Biology DNA structure & replication Nair

Worksheet- DNA Structure, Replication and Genetic Code 25 points.

1. What end product does DNA code for? Answer: proteins.

2. Name the three functions of proteins.

1. provide shape or structure

2. enzymes

3. peptide hormones

3. Draw and label correctly a the basic structural unit of DNA.

DNA STRUCTUREDNA is made of basic sub-units called nucleotides.

basePhosphate group

Deoxyribose- a sugarNucleotide base

4. Draw and label a 2 stranded model of DNA with at least six copies (3 on each strand) of DNA’s basic structural unit. Show the hydrogen bonds.

“Stacked” nucleotides

A little more realistic model

5. Is DNA a polymer? Explain your answer. Yes, DNA is a polymer. It is a bunch of repeating units called nucleotides.

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Biology DNA structure & replication Nair6. Explain the difference between a covalent bond and a hydrogen bond.

Covalent bonds exist when atoms share electrons to form a molecule. A hydrogen bond exists when hydrogen has a positive charge and attracts the negative end of another molecule.

7. Explain how the backbone of a DNA strand is held together.Covalent bonds.

8. Explain how the two strands of DNA are held together.

Hydrogen bonding.

9. Name the two parts of a nucleotide that are always the same.

1.The phosphate group and 2. deoxyribose.

10. What is the difference between a nucleotide base and a base, when you discuss DNA.Nothing.

11. Explain base pairing. Base pairing is the pairing up of Adenine and Thymine, Guanine and cytosine according to base pairing rules.

A

C

A

G

G

T

T

G

C

C

Base pairing of DNA

12. Draw a simplified picture of DNA & identify two strands.

. 13. Why does DNA need to be replicated? So that the cell can divide and give a copy to each new cell. If it wasn’t replicated (copied), there would not be a copy of every chromosome for each new cell.

14. Here is the base sequence for a strand of DNA. A A G C G T T A. In the space below, give the sequence for the complementary bases on the opposing strand.

T T C G C A A T

15. Why do we care about the sequence of bases in DNA?

The sequence of bases gives a code for what amino acids will be eventually made from DNA.

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Hydrogen bonds are broken by enzymes.

New bases are brought in and pair with original bases.

Enzymes control this as well.

This creates two new strands, each paired with one old strand.

Hydrogen bonds broken.

• DNA exists in two general physical forms-

• Chromosomes…– Which are DNA in

its tightly coiled state

– Formed when cell is going to divide.

• Chromatin– DNA in its uncoiled

state.

Biology DNA structure & replication Nair16. Suppose a piece of DNA lost a base. How would it know what base to replace it with? It would use base pairing rules, and its opposing base, to tell it what base would be needed.

17. Is it possible for a cell to have different DNA than other cells in the same organism? Explain your answer.NO! Every cell in an organism has the same DNA in the same amount, and all the DNA is exactly the same.

18. Draw a model of DNA replication.

19. A cell is about to divide. What must if first do with its DNA before it can begin to divide?It must replicate or copy its DNA.

20. Draw a picture of chromatin and chromosome & explain the difference between the two.

21. Why doesn’t a cell just pack DNA into a chromosome and then copy it?A chromosome is unreadable because it is too tightly packed. The cell has to copy chromatin and then make chromosomes from the two copies of the same DNA.

22. What are sister chromatids?Identical copies of chromosomes, which are either about to be separated, or have been separated.

23. What are daughter cells?Two cells that are the result of the division of a parent cell.

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Biology DNA structure & replication Nair24. Starting from the point where a cell has already replicated its DNA, put a number next to the two images, showing which one comes first, and which comes second, as the cell divides.

2_ ____1_

25. Imagine a cell that has two chromosomes. It replicates these chromosomes so it has two copies of each. Draw a picture of this cell just about to divide, with both copies of its chromosomes still attached to each other.

This is a cell in the act of dividing. Each copy of the chromosome will be pulled away from the other half.

26. Now draw the same cell after it has separated its chromosomes as it is dividing.

Single copies of each DNA molecule, coiled tightly as a chromosome, are separated. THIS CELL IS DIVIDING.

27. What is going to happen to this chromosome soon?

It will become unraveled into chromatin.

28. Explain your answer to question 24. The cell has to unravel the chromosome to be able to read it and make proteins.

29. You are given a series of bases as follows, from one strand of DNA….

A A A A T C G C T T A T T C G.

30. How many amino acids will this base sequence code for?

There are 15 bases. 3 bases will code for one amino acid. This sequence cods for 5 amino acids.Page 4 of 4