Components of the membrane. Module 1 Membranes 1.1.9 Communication and cell signalling.

Components of the membrane

Module 1Membranes

1.1.9 Communication and cell signalling

Cell signallingLearning Objectives

• Explain the role of cell signalling and membrane-bound receptors

Success Criteria• Explain the term cell

signalling (Grade D – C)

• Explain the role of membrane-bound receptors as sites where hormones and drugs can bind(Grade C –B)

• Describe examples of hormones and drugs as messenger molecules (Grade B – A)

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What is cell signalling?

Cells need to communicate with each other to control processes inside the body and to respond to changes in the environment. This is known as cell signalling.

Cells can signal to each other by direct contact or via messengers such as neurotransmitters and hormones.

However, most messengers are unable to directly cross the membrane and must bind to membrane-bound receptors.

1.Cell signalling starts when one cell releases a messenger molecule (hormone).

2.Molecule travels to another cell (target cell), it’s detected because it binds to a receptor (complementary shape) on it’s cell membrane.

3. The binding triggers a change in the cell (series of chemical signals is set off)


What are transmembrane receptors?

Many membrane-bound receptors are integral proteins, and are often called transmembrane receptors. These receptors have three main parts, or domains.

Extracellular domain: the part that sticks out of the cell and to which the messenger binds.

Transmembrane domain: the part that is buried within the membrane.

Intracellular domain: the part that sticks into the cell and which relays the signal to the cell by signal transduction.


Types of transmembrane receptors

G protein-coupled receptors, such as those for dopamine and serotonin (neurotransmitters), adrenaline and noradrenaline (hormones), and chemicals involved in inflammation.

Ligand-gated ion channels, such as those for the neurotransmitter acetylcholine.

There are many types of transmembrane receptors, including:

Metabotropic receptors, such as those for the neurotransmitter glutamate.


Transmembrane receptors


Exam practice

1)State what is meant by cell signalling.

(1 mark)

2) Explain how cell surface membranes contribute to the process of cell signallingIn your answer you should use appropriate technical terms, spelt correctly

(4 marks)


Hormones as messenger moleculesHormones work by binding to receptors in cell

membranes and triggering a response in the cell

Glucagon – hormone released when there is insufficient glucose in the blood. It binds to receptors on liver cells, causing liver cells to break down glycogen stores

FSH – Hormone released by pituitary gland during the menstrual cycle. It binds to receptors on cells in ovaries, causing an egg to mature for ovulation


Receptors as targets for drug action

Membrane receptors are involved in many diseases, and so these are targets for many medicinal drugs.

By finding out more about how membrane receptors work, scientists can

make new and more effective drugs.

Drugs that bind to receptors and mimic the body’s normal messengers are called agonists. Example is morphine – binds to the same receptor as endorphins also triggering a reduction in pain signals

Drugs that bind to receptors and block the body’s normal messengers are called antagonists. Example is antihistamines – Cell damage causes a release in histamines. Histamines binds to receptors on the surface of other cells causing inflammation. Antihistamines work by blocking histamine receptors, stopping inflammation.


• Task• Using pages 20 – 21• 1. Suggest how flu viruses infect human cells of

the respiratory tract.• 2. Name two target tissues for insulin. Describe

how one of the examples works.• 3. Botulinum toxin binds to the ends of nerves and

prevents them from releasing chemicals that normally cause muscles to contract. There are 8 different botulinum toxins, some stronger than others. Suggest why some of the toxin molecules are more potent than others.

• SA


• SA

1.Attach by surface antigens to a normal cell surface protein receptor found in these cells.

2.Liver cells and muscle tissue cells – increase glucose uptake and rate of respiration in many cells

3.Toxins have different shapes, so will attach more or less strongly to their target membrane proteins


Task

• Complete sheet on exam question June 09 Qu 2 and cell signalling worksheet

• Mark practical beetroot

Plenary - Exam Practice• Figure 4 shows part of a cell-surface membrane.

• (a) Describe two functions of the structure made from the parts labelled X. (2 marks)

• (b) Give one function of the molecule labelled Y. (1 mark)

Answers

• 4 (a) two of the following: • selectively permeable; • allows cell to maintain

different concentrations either side;

• gives flexibility/fluidity; 2

•• (b) (surface/extrinsic protein)

for cell recognition/binding to hormones/identification;

1

• Make sure that you only give two answers rather than a long list – note two in bold!

• The examiner will not choose the correct answers from your list. You must decide which you want to give. You will not be given extra marks and it wastes time.

Components of the membrane. Module 1 Membranes 1.1.9 Communication and cell signalling.

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