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Why Does Life Need Both DNA and RNA? (DNA vs RNA Animation)

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Every living cell uses both DNA and RNA. This video goes through the five differences between them: three in the chemistry (the sugar, the strands, the letters) and two in what that chemistry is for (how long each lasts, and the job each does), and why each difference fits its job.

The video is coming soon to the channel.

Vocabulary

In the order the video explains them.

DNA (deoxyribonucleic acid) 0:57
The cell's permanent record of its genes: kept for the cell's whole life and handed on when it divides. Its sugar is deoxyribose.
RNA (ribonucleic acid) 0:57
The cell's working copy of a gene's message, written when needed and broken down after use; some RNAs fold into shapes that do chemical work. Its sugar is ribose.
Nucleotide 1:09
The building block of DNA and RNA: a sugar, a phosphate and a base (the letter). Nucleotides join into a chain.
Base 1:09
The part of a nucleotide that carries the information: the letter (A, G, C, and T in DNA or U in RNA).
Ribose 1:16
RNA's sugar. It carries an OH group (an oxygen and a hydrogen) on its 2′ carbon.
2′ carbon ("two prime") 1:16
The second carbon of the sugar ring. The prime mark (′) numbers the sugar's carbons, to tell them apart from the atoms of the base.
OH group (hydroxyl) 1:16
An oxygen bonded to a hydrogen. On RNA's 2′ carbon it sits beside the link to the next nucleotide and can attack it, cutting the chain.
Deoxyribose 1:25
DNA's sugar: ribose missing the oxygen on its 2′ carbon ("deoxy" = without oxygen). The D in DNA.
Phosphate 1:34
The part of a nucleotide that links one sugar to the next, forming the chain's backbone.
Alkali 1:44
A strongly basic solution, such as lye. RNA falls apart in it; DNA's links hold.
Base pairing 2:04
Letters on two strands pairing across: A with T (or U in RNA), G with C.
Double helix 2:04
The shape of DNA's two paired strands, wound around each other.
Single strand 3:21
One chain with no partner strand. RNA is usually single stranded: it is written from one of a gene's two strands and is not copied to keep.
Thymine (T) 3:32
DNA's fourth letter. It is uracil with one extra methyl group, and it pairs with A.
Uracil (U) 3:32
RNA's fourth letter, in place of thymine. It pairs with A. In DNA, a U usually means a damaged cytosine.
Methyl group 3:42
One carbon with three hydrogens (CH₃). The extra piece that makes thymine out of uracil.
Cytosine (C) 4:41
One of the four letters in both DNA and RNA; it pairs with G.
Amino group 4:41
A nitrogen with hydrogens (NH₂). When water knocks it off a cytosine and leaves an oxygen, the cytosine becomes uracil.
Mismatch 5:00
Two letters across from each other that are not partners, such as a U across from a G.
Mutation 5:23
A change in the DNA's sequence that is kept and copied: here, a C-G pair that has become a T-A pair.
Repair enzyme (uracil-DNA glycosylase) 5:33
An enzyme that slides along DNA hunting for uracil, flips it out into a pocket and cuts the base off its sugar, leaving the backbone whole; other enzymes then put back a C.
Nucleus 7:09
The compartment of a plant or animal cell where most of its DNA is kept.
Ribosome 8:25
The machine that builds every protein. It is made of RNA and protein, but the spot where it joins amino acids together is RNA alone.
Amino acid
The building block of proteins; the ribosome joins amino acids into a chain.
RNA world
The idea, held by many biologists, that early life ran on RNA, which can both carry information and do chemistry, and that DNA evolved later as a safer place to keep the genes.

Study frame

The whole picture in one labelled frame, to save or print.

The finished table of the five differences between DNA and RNA: sugar, strands, letters, life span and job

Review questions

  1. Which carbon of the sugar carries the extra oxygen in RNA, and why does that oxygen make RNA less stable than DNA?

    Answer

    The 2′ carbon. Its OH group sits next to the link to the next nucleotide and can attack the phosphate, cutting RNA's own chain. DNA's sugar lacks that oxygen, so its chain is far tougher.

  2. Why can a damaged letter in DNA be repaired accurately?

    Answer

    DNA has two paired strands, so every letter has a partner across from it. The partner strand shows which letter belongs at the damaged spot.

  3. What does cytosine become when it loses its amino group, and what happens if the damage is not repaired before the DNA is copied?

    Answer

    It becomes uracil, which pairs with A instead of G. After two rounds of copying, the original C-G pair has become a T-A pair: a mutation.

  4. What is the leading idea for why DNA uses T instead of U?

    Answer

    If DNA used U as a normal letter, a real U and a damaged C would look the same, and the repair enzyme could not tell them apart. With T as the normal letter (marked by its methyl group), any U in DNA is a mistake and safe to cut out.

  5. Name the five differences between DNA and RNA.

    Answer

    The sugar (deoxyribose vs ribose), the strands (two vs one), the letters (T vs U), the life span (the cell's whole life vs minutes to more than a day), and the job (the record vs the message, and sometimes the machine).

  6. What fact about the ribosome supports the RNA world idea?

    Answer

    The spot where the ribosome joins amino acids is made of RNA alone: RNA, not protein, does that chemistry. RNA can carry information and do chemistry.

Chapters

Sources

39 sources. Each was checked against its record (Crossref, PubMed, the Protein Data Bank, or the textbook edition) and against the claim it supports.

Textbooks

Structures drawn