Communication within Multicellular Organisms Flashcards Preview

Advanced Higher Biology: Unit 1- Cells And Proteins > Communication within Multicellular Organisms > Flashcards

Flashcards in Communication within Multicellular Organisms Deck (27)
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1
Q

What are the 2 types of signalling systems cells have?

A

extracellular and intracellular

2
Q

What do signalling systems ensure each cell knows?

A

its

  • position
  • role
  • involvement in activities (cell growth, division & development)
3
Q

What are receptor molecules of target cells?

A

proteins with a binding site for a signal molecule.

4
Q

What does binding of receptor molecules do?

A

Binding changes the conformation of the receptor and this can alter the response of the cell.

5
Q

What do different cell types produce?

A

Different cell types produce specific signals which can only be detected and responded to by cells with the specific receptor. In a multicellular organism, different cell types may show a tissue-specific response to the same signal.

6
Q

Why can the receptor molecules of hydrophobic signals be found within the nucleus?

A

Hydrophobic signals can pass through membranes so their receptor molecules can be within the nucleus. They are able to do this because the tails of the phospholipids in the plasma membrane are also hydrophobic and allow the molecules to pass across.

7
Q

What can hydrophobic signals directly influence?

A

Hydrophobic signals can directly influence transcription of genes

8
Q

Give examples of hydrophobic signalling molecules?

A

The thyroid hormone thyroxine and steroid hormones e.g. testosterone, oestrogen and progesterone.

9
Q

Describe thyroxine.

A

Thyroxine is a hydrophobic hormone produced by the thyroid gland. It is involved in regulating the rate of metabolism. Because it is hydrophobic, it can cross the plasma membrane of a cell and interact with proteins inside the cell.

10
Q

Describe what occurs when thyroxine is not present.

A

Thyroxine receptor binds to DNA
Transcription of Na/K-ATPase gene is inhibited
Less Na/K-ATPase is transcribed
Metabolic rate reduces

11
Q

Describe what occurs when thyroxine is present.

A

Thyroxine binds to thyroxine receptor protein
Receptor undergoes a conformational change, meaning it can no longer bind to DNA
Gene for Na/K-ATPase is transcribed
Metabolic rate increases

12
Q

What are the receptor proteins for steroid hormone?

A

transcription factors.

13
Q

What is a transcription factor and what does it do?

A

A transcription factor is a protein which binds to DNA and controls the rate of transcription. Transcription factors can enhance or block the binding of RNA polymerase to specific genes, thereby controlling whether the gene is transcribed or not.

14
Q

Describe the action of testosterone? (6)

A

1) Lipid soluble so diffuses into the cells through the plasma membrane
2) Target cells have a specific hormone receptor protein in the cytoplasm or nucleus
3) Testosterone binds the hormone receptor protein to form an activated complex
4) Conformational change makes the hormone receptor complex into an active gene transcription factor (gene regulatory protein)
5) The complex binds to specific DNA sites and stimulates gene transcription
6) Proteins are synthesised that support sperm production and male sexual characteristics

15
Q

Give 2 examples of hydrophilic signalling molecules.

A

peptide hormones and neurotransmitters.

16
Q

What do hydrophilic signalling molecules require? Why?

A

Hydrophilic signals require receptor molecules to be at the surface of the cell because they are not capable of passing across the hydrophobic plasma membrane.

17
Q

What are the 3 stages of signal transduction?

A

Reception
Transduction
Response

18
Q

Describe reception for hydrophilic signalling molecules.

A

Transmembrane receptors change conformation when the ligand binds outside the cell; the signal molecule does not enter the cell but the signal is transduced across the membrane of the cell.

19
Q

Describe transduction for hydrophilic signalling molecules.

A

This is the transfer of the molecular signal within the cell. It is a cascade of events, at each stage, the signal is transduced or changed into a different form.

Several molecules are involved in signal transduction pathways:

  • Protein kinases
  • Cyclic AMP
  • Calcium ions.
20
Q

Describe response for hydrophilic signalling molecules.

A

Signal transduction pathway eventually leads to a response.

Such a response might include:

  • Opening/closing of an ion channel in plasma membrane
  • Rearrangement of cytoskeleton
  • Synthesis/degradation of enzymes or other proteins
  • Changes in gene expression.
21
Q

What are three types of signal transduction mechanisms?

A

Ion-channel linked receptors
Enzyme linked receptors
G-protein Coupled receptors

22
Q

Describe ion-channel linked receptors.

A

These are found on the surface of muscles and nerves and transduce a signal in the form of a neurotransmitter into an electrical voltage. Binding of the signal ligand causes a conformational change, ‘opening’ the channel.

23
Q

Describe enzyme linked receptors.

A

An enzyme linked receptor binds an extracellular signal molecule switching on an enzyme activity, usually a kinase, on the other side of the membrane. This kinase activity causes the phosphorylation of other intracellular proteins. These are found in all cells.

24
Q

Describe G-protein coupled receptors.

A

GPCRs activate the G-protein (G) in response to the signal binding. The G-protein acts on a target protein (T), which maybe an enzyme or an ion-channel protein. This generates the intracellular response.

25
Q

What does a G-protein act as?

A

a switch that is either on or off, depending on which of the two guanine nucleotides (GDP or GTP) is attached.

26
Q

Describe the switch function of G-proteins

A

Initially, when GDP is bound, the G-protein is inactive. On binding of a hydrophilic hormone to the receptor, GTP replaces GDP in the G-protein, and the G-protein becomes active.
The active G-protein stimulates an enzyme, leading to a response in the cell.

27
Q

Describe the sequence of events for GPCRs.

A
  1. When a hormone binds to the extracellular protein it changes to the active form. This starts a chain reaction called a signal transduction pathway.
  2. The receptor protein activates the G-protein so that it replaces GDP with GTP (guanosine triphosphate).
  3. The activated G-protein moves along the membrane and activates the enzyme.
  4. The activated enzyme releases hundreds of second messenger molecules.
  5. Second messenger molecules are small molecules (usually cyclic AMP). They activate the next step in the reaction.
  6. Cyclic AMP phosphorylates and activates kinase enzymes.
  7. Kinase enzymes phosphorylate and activate other kinase enzymes and so on until the final enzyme in the chain is activated. This enzyme produces a change in the cell.
  8. At each step the number of the activated enzymes increases. This is called signal amplification.