大阪大学大学院理学研究科生物科学専攻
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【１】1/2【１】イタリアの Varenna で開催された地球外生物探索の国際会議（2005 年）に関する以下の文章を読み、問に答えよ。
Where there’s water, there’s life. That, at least, is what our experience on
Earth has taught us, and when it comes to searching for life on other worlds, NASA
seems determined to follow the water. But is it right to see water as the sole medium forextraterrestrial life? Some think not. “Water is a terrible solvent for life,” says chemist
Steven Benner of the University of Florida. Benner is one of a number of biochemists,planetary scientists and philosophers who are trying to find out whether water is insome sense ‘fine-tuned’ for life. It is (a)a pertinent question. Scientists today aresearching for 1extraterrestrial life wherever they can, from the subsoil of Mars to planets
orbiting other stars. So far they have found nothing. But are they looking in the rightplaces? If Benner is right, perhaps they have become too fixated on chasing water. At ameeting in Varenna, Italy, researchers faced up to what many of them consider to be
their biggest challenge. How can we even begin to discuss the relationship between
water and life when we have only one example — life on Earth. And more to the point,
can the problem be dealt with in a rigorous, scientific manner?
For Benner the answer to (b)the latter question is yes. He argues that it ispossible to investigate experimentally whether water is essential for life. He hopes toprove that a type of biochemistry can occur without water. (c)Benner points out thatwater is generally not a good solvent for doing organic chemistry —which is, in the end,
what life is all about. For one thing, water is rather reactive, tending to split apart thebonds that link the building blocks of biomolecules together. It readily breaks peptide
bonds, for example, as well as many of the bonds in nucleic acids, such as RNA. “Thestructure of RNA screams ‘I did not arise in water!’ ” Benner asserts. He says that inabout four out of five cases, synthetic organic chemists will avoid using water as asolvent. The participants in Varenna generally agreed that life on Earth is adapted towater rather than the other way round. “(d)Life on Earth itself is fine-tuned to water — aconsequence of it evolving in close association with the medium,” says physicist JohnFinney at University College London.
(e)Bennersees several alternatives to water. Ammonia, which is liquid

between −78˚C and −33˚C at 1 atmosphere pressure, will dissolve many organic
compounds and can form hydrogen bonds. It is also relatively common in the cosmos:

【１】2/2

there is liquid ammonia in the clouds of Jupiter, for example. Benner considers water–ammonia mixtures, which may exist in some cold extraterrestrial environments such as
beneath the surface of Saturn’s moon Titan, as another promising candidate. Then there
is formamide, which is liquid over a wide range of temperatures and pressures,
dissolves salts and has hydrophobic-like effects. Formamide might be present below thesurface on Mars. Benner does not rule out more exotic possibilities, such as liquid
nitrogen or supercritical liquid hydrogen on gas-giant planets such as Saturn, Uranus
and Neptune. Or perhaps hydrocarbons such as liquid methane on Titan. “Organicreactivity in hydrocarbon solvents is no less versatile than in water,” he says.
Does widening the search for extraterrestrial life to places that don’t havewater make sense? But NASA’s quest for habitable planets remains focused on water.
出典：Nature 436, 1084-1085 (2005), doi:10.1038/4361084a, “Water and life: Seekingthe solution”（一部改変）
注釈：1extraterrestrial life, 地球外生物
問１

下線部 (a) および (b) の question とはそれぞれ何か。本文に即して日本語で答えよ。

問２

下線部 (c) を和訳せよ。

問３

下線部 (d) を和訳せよ。

問４

下線部 (e) で述べられている水に代わりうる物とは、具体的にどのような液体か。
Benner が主張している異なる特性をもつ 3 種類の液体を挙げ、それぞれの特性を説明せよ。

【２】1/2【２】寿命に関する以下の文章を読み、問に答えよ。
There are a few species in which aging seems to be optional, and these mayhold some important clues to how animals can live longer and retain their health. Turtles,
for instance, are a symbol of longevity in many cultures. Many turtle species not only
live a long time, they don’t seem to undergo a typical aging syndrome. Turtles seem to(a)have “negligible senescence,” in that their mortality rate does not increase with age, and1

their reproductive rate does not decrease with age. In these species, older females lay as
many eggs (if not more) as their younger counterparts. Miller (2001) showed that a(b)60-year-old female three-toed box turtle (Terrapene Carolina triunguis) lays as many
2eggs annually as she ever did. If turtle telomeres shorten with age, it happens (like somany turtle things) extremely slowly (Girondot and Garcia 1998; Hatase et al. 2008).
Interestingly, turtles have special adaptations against oxygen deprivation, and theseenzymes also protect against ROS (Congdon et al. 2003; Lutz et al. 2003; Krivoruchko
3and Storey 2010).
In monarch butterflies (Danaus plexippus), adults that migrate to wintering
4grounds in the mountains of central Mexico live several months (August-March),whereas their summer counterparts live only about 2 months (May-July). The regulationof this difference appears to be juvenile hormone (JH) (Herman and Tatar 2001). The
5

migrating butterflies are sterile because of suppressed syntheses of JH. If migrants aregiven JH in the laboratory, they regain fertility but lose their longevity. Conversely,
when summer monarchs have their corpora allata removed (so they can no longer make6JH), their longevity increases 100%. Mutations in the insulin signaling pathway ofDrosophila likewise decrease JH synthesis (Tu et al. 2005). This decrease in JH makes
the flies small, sterile, and long-lived, adding to whatever longevity-producing effectprotection against ROS might have.
(c)Finally, there may be organisms, especially cnidarians, that have actuallycheated death. Hydra appear to be immortal, retaining their stem cell populations. The
7hydrozoan cnidarian Turritopsis nutricula has evolved a remarkable variation on thistheme. It has both a polyp stage (like the hydra) and a medusa (jellyfish) stage in its
lifecycle. However, the Turritopsis medusa can revert to its polyp stage after becoming
sexually mature (Bavestrello et al. 1992; Piraino et al. 1996).

【２】2/2

出典：Scott F Gilbert 著 “Developmental Biology 10th edition
注釈： senescence, 老化; three-toed box turtle (Terrapene Carolina tringuis), カロリ
12ナハコガメ; ROS, 活性酸素種; monarch butterflies (Danaus plexippus), オオカバ
34マダラチョウ; juvenile hormone (JH), 幼若ホルモン; corpora allata, アラタ体;
576hydrozoan cnidarian Turritopsis nutricula, ヒドロ虫綱のベニクラゲ

問１下線部 (a) を和訳せよ。

問２

下線部 (b) を和訳せよ。

問３

オオカバマダラチョウにおいて幼若ホルモン (JH) が抑制された場合、どのような影響があらわれるか、本文に即して 2 つ述べよ。

問４

下線部 (c) を和訳せよ。

問５

この文章の題名として、最も適切なものを下の（ア）～（エ）の中から選べ。
（ア）A concept of the aging rule（イ）Exceptions to the aging rule（ウ）A definition of the aging rule（エ）Following the aging rule

【３】1/1【３】問１と問２の文章を英訳しなさい。
問１

基底角化細胞は表皮から分離可能で培養皿上で増殖でき、新たな基底細胞と最終分化した細胞を生ずる。すべて未分化に見える培養基底角化細胞の細胞群のなかにおいてさえ、増殖する能力には大きな差が存在する。
細胞を一つだけ取って新しいコロニーを形成する能力を試すと、いくつかは全く分裂することができず、別のいくつかはわずか 2、3 回の分裂サイクルを進めて停止し、さらに別のものは大きなコロニーを形成するのに十分な回数の分裂を行う。
参考：基底角化細胞, basal keratinocytes; 表皮, epidermis; 基底細胞, basalcells

問２

哺乳動物細胞の細胞質は極端に粘り気が強い。それはオルガネラで混みあい、細胞骨格繊維のネットワークで支持されており、これらすべてがバクテリアやウイルスキャプシドの大きさの粒子の拡散を阻害する。もし病原体が、その複製サイクルを実行するために細胞の特定部位へ到達する必要があるならば、能動的に細胞質を移動しなければならない。細胞内オルガネラの輸送と同様に、病原体も一般的に能動的な移動のために細胞骨格を利用する。
参考：哺乳動物(の), mammalian; 粘り気が強い, viscous; ウイルスキャプ
シド, a viral capsid; 病原体, pathogens