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Questions and Answers

What role does the plasma membrane serve in the cell?

Regulates enzymatic reactions

Stores genetic material

Acts as a selective barrier (correct)

Facilitates cell division

Which type of protein is loosely attached to the surface of the plasma membrane?

Transmembrane proteins

Intrinsic proteins

Peripheral proteins (correct)

Integral proteins

What is the general composition of the plasma membrane?

Proteins and lipids (correct)

Nucleic acids and carbohydrates

Mitochondria and ribosomes

Chloroplasts and vacuoles

Which component of phospholipids is responsible for their hydrophilic nature?

Phosphoryl group Signup and view all the answers

What distinguishes integral proteins from peripheral proteins?

Attachment method to the membrane Signup and view all the answers

Which region do the hydrophobic tails of phospholipids primarily interact with in the plasma membrane?

Other hydrophobic tails Signup and view all the answers

Which of the following is considered a function of cholesterol within the plasma membrane?

Increasing membrane fluidity Signup and view all the answers

What characteristic of cytoplasm allows organelles to move freely within the cell?

Liquid state Signup and view all the answers

Which of the following statements about simple diffusion is true?

Lipid soluble and small molecules can diffuse through the membrane. Signup and view all the answers

What distinguishes facilitated diffusion from simple diffusion?

Facilitated diffusion requires a membrane transport protein. Signup and view all the answers

Nature of the channels involved in facilitated diffusion can be described as:

Integral proteins that form specific pores for certain ions. Signup and view all the answers

Which of the following correctly defines active transport?

Utilization of ATP to move molecules against their concentration gradient. Signup and view all the answers

What role do transporter proteins play in the plasma membrane?

They bind specific molecules to facilitate their movement across the membrane. Signup and view all the answers

For which type of molecules is facilitated diffusion necessary?

Large and water-soluble molecules. Signup and view all the answers

What does the term ‘gated channels’ refer to in facilitated diffusion?

Channels that respond to specific stimuli to open or close. Signup and view all the answers

Which of the following molecules primarily participates in active transport?

Ions like Na+ and K+. Signup and view all the answers

Study Notes

Animal Cell Structure

All cells are enclosed by a plasma membrane, acting as a selective barrier.
The membrane controls which substances enter and leave the cell.
Nutrients enter the cell, while waste products leave.
The cell's interior is organized into specialized compartments called organelles, each surrounded by its own membrane.
Examples of organelles include the nucleus, mitochondria, lysosomes, endoplasmic reticulum, and Golgi apparatus.
Organelles are suspended in the cytoplasm, also known as the cytosol.

Plasma Membrane

A thin membrane, approximately 0.005 µm thick.
Encloses every living cell, separating it from the environment.
Acts as a barrier, regulating the passage of substances in and out of the cell.
Controls the entry of nutrients and the exit of waste products.

Chemical Composition of Plasma Membrane

Composed of lipids and proteins.
Lipids include phospholipids and sterols (e.g., cholesterol).
Proteins include peripheral (extrinsic) proteins and integral (intrinsic) proteins.

Phospholipid Bilayer

The fundamental structure of the plasma membrane.
Composed of two layers of phospholipid molecules.
Phospholipids have a hydrophilic (water-loving) head and hydrophobic (water-fearing) tails.
The hydrophobic tails face inward, while the hydrophilic heads face outward, interacting with the surrounding water.

Sterols

Found in the plasma membrane.
Have a complex ring structure, making them lipid-soluble.
Contain a hydroxyl group, making them water-soluble.
Cholesterol is a common type of sterol.

Membrane Proteins

Intrinsic (integral) proteins are firmly embedded within the lipid bilayer.
Some span the entire bilayer, forming channels or pores.
Others are embedded in one leaflet, interacting with the lipid bilayer.
Peripheral (extrinsic) proteins are loosely attached to the lipid bilayer.
Their attachment is typically to ionic bonds or calcium bridges, and they may also attach other intrinsic proteins.

Transport Across the Plasma Membrane

Substances cross the membrane via different methods.
Permeation (simple diffusion) is the direct movement of substances across the membrane.
Facilitated diffusion aids in the movement of substances, but doesn't require energy.
Active transport moves substances against their concentration gradient, requiring energy, often from the hydrolysis of ATP.
Types of transport include channel-mediated, carrier-mediated, and transport of particles.

Simple Diffusion

Substances move from an area of high concentration to an area of low concentration.
Lipid-soluble and small substances can readily permeate the membrane.
Large, water-soluble, and charged substances are blocked due to the hydrophobic nature of the lipid bilayer.

Facilitated Diffusion

Channels are integral proteins that provide pathways for ions and small molecules.
These channels may be gated, opening and closing based on specific conditions.
Many molecules, such as sugars and amino acids require transporter proteins, a type of carrier-mediated protein, which helps these substances fit through the bilayer.

Active Transport

The movement of substances against their concentration gradient (from low to high concentration).
Requires energy (often from ATP).
Sodium-potassium pumps are a well-known example of active transport; maintaining gradients of sodium and potassium across the cell membrane.