Plasma Membranes

Question 1

What is the plasma membrane and what are its components?

Answer 1

The fluid mosaic model describes the plasma membrane as a fluid combination of phospholipids, cholesterol, and proteins. Carbohydrates attached to lipids (glycolipids) and to proteins (glycoproteins) extend from the outward-facing surface of the membrane.

Separates internal cytoplasm of cell from external environment

3 Principle Components:
-Lipids (phospholipid bilayer)
-Proteins (integral proteins and peripheral proteins)
-Carbohydrates

Question 2

What are active and passive transport?

Answer 2

Passive: with diffusion, no energy required, high to low concentration, sometimes involves a protein channel

Active: against diffusion, low to high concentration, requires energy, always involves a protein channel

Question 3

Phospholipid Molecules

Answer 3

-Hydrophilic head w/ phosphate containing group attached to glycerol molecule

-2 Hydrophobic tails w/ saturated or unsaturated fatty acid

-In an aqueous solution, phospholipids tend to arrange themselves with their polar heads facing outward and their hydrophobic tails facing inward.

Question 4

Integral Proteins

Answer 4

Integrated completely into membrane structure

Question 5

Peripheral Proteins

Answer 5

Found on interior and exterior surface of membranes. Attached either to integral proteins or to phospholipids.

Question 6

Differential permeability

Answer 6

The capacity of a membrane to allow some particles to pass through but not others

Question 7

Diffusion

Answer 7

The movement of molecules or atoms from high to low concentration

-simple diffusion
-facilitated diffusion
-osmosis

Question 8

Osmosis

Answer 8

Diffusion of water across a semipermeable membrane (cell membrane restricts certain solutes, allows water to cross freely)

Question 9

Facilitated Diffusion

Answer 9

Diffusion with the help of a channel protein

Question 10

Simple Diffusion

Answer 10

Diffusion through a permeable membrane

Question 11

Tonicity

Answer 11

Ability of extracellular solution to make water move in or out of cell through osmosis

Question 12

Osmolarity

Answer 12

Total concentration of all solutes in a concentration

Question 13

Isotonic

Answer 13

Normal/Flaccid cell

Question 14

Hypotonic

Answer 14

Lysed/Turgid cell

Question 15

Hypertonic

Answer 15

Shriveled/Plasmolyzed cell

Question 16

Turgor Pressure

Answer 16

Depends on the tonicity of the solution a plant is in. Without enough water a plant loses turgor pressure, wilts.

Question 17

Protein accounts for ___% and lipids account for ___% of the human cell

Answer 17

50 and 40

Question 18

Phospholipid Bilayer

Answer 18

-External surface and cytoplasmic surfaces lined with hydrophilic polar heads

-Hydrophobic, non polar tails in sandwiched in between

Question 19

What roles can proteins on the cell membrane serve?

Answer 19

-Enzymes
-Structural attachments for cytoskeleton
-Part of cell’s recognition sites

Cell recognizes its own “cell specific” proteins and can attack foreign proteins associated with invasive pathogens.

Question 20

Glycoproteins help form the

Answer 20

Glycocalyx

Important for cell recognition

Question 21

What does it mean that the plasma membrane is amphiphilic

Answer 21

Both hydrophilic and hydrophobic regions

Question 22

Carrier proteins

Answer 22

Change shape as they move molecules across the membrane

Question 23

A paramecium uses a _____ to pump water out of its body

Answer 23

contractile vacuole

Question 24

Uniporter protein

Answer 24

Carrier protein that moves one molecules or ion

Question 25

Symporter protein

Answer 25

Carrier protein that moves two different molecules or ions both in the same direction

Question 26

Antiporter protein

Answer 26

Carrier protein that moves two different molecules or ions in opposite directions

Question 27

Electrochemical gradients arise from the combined effects of

Answer 27

concentration gradients
and electrical gradients

Ex: Na+ should be driven into the negative interior of the cell because of the electrical gradient, but it should be driven out of the cell because of the concentration gradient.

Question 28

Secondary Active Transport

Answer 28

An electrochemical gradient, created by primary active transport, can move other substances against their concentration gradients, a process called co-transport or secondary active transport.

Question 29

Bulk Transport

Answer 29

Cells need bulk transport mechanisms, in which large particles are moved across the membrane. This involves enclosing the substances

Question 30

Draw the bulk transport mechanism

Answer 30

1. molecule binds to protein receptor
2. receptor-molecule moves to clathrin coated pit.
3. cell membrane folds inwards
4. formation of coated vesicle
5. vesicle fuses with an endosome
6. receptors and molecules separate

Question 31

Endocytosis

Answer 31

Cellular process by which substances are brought into the cell. The material to be internalized is surrounded by the plasma membrane which then buds off to form a vesicles inside the cell.

Phagocytosis: process by which a cell engulfs a solid particle to form an internal compartment known as a phagosome. Phagocytosis is involved in the acquisition of nutrients for cells.

Pinocytosis: involves the internalization of the extracellular liquids through invagination.

Receptor-Mediated Endocytosis: Uptake targets a specific type of substance that binds to the receptor on the external surface of the cell membrane.

Question 32

Exocytosis

Answer 32

Vesicles containing substances fuse with the plasma membrane, and the contents are released to the exterior of the cell.

Question 33

Why is the cell surface important?

Answer 33

Glycoprotein and glycolipid patterns on the surfaces of cells give many viruses an opportunity for infection.

Question 34

What types of endocytosis was the research example shared in class of cholesterol accumulation in mouse?

Answer 34

Receptor-mediated endocytosis

Question 35

How many cells are in the human body?

Answer 35

30 trillion

Question 36

How many cell types are in the human body?

Answer 36

around 200

Question 37

What characteristic of a phospholipid contributes to the fluidity of the membrane?

Answer 37

Double bonds in the fatty acid tail

Question 38

What is the primary function of carbohydrates attached to the exterior of cell membranes?

Answer 38

Identification of the cell

Question 39

A scientist compares the plasma membrane composition of an animal from the Mediterranean coast with one from the Mojave Desert. Which hypothesis is most likely to be correct?

Answer 39

The cells from the Mojave Desert animal will have a higher cholesterol concentration in the plasma membranes.

Question 40

Imagine a cell can perform exocytosis, but only minimal endocytosis. What would happen to the cell?

Answer 40

The plasma membrane would increase in size over time.