electrons move from reaction center → PS I), charge separation, electron transfer, water splitting (replenish electrons), release O2 and pump H+ in thylakoid space to generate ATP

    • PS I: electrons move from reaction center → NADP+, NADP+ is the terminal electron acceptor (e- replenished from PS II), yielding NADPH (reducing power)

    • BOTH PS II and PS I: harvest photons energy in Antenna complex, generate high energy electron in reaction center, electron transport

• Stage 2: Chemical energy of ATP and NADPH converts CO2 to carbohydrate

  • ATP and NADPH generated from stage 1 is used to synthesize carbohydrate from CO2 and water (Calvin cycle)

  • Takes place in stroma!!! And can take place in the dark until all ATP and NADPH is exhausted

  • all energy exits the choroplast via sugar roduction since ATP and NADPH cant exit chloroplast directly

  • net product is G3P (converted to sucrose + feeds into glycolysis in the cytosol)

  • Rubisco enzyme: Enzyme that catalyzes the first step of the Calvin cycle, facilitating the fixation of CO2 to ribulose-1,5-bisphosphate (RuBP), leading to the production of 3-phosphoglycerate (3-PGA). MOST ABUNDANT PROTEIN ON EARTH

explain the role of rubisco and identify the products of the calvin cycle

Rubisco: Its function is to catalyze the addition of CO₂ to ribulose-1,5-bisphosphate during carbon fixation.

For every 3 molecules of CO2 that eneter in the cycle, 1 molecule of G3P is produced and 9 molecules of ATP + 6 Molecules of NADPH are consumed

why only 3 molecules? This is because the Calcin cycle is designed to fix 1 carbon atom from each CO₂, and in order to produce one net molecule of G3P, 3 CO₂ molecules are needed to fully regenerate ribulose-1,5-bisphosphate for the next cycle.

compare the role of O2 and CO2 in photosynthesis and cellular respiration

Photosynthesis:

• O2: produced when PS II splits water

• CO2: consumed during carbon fixation by rubisco

Cellular respiration

• O2: acts as terminal electron acceptor and is reduced to water

• CO2: released during oxidation of organic molecules

Photosynthesis consumes CO₂ and produces O₂, whereas cellular respiration consumes O₂ and produces CO₂.

compare electron transport in mitochondria and chloroplasts

explain the relationship between photosynthesis and respiration in plants

Photosynthesis and cellular respiration are interconnected metabolic processes.

• Photosynthesis uses light energy, CO₂, and H₂O to generate sugars and O₂.

• Cellular respiration uses sugars and O₂ to generate ATP, releasing CO₂ and H₂O.

• The sugars generated during photosynthesis can provide fuel for cellular respiration.

Additionally, the G3P produced by the Calvin cycle can feed into glycolysis in the cytosol.

Important: Photosynthesis generates and consumes ATP and NADPH within the chloroplast. ATP and NADPH cannot exit the chloroplast, so energy exits through sugar production.

describe the endosymbiotic theory and supporting evidence

The Endosymbiotic Theory proposes that mitochondria and chloroplasts evolved from bacteria engulfed by ancestral eukaryotic cells.

Origin of mitochondria:

An anaerobic ancestral eukaryote (archaea) engulfed an aerobic bacterium.

The aerobic bacterium eventually evolved into the mitochondrion.

The endosymbiotic relationship provided nutrients and a suitable environment in exchange for aerobic respiration and energy supply.

Origin of chloroplasts:

A photosynthetic cyanobacterium was acquired as another endosymbiont, eventually evolving into the chloroplast and contributing to the evolution of algae and plants.

Evidence (similarities in…):

• chromosome structure (circular)

• binary fission

• ribosome structure + proteins

• membrane proteins (cardiolipin in inner and porins in outer membranes)

what is the role of cytochrome c

it catalyzes the reduction of O2 to H2O as the terminal electron acceptor

How do the components of the proton-motive force drive coupled transport across the inner mitochondrial membrane?

the voltage gradient drives ADP/ATP exchange while the pH gradient drives phosphate and pyruvate import