Science 9
Name:_
ANSWER KEY_
2.3 – From DNA to Proteins Questions
Using your textbook, on pages 42-46, answer the following questions.
Answer in full sentences!
1. What is DNA? Using Figure 2 and your prior knowledge, why is it sometimes referred
to as a ladder-like structure?
DNA (deoxyribonucleic acid) is a very long molecule that looks
like a twisted ladder. It provides the directions for all the cell
structures and activities.
2. Draw what a nucleotide looks like. Use Figure 1 and make sure to label all three parts.
QuickTime™ and a
decompressor
are needed to see this picture.
3. What are the sides of the DNA molecule made of?
Sugar and phosphate molecules joined together.
4. Which part of the nucleotide attaches in the middle to make the “steps” of the
“ladder”?
Sugar
5. There are four different nitrogenous bases. For each one, write their full name and
the letter we use to abbreviate them. Use the table below.
Name of Base Letter Used to Represent it
Adenine
Thymine
Cytosine
Guanine
A
T
C
G
6. In order to make the DNA molecule look like a ladder, two bases need to pair up.
They do this in a specific way. Please explain which bases pair up together.
_____Adenine_____ always pairs up with __Thymine____ , and
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___Cytosine____ always pairs up with __Guanine____ .
7. Label the diagram below as it is in your textbook.
8. a) What does the DNA molecule do before a cell divides?
Each DNA molecule makes a copy of itself.
b) Explain how this happens, step by step. (You may answer this question in point
form.)
-DNA molecule splits (“unzips”) in many places between
the pairs of bases.
- new bases join up on the open sides of the ladder to form
2 identical DNA molecules.
9. The bases in a DNA molecule are like the letters in our alphabet. Explain why that
statement is true.
The bases (A,T,C,G) combine into 3 letter words.
10. DNA has a 4 character code (it has 4 letters in its alphabet) and each word codes
for the production twenty different amino acids.
a. How many letters are in each “word” that it forms?
There are 3 letters in each word.
b. What is an amino acid?
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It is a small molecule that forms the building blocks of
proteins. (3 bases long).
11. What is the genetic code sometimes called?
“the language of life”
12. What is a gene?
A short section of DNA that contains the instructions to
make a specific protein.
13. All of an organism’s genes are called its genome.
a. How many pairs of chromosomes does the human genome have?
23 pairs of chromosomes
b. How many chromosomes in total is that?
46 chromosomes in total
14. There are many steps involved in making a protein from a gene. Fill in the blanks and
answer the questions to find out how it does this.
a. First, the DNA from a gene makes another molecule called_RNA
(ribonucleic acid)_.
b. How is this new molecule different from DNA?
RNA only has 1 strand,
DNA has a double strand.
c. Next, a gene segment (or one
section of a gene) separates and
an __RNA molecule__ is
made from one half of the DNA.
d. This molecule (called RNA) then
carries the code, or information,
somewhere else. Where does it
go?
It carries the code from the nucleus to a ribosome within
the cytoplasm.
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e. The organelle from letter ‘d’ ( the _ribosome__ ) then “reads” the instructions
on the RNA and puts the small components of proteins, called amino acids, in
the right order to make the __protein__ .
15. Proteins are very, very important and have many functions. Complete the table
below. WARNING: These are NOT in order!
PROTEIN
Keratin
Enzymes
FUNCTION
Makes up hair and nails.
Control chemical reactions.
Antibodies
Helps protect the body against foreign substances. (for
health)
Hemoglobin
Carries oxygen in red blood cells.
Stimulates growth (cell division).
Growth
hormone
Insulin
Lactase
Controls the level of sugar in the blood.
Helps the body digest milk
16. How similar is human DNA to other organisms. Give at least two specific examples
from the text.
- 99.9% of the DNA in E.Coli is also found in humans.
- 35% of daffodil DNA is also found in humans.
- 98% of chimpanzee DNA is also found in humans.
17. Individuals from the same species have the same number of genes, why don’t they
all look identical?
Within a species, there are different versions of the same
gene. Different versions produce slightly different variations,
or traits, for each characteristic.
18. Do you have a hitchhiker’s thumb? (see Figure 6, page 45)
Circle one:
Yes
No
No
19. Why is variation good for a species?
Variation allows individual organisms to adapt to changing
environments.
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