Cell Communication and Cell Signaling Student Learning Guide

1. Steroid hormones (like testosterone and estrogen) regulate gene expression

In the previous tutorials, our discussion of hormones and signalling pathways has focused on activating dormant enzymes in the cytoplasm. This allows for quick responses, such as quickly breaking down glycogen into glucose for the fight or flight response. That’s why hormones are key components of homeostasis: the dynamic maintenance of optimal internal conditions, despite changes in the external environment.

Steroid hormones can have longer term effects on cells and organisms, and these effects involve the regulation of genes, switching them on and off, which changes the proteins a cell produces. Just think, for a moment, about the effect steroid hormones like testosterone and estrogen had on your body when you went through puberty. These hormones brought about long term changes in your body’s form (everything from the Adam’s apple in males to breasts in females) and function (sexual maturation in both sexes, the start of ovulation and menstruation in females).

How do steroid hormones work to activate genes? Let’s take a look at two of the most famous steroid hormones.

[qwiz qrecord_id=”sciencemusicvideosMeister1961-testosterone and estrogen (M11)”]

[h]Testosterone and estrogen

[i]

Estrogen

Testosterone

[q]How would you classify these hormones?

Estrogen

Testosterone

[c]carbohydrate

[f]No: carbohydrates are polymers of monosaccharides (simple sugars). No sugars are shown above.

[c*]lipid

[f]Excellent: estrogen and testosterone are lipids.

[c]protein

[f]No: proteins are polymers of amino acids, and have very complex three dimensional shapes. Make another choice next time.

[c]nucleic acid

[f]No: nucleic acids are polymers of nucleotides. Make another choice next time.

[q]In terms of their interaction with water, molecules like estrogen and testosterone are

Estrogen

Testosterone

[c*]Hydrophobic

[f]Yes. Despite the hydroxyl groups, the big fused carbon rings shown above are going to make this molecule non-polar, and therefore hydrophobic.

[c]Hydrophilic.

[f]No. Notice the four fused carbon rings that make up the bulk of these molecules. How do you think these rings are going to interact with water?

[x]So, note these two key ideas. Steroid hormones are lipids, and they’re hydrophobic. That sets up the way they’ll interact with cell membranes, which you’ll learn about below.

[/qwiz]

 

A general scheme for steroid hormone action is shown at right. The first thing to note is that because steroid hormones (“F”) are lipids (and therefore non-polar and hydrophobic), they, can pass right through the cell’s phospholipid bilayer (“B”) and diffuse into the cytoplasm (“C”).

Floating in the cytoplasm of the cells that are the targets for a steroid hormone are mobile receptors (“G”). The hormone binds with the receptor forming a receptor-hormone complex (“H”). This complex can pass through the nuclear membrane (“D”) at a nuclear pore (“E”), where it binds with DNA (“J”) and acts as a transcription factor (“I”).

Transcription factors cause genes to be expressed. That involves production of messenger RNA (“K”). The RNA diffuses out of the nucleus and into the cytoplasm. There, the messenger RNA is read by a ribosome (“L”), and then transcribed into protein (“M”). And to connect this back to puberty, this protein is what the changes in your body’s form and function were all about. Protein is the tissue that makes up the increased muscle mass that you gained if you’re a male. Protein is what makes up the skin and underlying structure of breast tissue if you’re female.

2. Some Water-Soluble Hormones have Signal Transduction Pathways that Regulate Genes

While steroid hormones are typically associated with gene regulation, there are some water soluble (polar) hormones that also work though regulating genes.

One example of this is growth hormone, which is secreted by the pituitary gland, in the brain. As its name indicates, growth hormone stimulates cell reproduction, and plays a key role in animal development. Click here to read more about growth hormone on Wikipedia.

Composed of 191 amino acids, growth hormone is much too big and polar to pass through the phospholipid bilayer. Consequently, it works through a mechanism that’s similar to what’s shown at left (though the actual pathway for growth hormone is much more complicated).

The process starts with the hormone being released from a vesicle in the cell of a hormone-producing gland (“1”). The hormone diffuses from the extracellular space into the bloodstream (“2”) and then circulates throughout the body, diffusing out of the bloodstream (“3”) and binding with target cells that have a complementary receptor (“4”). After binding with the receptor, the message needs to be transduced through a signal transduction pathway (“5”) in the cytoplasm (“B”). The last molecule in this pathway (“6”) diffuses into the nucleus (“C”) through a nuclear pore, and then interacts with the cell’s DNA (“7”), either activating or deactivating genes.

3. Quiz: Hormones and Gene Regulation

[qwiz random=”true” qrecord_id=”sciencemusicvideosMeister1961-Hormones and Gene Regulation (M11)”]

[h] Hormones and Gene Regulation

[i]

[q json=”true” dataset_id=”SMV_Hormones and Gene Regulation (cell communication)|6229b971a1fff” question_number=”1″] In the diagram below, which letter represents the cell membrane?

[textentry single_char=”true”]

[c*] B

[f] Yes. “B” represents the membrane.

[c] *

[f] No. Here’s a hint. The signal comes from outside the cell, and, in the case of a steroid hormone, diffuses through the membrane. If “A” represents the cell exterior, which letter represents the membrane?
[!!!]+++question 53++++++[/!!!!]

[c] Enter letter

[q json=”true” dataset_id=”SMV_Hormones and Gene Regulation (cell communication)|6223c21329bff” question_number=”2″] In the diagram below, which letter could represent a steroid hormone (such as testosterone or estrogen)?

[textentry single_char=”true”]

[c*] F

[f] Yes. “F” represents a steroid hormone.

[c] *

[f] No. Here’s a hint. The signal comes from outside the cell, then diffuses through the membrane. If “A” represents the cell exterior, which letter could represent the signal that’s about to enter into the cell?
[!!!]+++question 54++++++[/!!!!]

[c] Enter letter

[q json=”true” dataset_id=”SMV_Hormones and Gene Regulation (cell communication)|621e5fb7aa7ff” question_number=”3″] In the diagram below, which letter could represent a cytoplasmic receptor (before it binds with the signal)?

[textentry single_char=”true”]

[c*] G

[f] Yes. “G” represents a cytoplasmic receptor.

[c] *

[f] No. Here’s a hint. The signal comes from outside the cell, then diffuses through the membrane, then binds with a cytoplasmic receptor. If “F” represents the signal, then what inside the cell could represent an empty receptor that the signal can bind with?
[!!!]+++question 55++++++[/!!!!]

[c] Enter letter

[q json=”true” dataset_id=”SMV_Hormones and Gene Regulation (cell communication)|6217d356393ff” question_number=”4″] In the diagram below, which letter shows a receptor/hormone complex interacting with DNA?

[textentry single_char=”true”]

[c*] I

[f] Yes. “I” shows a receptor/hormone complex interacting with DNA.

[c] *

[f] No. Here’s a hint. The signal comes from outside the cell, then diffuses through the membrane, then binds with a cytoplasmic receptor, which then diffuses into the nucleus where it interacts with DNA. Find DNA inside the nucleus, figure out what the receptor is, and you’ll have your answer.
[!!!]+++question 56++++++[/!!!!]

[c] Enter letter

[q json=”true” dataset_id=”SMV_Hormones and Gene Regulation (cell communication)|6211b6b702bff” question_number=”5″] In the diagram below, which letter shows RNA that’s just been transcribed as a result of the hormone/receptor complex having interacted with the cell’s DNA?

[textentry single_char=”true”]

[c*] K

[f] Yes. “K” shows RNA that’s just been transcribed as a result of the hormone/receptor complex having interacted with the cell’s DNA.

[c] *

[f] No. Here’s a hint. “H” shows a receptor/hormone complex in the cytoplasm. Now, find DNA in the nucleus. Now, find a single stranded molecule that’s been produced as a result of the interaction between the receptor/hormone complex and DNA, and you’ll have your answer.
[!!!]+++question 57++++++[/!!!!]

[c] Enter letter

[q json=”true” dataset_id=”SMV_Hormones and Gene Regulation (cell communication)|620c545b837ff” question_number=”6″] In the diagram below, which letter shows a nuclear pore?

[textentry single_char=”true”]

[c*] E

[f] Yes. “E” shows a nuclear pore.

[c] *

[f] No. Here’s a hint. Nuclear pores are passageways for materials to enter and leave the nucleus. Find the nuclear membrane, and then locate a nuclear pore.
[!!!]+++question 58++++++[/!!!!]

[c] Enter letter

[q json=”true” dataset_id=”SMV_Hormones and Gene Regulation (cell communication)|6206a77e87bff” question_number=”7″] In the diagram below, which letter shows a ribosome?

[textentry single_char=”true”]

[c*] L

[f] Yes. “L” shows a ribosome.

[c] *

[f] No. Here’s a hint. Ribosomes translate the messages in RNA into protein, an activity that occurs in the cytoplasm. If “K” is RNA is the nucleus, then what letter could indicate a ribosome translating that RNA into protein?
[!!!]+++question 59++++++[/!!!!]

[c] Enter letter

[q json=”true” dataset_id=”SMV_Hormones and Gene Regulation (cell communication)|6200faa18bfff” question_number=”8″] In the diagram below, which letter shows a protein that’s produced as the cellular response to the steroid hormone signal?

[textentry single_char=”true”]

[c*] M

[f] Yes. “M” shows a protein that’s being synthesized as a result of the hormone signal that diffused into the cell, then bound with a receptor and activated a gene, ultimately resulting in this protein’s translation.

[c] *

[f] No. Here’s a hint. For steroid hormones, the cellular response is the production of a protein. If “L” represents a ribosome, the cell’s protein factory, then what could represent a protein that this ribosome is synthesizing?
[!!!]+++question 60++++++[/!!!!]

[c] Enter letter

[q json=”true” dataset_id=”SMV_Hormones and Gene Regulation (cell communication)|61fb98460cbff” question_number=”9″] In the diagram below, “I” represents [hangman].

[c] reception

[f] Yes, “I” represents reception.
[!!!]+++question 61++++++[/!!!!]

[q json=”true” dataset_id=”SMV_Hormones and Gene Regulation (cell communication)|61f5c62852bff” question_number=”10″] In the diagram below, “II” represents [hangman].

[c] transduction

[f] Yes, “I” represents transduction.
[!!!]+++question 62++++++[/!!!!]

[q json=”true” dataset_id=”SMV_Hormones and Gene Regulation (cell communication)|61f0194b56fff” question_number=”11″] In the diagram below, “III” (and “4”) represents a cellular [hangman].

[c] response

[f] Yes, “III” represents the cellular response.

[!!!]+++question 64++++++[/!!!!]
[q json=”true” dataset_id=”SMV_Hormones and Gene Regulation (cell communication)|61ea6c6e5b3ff” question_number=”12″] The diagram below shows a hormone that would be chemically classified as a [hangman].

[c] steroid

[f] Yes, The diagram is showing how a steroid hormone affects its target cell.

[q json=”true” dataset_id=”SMV_Hormones and Gene Regulation (cell communication)|61e4e4d21dbff” question_number=”13″] In the diagram below, which number or letter shows a hormone in a vesicle in a hormone secreting cell?

[textentry single_char=”true”]
[c*] 1

[f] Yes. “1” shows a hormone in a vesicle in a hormone secreting cell.

[c] *

[f] No. Here’s a hint. Vesicles are membrane-enclosed bubbles that often contain a substance that a cell is about to export. Which number is near something that could fit that description?

[c] Enter letter

 

[q json=”true” dataset_id=”SMV_Hormones and Gene Regulation (cell communication)|61df12b463bff” question_number=”14″] In the diagram below, which number or letter shows a signal transduction pathway?

[textentry single_char=”true”]
[c*] 5

[f] Yes. “5” shows a signal transduction pathway.

[c] *

[f] No. Here’s a hint. The signal transduction pathway occurs in the cytoplasm, which is region “b.” In this case, the pathway is taking a message from the membrane into the nucleus.

[c] Enter letter

[q json=”true” dataset_id=”SMV_Hormones and Gene Regulation (cell communication)|61d65787ccbff” question_number=”15″] What number or letter below shows a molecule from a signaling pathway interacting with DNA?

[textentry single_char=”true”]
[c*] 6

[f] Yes. “6” shows a protein kinase interacting with DNA.

[c] *

[f] No. Here’s a hint. DNA is inside the nucleus, which is region “c.”

[c] Enter letter

[q json=”true” dataset_id=”SMV_Hormones and Gene Regulation (cell communication)|61d0f52c4d7ff” question_number=”16″] Because of the way the hormone is binding with a membrane receptor, we can conclude that it must be [hangman].

[c] polar

 

[q json=”true” dataset_id=”SMV_Hormones and Gene Regulation (cell communication)|61ca8e0b9a7ff” question_number=”17″] Number “5” below is a signal [hangman] pathway.

[c] transduction

[q json=”true” dataset_id=”SMV_Hormones and Gene Regulation (cell communication)|61c1d2df037ff” question_number=”18″] The diagram below shows how a hormone circulates everywhere in the body, but only has an effect in [hangman] cells.

[c] target

[x]

[restart]

[/qwiz]

 Next Steps

This tutorial ends this series of tutorial about cell signaling. To pull it all together, take this comprehensive quiz about everything you’ve learned in this module. Then write up a short summary in your student learning guide. Then,