Chapter 5 - Plasma Membranes

Question 1

Define compartmentalisation

Answer 1

The formation of separate membrane -bound organelles

Question 2

Why are phospholipids suited as membranes?

Answer 2

Because their hydrophilic heads can interact with water

Question 3

What does the fluid-mosaic model show?

Answer 3

That the phospholipids are free to move within the layer relative to each other

Membrane is flexible

Because proteins embedded in the bilayer vary in shape, size and position

Question 4

What are intrinsic proteins?

Answer 4

Transmembrane proteins that are embedded through both layers of a membrane

Have aa w hydrophobic R-groups on external surfaces which interact w the hydrophobic core of the membrane

Question 5

Give 4 examples of intrinsic proteins

Answer 5

Channel proteins
carrier proteins
glycoproteins
glycolipids

Question 6

Why do we need compartmentalisation?

Answer 6

Because the metabolic reactions require different conditions (e.g. chemical gradients to be maintained)

Question 7

Describe the function of a channel protein?

Answer 7

To provide a hydrophilic channel that allows the passive movement of polar mol. and ions down a concentration gradient through membranes

Question 8

How are channel proteins held together?

Answer 8

Through the interactions between the hydrophobic core of membrane and hydrophilic R-groups on outside

Question 9

What is the role of a carrier protein?

Answer 9

Helps in the passive transport (down conc grad) and active transport (against conc) into cells

Question 10

Where are glycoproteins found?

Answer 10

Embedded in the cell surface membrane w attached carbohydrate chains of varying length and shape

Question 11

What role do glycoproteins have?

Answer 11

Cell adhesion and act as receptors for chemical signals

Question 12

How do glycoproteins help with cell signals?

Answer 12

When the chemical binds to the receptor it creates a response from the cell

Either direct response or set of a cascade of events

Question 13

Give examples of when cell signalling is used with glycoproteins

Answer 13

Receptors for neurotransmitters at nerve synapses

Question 14

Which protein can be both intrinsic and extrinsic?

Answer 14

Glycolipids

Question 15

What is the difference between glycolipids and glycoproteins?

Answer 15

Glycolipids are lipids with carbohydrate attached whereas glycoprotein is a protein

Question 16

What is the function of a glycolipid?

Answer 16

To act as cell markers or antigens, can be recognised by immune system as self

Question 17

What are extrinsic proteins?

Answer 17

Present in one side of the bilayer

Normally have hydrophilic R-groups on their outer surfaces and interact w polar heads of phospholipids or intrinsic proteins

Question 18

What is the function of cholesterol?

Answer 18

To regulate the fluidity of the membrane

Positioned between hydrophobic heads and interacts

Question 19

What is the effect of an increase in temperature on the phospholipid membrane?

Answer 19

1. Increase in temp = more KE
2. Each phospholipid moves more
3. Membrane becomes more fluid
4. Begins to lose its structure as the pplds move further away from each other
5. loss of structure increases the permeability of the mem, so easier for particles to cross it

Channel and carrier proteins in mem will be denatured at high temp

Question 20

What type of molecule can disrupt the bilayer?

Answer 20

Anything non-polar

Question 21

How does alcohol affect the bilayer?

Answer 21

The presents of the alcohol molecule disrupts the structure of the bilayer, the individual phospholipids are further apart

More fluid and more permeable

Question 22

Define diffusion

Answer 22

The net movement of particles from a region of higher concentration to a region of lower concentration down a concentration gradient

Question 23

Is diffusion active or passive?

Answer 23

Passive

Question 24

Suggest and explain two factors affecting diffusion

Answer 24

1. Temperature
   - higher temp, particles have more KE, move at higher speed, frequency of successful collisions increases
2. Concentration difference
   - The higher, the faster rate of diffusion bc the overall movement is larger

Question 25

What molecules is the membrane permeable to? and why

Answer 25

non-polar molecules e.g. O2 Polar molecules will repel with the hydrophobic interior Small polar molecules can pass (e.g. water)

Question 26

What factors affect diffusion across a membrane?

Answer 26

Surface area | Thickness of membrane

Question 27

What is facilitated diffusion?

Answer 27

Diffusion across a membrane through protein channels down a conc gradient When a mem is selectively permeable the membrane has protein channels which are specific to one mol or ion (or protein channel)

Question 28

What are the factors which affect facilitated diffusion?

Answer 28

Temperature Conc gradient Mem SA and thickeness number of channel proteins present

Question 29

Describe the process of active transport

Answer 29

1. The molecule or ion to be transported binds to receptors in channel of the carrier protein on the outside of the cell 2. On the inside of the cell ATP binds to the carrier protein and is hydrolysed into ADP and phosphate 3. The binding of the phosphate molecule to the carrier protein causes the carrier protein to change shape (opening up to the inside of the cell) 4. The molecule or ion is released to the inside of the cell 5. The phosphate molecule is released from the carrier protein and recombines with ADP --> ATP 6. The carrier protein returns to its OG shape - Process is selective (only specific proteins are transported)

Question 30

What is bulk transport?

Answer 30

A form of active transport where large molecules are moved into or out of the cell by endocytosis or exocytosis

Question 31

What is endocytosis and name the two types

Answer 31

Bulk transport of material into cells Phagocytosis - solids Pinocytosis - Liquid

Question 32

Describe the process of endocytosis

Answer 32

1. Cell surface membrane invaginates when it comes into contact with the material to be transported 2. Membrane enfolds the material until the membrane fuses forming a vesicle 3. Vesicle pinches off and moves into the cytoplasm via the cytoskeleton

Question 33

Describe the process of exocytosis

Answer 33

The vesicles usually formed by the Golgi Apparatus move towards and fuse w the cell surface membrane The microtubules allow the vesicles to move Contents released

Question 34

What is necessary for endo and exocytosis?

Answer 34

Energy in form or ATP to move vesicles along the cytoskeleton, changing shape to engulf materials

Question 35

What is water potential?

Answer 35

The pressure exerted by water molecules as they collide with a membrane or container Measured in Pa

Question 36

What is the water potential of pure water?

Answer 36

0kPa

Question 37

What is the hydrostatic pressure?

Answer 37

The pressure created by osmosis in an enclosed system

Question 38

What is cytolysis?

Answer 38

The bursting of an animal cell caused by increasing hydrostatic pressure as water enters by osmosis

Question 39

How do animals control that not all of their water is diffused out?

Answer 39

Blood, an isotonic solution (cells surrounded by aqueous solutions with an equal water potential)

Question 40

What is turgor?

Answer 40

The pressure exerted by the cell surface membrane against the cell wall in plants

Question 41

What happens in plasmolysis?

Answer 41

The contents of the plant cell shrink because of a lower water potential outside the cell

Question 42

Explain the difference between isotonic, hypertonic and hypotonic

Answer 42

Isotonic = no net water movement ( water potential is the same inside and out) Hypertonic = water flow out of cell ( lower wp outside than inside) Hypotonic = flow water into cell (higher wp outside than in)