Unit 2 Biological Molecules

Reading

I. Read the text. Some sentences have been taken out of the text and are listed below. Choose the correct sentence (a, b, c, etc) for each gap in the text (1, 2, 3, etc).

…. 1 …. As a result, the bodies of all organisms use the same basic types of molecules. For this reason, humans can obtain nutrients from other organisms, and our bodies, in turn, can become nutrients for other organisms after we die.

…. 2 …. How are these molecules formed? What roles do these biological molecules play in our bodies and in the bodies of plants, insects, and fungi? Here we are talking about the basic types of organic molecules – the carbohydrates [ka:bəuhaıdreıts], lipids, proteins [prəuti:nz], and nucleic acids – that form the basis of life on Earth.

…. 3 …. The term is derived from the ability of living organisms to synthesize and use these molecules. Inorganic molecules include carbon dioxide and all molecules without carbon, such as water.

Although the common structure and function of the types of organic molecules among organisms afford unity, the tremendous range of organic molecules accounts for the diversity of living organisms and for the diversity of structures within single organisms and even within individual cells. This vast array of organic molecules, in turn, is possible because the carbon atom is so versatile. A carbon atom has four electrons in its outermost shell, with room for eight. …. 4 …. They become stable by sharing four electrons with other atoms, forming up to four single covalent bonds or fewer double or triple covalent bonds. Molecules with many carbon atoms can assume complex shapes, including chains, branches, and rings.

Organic molecules are much more than just complicated skeletons of carbon atoms, however. Attached to the carbon backbone are groups of atoms, called functional groups that determine the characteristics and chemical reactivity of the molecules. …. 5 ….

…. 6 ….: (1) the use of the same set of functional groups in virtually all organic molecules in all types of organisms and (2) the use of the “modular approach” to synthesizing large organic molecules.

a) These functional groups are far less stable than the carbon backbone and are more likely to participate in chemical reactions.

b) All of the diverse forms of life, from bacteria to mushrooms to redwood trees to sea urchins to humans, evolved from a distant common ancestor.

c) Therefore, carbon atoms are able to form many bonds.

d) The similarity among organic molecules from all forms of life is a consequence of two main features:

e) What sorts of basic biological molecules make up living things?

f) In chemistry, the term organic is used to describe molecules that have a carbon skeleton and also contain some hydrogen atoms.

II. Give the headline of the extract in one word, as a word-combination and a whole sentence.

Language focus 1

The Use of Passive Structures

I. Explain the reasons for using passive structures in the following text.

Disaccharides Consist of Two Single Sugars linked by Dehydration Synthesis

Monosaccharides, especially glucose and its relatives have a short life span in a cell. Most are either broken down to free their chemical energy for use in various cellular activities or are linked by dehydration synthesis to form disaccharides or polysaccharides. Disaccharides are often used for short-term energy storage, especially in plants. Common disaccharides include sucrose (glucose plus fructose), which you stir into your breakfast coffee; lactose (milk sugar: glucose plus galactose), found in the milk you pour in your coffee; and maltose (glucose plus glucose, which will form in your digestive tract as you break down the starch in the pancakes you may have for breakfast). When energy is required, the disaccharides are broken apart into their monosaccharide subunits by hydrolysis.

II. Say whether the passive or active voice is appropriate in these sentences.

Transform those that you think should be in the passive.

1. Roots and seeds commonly form starch.

2. The saliva enzymes break the pancakes that you chew into component sugars.

3. Some lipids form waterproof coverings on plant and animal bodies.

4. We can classify lipids into three major groups: (1) oils, fats and waxes; (2) phospholipids; and (3) steroids.

5. Protein enzymes guide almost all the chemical reactions that occur inside cells.

6. Nature uses some proteins, such as elastine or keratine, for structural purposes; other proteins for energy and material storage (albumin, casein), transport (hemoglobin) and cell movement.

7. We commonly find twenty amino acids in the proteins of organisms.

Language focus 2

By or With?

We use “by” when we talk about an action – what we do to get a result. We use “with” when we talk about a tool or other object that we use to get a result.

I killed the spider by hitting it.

I killed the spider with a shoe.

‘I got where I am by hard work.’ – ‘No, you didn’t. You got there with your wife’s money.’ …

I. a) Fill in the gaps with by or with.

1 The decision was taken ............... a group of scientists.

2 There is only one way to do it - …………… a needle.

3 A meeting was held …………… the authorities on the central square of the town.

4 The reactions in cells are catalyzed …………… enzymes.

5 You could illustrate your idea …………… a picture.

6 You could illustrate your idea ……………. showing a picture.

b) Use the following word combinations in sentences of your own.

– by the process of photosynthesis – with a dropper

– by a computer – with your friend’s efforts

– by being polite – with that principle

Words, Words, Words

Using the words given, tell the class about:

A Amino acids

a chain a functional group

an amino group a carboxyl group a variable group

to be (in)soluble in water to link together

to differ in properties

B Proteins

highly organized molecules four levels of organization

to assume primary, secondary, tertiary [tə:ərı] and quaternary [kwətə:nərı] structures

a sequence of amino acids helix to be dissolved in water

C Nucleic acids

nucleotide 5-carbon sugar phosphate

nitrogen-containing bases adenine cytosine [saıtəzi:n]

thymine [Өaımi:n] guanine uracil [juərəsi:l]

to be strung in long chains deoribonucleic acid

ribonucleic acid to be formed in the chromosomes

to direct the synthesis of proteins

Review

I. Think through the topic of the unit and choose the right answer.

1. Which of the following is not a function of polysaccharides in organisms?

1. energy storage

2. storage of hereditary information

3. formation of cell walls

4. structural support

5. formation of exoskeletons

2. Characteristics of carbon that contribute to its ability to form an immense diversity of organic molecules include its:

1. tendency to form covalent bonds

2. ability to bond with up to four other atoms

3. ability to bond together to form extensive, branched or unbranched carbon skeletons

4. all of the above

3. Foods that are high in fiber are most likely to be derived from

1. plants

2. dairy products

c. meat

d. fish

5. all of the above

4. Proteins differ from one another because

1. the peptide bonds linking amino acids differ from protein to protein

2. the sequence of amino acids in the polypeptide chain differs from protein to protein

3. each protein molecule contains its own unique sequence of sugar molecules

4. the number of nucleotides in each protein varies from molecule to molecule

5. the number of nitrogen atoms in each amino acid differs from the number in all atoms

5. Which, if any, of the following choices does not properly pair an organic compound with one of its building blocks (subunit)?

1. polysaccharides - monosaccharide

2. fat - fatty acid

3. nucleic acid – glycerol

4. protein – amino acid

5. all are paired correctly

6. Which of the following statements about lipids is false?

1. Wax is a lipid.

2. Unsaturated fats are liquid at room temperature.

3. The body does not need any cholesterol.

4. Both male and female sex hormones are steroids.

5. Beef fat is highly saturated.

II. Translate into English (passive constructions are preferable).

1. Дисахариды и полисахариды образуются соединением нескольких моносахаридов в одну цепочку.

2. Дисахариды используются растениями для долгосрочного хранения энергии.

3. Молочный сахар можно определить в крови при помощи биохимических методов.

4. Водоотталкивающие покрытия на листьях и теле некоторых животных образуются благодаря липидам.

5. Практически все химические реакции в клетках проводятся с помощью протеиновых ферментов.

6. Некоторые белки используются организмами как строительный материал.

7. Ты добился всего благодаря деньгам твоего отца.

8. Жизнь клетки невозможно объяснить только химическими принципами.

9. Крахмал можно расщепить на молекулы глюкозы при помощи ферментов.

10. Моносахара объединяются в полимеры при помощи реакции дегидратации.

III. Use the following words and expressions in sentences of your own.

1. to have a short span of life 2. …is found in…

3. to be broken apart 4. commonly

5. to classify into 6. …the reactions that occur…

7. to illustrate by

IV. Read the text and count all prepositional passive structures contained in it.

The Use of Isotopes [aısəutəups] in Biology and Medicine

Although all atoms of a particular element have the same number of protons, the number of neutrons may vary. Neutrons do not affect the chemical reactivity of an atom very much, but they do make their presence felt in other ways. First, neutrons add to the atom’s mass, which can be detected by sophisticated instruments such as mass spectrometers. Second, nuclei with “too many” neutrons break apart spontaneously, or decay, often emitting radioactive participles in the process. Those particles can also be detected – for instance, with Geiger [gaıgə] counters. The process in which a radioactive isotope spontaneously breads apart is called radioactive decay.

A particularly fascinating and medically important application of radioactive isotopes is positron emission tomography, more commonly know as PET scans. In a common application of PET scans, a subject is given the sugar glucose that has been labeled with (that is, attached to) a harmless radioactive isotope of fluorine. When the nucleus of fluorine decays, it emits two bursts of energy that travel in opposite directions along the same line. Energy detectors are arranged in a ring around the subject. They record the nearly simultaneous arrival of the two energy bursts. A powerful computer then calculates the location within the subject at which the decay must have occurred and generates a map of the frequency of fluorine decays. As the fluorine is attached to glucose molecules, this map reflects the glucose concentration within the subject’s brain. The brain uses prodigious amounts of this sugar for energy; the more active a brain cell is, the more glucose is uses. How can this information be used in biological research?

Let us suppose that a neuroscientist is trying to locate the areas of the brain that are involved in memory. The researcher might give fluorine-labeled glucose to a few volunteer subjects and then ask them to memorize a word list, which is read aloud. Because brain regions that are active during this process would need more energy and would take more fluorine-glucose molecules than they would be taken by inactive regions, the active regions would have more fluorine decays. The PET scans would be taken during the memorization and then pinpoint brain regions active in storing memories of words.

Physicians also use PET scans in the diagnosis of brain disorders. For example, brain regions in which epileptic seizures originate generally have excessively high glucose utilization and show up in PET scans as “hot spots”. Many brain tumors also light up in PET scans. Abnormal metabolism of certain brain regions may also be detected in patients with some mental disorders, such as schizophrenia [skıtsəufri:njə].

V. Compose five questions in Russian relating to the text. In small groups of three practice translating and answering the questions (a curious Russian student asks his/her questions to an American expert in the field, the questions being translated by an interpreter; each student is to perform all three roles).

Listening.

Listen to the text “Protein Structure – a Hairy Subject” and answer the following questions: Which kinds of bonds or bridges between keratin molecules are altered when hair is (a) wet and allowed to dry on curlers; (b) given a permanent wave?

Render in English.

Образование биологических молекул

Живые организмы образуют всевозможные малые органические молекулы, называемые мономерами. Мономеры – это строительные блоки, или субъединицы, более крупных молекул. Они способны соединяться друг с другом, образуя полимеры, известные также под названием макромолекул. Людям давно знакомы такие органические полимеры, как шерсть, шелк, каучук или хлопок; человечество использует их уже не одну тысячу лет. С начала нашего века химики стали изготовлять органические полимеры, пластмассы, соединяя друг с другом различными способами малые органические мономеры, например, диметиловый эфир или этилацетат. Таким образом, возникло искусство или на худой конец ремесло, по сути дела имитирующее природу.

Организм строит свои макромолекулы, соединяя друг с другом мономеры. Процесс этот обратим: полимеры могут быть разрушены до мономеров, из которых они состоят. Именно это, в частности, и происходит в желудочно-кишечном тракте животных: макромолекулы пищи разрушаются здесь до малых молекул, которые затем всасываются в кровь и используются организмом для образования новых макромолекул, принадлежащих уже самому организму. Такое же разрушение, только в гораздо меньшем масштабе, происходит во всех живых клетках: в них также старые молекулы подвергаются расщеплению, а из обломков строятся новые, то есть идет процесс реутилизации.

Все живые организмы содержат четыре главных класса органических соединений: углеводы, липиды, белки и нуклеиновые кислоты. Соединения каждого класса построены из своих особых мономеров, объединяющихся в полимеры.