Plasma membranes

Question 1

True or False.
Plasma membranes only surround cells.

Answer 1

• False.
• Plasma membranes also surround membrane- bound organelles (ie. mitochondria/ nucleus.)
  -note: membrane of any organelles of eukaryotes

Question 2

Why are plasma membranes described as a “fluid mosaic model?”

Answer 2

• Mosaic: due to the mixture of molecules/ proteins found (vary in shape and size. )
• Fluid: The proteins, phospholipids, glycoproteins, glycolipids can move around.

Question 3

How are molecules (ie glycoproteins, channel proteins, glycolipids) arranged in the phospholipid bi- layer ? What does this create?

Answer 3

• They are either within or on the outside of the bi- layer.
• Creates the partially- permeable membrane (only certain molecules can pass through other molecules in bi- layer. )

Question 4

What does an unsaturated fatty acid chain look like in comparison to a saturated fatty acid?

Answer 4

• It has a kink ( bends) due to the double bond between carbon atoms.

Question 5

What is the role of cholesterol in plasma membranes?

Answer 5

• Restricts movement of other molecules (making up membrane.)
• Makes plasma membrane more rigid.

Question 6

What 4 molecules are found in plasma membranes that can move?

Answer 6

1.) Phospholipids
2.) Proteins (ie. channel/ carrier.)
3.) Glycoproteins
4.) Glycolipids.

Question 7

What are the 2 types of proteins in plasma membranes? What is the difference between the two?

Answer 7

• Intrinsic: proteins that span across from one side of the bi- layer to the other.
• Extrinsic: Do not extend completely across/ through the membrane.

Question 8

What are extrinsic proteins used for in the plasma membrane?

Answer 8

• Provide mechanical support or they are connected to proteins or lipids to make glycoproteins/ glycolipids.
• Function of glycoproteins/ glycolipids —> cell recognition (ie. receptors. )

Question 9

In what case is it useful for cholesterol to make plasma membranes more rigid/ less fluid?

Answer 9

• Useful: makes membrane less fluid at high temperatures and prevents water/ dissolved ions from leaking out of the cell - could cause dehydration/ cells bursting.

(more fluid membrane is = more gaps in membrane.)
() - extra info for clarification.

Question 10

What are intrinsic proteins used for in the plasma membrane?

Answer 10

• Protein carriers/ channel proteins involved in transport of molecule across the membrane.

Question 11

What sort of molecules are transported by channel proteins? Give 4 examples.

Answer 11

• Water/ amino acids/ potassium/ sodium.

Question 12

How exactly do carrier proteins transport molecules into the cell?

Answer 12

• Larger molecules will bind to the carrier protein.
• The carrier protein will change shape to transport molecules to other side of membrane.

Question 13

What are the molecules that can pass easily through the plasms membrane? Give examples?

Answer 13

• Lipid-soluble substances (ie. hormones.)
• Non-polar, very small molecules (ie. O₂, CO₂,)

Question 14

What molecules cannot pass through the plasma membrane by simple diffusion? Give examples?

Answer 14

• Polar molecules (water)
• And large molecules (glucose.)
• Water-soluble substances (ie. sodium/ potassium/ amino acids.)

Question 15

If you have more unstaured fatty acids in a plasma membrane, what does this do to the membrane?

Answer 15

• More unssaturated fatty acids = increase in fluidity/ flexibility/ lower melting point.