Module 1 - Cells

Question 1

Which molecules are able to pass through the cell membrane if they are small enough?

Answer 1

Hydrophobic

Question 2

What can exocytosis be used for?

Answer 2

• removal of cell waste

- distribute materials produced within the cell

Question 3

What can endocytosis be used for?

Answer 3

• e.g. to bring polysaccharides or other large molecules into the cell

Question 4

Describe co-transport

Answer 4

One molecule moves with its concentration gradient and one moves against 
- uses a transport protein 
Example?
Sodium - potassium ATPase 
3 Na pumped out, 2 K brought in

Question 5

Which direction does osmosis occur?

Answer 5

From the hypotonic (low solute concentration) to hypertonic (high solute concentration) side in an attempt to equalise the concentrations

Question 6

What can occur if a cell gains too much water (hypotonic)?

Answer 6

Cell lysis = the cell bursts

Question 7

How is osmolarity calculated?

Answer 7

Take the M (mol/L) and multiply by how many ions are present
E.g.
[CaCl2] = 0.5
Osmolarity = 1.5
Remember: if a molecule can easily diffuse across the cell membrane, no osmolarity calculations are necessary

Question 8

What does cholesterol do to the structure of a cell membrane in different temperatures?

Answer 8

It’s ring-like structure is inserted into the membrane.
High temperature - stops the membrane from becoming too fluid
Low temperature - increases fluidity

Question 9

Describe the structure of a GPCR?

Answer 9

Wraps in and out of the cell membrane 7 times = 7 trans membrane alpha helices.
Only in eukaryotic cells

Question 10

What do G-protein coupled receptors do?

Answer 10

Bind to G proteins - Proteins that bind GTP and GDP
G proteins have 3 subunits - alpha, beta and gamma
Once a protein is bound to the GPCR, the GPCR changes shape, altering / beginning cell functions - cAMP is used as a second messenger to relay messages in the cell - therefore GCPRs are slower than other receptors

Question 11

What are the two types of local signalling in cell communication?

Answer 11

1. Paracrine signalling
   Cell produces a signal that acts on nearby target cells
2. Synaptic signalling
   Similar to paracrine, a chemical is released from a nerve cell through exocytosis which travels across the synapse to its target cell (e.g. a neuron and muscle)

Question 12

What is long distance signalling?

Answer 12

Endocrine (hormonal) signalling = a hormone is released from a cell, then travels in the blood to other cells that have receptors for that specific hormone

Question 13

Explain the 3 stages of cell-cell communication.

Answer 13

1. Reception
   Signal molecule finds a cell with a complementary receptor in its membrane
2. Transduction
   Signalling molecule travels to cells’ interior. It then becomes active and may change shape
3. Response
   Activation of cellular response - I.e. how the cell is impacted by the signalling molecule

Question 14

Describe tyrosine kinase receptors

Answer 14

Another class of cell receptors
Binds to peptide / protein hormones
Ligand binds to it for it to be activated

Question 15

What are steroid receptors?

Answer 15

They are found inside the cell (therefore, intracellular receptors) typically in the nucleus or cytosol.
It then moves into the nucleus, binds to DNA - either activating or deactivating it. It then causes changes to genes by inhibiting transcription or some other way.
Very slow process