Module 2.5 Biological Membranes

Question 1

How thick are membranes?

Answer 1

7-10nm

Question 2

Describe the phospholipid bilayer

Answer 2

Hydrophilic phosphate heads make up outside
Hydrophobic fatty acid tails make up inside
2 layers of phospholipid make up the bilayer

Question 3

Is the phosphate head evenly charged?

Answer 3

No

Question 4

Intrinsic protein

Answer 4

Spans whole bilayer

Question 5

Extrinsic protein

Answer 5

Partially embedded inside or outside

Question 6

Glycolipids and glycoproteins

Answer 6

For cell signalling 
Allow self recognition 
Receptors for drugs + hormones
Antigens 
Glycoproteins can bind cells in tissues

Question 7

Channel proteins

Answer 7

Allow small ions/small water soluble molecules to diffuse through

Question 8

Carrier proteins

Answer 8

Help large molecules to diffuse through

Used in active transport

Question 9

Cholesterol

Answer 9

For stability and to regulate fluidity

Question 10

Cells communicate w/hormones

Answer 10

Hormones bind to receptors (complimentary shape)

Response occurs in target cell e.g. gene/DNA activated

Question 11

Insulin

Answer 11

Made in beta cells in the islets of langerhans in the pancreas
Released when glucose level of blood too high
Target cells are muscle tissue, adipose tissue + liver cells
Effect is glucose taken out of blood = blood glucose level lowered

Question 12

Beta blockers

Answer 12

Stop heart muscle beating to fast which could cause a heart attack

Question 13

Poisons

Answer 13

Bind w/receptors

Botox paralyses facial muscles

Question 14

Hijacking receptors

Answer 14

Viruses can bind with receptors e.g. HIV and AIDS
HIV virus can bind with receptors on T-lymphocytes
Lowers immune system
HIV bursts WBCs

Question 15

🌟Diffusion

Answer 15

Net movement
High to low conc.
Down conc. gradient
Passive process

Question 16

🌟Osmosis

Answer 16

Net movement of water
From high water pot. to lower water pot. 
Across partially permeable membrane
Down water pot. gradient
Passive process

Question 17

🌟Active transport

Answer 17

Net movement of molecules/ions
Low to high conc.
Against conc. gradient
Uses ATP
Requires energy 
Across partially permeable membrane
Needs carrier proteins/channel proteins

Question 18

Channel proteins

Answer 18

Polar molecules/ions

Question 19

Carrier proteins

Answer 19

Large molecules

Question 20

Hypertonic

Answer 20

Lots of salts and sugars

Question 21

Isotonic

Answer 21

The same water pot. in and out =no net movement

Question 22

Hypotonic

Answer 22

High water pot.

Question 23

Water pot. of pure water

Answer 23

0 kPa

Question 24

More concentrated solution

Answer 24

Lower water pot. = more negative number

Question 25

Water moves from a

Answer 25

Higher water potential (less neg. number) to a lower water potential (more neg. number)

Question 26

Water potential

Answer 26

Solute potential + pressure potential

Question 27

What happens when a cell is placed in a hypotonic solution?

Answer 27

Water moves into the cell (via osmosis) Animal cells will burst (haemolysed) Plant cells will become turgid (cytoplasm and vacuoles will push the membrane against the cellulose cell wall)

Question 28

What happens when a cell is placed in a hypertonic solution?

Answer 28

Water moves out of the cell (via osmosis) Animal cells shrink (crenated) Plant cells become plasmolysed (cell membrane pulls away form cell wall)

Question 29

🌟Basic structure of cell surface membranes

Answer 29

Phospholipids form bilayer Hydrophobic tails pointing inwards Hydrophilic heads pointing out Role of phospholipids: to provide a barrier to large/polar molecules and ions Carrier/channel proteins for active transport/facilitated diffusion Cholesterol stabilises the membrane and regulates fluidity Glycoproteins which act as receptors for cell communication

Question 30

🌟Roles of cell surface membranes inside cells

Answer 30

Form edge of organelles within a cell Isolation of contents of organelles from cytoplasm Site of attachment of enzymes and ribosomes (on RER) Provide selective permeability - controls what enters and leaves organelles Separates areas of differing concentration to provide gradients

Question 31

🌟Cell signalling - how receptors work

Answer 31

Release of signal molecules e.g. hormones by exocytosis into the blood Proteins/glycoproteins/glycolipids act as receptors for hormones and drugs The receptor is specific as the shape of the receptor and hormone are complementary in shape The hormone binds to the receptor Binding causes a change inside the cell which brings about a response

Question 32

🌟Role of glycoproteins

Answer 32

Cell signalling - communication between cells to help them work together Act as antigens for... Cell recognition - self/non-self Receptors found on target cells For hormones/cytokines to trigger reactions/responses in cells Cell adhesion in tissues Form bonds with water molecules to stabilise the membrane Receptors on transport proteins

Question 33

🌟Small, non-polar substances

Answer 33

Diffuse through the phospholipid bilayer

Question 34

🌟Larger substances

Answer 34

Use carrier proteins Specific to certain molecules The protein changes shape to allow the molecule through to the other side Facilitated diffusion/active transport (uses ATP, against gradient, faster, one way) Endocytosis/exocytosis Bulk transport

Question 35

🌟Polar substances

Answer 35

Through channel proteins Facilitated diffusion

Question 36

🌟Compare active transport and facilitated diffusion

Answer 36

Active transport: - Carrier proteins - Anything from low to high conc. - Uses ATP - Only goes in one direction - Much quicker than diffusion Facilitated diffusion: - Carrier proteins - Channel proteins - Larger molecules e.g. glucose - Ions/polar molecules e.g. K+ and Ca2+ - Needed when phospholipid bilayer won't allow large/polar/water soluble molecules to cross - No ATP needed

Question 37

🌟Compare the roles of carrier proteins and channel proteins and how they work

Answer 37

Carrier proteins: - Specific to molecule - Molecule attaches on one side of the membrane - Protein changes shape - Releases molecule on the other side of the membrane - Carries large molecules across the membrane in facilitated diffusion (doesn't require energy) - Carries all molecules across the membrane in active transport (requires energy) Channel proteins: - Specific to molecule - Forms a pore through the centre of the protein - Hydrophilic conditions inside the pore - Allows charged and polar substances across the membrane in facilitated diffusion

Question 38

🌟Facilitated diffusion

Answer 38

``` Net movement High conc. to lower conc. Down conc. grad. Through carrier proteins (large molecules) Channel proteins (ions) Passive process ```

Question 39

🌟Stages of exocytosis

Answer 39

Vesicle moves towards cell surface membrane along microtubules Vesicle fuses w cell surface membrane Protein released out of cell by exocytosis Movement of vesicles on microtubules and fusion of vesicles w membrane requires ATP

Question 40

🌟Stages of endocytosis

Answer 40

Molecule binds w receptor Cell surface membrane invaginates (ATP required) Membrane fuses w itself Vesicle formed Vesicle moves through cytoplasm to destination organelle