Plasma Membranes

Question 1

Define: plasma membrane

Answer 1

a selectively (semi/differentially) permeable membrane that surrounds cells and most organelles that separates their contents from the external environment. It containing a phospholipid bilayer and associated proteins.

Question 2

Define: external environment

Answer 2

blood plasma and extracellular fluid

Question 3

Does the plasma membrane surround organelles?

Answer 3

most

Question 4

How big is the plasma memrbane? how can they be seen?

Answer 4

8 nanometres, with transmission electron microscope.

Question 5

2 components of the plasma membrane?

Answer 5

Phospholipids and proteins

Question 6

Describe the phospholipid bilayer (4 parts!)

Answer 6

Phospholipids, WHICH CAN INTERACT WITH WATER, containing:
-> Hydrophilic heads, containing a phosphate group
-> Hydrophilic tails which INTERACT POORLY WITH WATER, containing 2 fatty acid chains that are liquid at HBT
Arranged into a phospholipid bilayer, with hydrophilic heads facing aqueous solutions as they are ok to sit near the water, and hydrophobic tails facing inwards as they don’t mix with water

Question 7

Define: integral proteins

Answer 7

FUNDAmental components of the plasma membrane that are embedded into the plb

Question 8

Define: transmembrane proteins

Answer 8

when oart of a protein is exposed on both sides of a membrane.

Question 9

What are glycoproteins/lipids?

Answer 9

Carbohydrate group attached to a protein/lipid

Question 10

Define: peripheral protein

Answer 10

proteins anchored to the exterior of the plasma membrane through bonding with lipids or are indirectly associated with the plasma membrane through interaction with integral proteins

Question 11

Are peripheral or integral proteins easier to separate from the plb?

Answer 11

peripheral

Question 12

What does the fluid mosaic model propose?

Answer 12

• Plasma membranes surround all cells and many organelles
• Plasma membranes are very flexible and can change shape, because the fatty acid chains are liquid at human body temperature (fluid)
• Plasma membranes are studded with proteins (mosaic)

Question 13

4 purposes of the plasma membrane?

Answer 13

1. active and selective boundary
2. denotes cell identity
3. some proteins are receptor molecules, receiving signals from outside the cell
4. enables transport

Question 14

How is the plasma membrane an active and selective boundary?

Answer 14

Controls when, what and how much of a substance passes through it; enables cells (and organelles) to maintain conditions that are unique from outside of the memrane

Question 15

How does the plasma membrane denote cell identity?

Answer 15

Glycoproteins act as cell surface markers (including antigens etc); each cell type has a different combination of surface markers.

Question 16

Define: receptors

Answer 16

trans-membrane proteins that receive signals from outside of the cell

Question 17

How do receptor proteins work?

Answer 17

THe signal binds to the receptor protein and this changes its shape; starting a specific response in the cell

Question 18

Describe transport due to the cell memrbane.

Answer 18

Some substances can pass directly through the cell membrane but sometimes transport proteins are required to enable this.