U1: KA4 Communication and signalling

Question 1

Multicellular organisms signal between cells using what?

Answer 1

Extracellular signalling molecules.

Question 2

What are examples of extracellular signalling molecules?

Answer 2

Steroid hormones, peptide hormones and neurotransmitters.

Question 3

What are receptor molecules of target cells?

Answer 3

Proteins with a binding site for specific signal molecules.

Question 4

What initiates a response within the cell?

Answer 4

Binding changes conformation of receptor

Question 5

Why may signalling molecules have different effects on different target cell types?

Answer 5

Differences in intracellular signalling molecules and pathways that are involved.

Question 6

Hydrophobic signalling molecules can…

Answer 6

Diffuse directly through phospholipid bilayers of membranes and so bind to intercellular receptors.

Question 7

The receptors of hydrophobic signalling molecules are transcription factors. What are transcription factors?

Answer 7

Proteins that when bound to DNA either stimulate or inhibit initiation of transcription. They can enhance or block the binding of RNA polymerase to specific genes thereby controlling whether the gene is transcribed and therefore expressed.

Question 8

Examples of Hydrophobic signals are?

Answer 8

Thyroxine
Steroid hormones - testosterone and oestrogen

Question 9

Steroid hormones bind to specific receptors in the cytosol or ……

Answer 9

The nucleus forming hormone-receptor complex. The hormone-receptor complex moves to the nucleus where it binds to specific sites on DNA.

Question 10

The specific DNA sequences that the hormone-receptor complex binds to are called?

Answer 10

Hormone response elements (HREs)

Question 11

Binding at HREs influences what?

Answer 11

Rate of transcription with each steroid hormone affecting the gene expression of many different genes.

Question 12

Hydrophilic signalling molecules bind to …..

Answer 12

Transmembrane receptors and do not enter the cytosol.

Question 13

Why do hydrophilic signals not enter cytosol?

Answer 13

Because they are not capable of passing across the hydrophobic plasma membrane.

Question 14

When do Transmembrane receptors change conformation?

Answer 14

When ligand binds to extracellular face; the signal molecule does not enter the cell.

Question 15

What happens after the transmembrane receptor changes conformation?

Answer 15

Signal is transduced across plasma membrane, they act as signal transducers by converting the extracellular ligand-binding event into intracellular signals, which alters the behaviour of the cell.

Question 16

What do transduction hydrophilic signals often involve?

Answer 16

G-proteins
Cascade of phosphorylation by kinase enzymes.

Question 17

How do G-proteins work?

Answer 17

Relay signals from activated receptors (receptors that have bound a signalling molecule) to target proteins such as enzymes and ion channels.
Enzymes then catalyse reactions in cell
Ion channels will then either open or close to control ion movement.

Question 18

Phosphorylation cascades involve a series of events with?

Answer 18

One kinase activating the next

Question 19

Phosphorylation cascades can result
In?

Answer 19

The phosphorylation of many proteins as a result of the original signaling event.

Question 20

Phosphorylation allows more than one what?

Answer 20

Intracellular signalling pathway to be activated.

Question 21

What 2 hormones control levels of glucose?

Answer 21

Insulin
Glucagon

Question 22

Features of insulin?

Answer 22

Made when there is increase in blood glucose concentration
Made by cells in the pancreas
Hydrophilic peptide hormone
Allows fat tissue and skeletal muscles to absorb glucose from the bloodstream.

Question 23

How does glucose pass into the cells?

Answer 23

Travelling through a transporter protein called GLUT4 by facilitated diffusion.

Question 24

Describe type 1 diabetes.

Answer 24

Failure to produce insulin in pancreas. Treated with regular injections throughout the day

Question 25

Describe type 2 diabetes?

Answer 25

Caused by a loss of insulin receptor function usually associated with obesity.
Exercise triggers recruitment of GLUT4 so can improve uptake of glucose to fat and muscle cells.

Question 26

All cells have an electrical potential difference across there plasma membrane this voltage is called?

Answer 26

Membrane potential - the difference in electrical charge on the two sides of the membrane.

Question 27

What is the resting point?

Answer 27

Membrane potential of a neuron that is not transmitting signals. State where there is no net flow of ions.

Question 28

Nerve transmission is a ….

Answer 28

Wave of depolarisation of the resting potential of a neuron.

Question 29

Depolarisation is a change in?

Answer 29

Membrane potential to a less negative value inside.

Question 30

What is an action potential?

Answer 30

If change in membrane potential is big enough it may trigger action potential. Action potential is a wave of electrical excitation along the neurons plasma membrane

Question 31

Neurotransmitters initiate a response by binding to their receptors at a ……. Neurotransmitter receptors are …….

Answer 31

Synapse
Ligand-gated ion channels