Bio 120 Structured Study Session
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Questions and Answers

What is the role of cholesterol in the plasma membrane?

  • Decreases the movement of fatty acid tails at high temperatures (correct)
  • Facilitates the transport of proteins across the membrane
  • Increases the fluidity of the membrane at all temperatures
  • Repels water molecules from associating with the membrane

Which situation would most likely result in increased membrane fluidity?

  • Phospholipids that are saturated
  • Phospholipids with double bonds (correct)
  • Phospholipids that tightly associate with each other
  • Phospholipids with long tails

Which of the following is NOT a role of membrane proteins?

  • Signal transduction
  • Cell surface attachment and recognition
  • Energy production in mitochondria (correct)
  • Transport of molecules across the membrane

What characterizes phospholipids that contribute to their behavior in a membrane?

<p>Hydrophilic head and hydrophobic tail (A)</p> Signup and view all the answers

Which factor contributes to the decrease in membrane fluidity?

<p>Saturated phospholipids (D)</p> Signup and view all the answers

What type of molecules can pass through the plasma membrane without assistance?

<p>Small nonpolar molecules (A)</p> Signup and view all the answers

How do desaturases affect membrane fluidity as temperature decreases?

<p>They add double bonds to fatty acids, increasing fluidity (D)</p> Signup and view all the answers

What happens to phospholipids with long tails in terms of membrane fluidity?

<p>They lead to tighter packing in the membrane (A)</p> Signup and view all the answers

What term describes a solution with a lower concentration of solutes compared to another solution?

<p>Hypotonic (B)</p> Signup and view all the answers

What is the primary movement of water during osmosis?

<p>Into an area with a higher solute concentration (C)</p> Signup and view all the answers

How does temperature affect desaturase concentration?

<p>It would decrease (A)</p> Signup and view all the answers

In a hypertonic solution, how will water move in relation to the cell?

<p>Water will move out of the cell (A)</p> Signup and view all the answers

Which organism is likely to have cholesterol in its cell membrane?

<p>Wolf (A)</p> Signup and view all the answers

What is the role of aquaporins in osmosis?

<p>They facilitate the movement of water (A)</p> Signup and view all the answers

What happens when a cell is placed in an isotonic solution?

<p>There will be no net movement of water (D)</p> Signup and view all the answers

What defines a hypertonic solution?

<p>It has a higher concentration of solutes than another solution (B)</p> Signup and view all the answers

What is the role of membrane fluidity in the plasma membrane?

<p>It affects the permeability and movement of proteins within the membrane. (B)</p> Signup and view all the answers

Which statement accurately describes passive transport?

<p>It can occur through simple diffusion or facilitated diffusion. (B)</p> Signup and view all the answers

What type of transport occurs when potassium moves out of the cell via a channel protein?

<p>Facilitated diffusion (C)</p> Signup and view all the answers

What type of molecules can pass directly through the cell membrane via simple diffusion?

<p>Small, uncharged molecules like oxygen (A)</p> Signup and view all the answers

Which of the following best characterizes glucose transport across the plasma membrane?

<p>It requires a carrier protein due to its size and polarity. (D)</p> Signup and view all the answers

What type of transport is exemplified by the Na-K-ATPase which moves 3 sodium out of the cell and 2 potassium into the cell?

<p>Antiport (A)</p> Signup and view all the answers

What is primary active transport primarily responsible for?

<p>Utilizing ATP to move molecules against their concentration gradient. (A)</p> Signup and view all the answers

What characterizes passive transport?

<p>It includes processes like simple diffusion and osmosis. (B)</p> Signup and view all the answers

Which process involves a cell engulfing a large particle such as a bacterial cell?

<p>Phagocytosis (D)</p> Signup and view all the answers

Receptor-mediated endocytosis begins with a ligand binding to what structure on the cell's surface?

<p>Receptor (D)</p> Signup and view all the answers

What does diffusion refer to?

<p>The tendency of substances to spread out and increase entropy. (D)</p> Signup and view all the answers

What distinguishes facilitated diffusion from simple diffusion?

<p>Facilitated diffusion involves specific transporter proteins. (B)</p> Signup and view all the answers

What role do channel proteins play in the plasma membrane?

<p>They form openings that allow specific substances to pass through the membrane. (C)</p> Signup and view all the answers

Which of the following accurately describes simple diffusion?

<p>It does not require energy and occurs down the concentration gradient. (C)</p> Signup and view all the answers

What is the process where a cell expels large molecules, such as metabolic wastes, from itself?

<p>Exocytosis (D)</p> Signup and view all the answers

Which of these describes an example of secondary active transport?

<p>Transporting glucose into the cell along with sodium ions. (C)</p> Signup and view all the answers

Which endocytic process is often referred to as 'cellular drinking'?

<p>Pinocytosis (D)</p> Signup and view all the answers

What happens to the scent molecules from cooking food in a kitchen?

<p>They spread out into available space due to diffusion. (B)</p> Signup and view all the answers

Why do larger molecules like glucose require assistance to cross the cell membrane?

<p>They cannot pass through the membrane directly due to their size or charge. (A)</p> Signup and view all the answers

The Na-K-ATPase transport mechanism utilizes what kind of energy?

<p>Chemical energy (C)</p> Signup and view all the answers

Why is a carrier protein necessary for glucose transport?

<p>Glucose is too large and polar to pass through the lipid bilayer unaided. (B)</p> Signup and view all the answers

What is a concentration gradient?

<p>The difference in concentration of molecules across a membrane. (A)</p> Signup and view all the answers

What distinguishes receptor-mediated endocytosis from pinocytosis?

<p>Specificity of molecule uptake (A)</p> Signup and view all the answers

What role does the clathrin-coated pit play in receptor-mediated endocytosis?

<p>Forms the vesicle for uptake (C)</p> Signup and view all the answers

Which of the following statements about osmosis is true?

<p>It involves the movement of water across a semi-permeable membrane. (C)</p> Signup and view all the answers

During exocytosis, the contents of the vesicle are expelled into the environment after what event?

<p>Fusing with the cell membrane (C)</p> Signup and view all the answers

What is required for facilitated diffusion to occur?

<p>A concentration gradient (B)</p> Signup and view all the answers

Which transport mechanism requires energy input?

<p>Active transport (D)</p> Signup and view all the answers

What is the primary role of ion channels in facilitated diffusion?

<p>To allow ions to move through the membrane (B)</p> Signup and view all the answers

Which type of transporter moves two molecules in the same direction?

<p>Symport (A)</p> Signup and view all the answers

Which method involves the breakdown of ATP to facilitate transport?

<p>Primary active transport (A)</p> Signup and view all the answers

What type of transport is exemplified by the sodium-glucose transporter?

<p>Secondary active transport (D)</p> Signup and view all the answers

What happens to a carrier protein during primary active transport?

<p>It undergoes a conformational change (B)</p> Signup and view all the answers

In which scenario does potassium typically have a higher concentration?

<p>Inside the cell compared to outside (D)</p> Signup and view all the answers

Which of the following statements about active transport is true?

<p>It requires energy input. (A)</p> Signup and view all the answers

Flashcards

What kind of molecules can pass directly through the membrane?

Small, uncharged molecules such as oxygen (O2) and carbon dioxide (CO2) can pass directly through the cell membrane.

What kind of molecules need help to cross the membrane?

Larger molecules like glucose or charged molecules like ions require help from membrane proteins to cross the cell membrane.

What is diffusion?

Diffusion is the process where substances naturally spread out into available space, moving from a high concentration area to a low concentration area.

What is entropy?

Entropy represents randomness or disorder in a system. Diffusion increases entropy as molecules spread out.

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What is passive transport?

Passive transport refers to the movement of molecules across a cell membrane without requiring energy input.

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What is a concentration gradient?

A concentration gradient is the difference in concentration of a substance across a membrane, from a higher concentration area to a lower concentration area.

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What is simple diffusion?

Simple diffusion is a type of passive transport where small, uncharged molecules move across the cell membrane directly, from a high to low concentration area.

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What is facilitated diffusion?

Facilitated diffusion is a type of passive transport where membrane proteins help larger or charged molecules move across the cell membrane, from a high to a low concentration area.

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Plasma Membrane Structure

The plasma membrane is a selectively permeable barrier that encloses the cell. It's made of a phospholipid bilayer with embedded proteins that regulate the passage of molecules in and out of the cell.

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Membrane Fluidity

The ability of the plasma membrane to move and change shape. This fluidity is important for various cell functions, including cell signaling and transport.

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Simple Diffusion

The movement of molecules from a region of high concentration to low concentration across a membrane, without requiring energy.

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Channel Protein

A type of membrane protein that creates a passageway for specific ions or molecules to cross the membrane.

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Carrier Protein

A type of membrane protein that binds to a molecule and transports it across the membrane. It often changes shape to facilitate transport.

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Passive Transport

The movement of molecules across a membrane without requiring energy. Examples include simple diffusion, facilitated diffusion, and osmosis.

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Active Transport

The movement of molecules across a membrane against their concentration gradient, requiring energy. It involves specific membrane proteins that use ATP to move substances.

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Primary Active Transport

A type of active transport that directly uses ATP to move a molecule against its gradient.

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Concentration Gradient

A difference in the concentration of a substance between two areas, like inside and outside a cell.

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Osmosis

The movement of water across a semi-permeable membrane from a region of high water concentration to a region of low water concentration.

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Hypertonic Solution

A solution that has a higher concentration of solutes than the cell. Water will move out of the cell.

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Hypotonic Solution

A solution that has a lower concentration of solutes than the cell. Water will move into the cell.

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Isotonic Solution

A solution that has the same concentration of solutes as the cell. There is no net movement of water.

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Aquaporins

Specialized channels in the cell membrane that allow water to pass through quickly.

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Desaturase Concentration

The amount of desaturase enzyme present in a cell, involved in making unsaturated fatty acids.

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Desaturase and Temperature

Higher temperatures usually lead to more unsaturated fatty acids, thus more desaturase.

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Membrane Protein Functions

Membrane proteins play crucial roles in various cellular processes. They facilitate the transport of molecules across the membrane, act as enzymes for chemical reactions, transmit signals into and out of the cell, and participate in cell adhesion and recognition.

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What Affects Membrane Fluidity?

The fluidity of the plasma membrane is influenced by the properties of its phospholipids. Phospholipids with longer tails and without double bonds (saturated) make the membrane less fluid. Conversely, shorter tails and the presence of double bonds (unsaturated) increase fluidity.

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Desaturase's Role in Fluidity

Desaturases are enzymes that add double bonds to fatty acids. As temperatures drop, the concentration of desaturases increases, leading to the introduction of more double bonds in phospholipids. This enhances membrane fluidity in cold conditions.

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Cholesterol's Influence on Fluidity

Cholesterol is found only in animal cells and regulates membrane fluidity at both high and low temperatures. At low temperatures, it prevents fatty acid tails from packing tightly, increasing fluidity. At high temperatures, it restricts their movement, maintaining stability.

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Passive Membrane Transport

Some molecules can cross the plasma membrane directly, without the need for protein assistance. This is known as passive transport. It doesn't require energy from the cell.

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Why Channel Proteins are Crucial

Channel proteins are essential for facilitating the passage of molecules across the plasma membrane, especially those that are large or charged. These proteins create pathways for molecules to move across the membrane efficiently.

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Cholesterol in Cell Membranes

Cholesterol is a lipid found in the cell membranes of eukaryotic organisms, providing structural integrity and regulating membrane fluidity.

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Facilitated Diffusion

The movement of molecules across the cell membrane with the help of transport proteins, following the concentration gradient, and without requiring energy.

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Ion Channels

Specialized protein channels embedded in the cell membrane that allow the selective passage of ions, facilitating the movement of charged particles across the membrane.

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Sodium-Potassium Pump (Na-K ATPase)

An important primary active transport system that pumps sodium ions out of the cell and potassium ions into the cell, maintaining ionic gradients and supporting nerve impulse transmission.

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Secondary Active Transport

A type of active transport that uses the energy stored in the concentration gradient of one molecule to move another molecule against its gradient, involving carrier proteins.

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Uniport, Antiport, and Symport

Types of membrane transporters that differ in the direction and number of molecules they move: uniport (one molecule), antiport (two molecules in opposite directions), and symport (two molecules in the same direction).

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Potassium Concentration Gradient

Potassium ions (K+) are generally more concentrated inside the cell than outside, contributing to the membrane potential and influencing the electrical signals in cells.

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Na-K-ATPase

A primary active transporter protein that pumps 3 sodium ions out of the cell and 2 potassium ions into the cell against their respective concentration gradients. This requires energy from ATP hydrolysis and maintains the electrochemical gradient across the cell membrane.

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Antiport

A type of membrane transport where two molecules move across the cell membrane in opposite directions. One molecule moves down its concentration gradient, providing the energy for the other molecule to move against its gradient.

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Symport

A type of membrane transport where two molecules move across the cell membrane in the same direction. One molecule moves down its concentration gradient, providing the energy for the other molecule to move against its gradient.

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Endocytosis

The process by which cells internalize large molecules or particles from the extracellular environment by engulfing them in membrane-bound vesicles.

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Phagocytosis

A type of endocytosis where cells engulf large particles, like bacteria or cellular debris, by forming a phagosome around them.

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Exocytosis

The process by which cells export large molecules or particles from the cytoplasm to the extracellular environment by fusing vesicles containing these materials with the plasma membrane.

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Study Notes

Structured Study Sessions

  • Structured Study Sessions (SSS) are peer-led study sessions
  • Bio 120
  • Led by Janelle and Steve
  • October 1, 2024
  • Sessions are developed by peer mentors, not course professors
  • Session materials selected based on peer mentor experience and input from the SSS Peer Mentor Team

Question of the Day

  • Students asked their names and favorite season

Topics Covered Today

  • Plasma membrane structure - review
  • Membrane fluidity
  • Diffusion
  • Passive and active transport

Glucose Transport

  • Glucose requires a carrier protein for passage through the plasma membrane
  • It does NOT cross the membrane via simple diffusion

Primary Active Transport

  • Directly uses ATP energy to move a molecule against its concentration gradient.
  • Does not use concentration gradients for movement

Plasma Membrane

  • Composed of phospholipids and proteins
  • Phospholipids have hydrophilic heads and hydrophobic tails
  • Tails of phospholipids cluster together to form the membrane to avoid contact with water
  • Proteins are embedded in and move within the phospholipid bilayer

Membrane Protein Roles

  • Transport of molecules
  • Enzymatic activity
  • Signal transduction
  • Cell surface attachment and recognition

Membrane Fluidity

  • Some phospholipids have more freedom of movement than others
  • Membrane fluidity is affected by tail length and presence of double bonds.
  • Saturated phospholipids have longer tails and less movement, making the membrane less fluid.
  • Unsaturated phospholipids have shorter tails and double bonds, allowing for more movement and making the membrane more fluid
  • Other factors like desaturases and temperature affect fluidity
  • Desaturases add double bonds to fatty acids as temperature decreases

Cholesterol in the Membrane

  • Found only in animal cells
  • Regulates membrane fluidity at different temperatures.
  • At low temperatures, cholesterol prevents fatty acid tails from tightly associating, maintaining fluidity
  • At high temperatures, it reduces fatty acid tail movement, reducing fluidity.

Molecules Passing Through the Membrane

  • Small, uncharged molecules (e.g., oxygen, carbon dioxide) can pass directly through the plasma membrane
  • Larger molecules, charged molecules and ions need the help of membrane proteins

Diffusion

  • Substances move from areas of high concentration to low concentration to increase entropy (randomness)
  • Explains molecule dispersal in environments like smells spreading through a house
  • Also, explains how molecules move across cell membranes

Passive Transport

  • Any membrane transport that does not require energy input
  • Molecules move down their concentration gradient (higher to lower concentration)
  • Examples include simple diffusion, facilitated diffusion, and osmosis

Simple Diffusion

  • Passive transport of small, uncharged molecules across the cell membrane
  • Molecules move from a higher to lower concentration area
  • Doesn't require energy

Concentration Gradient

  • A difference in the concentration of a substance across a distance.
  • Molecules move from areas of higher to lower concentration

Osmosis

  • The movement of water across a semipermeable membrane from an area of lower solute concentration to an area of higher solute concentration
  • Doesn't require energy input
  • Can occur directly across the membrane or through aquaporins, protein channels.

Osmosis - Important Terms

  • Hypotonic, Hypertonic, and Isotonic solutions are defined by the concentration of solutes within them and their effect on the movement of water into or out of a cell

Desaturase Concentration

  • Increases when temperature decreases

Hypertonic Solution

  • Water moves out of the cell

Cholesterol: Organism

  • Found in wolves (animals)

Facilitated Diffusion

  • Still passive transport, no energy input
  • Molecules can't move through the phospholipid bilayer, need help from special channels (e.g., ion channels) or carrier proteins to pass.
  • Important for transporting ions and larger molecules like glucose

Facilitated Diffusion Examples

  • Sodium and potassium ion channels are essential for generating electrical signals in cells
  • Channels are specific to the ion they transport due to differences in their shape and size

Active Transport

  • Requires energy input (e.g., ATP)
  • Molecules move against the concentration gradient (lower to higher concentration)
  • Three types: primary active, secondary active, and vesicular

Primary Active Transport Example

  • Na-K ATPase moves 3 sodium out and 2 potassium into the cell

Secondary Active Transport

  • Uses energy stored in a concentration gradient of one molecule to move another molecule against its gradient
  • Example: sodium-glucose transporter.

Types of Transporters

  • Uniport (one molecule)
  • Antiport (different directions)
  • Symport (same direction)

These transporters can be involved in secondary active transport or other types of membrane transport using carrier proteins

Potassium Transport

  • Potassium moves out of the cell via a channel protein in facilitated diffusion

Endocytosis

  • Used to transport larger molecules that can't be transported across membranes using membrane proteins.
  • Three types: phagocytosis, receptor-mediated endocytosis, and pinocytosis

Phagocytosis

  • Cell engulfs a large particle (e.g., bacteria) by extending its plasma membrane around it, forming a phagosome.

Receptor-Mediated Endocytosis

  • Ligand binds to a receptor on the cell's surface
  • Receptor and lignad migrate to a coated pit
  • Indentation folds inward to form a vesicle and moves ligand into the cell

Pinocytosis

  • Cellular "drinking"
  • Less specific.
  • Cell takes in some of the fluid surrounding, collecting any nutrients or other small molecules in that fluid.
  • Membrane folds inward to form a vesicle

Exocytosis

  • Large molecules expelled from the cell.
  • Vesicle fuses with the cell membrane and expels contents to the outside of the cell

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Join the peer-led Structured Study Session for Bio 120, focusing on essential topics like plasma membrane structure, diffusion, and transport mechanisms. Led by Janelle and Steve, this session is designed to enhance your understanding through collaborative learning among peers.

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