Telomeres: a role in cancer?

Telomeres contain repeating sequences of bases which are synthesised with the help of an RNA-containing enzyme called telomerase. Telomerase activity is suppressed in normal human somatic (body) cells. However, in cancerous cells, telomerase is active and maintains the telomere length so that the cells continue to divide. It is thought that this abnormal retention of the telomeres is involved in the development of some types of cancer.

■ Glossary of essential terms for you to know

■ Your Essential Assignments:

I. Quick check:

1. What is a nucleosome?

2. Centromeres contain no genes. What is their main function?

3. Why have telomeres been compared with the tips of shoelaces?

II. Suggest Russian equivalents for the following word combinations:

III. Fill in the gaps with the words and expressions from the text:

1. The artificial chromosome remains … and functions as ….

2. Chromosomes also contain small amounts of ….

3. Chromosomal DNA … and … to protein molecules called histones.

4. The complex formed between … is called chromatin.

5. Each DNA molecule … histones arranged in groups of eight known as octamers.

6. The DNA and octamers form … known as ….

7. Centromere appears as … when the chromosomes condense during mitosis and meiosis.

8. Centromeres do not contain any ….

IV.Find English equivalents for the following word combinations:

V.Answer the following questions. Use all information given before:

1. What is a nucleosome?

2. Centromeres contain no genes. What is their main function?

3. Why have telomeres been compared with the tips of shoelaces?

4. What risks might be associated with changing the length of telomeres in body cells?

5. What is the total length of DNA in the nucleus of a human cell?

6. What are histones?

7. What happens if the telomeres are removed?

8. When and where was the first artificial human chromosome made?

9. How could synthetic chromosomes be used?

10. How is DNA packaged in chromosomes?

VI. Read and translate the short text without a dictionary:

Fact of life:

In February 1997, the first artificial human chromosome was made by Dr Huntington Willard and his colleagues from the Case Western Reserve University in Cleveland, Ohio. According to their report, this achievement should: '... open the door to a whole new avenue of research in chromosome biology and gene therapy.' A synthetic chromosome containing a specific gene could be introduced into human cells to treat a genetic disease. The artificial chromosome remains independent within host cells and functions as an 'extra' or accessory chromosome.

VII. Food for thought:

In January 1998, a paper in the journal Science explained how telomeres can be lengthened by introducing a gene for an enzyme called telomerase reverse transcriptase (hTRT). This enzyme causes cells to produce active telomerase, the enzyme that repairs telomeres. Suggest how techniques for manipulating telomere length might be used to treat age-related diseases and cancers. What risks might be associated with deliberately changing the length of telomeres in body cells?

VIII. Translate into English using all the active possible:

1. Искусственная хромосома остается независимой внутри клетки хозяина и функционирует в качестве дополнительной хромосомы.

1. Ген является основным звеном наследственности.

2. ДНК упаковывается с помощью белков и образует сложную структуру.

3. Хромосомальная ДНК замысловато складывается и тесно связывается с белковыми молекулами, называемыми гистонами, которые богаты аминокислотами лизином и/или аргинином.

4. Этот комплекс, образованный между ДНК и гистонами, называется хроматином.

5. Отдельные хромосомы могут быть увидены только во время деления клетки.

6. Положительно заряженные группы на боковых цепях гистонов образуют сильные (крепкие) ионные связи с отрицательно заряженными фосфатными группами в основании ДНК.Каждая хромосома имеет центромер, который обычно появляется в качестве ограничения, когда хромосомы уплотняются во время деления клетки (митоза или мейоза).

7. Центромеры контролируют распределение хромосом во время деления клетки.

8. Теломеры поддерживают стабильность хромосом, закрывая концы линейной ДНК.

9. Процесс старения связан с повреждением теломера.

IX. Use a monolingual English dictionary and write down what could the words given below mean:

to treat; host; aid; complex; distribution; vital; to maintain; abnormal.

X. Read the text and render it in English:

Сколько лет проживем?

Скоро каждый желающий сможет узнать, сколько лет ему отпущено природой. Разработанный испанцами тест измеряет длину ДНК на концах хромосом. Эти участки, называемые теломерами, защищают ДНК от повреждений. Со временем теломеры становятся слишком короткими, в результате чего клетка перестает делиться и умирает, что ускоряет процесс старения. На основе этого был сделан вывод, что люди с короткими теломерами живут меньше.

Исследователи считают, что тест получит широкое распространение в ближайшие 5-10 лет и поможет в борьбе с раком, сердечно-сосудистыми заболеваниями и болезнью Альцгеймера.

XI. Prepare a short presentation reflecting the following issues:

▪ discuss the role of telomeres;

▪ describe the structure and function of centromeres;

▪ explain how DNA is folded in a chromosome.

■ Have Some Fun! Biologist Joke!

Enzymes are things invented by biologists that explain things which otherwise require harder thinking.

INIT IV. INHERITANCE

Text 4.1. Variation

■ Essential targets:

By the end of this text you should be able to:

·define the following genetic terms: allele; homozygous; heterozygous; dominant; recessive; polygenic

·distinguish between genotype and phenotype

·distinguish between continuous variation and discontinuous variation

·explain how mutations contribute to variation.

Pre-reading

■ Discuss these questions with your partner. Then scan the text quickly to find the answers.

1. What is variation?

2. What is mutation?

3. Are mutations harmful or beneficial?

4. How do X-rays influence the mutation rate?

Exercise A. Match the words with their definitions:

■ Read and translate the given text and make your essential assignments:

The Earth is inhabited by billions of organisms, every one of which is unique. Individuals belonging to different species are usually easy to distinguish; members of the same species may differ only in small ways; but even clones (such as identical twins) show some subtle differences. The differences between individuals of the same species are called variation.These differences may be the result of genetic differences, the influence of the environment, or a combination of genetic and environmental influences.

Genetic variation

Genetic differences reflect the genotypeof an organism, that is, its genetic make-up. A diploid organism has two sets of chromosomes and two forms (alleles)of each particular gene. These alleles may be the same (the organism is homozygous for that gene) or different (the organism is heterozygousfor that gene). If different, one of the alleles (the dominant allele)may mask the other allele (the recessive allele).The dominant allele is therefore expressed in either the heterozygous or the homozygous condition, whereas the recessive allele is expressed only in the homozygous condition. If an organism is haploid (that is, it has only one set of chromosomes), all its alleles will be expressed and will be reflected in its observable or measurable characters(the features or traits transmitted from parent to offspring).

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