ch. 5 biology

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Questions and Answers

What distinguishes facilitated diffusion from simple diffusion?

Facilitated diffusion is slower than simple diffusion.

Facilitated diffusion requires energy input.

Facilitated diffusion occurs against the concentration gradient.

Facilitated diffusion uses transport proteins. (correct)

Why are polar or charged substances unable to easily diffuse across cell membranes?

They cannot interact with transport proteins.

Cell membranes are exclusively permeable to hydrophobic substances. (correct)

They require ATP for movement.

Their charge disrupts the membrane lipid bilayer.

What role does ATP play in active transport?

ATP increases the membrane permeability.

ATP supplies energy to move solutes against their concentration gradients. (correct)

ATP is used to create transport proteins.

ATP helps maintain the cell's resting potential.

How does aquaporin enhance the transport of water in cells?

It allows rapid diffusion of water across the membrane. Signup and view all the answers

What characteristic of calcium ion transport illustrates active transport?

Calcium ions are moved against their concentration gradient outside the cell. Signup and view all the answers

What was significant about Dr. Peter Agre's research on aquaporins?

It led to the discovery of a previously unknown function of water channels in cells. Signup and view all the answers

What defines the concept of selective permeability in cell membranes?

The ability of the membrane to selectively allow certain substances to cross while restricting others. Signup and view all the answers

Why would a researcher use frog eggs to test the function of a transport protein?

Frog eggs allow for easy manipulation and observation of membrane changes. Signup and view all the answers

What is the primary role of cofactors in enzymatic reactions?

To assist in catalysis by binding to the active site Signup and view all the answers

How do competitive inhibitors affect enzyme activity?

By preventing substrate molecules from entering the active site Signup and view all the answers

Which statement accurately describes noncompetitive inhibitors?

They change the enzyme's shape without entering the active site. Signup and view all the answers

What is the role of feedback inhibition in metabolic regulation?

To conserve resources by inhibiting pathway components when not needed Signup and view all the answers

What distinguishes coenzymes from cofactors?

Coenzymes are organic and often vitamins, whereas most cofactors are inorganic. Signup and view all the answers

Which of the following statements about enzyme inhibitors is true?

Enzyme inhibitors can be used in drugs, pesticides, and poisons. Signup and view all the answers

Why are vitamins important in the context of coenzymes?

They often function as coenzymes necessary for enzyme activity. Signup and view all the answers

In which way can an allosteric site influence enzyme function?

By changing the enzyme's shape and thereby affecting substrate binding Signup and view all the answers

What is the primary difference between kinetic energy and potential energy?

Kinetic energy is energy of motion, while potential energy is stored energy. Signup and view all the answers

Which statement accurately describes the first law of thermodynamics?

Energy can change form but cannot be created or destroyed. Signup and view all the answers

In what way do exergonic reactions differ from endergonic reactions?

Exergonic reactions release energy, while endergonic reactions require energy. Signup and view all the answers

Which process describes the breakdown of compounds to release energy?

Catabolism Signup and view all the answers

What is the significance of ATP in cellular work?

ATP powers nearly all forms of cellular work. Signup and view all the answers

How do catabolic and anabolic processes relate to body weight?

Body weight results from catabolism minus anabolism. Signup and view all the answers

Which of the following statements about entropy is true?

Entropy increases during energy transfers or transformations. Signup and view all the answers

What role does phosphorylation play in cellular processes?

It transfers a phosphate group from ATP to other molecules. Signup and view all the answers

What characterizes passive transport across a cell membrane?

It is driven by the natural tendency of particles to spread out evenly. Signup and view all the answers

Which statement accurately describes osmosis?

It involves the net movement of water towards a higher concentration of solute. Signup and view all the answers

What happens to animal cells placed in a hypertonic solution?

They lose water and shrink. Signup and view all the answers

In what condition do plant cells become flaccid?

In an isotonic solution. Signup and view all the answers

What is the effect of placing cells in a 0.5% sucrose solution when separated from a 2% sucrose solution?

Water will move from the 0.5% to the 2% sucrose solution. Signup and view all the answers

What is tonicity in relation to cell membranes?

It describes the ability of a solution to influence cellular water balance. Signup and view all the answers

Which of the following distinguishes a hypotonic solution?

It causes cells to swell due to a lower solute concentration. Signup and view all the answers

What role do contractile vacuoles serve in freshwater Paramecium?

They expel excess water to maintain osmotic balance. Signup and view all the answers

How does ATP transfer energy during cellular processes?

Through hydrolysis followed by phosphorylation. Signup and view all the answers

What role do enzymes play in cellular reactions?

Catalyze reactions by decreasing activation energy. Signup and view all the answers

What is the significance of the ATP cycle in cells?

It ensures a constant supply of energy through continuous regeneration. Signup and view all the answers

Which statement accurately describes the role of active sites in enzymes?

Active sites provide a specific area where substrates can bind and react. Signup and view all the answers

What happens during the hydrolysis of ATP?

The molecule of ATP is transformed into ADP and inorganic phosphate. Signup and view all the answers

Why do enzymes not get consumed in the reactions they catalyze?

They are recycled and can catalyze multiple reactions. Signup and view all the answers

How is energy coupling achieved using ATP?

By transferring a phosphate group to drive endergonic reactions. Signup and view all the answers

What defines the specificity of an enzyme for its substrate?

The shape and charge compatibility at the active site. Signup and view all the answers

How would you classify a solution with a higher solute concentration outside a cell than inside, affecting cell volume?

Hypertonic Signup and view all the answers

What role do transport proteins play in cellular processes?

They facilitate the movement of substances across a membrane. Signup and view all the answers

Which process involves the engulfing of solid particles by a cell?

Phagocytosis Signup and view all the answers

What is the difference between kinetic energy and potential energy?

Kinetic energy is related to motion, while potential energy is stored due to position. Signup and view all the answers

Which of the following correctly states one of the laws of thermodynamics?

The total energy in an isolated system remains constant. Signup and view all the answers

In which type of reaction do products contain more energy than reactants?

Endergonic reactions Signup and view all the answers

What is the primary function of ATP in cells?

Serving as an energy shuttle for biochemical processes. Signup and view all the answers

Study Notes

Introduction to Cell Biology

The plasma membrane and its proteins enable cells to survive and function.
Key processes covered in the chapter include membranes, energy, and enzymes.

Membrane Structure and Function

Biologists use the fluid mosaic model to describe membrane structure. It involves diverse protein molecules suspended in a fluid phospholipid bilayer.
Plasma membranes exhibit selective permeability.
Membrane proteins perform various functions.

Membrane Proteins

Junction Proteins: Form intercellular junctions that connect adjacent cells.
Enzyme Proteins: Fix to membranes, localizing metabolic pathways.
Transport Proteins: Facilitate diffusion and active transport.
Receptor Proteins: Bind to signaling molecules, activating other molecules within the cell.
Attachment Proteins: Attach to the extracellular matrix and cytoskeleton, coordinating internal and external changes.
Glycoproteins: Serve as ID tags, recognized by membrane proteins of other cells.

Transport

Diffusion: The tendency of particles to spread evenly in an available space.
Simple Diffusion: Movement of small nonpolar molecules across a membrane.
Facilitated Diffusion: Polar or charged substances require specific transport proteins to move down their concentration gradient, which doesn't use energy
Osmosis: The diffusion of water across a selectively permeable membrane.
Active Transport: Cells require energy input to move molecules against their concentration gradient.
- Primary Active Transport: Direct use of ATP hydrolysis
- Secondary Active Transport: Coupled with another solute.
Aquaporins: Special protein channels allowing rapid water diffusion across cell membranes
Kidney Dialysis: Net diffusion of toxins from blood to dialysis fluid.
Isotonic: Solutions with the equal solute concentration compared to inside the cell, normal for animal cells, flaccid for plant cells.
Hypertonic: Solutions with higher solute concentration than inside the cell; cells shrink.
Hypotonic: Solutions with lower solute concentration than inside the cell; cells swell.

Exocytosis and Endocytosis

Exocytosis: Exports bulky molecules (proteins or polysaccharides).
Types of Endocytosis:
- Phagocytosis: Engulfment of particles (forming a vacuole).
- Pinocytosis: Engulfment of liquids (forming a vacuole).
- Receptor-mediated endocytosis: Specific molecules bound to receptors in coated pits for entry into the cell.
Material is packaged inside vesicles for transport and fusing with the membrane for release.

Energy and Cells

Energy: The capacity to cause change or do work.
Kinetic Energy: Energy of motion.
Potential Energy: Stored energy, including chemical energy.
Thermodynamics:
- First Law: Energy can change form but cannot be created or destroyed.
- Second Law: Energy transformations increase entropy and some energy is lost as heat.
Exergonic Reaction: Releases energy.
Endergonic Reaction: Requires energy.
Metabolism: All chemical reactions in a cell.
Catabolism: Breakdown of molecules.
Anabolism: Building of molecules.

ATP

ATP: Powers nearly all forms of cellular work.
Phosphorylation: Transfer of a phosphate group from ATP to another molecule.
ATP cycle involves continuous phosphorylation and hydrolysis.

Enzymes

Enzymes: Catalysts, decreasing activation energy for reactions without being consumed.
Active site: Specific region where the substrate fits, creating an induced fit.
Cofactors: Nonprotein helpers binding to the active site and functioning in catalysis.
Coenzymes: Organic cofactors often vitamins.
Enzyme inhibitors: Substances that decrease enzyme activity.
- Competitive Inhibitors: Block the active site.
- Non-competitive Inhibitors: Bind to a different site, changing the enzyme's shape
- Feedback Inhibition: The end product of a metabolic pathway inhibits an enzyme early in the pathway.

Research on Membrane Proteins

Dr. Peter Agre received the 2003 Nobel Prize in Chemistry for his discovery of aquaporins.

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