Biology Chapter 5: Cellular Membranes

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Questions and Answers

Which of the following membrane visualization techniques allows for the study of the inside of the membrane?

Scanning Electron Microscope (SEM)

Light Microscope

Transmission Electron Microscope (TEM)

Freeze-fracture (correct)

What is the main function of cell surface markers?

To regulate cell growth and division

To provide structural support to the cell

To provide a barrier to permeability

To facilitate cell-cell recognition and signaling (correct)

What is the polar and hydrophilic part of a phospholipid?

Hydrocarbon tail

Glycerol backbone

Fatty acid chain

Phosphate group (correct)

How do unsaturated fatty acids affect membrane fluidity compared to saturated fatty acids?

They make the membrane more fluid Signup and view all the answers

What is the function of sterols like cholesterol in membranes?

To modulate membrane fluidity, depending on the temperature Signup and view all the answers

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

Their location in the membrane Signup and view all the answers

What is the term for the model of membrane structure that describes it as a mosaic of proteins floating in a fluid lipid bilayer?

Fluid mosaic model Signup and view all the answers

What is the function of fatty acid desaturases in bacteria that are cold-tolerant?

To introduce double bonds into fatty acids Signup and view all the answers

What is the primary function of anchoring molecules in peripheral proteins?

To insert into the internal portion of the lipid bilayer Signup and view all the answers

What type of proteins have extensive nonpolar regions that create a pore through the membrane?

Channel proteins Signup and view all the answers

What is the primary function of facilitated diffusion?

To move molecules from high to low concentration Signup and view all the answers

What type of transport requires energy and moves substances from low to high concentration?

Active transport Signup and view all the answers

What is the function of the sodium-potassium pump?

To move ions against their concentration gradient Signup and view all the answers

What is the term for the net diffusion of water across a membrane toward a higher solute concentration?

Osmosis Signup and view all the answers

What is the function of aquaporins?

To facilitate osmosis Signup and view all the answers

What is the term for the force needed to stop osmotic flow?

Osmotic pressure Signup and view all the answers

What type of transport uses the energy released from a molecule moving by diffusion to supply energy to active transport of a different molecule?

Coupled transport Signup and view all the answers

What is the term for the movement of substances into the cell?

Endocytosis Signup and view all the answers

Study Notes

Membrane Structure

Phospholipids are arranged in a bilayer with globular proteins inserted in the lipid bilayer, forming a fluid mosaic model
The fluid mosaic model describes proteins floating in or on the fluid lipid bilayer, like boats on a pond

Cellular Membrane Components

4 main components of cellular membranes:
- Phospholipid bilayer (flexible matrix, barrier to permeability)
- Transmembrane proteins (integral membrane proteins)
- Interior protein network (peripheral membrane proteins)
- Cell surface markers (glycoproteins and glycolipids)

Phospholipid Structure

Consists of:
- Glycerol (a 3-carbon polyalcohol)
- 2 fatty acids attached to the glycerol (nonpolar and hydrophobic)
- Phosphate group attached to the glycerol (polar and hydrophilic)
Spontaneously forms a bilayer with fatty acids on the inside and phosphate groups on both surfaces

Membrane Fluidity

Bilayers are fluid due to hydrogen bonding between water molecules, allowing individual phospholipids and unanchored proteins to move through the membrane
Environmental influences on membrane fluidity:
- Saturated fatty acids make the membrane less fluid than unsaturated fatty acids
- Warm temperatures make the membrane more fluid than cold temperatures
- Sterols like cholesterol can increase or decrease membrane fluidity depending on the temperature

Membrane Proteins

Various functions:
- Transporters
- Enzymes
- Cell-surface receptors
- Cell-surface identity markers
- Cell-to-cell adhesion proteins
- Attachments to the cytoskeleton
Structure relates to function:
- Diverse functions arise from diverse structures of membrane proteins
- Common structural features related to their role as membrane proteins
Types of membrane proteins:
- Peripheral proteins (anchoring molecules attach membrane protein to surface)
- Integral membrane proteins (span the lipid bilayer, with nonpolar regions embedded in the interior and polar regions protruding from both sides)

Passive Transport

Movement of molecules through the membrane without energy input
Diffusion: movement of molecules from high to low concentration
Diffusion will continue until concentration is equal in all regions
Factors affecting permeability:
- Hydrophobic interior of the membrane repels polar molecules but not nonpolar molecules
- Limited permeability to small polar molecules
- Very limited permeability to larger polar molecules and ions
Facilitated diffusion:
- Molecules that cannot cross the membrane easily move through proteins
- Channel proteins: hydrophilic channel when open
- Carrier proteins: bind specifically to molecules they assist

Osmosis

Net diffusion of water across a membrane toward a higher solute concentration
Osmotic concentration:
- Hypertonic solution: higher solute concentration
- Hypotonic solution: lower solute concentration
- Isotonic solution: same osmotic concentration as the cell
Osmotic pressure:
- Force needed to stop osmotic flow
- Cell in a hypotonic solution gains water, causing cell to swell and creating pressure

Active Transport

Requires energy input (ATP) to move substances from low to high concentration
Uses highly selective carrier proteins
Types of carrier proteins:
- Uniporters: move one molecule at a time
- Symporters: move two molecules in the same direction
- Antiporters: move two molecules in opposite directions
Sodium-potassium (Na+-K+) pump: direct use of ATP for active transport, moving 3 Na+ out of the cell and 2 K+ into the cell against their concentration gradient

Bulk Transport

Endocytosis:
- Movement of substances into the cell
- Phagosytosis: cell takes in particulate matter
- Pinocytosis: cell takes in only fluid
- Receptor-mediated endocytosis: specific molecules are taken in after binding to a receptor
Exocytosis:
- Movement of substances out of the cell
- Requires energy

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Description

Learn about the structure and components of cellular membranes, including phospholipid bilayers and globular proteins, and the fluid mosaic model.