4. Cellular signals and apoptosis Part 1

Question 1

List the 6 cellular processes regulated by chemical signalling in multicellular organisms:

Answer 1

• Gene expression
• Metabolism
• Apoptosis
• Reproduction
• Cell communication
• Transport of nutrients and molecules

Question 2

What is gene expression?

Answer 2

Switching genes on and off

Question 3

What is metabolism?

Answer 3

Catabolic (digestion) reactions provide energy for anabolic (synthesis) reactions

Question 4

What is apoptosis?

Answer 4

Programmed cell death

Question 5

What is cell communication?

Answer 5

The coordination of the functioning of a whole organism

Question 6

Where does the transport of nutrients and molecules occur?

Answer 6

Between organelles and across cell membranes

Question 7

Name the 2 integrally related systems involved in communication networks:

Answer 7

• Endocrine system

- Nervous system

Question 8

What does communication rely on in plants?

Answer 8

Chemical signal molecules transferring messages between cells.

Question 9

What does the endocrine system generally regulate? Give some examples:

Answer 9

Activities that require duration rather than speed.

Eg. Water and electrolyte balance, stress, growth and development, reproduction, and circulation

Question 10

What are the endocrine glands? Give some examples of the hormones they produce:

Answer 10

Specialised cells/glands which produce hormones which travel in the blood to target cells that contain the specific receptor for the hormone.
Eg. Insulin, glucagon, adrenaline, oestrogen, and testosterone.

Question 11

What is a hormone and list its 3 types:

Answer 11

Are chemical messengers that:
-Are produced in endocrine glands
-Travel in very low concentrations, in general circulation in the bloodstream, producing a response in their target cells somewhere else in the body (not in the tissue that produces the hormone)
Eg. Steroids, anime, and peptide

Question 12

What is the chemical nature of anime hormones and what are their features?

Answer 12

• Are small molecules structurally related to simple amino acids
• Are water soluble, and travel in the bloodstream but are unable to pass through cell membranes

Question 13

List the 3 main types of signalling:

Answer 13

• Reception
• Transduction
• Induction/response

Question 14

What do steroid hormones consist of and what are they involved in? Give some examples of steroids:

Answer 14

-Are lipids (fats) derived from cholesterol
-Can diffuse through the phospholipid bilayer and bind with an intracellular receptor, because they are non-polar.
-Are long-lasting
-Are involved in transport as they are bound to plasma proteins to make them soluble
Eg. Testosterone, oestrogen

Question 15

What are steroid hormones produced by and why can’t they be stored?

Answer 15

• Produced by the gonads, adrenal cortex, and placenta

- Can’t be stored, so they exit the cell after being produced immediately, by diffusing through membranes

Question 16

Why are steroid hormones slow to create and slow to act?

Answer 16

• Are slow to create, since the enzymes that make the steroids need to be activated or synthesised first
• Are slow to act since steroids usually activate transcription factors (although they can also activate genes)

Question 17

What do peptide/protein hormones consist of, why do they have rapid responses, and what are they involved in? Give some examples of peptides:

Answer 17

-Are chains of amino acids (products of translation) or enzyme-modified amino acids (anime hormones), which are hydrophilic and lipophobic (cannot pass through cell membranes but instead bind to cell membrane receptors).
-Very rapid responses since they are already packaged (can be stored in vesicles for long periods of time)
-Are involved in transport as they dissolve in plasma, and often activate enzymes
Eg. Adrenaline, insulin, and glycogen

Question 18

List and describe the 4 sub-types of the signaling process:

Answer 18

-Stimulus (Protein hormone)
-Receptor (Hormone receptor)
-Effector (Activation of enzymes in cell)
Response (Cell processes change)

Question 19

What is signal transduction?

Answer 19

A chain of events that converts an external signal from a signaling molecule, such as a hormone or neurotransmitter into a specific cellular response.

Question 20

Describe the process of steroid hormone action:

Answer 20

1. Steroid hormone diffuses through the phospholipid bilayer
2. Having entered the cell, it binds to a receptor that is inside the cell (an intracellular receptor)
3. The binding causes a conformation change of the receptor which then typically enters the nucleus and interacts with the DNA, either promoting or inhibiting the transcription of a particular gene

Question 21

What is the role of second messengers in signal amplification? Give an example:

Answer 21

-The second messenger system amplifies the response which explains why hormones are found in such small quantities.
-Occurs with both protein/anime and lipid-based systems
Eg. Cyclic AMP system

Question 22

What are tropisms and list and describe its 2 types:

Answer 22

Are growth responses.

• Positive tropism: Growth towards a stimulus
• Negative tropism: Growth away from the stimulus

Question 23

What are pheromones?

Answer 23

Are chemicals produced and emitted by animals and plants as messengers that affect the behaviour of other individuals of the same species

• Derived from Greek words pherein, to transfer and hormone, to excite
• In many species, they signal readiness to mate or alert others to danger

Question 24

What are cytokines?

Answer 24

Are chemical messengers that coordinate the movement and behaviour of cells and tissues of the immune system.

Question 25

What is the difference between nervous communication (Eg. neurotransmitters) and hormonal communication (Eg. hormones)?

Answer 25

Hormonal communication is:

• Slower
• Sustained for longer
• Less specific
• Transmitted chemically (whereas nervous communication is both electrical and chemical)

Question 26

Are hormones specific?

Answer 26

• They are very specific to the receptors on the surface of their target cells.
• Only cells with a receptor for that hormone will respond to the hormone.
• However, when we sat that hormonal responses are less specific, it is because if a hormone affects skeletal muscle cells, it is likely to affect all skeletal muscle cells as they will all have the receptor specific to that hormone.
• Nervous messages, however, may stimulate a response in a single skeletal muscle, and so are more specific

Question 27

Give an example of a plant growth regulator (plant hormone):

Answer 27

• Ethylene causes ripening of fruit and development of lowers.
• When one fruit ripens, it releases ethylene, which binds to receptors on the surface of cells of unripe fruit.
• This signal is transduced in such a way that it stimulates the ripening of that fruit.