Chapter 5 Hillis Textbook

Unit 2: Cells, Membranes and Signaling …

CELL MEMBRANE

HOW DOES THE LAB RELATE TO THE NEXT CHAPTER?

SURFACE AREA: the entire outer covering of a cell that enables materials pass.

VOLUME: the inside spare that can be filled with organelles/etc.

CELLS WITH MORE SURFACE AREA AND LESS VOLUME WILL BE VERY EFFICIENT!!!

You looked at the rate of diffusion

Which cell could diffuse materials quicker and more efficiently?

HOW DO MOLECULES GET IN AND OUT OF THE CELL?

• MANY different molecules nee to get into the cells…

• For example, after we eat BIOMOLECULES are broken into monomers and absorbed by the small intestines, into the blood and traveled all around the body to the CELLS!

• Biomolecules must get into the cells for the cells to use them

Ex: Mitochondria need glucose, ribosomes need amino acids…

CELL MEMBRANE needs lipids, carbs and proteins

These molecules get in and out of the cell by the CELL MEMBRANE!

PART ONE: PROPERTIES OF THE CELL MEMBRANE PHOSOPHOLIPID BILAYER

A membrane’s structure and functions are determined by its constituents: lipids, proteins, and carbohydrates.

The general structure of membranes is known as the fluid mosaic model.

Phospholipids form a bilayer which is like a “lake” in which a variety of proteins “float.”

LIPIDS

Lipids form the hydrophobic core of the membrane.

Most lipid molecules are phospholipids with two regions: Hydrophilic regions electrically charged “heads” that associate with watermolecules Hydrophobic regions nonpolar fatty acid “tails” that do not dissolve in water

BILAYER:

A bilayer is formed when the fatty acid “tails” associate with each other and the polar “heads” face the aqueous environment (Water).

Bilayer organization helps membranes fuse during vesicle formation and phagocytosis.

FLUID MOSAIC:

Membranes are fluid due to the flexible composition and mosaic due to the patterns that form from lipids and proteins

Two important factors in membrane fluidity: Lipid composition—types of fatty acids can increase or

decrease fluidity Temperature—membrane fluidity decreases in colder

conditions Proteins are randomly scattered within the cell membrane to form a mosaic pattern

PROTEINS:Biological membranes contain proteins, with varying ratios of phospholipids.

• Peripheral membrane proteins lack hydrophobic groups and are not embedded in the bilayer.

• Integral membrane proteins are partly embedded in the phospholipid bilayer.

Anchored membrane proteins have lipid components that anchor them in the bilayer.

Proteins are asymmetrically distributed on the inner and outer membrane surfaces.

• A transmembrane protein extends through the bilayer on both sides, and may have different functions in its external and transmembrane domains.

Some membrane proteins can move within the phosopholipid bilayer, while others are restricted.

Proteins inside the cell can restrict movement of membrane proteins, as can attachments to the cytoskeleton.

CARBOHYDRATES:

Plasma membrane carbohydrates are located on the outer membrane and can serve as recognition sites.

• Glycolipid—a carbohydrate bonded to a lipid

• Glycoprotein—a carbohydrate bonded to a protein

SELECTIVELY PERMEABLE (SEMI-PERMEABLE):

Biological membranes allow some substances, and not others, to pass. This is known as selective permeability.

Two processes of transport:

• Passive transport does not require metabolic energy.

• Active transport requires input of metabolic energy.