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 STRUCTURE
DNA is made of basic sub-units called
nucleotides.
e
bas
Phosphate
group
Deoxyribose- a sugar
Nucleotide
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
Nair
6. 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
T
C
G
A
T
G
G
Base pairing of DNA
C
C
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.
TTCGCAAT
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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Biology
DNA structure & replication
Nair
16. 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.
Hydrogen bonds
are broken by
enzymes.
New bases are
brought in and
pair with original
bases.
Enzymes control
this as well.
Hydrogen bonds
broken.
This creates two
new strands,
each paired with
one old strand.
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.
• 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.
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
Nair
24. 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.
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