F211-Membranes&Cell Signalling

Question 0

What does the fluid part of the fluid mosaic model represent?

Answer 0

The fluid part represents how some parts of the membrane can move around freely- they are not in a fixed position.

Question 1

What does the fluid mosaic model represent?

Answer 1

The cell membrane

Question 2

What does the ‘mosaic’ part of the fluid mosaic model illustrate?

Answer 2

The ‘mosaic’ part illustrates the “patchwork” of proteins that is found in the Phospholipid Bilayer and this makes the membrane look like a mosaic when viewed from above.

Question 3

Describe the structure of a phospholipid

Answer 3

The phospholipid has a phosphate and glycerol head which is hydrophilic( is attracted to water-polar)

The phospholipid had 2 fatty acid tails which is hydrophobic (not attracted to water-non polar)

Question 4

What do phospholipids form?

Answer 4

They form a lipid Bilayer in which their hydrophilic areas spontaneously arrange and align themselves to face the aqueous cytosol and the extracellular fluid.
While their hydrophobic tail areas face away from the cytosol and extracellular fluid.

Question 5

Why do the hydrophilic heads appear as dark lines in comparison to hydrophobic tails when observed using a microscope?

Answer 5

The again is in solution therefore the hydrophobic tails won’t mix with it but the hydrophilic heads will. This makes only the heads stained and appear darker.

Question 6

The lipid Bilayer is…

Answer 6

Partially permeable, allowing only certain molecules to diffuse across the membrane to enter or exit the cell

Question 7

What is the function of the phospholipid Bilayer?

Answer 7

• to act as a barrier to polar/charged particles
• to allow the passage of non polar/lipid soluble particles by simple diffusion
• select what enters or leaves the cell

Question 8

What is the function of cholesterol?

Answer 8

• to stabilise the membrane
• to maintain fluidity
• to reduce permeability to polar/charged particles

Question 9

What is the function of channel proteins?

Answer 9

• to allow the passage of polar/charged substances across the membrane by facilitated diffusion (Na+ ions)

Question 10

What is the function of carrier proteins?

Answer 10

• to allow the passage of large substances across the membrane by facilitated (eg.glucose)
• to allow the passage of any substance against the concentration gradient by active transport

Question 11

What is the function of glycoproteins/glycolipids?

Answer 11

• acting as antigens
• recognition of cells as self/non-self
• cell signalling
• receptor/binding site for hormone/chemical signal/ drugs
• trigger on transport proteins
• cell adhesion/to hold cells together
• attach to water molecules to stabilise the membrane

Question 12

Define cell signalling

Answer 12

The communication between cells

Question 13

What is the role of the cell surface membrane?

Answer 13

• endocytosis/exocytosis
• provide selective permeability
• separate cell from environment
• cell to cell attachment
• phospholipid bulgar allows the passage of non polar, soluble molecules
• control entry/exit of molecules
• receptors
• cell recognition
• microvilli increase SA of cell

Question 14

What is the role of membranes within cells?

Answer 14

• forms vesicles
• site for attachment of ribosomes
• isolates DNA
• surrounds vacuole
• forms compartments/organelles within a cell
• intercellular transport
• site for attachment of enzymes
• protects cells from hydrolytic enzymes in lysosomes

Question 15

What two things in the plasma membrane can act as receptors?

Answer 15

Glycoproteins & Glycolipids

Question 16

Describe and explain cell signalling..

Answer 16

• Cell signalling is the communication between cells.
• Signal molecules are released from one cell by exocytosis.
• The signal molecule then binds or attaches to a receptor or glycoprotein on the plasma membrane of the second cell or target cell.
• The receptor and signal molecules are specific.
• They have complementary shapes.
• The bonding of the signal molecule to receptor triggers a response inside the cell.

Question 17

Describe insulin as an example of cell signalling

Answer 17

Insulin is a signal molecule allowing communication between the pancreas and the muscle tissue. When insulin binds to receptors in the plasma membrane of muscle cells it causes channel proteins to open allowing glucose to be taken into the cell from the bloodstream. The effect of insulin binding to muscle cells is a reduction in blood glucose concentration.