Which element do proteins contain that carbohydrates and lipids do not?
Reveal answer
Nitrogen (some proteins also contain sulfur).
Key words: nitrogen
2(c) BIOLOGICAL MOLECULES · RECALL
2.7 Elements in carbohydrates, proteins and lipids
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What is meant by the term element?
Reveal answer
A substance made from only one type of atom.
Key words: element
What is meant by the term atom?
Reveal answer
The smallest particle of an element that retains its chemical properties.
Key words: atom
What is meant by the term molecule?
Reveal answer
Two or more atoms joined by covalent bonds.
Key words: molecule
What is meant by the term compound?
Reveal answer
A substance containing atoms of two or more elements chemically bonded.
Key words: compound
Elemental composition at a glance: for Carbohydrates, give the core elements and the precision note.
Reveal answer
Core elements: Carbon, hydrogen and oxygen (CHO). Precision note: Elemental composition alone does not distinguish sugars from starch.
Key words: Carbohydrates
Elemental composition at a glance: for Lipids, give the core elements and the precision note.
Reveal answer
Core elements: Carbon, hydrogen and oxygen (CHO). Precision note: Usually contain proportionally less oxygen than carbohydrates.
Key words: Lipids
Elemental composition at a glance: for Proteins, give the core elements and the precision note.
Reveal answer
Core elements: Carbon, hydrogen, oxygen and nitrogen (CHON). Precision note: Some proteins also contain sulfur from particular amino acids.
Key words: Proteins
True or false, and why? “All biological molecules are huge polymers.”
Reveal answer
False. Many are small, including glucose and amino acids; lipids are not true polymers of repeating monomers.
True or false, and why? “Only carbohydrates contain carbon.”
Reveal answer
False. All three groups here contain carbon, hydrogen and oxygen.
True or false, and why? “Proteins contain only CHON.”
Reveal answer
False. CHON is the core specification answer; some amino acids and proteins also contain sulfur.
True or false, and why? “Knowing the elements tells you the molecule’s function.”
Reveal answer
False. Arrangement, bonding and three-dimensional structure are also essential.
Which three elements are found in every carbohydrate?
Reveal answer
Carbon, hydrogen and oxygen.
Key words: carbon · hydrogen · oxygen
A food molecule contains only carbon, hydrogen and very little oxygen. Which food group is it most likely to be?
Reveal answer
A lipid (fats and oils contain proportionally less oxygen than carbohydrates).
Key words: lipid
Why must a plant absorb nitrate ions to make proteins?
Reveal answer
Proteins contain nitrogen → amino acids need nitrogen → plants take it up from the soil as nitrate ions.
Key words: nitrogen · nitrate