Membrane Structure and Function

Which of the following are component of a cell's plasma membrane? A) carbohydrates B) Lipids C) Nucleic Acids D) Proteins

A, B, C, D

For a cell to be alive, they have to be able to do ______

Chemical reactions

Bulk Transport

Large molecules, such as proteins and polysaccharides, and large particles move across the cell membrane in vesicles. This requires energy.

Why do they call it the Fluid Mosaic Model?

This is where the plasma proteins and the phospholipid membranes within the cell membrane fit together like the pattern in a mosaic and they are fluid because they are not in a fixed position and are constantly changing from movement to movement.

Integral Protein:

runs the length of the entire membrane (embedded in the membrane, goes through both hydrophobic/philic regions). This allows active or passive transport of ions/molecules/solutes that cannot pass through the permeable membrane.

Only certain molecules are able to cross the cell membrane, not all molecules. Because of this, we say that a cell membrane is ______

selectively permeable

Channel proteins

serve as a hydrophilic channel. These channel proteins allow specific molecules/ions (eg. Na+) to pass through, thus crossing the membrane.

Transport proteins 2 types:

span the plasma membrane and help certain ions and polar molecules to enter and exit the cell. 2 types: channel and carrier

Fluid Mosaic Model

In this model, a flexible layer made of lipid molecules is interspersed with large protein molecules that act as channels through which other molecules enter & leave the cell.

Hydrophilic

molecules forming ionic or a hydrogen bond with the water molecule

Active Transport

moving substances from against their concentration gradient requires energy. - Primary active transport is directly powered by adenosine triphosphate, or ATP. - A cell must use active transport if it wants to concentrate certain substances inside that might want to diffuse out or get rid of substances that might want to diffuse back in. Active transport works against diffusion; that's why it requires energy.

Selective permeability

one that allows certain molecules or ions to pass through it by means of active or passive transport. Substances move through the membrane at different rates. example: lipid bilayer itself is selectively permeable.

Peripheral Membrane Protein

only attached to the outside of the phospholipid bilayer (the hydrophilic region) toward the outside environment.

Most abundant lipids in the molecule ______ .

phospholipids

Endocytosis

process of capturing a substance or particle from outside the cell by engulfing it with the cell membrane and bringing it into the cell.

Effect of cholesterol on fluidity of membrane at various temperatures:

- AT high temperature, cholesterol blocks phospholipid movements, but at colder temperatures it hinders close packaging of phospholipid.

Effect of saturated/unsaturated hydrocarbon tails on fluidity at cold temperatures:

- If saturated fatty acids are compressed by decreasing temperature, they press in on each other, making a dense & fairly rigid membrane - If Unsaturated fatty acids are compressed, the "kinks" in their tails push adjacent phospholipid molecules away, which helps maintain fluidity in the membrane.

Phospholipids are

- amphipathic with a hydrophilic head & hydrophobic tails

What are the two membrane proteins?

1. integral 2. peripheral

3 types of endocytosis

1. phagocytosis, 2. pinocytosis, 3. receptor-mediated endocytosis

Two functions of a cell membrane:

1. separation from environment 2. selective permeability

Six function of membrane proteins:

1. transport: exchange materials with surrounding in part to take in nutrients & give off waste (hydrophilic proteins) 2. enzymatic reaction: catalyzing reaction of some sort (sequential steps in metabolic pathways) 3. signal transduction: how a cell carries a signal from external environment to the cell 4. intercellular joining: gap & tight functions 5. cell to cell recognition: helps cell recognize each other and what it does. (glycoprotein identification tags) 6. attachment the cytoskeleton & extracellular matrix:

Match the following. A. Large molecules and particles moving out of the cell. B. Molecules moving from low concentration to high concentration across the membrane. C. Non-polar molecules, such as O2 and CO2, moving from high concentration to low concentration across the membrane. D. Polar Molecules, such as water, moving from high concentration to low concentration across the membrane. ----------- 1. Bulk transport, specifically exocytosis 2. Facilitated diffusion by a channel protein, a type of passive transport 3. Simple diffusion 4. Active transport utilizing a carrier protein

A-1 B-4 C-3 D-2

Match the following: A. Allows water to enter the cell through passive diffusion B. Uses energy from ATP to transport specific polar molecules across the membrane C. Creates a selectively permeable barrier that encloses the cytoplasm of a cell. D. Functions as a nametage in the cell's recognition system. ------ 1. Phospholipid layer 2. Channel protein 3. Carrier protein 4. Glycoprotein

A-2 B-3 C-1 D-4

Why does a freeze-fractured membrane peel apart between the two layers of fatty acids?

Because it was non polar, there was no attraction therefore they split in the middle when frozen. Also, the water that is present in the middle of the bilayer freezes and is easily fractured.

Why is that the movement of phospholipids & proteins move laterally

Because proteins are larger than the phospholipid & having more extensive polar regions, makes it less likely for them to flip- fop. Proteins move laterally to maintain the membrane's fluidity. The lateral movement allows fluidity so molecules can pass through, wile maintaining it's structure.

Which one of the following would be most solidified at cold temperatures? A membrane with.. A) Saturated fatty acids tails and cholesterol B) Saturated fatty acid tails and no cholesterol C) Unsaturated fatty acids and cholesterol D. Unsaturated fatty acids and no cholesterol

C

Hydrophobic

Nonpolar molecules that repel the water molecule

Simple Diffusion

Nonpolar solutes cross the cell membrane by simple diffusion from high concentration outside the cell to low concentration inside the cell.

The effect of temperature on fluidity and solidification:

The temperature at which solidification occurs depends on the specific type of phospholipids in the membrane.

How does the structure of a cell membrane allow selective permeability?

The cell membrane functions as a barrier that makes it possible for the cytoplasm to maintain a different composition from the material surrounding the cell. The unit membrane is freely permeable to water molecules but very impermeable to ions and charged molecules. It is permeable to small molecules in inverse proportion to their size but in direct proportion to their lipid solubility. OR The cell membrane is made up of the phospholipid bilayer which has many proteins scattered on it (hence the term 'fluid mosaic'). There may a few different kinds of proteins, such as channel proteins and carrier proteins. These proteins have specific conformation which can bind to specific molecules only, allowing them to enter the cell. Thus, only molecules which can bind to the carrier / channel proteins can enter into the cell. Water moves into the cell by osmosis, and small uncharged particles can pass through the bilayer into the cell. However, large polar particles only can pass through the proteins because the bilayer is hydrophobic.

In what way is a cell membrane a structural and functional mosaic?

The fluid mosaic model describes the plasma membrane structure as a mosaic of phospholipid, cholesterol, proteins and carbohydrates. - Because the plasma membrane has the consistency of vegetable oil at body temperature, the proteins and other substances are able to move across it. (fluid)

Exocytosis

The process of vesicles fusing with the plasma membrane and releasing their contents to the outside of the cell. - Exocytosis Many secretory cells use exocytosis to export products.

What molecules hold the phospholipid bilayer together?

Van der Waals forces hold the hydrophobic tails of the phospholipid bilayer together, and then hydrogen bonding keeps the hydrophilic heads (opposite the tails) together as well as interact with water surrounding the bilayer, which helps stabilize the lipid bilayer structure.

Faciliated Diffusion

a process where polar molecules diffuse passively into the cell with help of transport proteins - they carry only certain molecules - very specific

Carrier proteins

grab their special molecule and hold onto it while they change shape in a way that moves the molecule across the membrane. Each carrier protein is specific for a certain substance

Glycoprotein:

membrane protein with an attached short branched carbohydrate chain -cells recognize other cells is by binding to surface molecules, often carbohydrates, on the plasma membrane.