Download DNA - The Double Helix

DNA - The Double Helix
Recall that the nucleus is a small spherical, dense body in a cell. It is often called the "control center" because it controls all the
activities of the cell including cell reproduction, and heredity. Chromosomes are microscopic, threadlike strands composed of the
chemical DNA (short for deoxyribonucleic acid). In simple terms, DNA controls the production of proteins within the cell. These
proteins in turn, form the structural units of cells and control all chemical processes within the cell. Think of proteins as the the building
blocks for an organism, proteins make up your skin, your hair, parts of individual cells. How you look is largely determined by the
proteins that are made. The proteins that are made is determined by the sequence of DNA in the nucleus.
Chromosomes are composed of genes, which is a segment of DNA that codes for a particular protein which in turn codes for a trait.
Hence you hear it commonly referred to as the gene for baldness or the gene for blue eyes. Meanwhile, DNA is the chemical that
genes and chromosomes are made of. DNA is called a nucleic acid because it was first found in the nucleus. We now know that DNA
is also found in organelles, the mitochrondria and chloroplasts, though it is the DNA in the nucleus that actually controls the cell's
workings.
In 1953, James Watson and Francis Crick established the structure of DNA. The shape of DNA is a double helix which is like a twisted
ladder. The sides of the ladder are made of alternating sugar and phosphate molecules. The sugar is deoxyribose. Color all the
phosphates red (one is labeled with a "p"). Color all the deoxyriboses blue (one is labeled with a "D") .
The rungs of the ladder are pairs of 4 types of nitrogen bases. The bases are known by their coded letters A, G, T, C. These bases
always bond in a certain way. Adenine will only bond to thymine. Guanine will only bond with cytosine. This is known as the "BasePair Rule". The bases can occur in any order along a strand of DNA. The order of these bases is the code that contains the
instructions. For instance ATGCACATA would code for a different gene than AATTACGGA. A strand of DNA contains millions of
bases. (For simplicity, the image only contains a few.)
Color the thymines orange.
Color the adenines green.
Color the guanines purple.
Color the cytosines yellow.
Note that that the bases attach to the sides of the ladder at the sugars and not the phosphate.
The DNA helix is actually made of repeating units called nucleotides. Each nucleotide consists of three molecules: a sugar
(deoxyribose), a phosphate which links the sugars together, and then one of the four bases. Two of the bases are purines - adenine
and guanine. The pyrimidines are thymine and cytosine. Note that the pyrimidines are single ringed and the purines are double ringed.
Color the nucleotides using the same colors as you colored them in the double helix.
The two sides of the DNA ladder are held together loosely by hydrogen bonds. The DNA can actually "unzip" when it needs to replicate
- or make a copy of itself. DNA needs to copy itself when a cell divides, so that the new cells each contain a copy of the DNA. Without
these instructions, the new cells wouldn't have the correct information. The hydrogen bonds are represented by small circles. Color the
hydrogen bonds black.
The Blueprint of Life
Every cell in your body has the same "blueprint" or the same DNA. Like the blueprints of a house tell the builders how to construct a
house, the DNA "blueprint" tells the cell how to build the organism. Yet, how can a heart be so different from a brain if all the cells
contain the same instructions? Although much work remains in genetics, it has become apparent that a cell has the ability to turn off
most genes and only work with the genes necessary to do a job.
Name____________________________
Directions: Fill in the blanks with the correct answers based on the reading.
1. Write out the full name for DNA. __________________________________________________________________________
2. What is a gene? ______________________________________________________________________________________
3. Where in the cell are chromosomes located? _______________________________________________________________
4. DNA can be found in what two organelles? _________________________________________________________________
5. What two scientists established the structure of DNA? ________________________________________________________
6. What is the shape of DNA? _____________________________________________________________________________
7. What are the sides of the DNA ladder made of? ______________________________________________________________
8. What are the "rungs" or “steps” of the DNA ladder made of? ___________________________________________________
9. What sugar is found in DNA? _____________________________
10. How do the bases bond together? A bonds with _____
G bonds with _______
11. The two purines in DNA are ____________________________________________________________________________
12. DNA is made of repeating units called _______________________________________________
13. How do some cells become brain cells and others become skin cells, when the DNA in ALL the cells is exactly the same. In other
words, if the instructions are exactly the same, how does one cell become a brain cell and another a skin cell?
14. Why is DNA called the "Blueprint of Life"?
If you have not colored your picture at this point- STOP and color. Once the picture is colored, answer the follow up
questions.
Follow up Questions:
1. What are the 4 different types of nitrogen bases?
2.
How many thymine are in the model of DNA you colored?__________How many adenine?______________
3. If a sample of DNA has 30% adenine, how much thymine does it have?
4. If 20% of the bases in DNA are adenine, how much cytosine does it have? (Think)
5. What do the circular dots between the bases represent?
Name __________________________________
Directions: Color the images according to the instructions. Be careful and think it through before you color.
Transcription & Translation Coloring
RNA
RNA, Ribonucleic Acid is very similar to DNA. RNA normally exists as a single strand (and not the double stranded double
helix of DNA). It contains the same bases, adenine, guanine and cytosine. However, there is no thymine found in RNA,
instead there is a similar compound called uracil.
Transcription
Transcription is the process by which RNA is made from DNA. It occurs in the nucleus. Follow the directions below to
complete the illustration of transcription.
1. Label the box with the x in it near the nucleus with the word TRANSCRIPTION.
2. Color the bases according to the key below
Thymine = orange
Adenine = dark green
Guanine = purple
Cytosine = yellow
Uracil = brown
3. Color the strand of DNA dark blue (D) and the strand of RNA light blue (R).
4. Color the nuclear membrane (E) gray.
Translation
Translation occurs in the cytoplasm, specifically on the ribosomes. The mRNA made in the nucleus travels out to the
ribosome to carry the "message" of the DNA. Here at the ribosome, that massage will be translated into an amino acid
sequence. Follow the directions below to complete the illustration of transcription.
1. Color the ribosome light green (Y) and note how the RNA strand threads through the ribsosome like a tape measure
and the amino acids are assembled.
2. The RNA strand in the translation area should also be colored light blue, as it was colored in the nucleus.
3. Label the box with the X in the translation area with the word TRANSLATION.
4. Important to the process of translation is another type of RNA called Transfer RNA (F) which function to carry the amino
acids to the site of protein synthesis on the ribosome.
5. Color the tRNA red.
6. A tRNA has two important areas. The anticodon, which matches the codon on the RNA strand. Remember that codons
are sets of three bases that code for a single amino acid. Make sure you color the bases of the anticodon the same color
as the bases on your DNA and RNA strand - they are the same molecules!
7. At the top of the tRNA is the amino acids. There are twenty amino acids that can combine together to form proteins of
all kinds, these are the proteins that are used in life processes. When you digest your food for instance, you are using
enzymes that were originally proteins that were assembled from amino acids. Each tRNA has a different amino acid which
link together like box cars on a train. Color all the amino acids (M) pink.
Questions:
1. How many different kinds of bases can be found on DNA _____
2. What base is found on RNA but not on DNA? _____________
3. How many bases are in a codon? ______ In an anticodon? ____________
4. How many amino acids are attached to a single transfer RNA? _______
5. Transcription occurs in the _________; translation occurs in the ____________.
6. The process of making RNA from DNA is called ___________________ and it occurs in the ___________________
7. The process of assembling a protein from RNA is called _________________ and it occurs in the
_____________________