Physiology Membrane Lecture 1 - What is a Membrane?

Question 1

Why are membranes important?

Answer 1

Plasma membrane forms an outer boundary of every cell which is essential for maintaining the environment inside and outside of the cell.
Selectively permeable.
Controls the entry of nutrients and exit of waste (and secretory) products.
Maintains differences in ion concentration inside and outside the cell.
Participates in joining of cells to form tissues and organs.
Enables a cell to respond to changes (signals) in the cell’s environment.
Membrane functions are crucial for cell survival
Many functional differences between cell types are due to variations in the composition of their plasma membranes - Different cells interact in different ways with essentially the same ECF.

Question 2

Gives some example of secretory products!

Answer 2

Hormones
Neurotransmitters
Enzymes

Question 3

What is a plasma membrane?

Answer 3

A fluid phospholipid bilayer embedded with proteins

Question 4

What appearance does the plasma membrane have down an electron microscope?

Answer 4

Trilaminar - like a train tracks!

Question 5

What makes up the lipid part of the plasma membrane?

Answer 5

Phospholipids and cholesterol

Question 6

Describe the head of a phospholipid!

Answer 6

Phosphate group
Negatively charged
Polar
Hydrophilic

Question 7

Describe the tail of a phospholipid!

Answer 7

Fatty chains
Uncharged
Non-polar
Hydrophobic

Question 8

What does hydrophilic mean?

Answer 8

Water loving

Question 9

What does hydrophobic mean?

Answer 9

Water hating

Question 10

Describe the organisation of phospholipid in the plasma membrane.

Answer 10

They for a lipid bilayer where the hydrophilic heads face toward the outside of the plasma membrane and the hydrophobic tails face towards each other.

Question 11

Describe the fluidity of the plasma membrane.

Answer 11

The phospholipids are constantly moving - they twirl, vibrate and move around their own half of the membrane millions of times per second.

Question 12

Why can phospholipids move around their half of the plasma membrane?

Answer 12

The bonds between the phospholipids are not strong!

Question 13

What is the cholesterol in the plasma membrane for?

Answer 13

Fluidity and Stability by helping to prevent the phospholipids from packing together. There are different amounts of cholesterol in the different cell types.

Question 14

Name the types of membrane proteins!

Answer 14

Integral proteins
Transmembrane proteins
Peripheral proteins

Question 15

Describe integral proteins!

Answer 15

They are embedded in the lipid bilayer e.g. receptors for hormones which bond to these integral proteins and activate a peripheral protein.

Question 16

Describe Transmembrane proteins!

Answer 16

They extend through the membrane and can span the lipid bilayer multiple times. Examples are transporters and channels.

Question 17

Describe peripheral proteins!

Answer 17

They do not penetrate the membrane and are more common intracellularly. An example is a receptor-associated enzyme.

Question 18

Where are membrane carbohydrates located?

Answer 18

On the outer surface of the cell. Can be known as a sugar coating!

Question 19

What are glycoproteins?

Answer 19

When short carbohydrate chains are bound to a membrane protein.

Question 20

What are glycolipids?

Answer 20

When short carbohydrate chains are bound to a lipid.

Question 21

What is more common, a glycoprotein or a glycolipid?

Answer 21

Glycoprotein

Question 22

Together what do glycoproteins and glycolipids form?

Answer 22

A layer call the glycocalyx

Question 23

What are the 3 important functions of the lipid bilayer as a basic structural barrier that encloses a cell?

Answer 23

1. It forms the basic structure of the membrane.
2. Its hydrophobic interior serves as a barrier. The cell can maintain differences in solute composition and concentrations inside/outside the cell.
3. It is responsible for the fluidity of the membrane. Enables the cell to change shape (e.g. RBC squeezing through capillaries or a muscle cell)

Question 24

Some transmembrane proteins form water-filled highly-selective ions channels. Name two!

Answer 24

Leak channels

Gated channels

Question 25

Describe leak channels.

Answer 25

Channels that are always open!

Question 26

Describe gated channels.

Answer 26

Channels that only open in response i.e. to a chemical message

Question 27

Give an example of a disease that is caused by a genetic mutation in channels.

Answer 27

Cystic fibrosis

Question 28

Give an example of a drug that targets channels.

Answer 28

Ca2+ channel blockers are used to manage hypertension an abnormal heart rhythms

Question 29

Describe carrier or transport proteins?

Answer 29

Span the membrane
Exhibit substrate specificity - Accept only a particular molecule (or ion) or group of closely related molecules.
Different cell types express different kinds of carriers.
E.g. Thyroid gland cells and iodine

Question 30

What are docking-marker acceptors?

Answer 30

Membrane proteins located on the inner surface of the membrane. They interact with secretory vesicles leading to exocytosis of the vesicle content.

Question 31

What membrane protein is involved with exocytosis?

Answer 31

Docking-marker acceptors

Question 32

Describe membrane bound enzymes!

Answer 32

Peripheral proteins that can be located on either side of the membrane but are most commonly found intracellularly e.g. protein kinase A

Question 33

Describe receptor in relation to the plasma membrane!

Answer 33

Are proteins most commonly found on the outer surface of the cell. They bind specific molecules (lock and key) e.g. hormones

Question 34

What are cell adhesion molecules?

Answer 34

They are membrane proteins also know as CAMs

Question 35

Give two example of cell adhesion molecules!

Answer 35

1. Cadherins (helps hold cells within tissues together)

2. Integrins (span the plasma membrane acting as a link between extra- and intra-cellular environments)

Question 36

What do membrane carbohydrates serve as?

Answer 36

Self-identity markers

Question 37

Describe self-identify markers!

Answer 37

Short carbohydrate chains on the outer membrane surface serve as self-identity markers that enable cells to identify and interact with one another

Question 38

Why is it important that different types of cells have different markers (self-identify markers)?

Answer 38

It is important in cell-to-cell interactions, especially during embryonic development

Question 39

What is the role of membrane carbohydrates in tissue growth?

Answer 39

So that cells do not overgrow their own territory.

Question 40

What does abnormal surface markers (membrane carbohydrates) cause?

Answer 40

Cancer cell growth or excessive cell growth

Question 41

What are specialised cell junctions?

Answer 41

When some cells are directly linked

Question 42

What are the three types of specialised cell junctions?

Answer 42

1. Desmosomes
2. Tight junctions
3. Gap junctions

Question 43

Describe the specialised cell junction: Desmosomes!

Answer 43

Adhering junctions that anchor cells together, especially in tissues subject to stretching. E.g. skin, heart, uterus

Question 44

Describe the specialised cell junction: Tight junction!

Answer 44

Join the lateral edges exclusively of epithelial cells near their lumenal (apical) membranes. (tight or leaky)
They are protein junctions.

Question 45

Describe the specialised cell junction: Gap junctions!

Answer 45

‘Communicating’ junctions that allow the movement of charge carrying ions and small molecules between two adjacent cells.