Biological Membranes

Question 1

What is the fucntion of the plasma membrane?

Answer 1

• acts as a barrier between the cell and the enviroment
• cell recognition (glycoproteins act as antigens)
• cell communication (receptors on the plasma membrane bind to hormones and chemicals)

Question 2

What is the fucntion of intracellular membranes?

Answer 2

• barriers between organelle and cytoplasm
• site of chemical reactions
• controls what goes in and out of the organelle
• they form vesicles

Question 3

Why is the plasma membrane described as a fluid mosaic model?

Answer 3

• ‘ fluid’ because the phospholipids are constantly moving around
• ‘mosiac’ because proteins are scattered through the phospholipids like mosaic tiles

Question 4

What is the structure of the plasma membrane?

Answer 4

Bilayer of phospholipids with proteins and cholesterol

Question 5

What are glycolipids?

Answer 5

Phospholipids with sugars attached to them

Question 6

What is the fucntion of glycolipids?

Answer 6

• they acts as an antigen or recognition sites
• they increase membrane stability as they can form hydrogen bonds with water

Question 7

What are glycoproteins?

Answer 7

Proteins with sugar molecules attached to them.

Question 8

What do glycoproteins do?

Answer 8

They act as recognition sites or antigens

Question 9

What are intrinsic proteins?

Answer 9

Proteins that span both bilayer of the plasma membrane

Question 10

What is the function of the intrinsic proteins?

Answer 10

They act as channel or carrier proteins

Question 11

What is an extrinsic protein?

Answer 11

Protein found on the surface of the plasma membrane

Question 12

What is the function of extrinsic proteins?

Answer 12

Usually function as enzymes

Question 13

What is the function of glycolipids?

Answer 13

• act as receptor sites and/or antigens on the plasma membrane
• increase membrane stability by forming hydrogen bonds with water

Question 14

What is a glycoprotein?

Answer 14

Proteins with sugars attached to them

Question 15

What is the function of glycoproteins?

Answer 15

They act as recognition sites and/or antigens on the plasma membrane

Question 16

What are intrinsic proteins?

Answer 16

Proteins which span both bilayer of the membrane

Question 17

What is the function of intrinsic proteins?

Answer 17

Act as channel or carrier proteins

Question 18

What are extrinsic proteins?

Answer 18

Proteins on the surface of the membrane

Question 19

What is the function of extrinsic proteins?

Answer 19

Usually act as enzymes

Question 20

What happens to membrane permeability below freezing?

Answer 20

The membrane permeability increases

Question 21

Why does membrane permeability increase at temperatures below freezing?

Answer 21

• Proteins on the membrane unfold and become deformed.
• Water freezes into ice which punctures the cell membrane

Question 22

What happens to membrane permeability at 0°C - 45°C?

Answer 22

Membrane is partially permeable
- the more energy you add, the more fluid it becomes, the more substances moves through

Question 23

What happens to membrane permeability after 45°C?

Answer 23

Permeability increases rapidly

Question 24

Why does membrane permeability increase rapidly past 45°C?

Answer 24

• Proteins being to denature and unfold, increasing permeability
• Water in the cell cytoplasm expands putting pressure on the membrane, causing gaps

Question 25

What happens to membrane permeability as ethanol concentration increases?

Answer 25

Increases because ethanol dissolves non-polar substances such as lipids

Question 26

What is facilitated diffusion?

Answer 26

Net movement of particles from an area of high concentration to an area of low concentration across a membrane with either a channel or carrier protein. - passive process

Question 27

What is an isotonic solution?

Answer 27

Two solutions with the same water potential

Question 28

What is a hypertonic solution?

Answer 28

Solution that is concentrate

Question 29

What is a hypotonic solution?

Answer 29

A solution that is dilute

Question 30

What happen to a plant cell in a hypertonic (concentrate) solution?

Answer 30

Water moves out and cell becomes flaccid. This is because due to plasmolysis.

Question 31

What is plasmolysis?

Answer 31

When the cell membrane pulls away from the cell wall

Question 32

What happens when a plant cell is put in a hypotonic (dilute) solution?

Answer 32

Water moves in, cell becomes turgid

Question 33

Why does a plant cell become turgid in dilute conditions?

Answer 33

Vacuole swells and cytoplasm pushes agains cell wall

Question 34

What happens to an animal cell in a hypertonic (concentrate) solution?

Answer 34

Cell shrinks -> crenation

Question 35

What happens to an animal cell in a hypotonic (dilute) solution?

Answer 35

Cell bursts - lysis -> no cell wall to maintain the turgor pressure

Question 36

What is active transport?

Answer 36

Movement of molecules from a low concentration to a high concentration against a concentration gradient involving carrier proteins. —> active process

Question 37

What affects the rate of active transport?

Answer 37

1) Number of carrier proteins 2) Speed of each carrier protein 3) Rate of respiration (active transport required ATP)

Question 38

What is endo/exocytosis?

Answer 38

Movement of large molecules in or out of the cell - active process

Question 39

What happens during endocytosis?

Answer 39

1) Plasma membrane surrounds particles 2) Membrane pinches off to form a vesicle 3) vesicles move into cell interior

Question 40

What happens during exocytosis?

Answer 40

1) Vesicle containing particles moves towards membrane 2) Vesicle fuses with plasma membrane 3) Vesicle contents released outside cell