Teacher guide

Predict

Many adults drink coffee in the morning to wake up. Coffee has a chemical in it called caffeine. Does the caffeine in coffee give your body energy?

Circle one. Yes / No

Watch

1. Coffee doesn’t give you energyyoutube.com/shorts/qIIaPqW8qkk

Word of the day

Adenosine (uh-DEN-uh-seen). A molecule found in all living cells. In the brain, adenosine builds up while you’re awake and helps signal that you’re tired.

• Your adenoids, at the top of your throat, have the same aden- root.
• Caffeine has the same -ine ending. Its name comes from café, the French word for coffee.

Bonus word. Receptor (rih-SEP-tur). A protein on a cell with a spot, like a seat, that one kind of molecule fits into. The word comes from Latin and is related to the word receive.

Questions

1. Your brain uses energy all day long. Adenosine is a leftover from the brain’s energy use, and it builds up while you are awake. As adenosine builds up, what message does it send your brain?

   Hint. Think about how you feel at the end of a long day.

2. Adenosine sends its message by fitting into receptors on brain cells. In the video, Raven says caffeine is shaped enough like adenosine to sit in the same receptors. What happens to the tired message when caffeine takes adenosine’s seat?

   Circle one. The tired message gets stronger / The tired message gets blocked / The adenosine turns into energy

   Hint. Caffeine fits in the receptor, but caffeine doesn’t send the tired message.

3. In the video, Raven says adenosine keeps building up while caffeine sits in the receptors. What happens when the caffeine finally leaves adenosine’s receptors?

   Hint. Think about all the adenosine that was waiting for a receptor.

4. When you drink coffee, caffeine moves from your small intestine into your blood. Your blood carries caffeine to your brain and your heart. Name two body systems that caffeine travels through or changes.

   Hint. Follow the caffeine from your mouth to your brain. Which body systems move the caffeine along the way?

Exit ticket

Predict

Many adults drink coffee in the morning to wake up. Coffee has a chemical in it called caffeine. Does the caffeine in coffee give your body energy?

Circle one. Yes / No

Watch

1. Coffee doesn’t give you energyyoutube.com/shorts/qIIaPqW8qkk

Word of the day

Adenosine (uh-DEN-uh-seen). A molecule made of adenine joined to the sugar ribose. In the brain, adenosine builds up during waking and signals the need for sleep.

• Your adenoids, at the top of your throat, carry the same aden- root.
• Caffeine has the same -ine ending. Its name comes from café, the French word for coffee.

Bonus words. Receptor (rih-SEP-tur) is a protein on or in a cell that a molecule binds to, starting a change in the cell. The word comes from Latin and is related to receive. Antagonist (an-TAG-uh-nist) is a molecule that binds a receptor and blocks the receptor’s signal. The word comes from the Greek antagōnízesthai, “to contend against.” In a story, the antagonist is the hero’s opponent.

Questions

1. Caffeine is an adenosine receptor antagonist. An antagonist binds a receptor and blocks the receptor’s signal without turning the receptor on. Caffeine gives brain cells no energy. Why does blocking adenosine receptors still make a person feel more alert?

   Hint. Think about what adenosine’s signal does in the brain. What happens when less of adenosine’s signal gets through?

2. Caffeine blocks two kinds of adenosine receptors, A1 and A2A, about equally. In one set of experiments, caffeine still kept mice awake when the mice had no working A1 receptors. Caffeine did not disrupt sleep in mice with no working A2A receptors. Which receptor do the mouse experiments point to for caffeine’s wake-up effect?

   Circle one. A1 / A2A / Both equally

   Hint. Find the mice that slept normally after caffeine. Which receptor were those mice missing?

3. Caffeine is absorbed in the small intestine and carried by the blood. Caffeine binds adenosine receptors in the brain and in organs such as the heart and blood vessels. In a 1978 study, 250 mg of caffeine raised adrenaline in the blood by 207% and raised blood pressure within an hour. Caffeine goes in your mouth and ends up changing both your brain and your heart. How does caffeine get there? Name the body systems at each step.

   Hint. Trace caffeine from the small intestine to the brain and the heart. Which systems carry the caffeine, and which systems respond?

4. In rats and mice, daily caffeine increased the number of adenosine receptors in the brain. How could extra adenosine receptors change what a daily coffee drinker feels when the caffeine wears off?

   Hint. Picture the receptors once caffeine leaves. Which molecule is waiting to bind, and how many places can that molecule bind now?

Claim, evidence, reasoning

Going further: caffeine and energy

1. In a 2013 study, adults took 400 mg of caffeine 6 hours before bed. Use a 5-hour half-life. About how much of the 400 mg dose was still in the body at bedtime?

   Circle one. About 50 mg / About 100 mg / About 175 mg / About 400 mg

   Hint. After 5 hours, half of the 400 mg is left. The sixth hour removes a little more.

2. ATP, short for adenosine triphosphate, carries energy inside cells. Cellular respiration breaks down food and oxygen and forms new compounds that carry energy, such as ATP. Brain cells make adenosine when brain cells use up ATP. Why can’t caffeine give cells energy the way food does?

   Hint. Follow where the energy in ATP comes from. Then think about what caffeine does at the receptor.

Exit ticket

Watch

1. Coffee doesn’t give you energyyoutube.com/shorts/qIIaPqW8qkk

Word of the day

Adenosine (uh-DEN-uh-seen). A nucleoside formed from the purine base adenine and the sugar ribose. In the brain, extracellular adenosine rises during waking and is proposed as a signal of sleep need.

• Your adenoids, at the top of your throat, carry the same aden- root.
• Caffeine has the same -ine ending. Its name comes from café, the French word for coffee.

Bonus word. Antagonist (from the Greek antagōnízesthai, “to contend against”) describes a substance that interferes with the action of another substance, especially by binding and blocking its receptor. Caffeine is an adenosine receptor antagonist.

Predict

1. The study below gave adults 400 mg of caffeine 6 hours before bed and measured their sleep with a headband monitor. Make your guess before you read the paper, and give your reason in one sentence. How many minutes of sleep do you think 400 mg of caffeine, taken 6 hours before bed, cost compared with a placebo night?

   Hint. In adults, half of a caffeine dose leaves the body every 3 to 7 hours. How much of the dose would still be in the body at bedtime?

Read the paper

Drake, Roehrs, Shambroom and Roth, “Caffeine effects on sleep taken 0, 3, or 6 hours before going to bed,” Journal of Clinical Sleep Medicine, 2013. The paper is free to read.

Twelve healthy adults, ages 19 to 48, who regularly use caffeine slept at home for four test nights. On each test day they swallowed three pills, at 6, 3 and 0 hours before their usual bedtime. On three of the nights, one pill held 400 mg of caffeine and the other two were placebos. On the fourth night, all three pills were placebos. Neither the participants nor the researchers knew which pill held caffeine. Each morning, participants recorded their sleep in a diary (Table 2 of the paper), and a headband monitor that records brain waves measured their sleep each night (Table 3). The table below gives the mean total sleep time from both tables.

1. Quantitative reasoning Fill in the last column of the table. Subtract each caffeine row from placebo, then multiply by 60. In Table 3, all three caffeine nights differed from placebo (p < 0.05). How many minutes of sleep did caffeine cost at each time? Did taking caffeine earlier in the evening shrink the loss?

   Hint. Compare your three answers with one another, then with 60 minutes.

2. Process of science In the diaries, caffeine taken 6 hours before bed cut sleep by 41 minutes, a difference that was not statistically significant (p = 0.08). The monitor showed a larger loss on the same nights. Why might the diary and the monitor disagree at 6 hours? Which features of the study design make the monitor result more convincing?

   Hint. Think about what a sleeping person can notice. Then look at the pills, the placebo night and who knew which pill held caffeine.

3. Structure and function Caffeine is a purine alkaloid, and adenosine contains adenine, a purine base. Caffeine binds A1 and A2A adenosine receptors with roughly equal affinity without activating the receptors. In adults, caffeine’s half-life runs from 3 to 7 hours. Use a 5-hour half-life. About how much of the 400 mg dose remained at bedtime in the 6-hour condition? How does caffeine’s structure explain why that amount still shortened sleep?

   Hint. Remaining caffeine = 400 × (1/2)^(6 ÷ 5). Then think about what the adenosine that accumulated during the day can do at a blocked receptor.

4. Pathways and transformations of energy and matter Adenosine forms when brain cells break down ATP, the molecule that carries energy in cells. The liver breaks caffeine down mainly with the enzyme CYP1A2. Caffeine’s main breakdown product, paraxanthine, also binds A1 and A2A receptors in animal studies. Why does caffeine change how tired a person feels without adding energy to cells? How could paraxanthine change how long caffeine’s effect lasts?

   Hint. Follow the matter. Where does adenosine come from, and what does the liver turn caffeine into?

Exit ticket