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Часть С. Дайте полный, развернутый ответ.


С 1. Каково строение нуклеотидов ДНК и РНК? Как нуклеотиды соединяются в одну полинуклеотидную цепь?

С 2. На какие группы делятся все элементы клетки? По какому принципу?


С 3. Сколько содержится Т, А, Ц нуклеотидов в отдельности во фрагменте молекулы ДНК, если в нем обнаружено 660 Г, которые составляют 22% от их общего количества. Какова длина и масса этого фрагмента ДНК?
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Упражнения 3. Раскройте скобки, употребляя глаголы в Past Simple или Past Continuous.
1. When I (to come) home, my little sister (to sleep). 2. When Nick (to come) home, his brother (to play) with his toys. 3. When mother (to come) home, I (to do) my homework. 4. When father (to come) home, Pete (to sleep). 5. When mother (to come) home, the children (to play) on the carpet. 6. When I (to get) up, my mother and father (to drink) tea. 7. When I (to come) to my friend's place, he (to watch) TV. 8. When I (to see) my friends, they (to play) football. 9. When I (to open) the door, the cat (to sit) on the table. 10. When Kate (to open) the door, the children (to dance) round the fir-tree. 11. When Tom (to cross) the street, he (to fall). 12. When I (to go) to school, I (to meet) my friend. 43. When we (to go) to the cinema, we (to meet) grandmother. 14. When grandmother (to go) home, she (to see) many children in the yard. 15. When Henry (to walk) about in the forest, he (to find) a bear cub. 16. When we (to walk) about in the forest, we (to see) a hare. 17. When I (to wash) the floor, I (to find) my old toy under the sofa. 18. When granny (to read) a book on the sofa, she (to fall) asleep. 19. When I (to play) in the yard, I suddenly (to see) my old friend. 20. When Nick (to run) about in the yard, he (to fall). Упражнения^. Раскройте скобки, употребляя глаголы в Past Simple или Past Continuous. 1. They (to drink) tea when I (to come) home. 2. He (to walk) along the river when a boat (to pass). 3. The old man (to think) about his plan when he (to fall) asleep. 4. We (to listen) to an interesting lecture yesterday. 5. When I (to enter) the classroom, the teacher (to write) words on the blackboard and the pupils (to copy) them into their exercise-books. 6. They (to get) ready to go out when it (to begin) raining. 7. Yesterday at one o'clock I (to have) lunch at the canteen. 8. When he (to come) in, I (to do) my exercises. 9. What you (to do) at eight o'clock yesterday? 10. At this time yesterday I (to go) home. 11. You (to sleep) when I (to go) out. 12. He (to read) on the sofa when I (to come) in and (to sit) down beside him. 13. I (to walk) along the street with my friend when a tram (to pass). 14. She (to look) out of the window when I (to see) her. 15. We (to answer) the teacher's questions when the headmistress (to enter) the classroom.