Bio-H Chapter 4.3: Cell Membrane Structure

plasma membrane

A selectively-permeable phospholipid bilayer forming the boundary of the cells

adhesion protein

Plasma membrane protein that helps cells stick together in animal tissues.

fluid mosaic model

Model of a cell membrane as a two-dimensional fluid of mixed composition.

receptor protein

Membrane protein that triggers a change in cell activity in response to a stimulus such as binding a hormone.

transport protein

Protein that moves specific ions or molecules across a membrane.

What does a plasma membrane do?

it separates a cell's external and internal environments while acting as a gateway on what can enter/exit

What is the foundation of all cell membranes?

phospholipids

Why will phospholipids spontaneously organize themselves into lipid bilayer sheets?

Because of the nonpolar tails and the polar head

In the lipid bilayer, the heads face ___ while the tails face ___.

outward; inward

Other molecules, including cholesterol, proteins, glycoproteins, and glycolipids, are ___or ___ to the lipid bilayer of a cell membrane.

embedded in; attatched to

cholesterol

"fluidity buffer" to maintain stability: it prevents membranes from becoming too rigid at low temperatures

glycoproteins

Membrane carbohydrates that are covalently bonded to proteins.

glycolipids

Membrane carbohydrates that are covalently bonded to lipids.

What is this?

fluid mosaic model

Where is the "mosaic" in a mosaic model from?

the many molecules, and many different types of molecules, in the membrane.

Why does membrane fluidity occur?

because the phospholipids are no chemically bonded together

Phospholipids stay organized as a result of collective ___ and ___ ___.

hydrophobic; hydrophilic; attractions

How do individual phospholipids behave in the bilayer?

They drift sideways, spin around their long axis, and their tails wiggle.

How are the interactions between the phospholipids in terms of strength?

they are relatively weak

A cell membrane's properties vary depending on the ___ and ___ of molecules composing it.

types; proportions

As cholesterol content increases, membrane fluidity…

decreases

What factors influence a membrane's fluidity?

The length and saturation of its phospholipids' fatty acid tails.

What unique feature do archaeal phospholipids have compared to those of bacteria and eukaryotes?

Archaeal phospholipids use molecules with reactive side chains instead of fatty acids.

How do the tails of archaeal phospholipids bond?

They form covalent bonds with one another due to rigid crosslinking.

What effect does the rigid crosslinking of archaeal phospholipids have on membrane behavior?

It prevents the phospholipids from drifting, spinning, or wiggling in a bilayer.

Why might the stiffness of archaeal membranes be advantageous?

It may help archaea survive in extreme habitats.

What are the two types of attachment for membrane proteins?

Some are temporarily or permanently attached to the lipid bilayer's surfaces.

What feature allows some membrane proteins to anchor permanently in the lipid bilayer?

A hydrophobic domain.

What role do filaments inside the cell play regarding membrane proteins?

They fasten some membrane proteins in place.

Different cell membranes can carry out ___ depending on which ___ they include

different tasks; proteins

What is an additional function of adhesive proteins?

they also provide a cell with information

about its position relative to other cells or structures

metabolism, movement, division, or even cell death are often involved with…

receptor proteins

What do receptor proteins react to?

stimuli (such as a hormone binding to it)

What types of molecules do membrane enzymes interact with?

Membrane enzymes interact with other proteins and lipids.

Can enzymes in cell membranes have multiple functions?

Yes, some enzymes act on different substrates or work in series.

What is the significance of the membrane in enzyme activity?

The membrane provides a structural framework for enzymes to function effectively.

Why are transport proteins important?

lipid bilayers are impermeable to most substances that cells must take in and expel on a regular basis

What are some examples of what a lipid bilayer is impermeable to?

ions and polar molecules