Chapter 7: Membrane Structure and Transport

What model describes the structure of the plasma membrane?

The fluid mosaic model.

Why do phospholipids form a bilayer in water?

Hydrophilic heads face water while hydrophobic tails face inward.

What primary interaction holds the cell membrane together?

Hydrophobic interactions among the fatty acid tails.

What is the approximate thickness of the plasma membrane?

Approximately 7 to 8 nanometers.

How does temperature affect membrane fluidity?

Higher temperatures increase fluidity; lower temperatures decrease fluidity.

How do unsaturated fatty acids affect membrane fluidity?

They increase fluidity because their cis-double bonds prevent tight packing.

How do saturated fatty acids affect membrane fluidity?

They decrease fluidity by packing tightly together.

What is the structural difference between integral and peripheral membrane proteins?

Integral proteins are embedded in the bilayer; peripheral proteins attach to one side.

What is the role of oligosaccharides on the cell membrane?

They contribute to cell-cell recognition.

Where are membrane proteins synthesized?

By bound ribosomes on the rough endoplasmic reticulum.

What determines the orientation of a protein within the membrane?

The distribution of its hydrophobic and hydrophilic amino acids.

What is the primary function of cell junction proteins?

To connect neighboring cells together to form tissues.

In which direction do solutes move during diffusion?

Down their concentration gradient, from high to low concentration.

What happens to an animal cell in a hypotonic solution?

Water enters the cell, causing it to swell and potentially lyse.

What happens to an animal cell in a hypertonic solution?

Water leaves the cell, causing it to shrivel.

Why do plant cells prefer a hypotonic environment?

Water entry builds turgor pressure against the rigid cell wall.

How do channel proteins facilitate passive transport?

By forming hydrophilic pores that allow specific ions or water to pass.

How do carrier proteins transport solutes across a membrane?

They bind the specific solute and change shape to move it across.

What is the direct energy source for primary active transport?

Adenosine triphosphate (ATP).

What powers secondary active transport (cotransport)?

Energy stored in an ion gradient created by primary active transport.