Cell Biology: Membrane Structure and Function

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Questions and Answers

What is the main function of photosystems in photosynthesis?

To split water molecules.

To generate ATP directly.

To fix carbon dioxide.

To capture and transfer light energy. (correct)

Which of the following correctly describes the electron transport chain in photosynthesis?

It produces glucose directly.

It uses ATP and NADH to transport electrons.

It oxidizes glucose to produce energy.

It pumps protons into the thylakoid lumen creating a proton gradient. (correct)

What are the products of the water-splitting reaction during photosynthesis?

Oxygen, protons, and electrons. (correct)

Carbon dioxide and glucose.

Light energy and heat.

NADPH and ATP.

In the Calvin cycle, what is the primary role of ATP and NADPH?

To convert CO2 into glucose. Signup and view all the answers

How does the citric acid cycle differ from the Calvin cycle?

The citric acid cycle focuses on ATP production while the Calvin cycle synthesizes glucose. Signup and view all the answers

Which type of energy is defined as stored energy within chemical bonds?

Chemical Energy Signup and view all the answers

What happens to entropy in a closed system as energy is dispersed?

Entropy increases. Signup and view all the answers

Which reaction type releases free energy?

Exergonic Reactions Signup and view all the answers

What characterizes a spontaneous reaction?

Increases the entropy of the universe. Signup and view all the answers

How do enzymes affect chemical reactions?

They speed up reactions by lowering activation energy. Signup and view all the answers

What is the main role of ATP in cellular processes?

It is the primary energy carrier storing energy in high-energy bonds. Signup and view all the answers

What effect does a competitive inhibitor have on an enzyme-catalyzed reaction?

It blocks substrates from binding to the active site. Signup and view all the answers

Reaction coupling is primarily used to:

Link an exergonic reaction with an endergonic reaction to drive the latter. Signup and view all the answers

What is the primary role of activation energy in chemical reactions?

To lower the barrier for reactions to occur Signup and view all the answers

Which of the following best describes cellular respiration?

It breaks down glucose to release energy. Signup and view all the answers

Which process involves the oxidation of glucose and reduction of oxygen?

Cellular Respiration Signup and view all the answers

In which location of the cell does glycolysis take place?

Cytoplasm Signup and view all the answers

What is the primary function of NAD in cellular respiration?

To act as an electron carrier Signup and view all the answers

What is produced during the citric acid cycle from two Acetyl-CoA molecules?

4 CO2, 6 NADH, 2 FADH2, and 2 ATP Signup and view all the answers

What mechanism generates ATP during oxidative phosphorylation?

Electron transport through the proton gradient Signup and view all the answers

During pyruvate oxidation, which products are generated from 2 pyruvate molecules?

2 Acetyl-CoA, 2 NADH, and 2 CO2 Signup and view all the answers

What feature of phospholipids contributes to the formation of a cell membrane bilayer?

They have a hydrophilic head and hydrophobic tails. Signup and view all the answers

Which factor is known to decrease membrane fluidity?

Saturated fatty acids. Signup and view all the answers

What role does cholesterol play in membrane structure?

It stabilizes the membrane by maintaining fluidity. Signup and view all the answers

Which of the following molecules can easily cross the cell membrane without transport proteins?

Oxygen. Signup and view all the answers

What process describes water movement from a low solute concentration to a high solute concentration?

Osmosis. Signup and view all the answers

Which statement accurately describes active transport?

Requires energy to transport substances. Signup and view all the answers

What is co-transport in cellular membranes?

Simultaneous transport of two substances, one with and one against its gradient. Signup and view all the answers

In which process does a cell take in large materials by engulfing them?

Phagocytosis. Signup and view all the answers

What is the primary effect of anaerobic conditions on ATP production?

It causes a buildup of lactic acid or ethanol. Signup and view all the answers

How does reduced blood flow affect cellular respiration?

It increases reliance on anaerobic pathways. Signup and view all the answers

What role do autotrophs play in energy flow within ecosystems?

They produce their own food through photosynthesis. Signup and view all the answers

Where do light reactions of photosynthesis occur?

In the thylakoid membranes of chloroplasts. Signup and view all the answers

What is the main purpose of the Calvin cycle in photosynthesis?

To synthesize glucose from CO2 using energy carriers. Signup and view all the answers

Which pigments primarily absorb light for photosynthesis?

Different pigments absorb primarily blue and red light. Signup and view all the answers

What initiates the excitation of electrons in chlorophyll during photosynthesis?

Absorption of photons. Signup and view all the answers

What is the main product of the light reactions in photosynthesis?

ATP and NADPH. Signup and view all the answers

Study Notes

Fluid Mosaic Model

The cell membrane is a flexible layer of phospholipids with proteins embedded.
Phospholipids are amphipathic with a hydrophilic head and hydrophobic tails.
The phospholipid bilayer has heads facing outward and tails facing inward.

Membrane Fluidity

Temperature affects membrane fluidity.
Higher temperatures lead to increased fluidity (more movement).
Unsaturated fatty acids increase fluidity due to kinks preventing tight packing.
Saturated fatty acids decrease fluidity as they pack tightly.

Cholesterol's Role

Cholesterol helps maintain membrane fluidity by preventing it from becoming too rigid or too fluid.

Membrane Protein Functions

Transport proteins help move substances in and out of the cell.
Receptor proteins receive signals from outside the cell.
Enzymes catalyze reactions at the membrane.

Movement Across Membranes

Small nonpolar molecules (O2, CO2) can easily cross the membrane.
Large or charged molecules (glucose, ions) require transport proteins.

Types of Passive Transport

Simple diffusion: Movement of small molecules directly through the membrane.
Facilitated diffusion: Movement of larger molecules through protein channels.

Diffusion vs. Osmosis

Diffusion involves the movement of molecules from high to low concentration.
Osmosis is the movement of water from low solute concentration to high solute concentration.

Tonicity Terms

Hypertonic solutions have a higher solute concentration outside the cell, causing water to move out (cell shrinks).
Hypotonic solutions have a lower solute concentration outside the cell, causing water to move in (cell swells).

Active Transport vs. Passive Transport

Active transport moves substances against their concentration gradient, requiring energy (ATP).
Passive transport moves substances down their concentration gradient without energy.

Co-Transport

Co-transport involves the simultaneous transport of two substances across a membrane.
One substance moves with its concentration gradient, providing energy for the other substance to move against its gradient.

Bulk Transport

Endocytosis: The cell takes in large materials by engulfing them (e.g., phagocytosis for solids).
Exocytosis: The cell expels materials using vesicles that fuse with the membrane.

Catabolic vs. Anabolic Reactions

Catabolic reactions break down larger molecules into smaller ones, releasing energy (e.g., cellular respiration).
Anabolic reactions build larger molecules from smaller ones, requiring energy (e.g., protein synthesis).

Types of Energy

Potential energy is stored energy (e.g., energy in chemical bonds).
Chemical energy is potential energy stored in molecular bonds (e.g., glucose).
Kinetic energy is the energy of motion (e.g., moving molecules).
Thermal energy is a form of kinetic energy related to molecular motion.
Heat is energy transferred due to temperature differences and is not usable for work.

Entropy

Entropy measures disorder or randomness in a system.
In a closed system, entropy increases as energy is dispersed (e.g., ice melting).
Living organisms maintain order by using energy to counteract increasing entropy.

Free Energy

Free energy is the energy available to do work in a system.
Reactions with products having lower free energy than reactants are likely to proceed spontaneously.
Exergonic reactions release free energy (e.g., cellular respiration).
Endergonic reactions require free energy (e.g., photosynthesis).

Spontaneous Reactions

Spontaneous reactions occur without external input and increase the entropy of the universe.
A reaction can be spontaneous even if it is slow.

Reaction Coupling

Reaction coupling links an exergonic reaction with an endergonic reaction.
Energy released from the exergonic reaction (e.g., ATP hydrolysis) is used to power the endergonic reaction.

Role of ATP

ATP (adenosine triphosphate) is the primary energy carrier in cells.
It stores energy in its high-energy phosphate bonds and releases energy when hydrolyzed to ADP.

Enzymes and Chemical Reactions

Enzymes speed up reactions by lowering activation energy.
Substrates bind to the active site of the enzyme, allowing the enzyme to be reused.

Reaction Rates and Energy Levels

Lowering the energy level of the transition state increases the reaction rate.
Adding or removing enzymes changes reaction rates.
Competitive inhibitors block active sites, slowing reactions.
Non-competitive inhibitors change enzyme shape, also slowing reactions.

Activation Energy and Regulation

Enzymes lower activation energy, making reactions easier to start and enabling regulation of metabolic pathways.

Relationship Between Cellular Respiration and Photosynthesis

Photosynthesis captures light energy and converts it into chemical energy (glucose).
Cellular respiration breaks down glucose to release energy for cellular processes.
Cellular respiration (glucose + oxygen --> carbon dioxide + water + ATP) is essentially the reverse of photosynthesis.

Energy Change Diagram

Glucose and oxygen are reactants, and carbon dioxide, water, and ATP are products.
The energy change during cellular respiration is a release of energy.

Redox Reactions

Oxidation is the loss of electrons.
Reduction is the gain of electrons.
The oxidizing agent gains electrons and is reduced.
The reducing agent loses electrons and is oxidized.

Redox Reactions in Cellular Processes

Combustion is similar to cellular respiration, with the oxidation of fuel (glucose) producing carbon dioxide and water.
Cellular respiration involves redox reactions where glucose is oxidized and oxygen is reduced.

Function of NAD

NAD (nicotinamide adenine dinucleotide) is an electron carrier.
It becomes NADH when it gains electrons during metabolic reactions, which is crucial for energy production in cellular respiration.

Major Steps of Cellular Respiration

Glycolysis:
- Location: Cytoplasm
- Reactants: Glucose
- Products: 2 pyruvate, 2 ATP, 2 NADH
Pyruvate Oxidation:
- Location: Mitochondrial matrix
- Reactants: 2 pyruvate
- Products: 2 Acetyl-CoA, 2 NADH, 2 CO2
Citric Acid Cycle (Krebs Cycle):
- Location: Mitochondrial matrix
- Reactants: 2 Acetyl-CoA
- Products: 4 CO2, 6 NADH, 2 FADH2, 2 ATP
Oxidative Phosphorylation:
- Location: Inner mitochondrial membrane
- Reactants: NADH, FADH2, O2
- Products: ATP, H2O

ATP Generation

Substrate-level phosphorylation: Direct transfer of phosphate to ADP to form ATP (occurs in glycolysis and the citric acid cycle).
Oxidative phosphorylation: ATP synthesis powered by the transfer of electrons through the electron transport chain, utilizing the proton gradient.

Effects of Oxygen Supply

Anaerobic conditions: If oxygen is scarce, cells switch to anaerobic respiration (e.g., fermentation).
Fermentation results in the buildup of lactic acid or ethanol instead of CO2 and water.

Response to Oxygen Demand

Anaerobic conditions: When oxygen is scarce, ATP production is less efficient leading to fatigue during intense exercise.
Cells may switch to anaerobic pathways (e.g., lactic acid fermentation) to produce ATP.

Impact of Circulatory System Changes

Reduced blood flow can lead to decreased oxygen delivery, impairing aerobic respiration, and causing reliance on anaerobic pathways, reducing ATP yield.

Flow of Matter and Energy

Autotrophs (like plants) produce their own food through photosynthesis, converting light energy into chemical energy (glucose).
Heterotrophs (like animals) obtain energy by consuming autotrophs or other heterotrophs.
Energy flow: Energy from the sun is captured by autotrophs, producing glucose which is consumed by heterotrophs, transferring energy and matter through food chains.

Structure of Leaves and Chloroplasts

Leaves have broad, flat surfaces to maximize light absorption.
Chloroplasts contain chlorophyll and have a double membrane structure with thylakoids (light reactions) and stroma (Calvin cycle).
Chloroplasts are arranged in leaves to optimize light capture and gas exchange.

Net Reaction for Photosynthesis

Chemical equation: Carbon dioxide + water + light energy --> glucose + oxygen
Carbon in glucose originates from carbon dioxide, while oxygen comes from water.

Stages of Photosynthesis

Light Reactions: Convert solar energy into chemical energy (ATP and NADPH).
- Location: Thylakoid membranes
Calvin Cycle: Uses ATP and NADPH to convert CO2 into glucose.
- Location: Stroma
Light reactions produce energy carriers needed to power the Calvin cycle.

Light Absorption and Energy Harvesting

Different pigments (e.g., chlorophyll) absorb different wavelengths of light, mainly blue and red light.
Absorption spectra show the amount of light absorbed at different wavelengths, indicating which pigments are present and how they affect photosynthesis.

Chlorophyll Excitation

Chlorophyll absorbs light energy, exciting electrons to a higher energy state, which can be used in photosynthesis.
When excited electrons fall back to their original state, energy is released, often as heat or light.

Photosystems

Located in the thylakoid membranes.
Capture and transfer light energy to drive the electron transport chain.

Energy and Matter Flow

Electron Transport Chain: Energized electrons from photosystems are passed along a series of proteins, releasing energy used to pump protons into the thylakoid lumen, creating a proton gradient.
ATP and NADPH Production: ATP synthase uses the proton gradient to synthesize ATP, while electrons ultimately reduce NADP+ to NADPH.

Water Splitting Reaction

During light reactions, water is split into oxygen, protons, and electrons.
Oxygen is released as a byproduct, and electrons replenish those lost by chlorophyll.

Calvin Cycle

Three phases:
- Carbon Fixation: CO2 is added to ribulose bisphosphate (RuBP).
- Reduction: ATP and NADPH convert 3-PGA to G3P (sugar).
- Regeneration: RuBP is regenerated to continue the cycle.
ATP and NADPH are required for the energy and reducing power to convert CO2 into glucose.

Comparison of Photosynthesis and Cellular Respiration

Both use electron carriers (NADPH in photosynthesis, NADH in respiration) to transport electrons.
Both create gradients (protons in photosynthesis and respiration) to drive ATP synthesis via ATP synthase.

Citric Acid Cycle vs. Calvin Cycle

The citric acid cycle (catabolic) produces ATP, NADH, and FADH2 from the breakdown of glucose.
The Calvin cycle (anabolic) uses ATP and NADPH to synthesize glucose.

Predicting Changes in Closed Systems

Plant-only system: CO2 levels decrease, O2 levels increase.
Animal-only system: CO2 levels increase, O2 levels decrease.
Mixed system: Levels depend on the ratio of plants to animals, achieving a balance.

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Description

Explore the intricacies of the fluid mosaic model and how membrane components contribute to cell functions. This quiz covers topics like phospholipid bilayers, membrane fluidity, the role of cholesterol, and various types of membrane proteins. Test your understanding of how substances move across cell membranes.