Cell Transport

Question 1

What is a phospholipid bilayer? Where is it seen and why?

Answer 1

2 layers of phospholipids - the hydrophyllic heads on the outside, and the hydrophobic tails on the inside. It is seen in a cell membrane, and being arranged like this means lipid soluble substances can get through

Question 2

Cell membranes have pores. True or false?

Answer 2

True - its how small molecules can get into and out of the cell

Question 3

What is the function of a plasma membrane?

Answer 3

To control the movement of substances in and out of the cell (osmosis, diffusion, active transport)

Question 4

What is the fluid mosaic model? Why is it called that?

Answer 4

A model for what cell membranes look like
Fluid - because it is constantly moving (phospholipid bilayer)
Mosaic - because it is made from lots of different substances
Model - visual representation how we think/ know something to work

Question 5

What substances make up the fluid mosaic model?

Answer 5

1) Phospholipid molecules - form a continuous bilayer. Constantly moving - a fluid like
2) Cholesterol - looks as if inserted in bilayer. It keeps the shape more stable and reduces the permeability of the membrane
3) Proteins - scattered throughout the membrane. Such as channel & carrier proteins, but more too
4) Glycoproteins & glycolipids

Question 6

Name a type of cell with lots of cholesterol in the cell membrane, and why

Answer 6

Red blood cells, because they need to keep their biconcave shape in order to transport molecules around the body. Cholesterol helps keep the shape rigid

Question 7

Compare:

a) Carrier proteins
b) Protein channels

Answer 7

a) has to change shape, whereas b) creates a path straight through the cell membrane. a) has different kinds, which can allow either facilitated diffusion or active transport (so ATP must bind too! Because it has stronger bonds, so needs the extra energy to break the bonds, change shape allowing the substance through), but b) only allows facilitated diffusion and needs no ATP. Both are specific, with receptors only allowing one substance through, and one at a time

Question 8

What is facilitated diffusion?

Answer 8

Diffusion for molecules that are too big or too slow to pass through the phospholipid bilayer (e.g. ions). It needs a carrier protein or protein channel. Still goes from a high to low concentration, so doesn’t need energy/ ATP

Question 9

Facilitated diffusion can reach a maximum rate. True or false?

Answer 9

True - because it uses carrier and channel proteins instead of just passing though the phospholipid bilayer, so it can reach a max rate when all the carrier proteins & protein channels are occupied

Question 10

A substance is too large to pass through the phospholipid bilayer, and needs to go from a low to a high concentration. Does it go through a carrier protein or protein channel?

Answer 10

A carrier protein, as it can allow active transport as well as facilitated diffusion - a protein channel only allows facilitated diffusion

Question 11

How does a molecule pass through a carrier protein?

Answer 11

When the molecule binds to the receptors on a carrier protein, it breaks some of the hydrogen bonds formed in tertiary structure. This causes its shape to change around the molecule, so it closes behind the molecule and it is now on the other side of the cell

Question 12

What bonds link the fatty acids to the glycerol of triglycerides?

Answer 12

Ester bonds!

Question 13

What do co-transporters do?

Answer 13

They are a protein in the cell membrane which can bind to 2 proteins at the same time (up down, down down, or up up). It sends one molecule down their concentration gradient to power the other molecule to move against its concentration gradient. Indirect active transport

Question 14

What is indirect active transport?

Answer 14

What co-transporters do - using the energy of moving one substance along its concentration gradient to power moving the other substance moving against its own concentration gradient

Question 15

Where are co-transporters?

Answer 15

In the cell membrane of the small intestine cells. Especially in the ileum

Question 16

Why does the ileum have more co-transporters?

Answer 16

Because the concentration of glucose in the intestine is lower than the glucose now in the blood. So, facilitated diffusion will no loger work. Co-transporters means the body can use sodium ions moving down their concentration gradient to empower the glucose moving against its concentration gradient - into the blood (note though, to get the sodium ions from the blood into the small intestine first, it uses active transport, so needs energy to go through the sodium protein carrier)