DNA and RNA pieces guide

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DNA and RNA pieces guide Powered By Docstoc
					                                                Names ____________________________


                                                  RNA Transcription
RNA Structure                                        Cut out the six RNA nucleotide
         Besides ensuring the exact                    models. Cut only the solid lines.
replication of chromosomes, the sequence
(order) and pairings of bases are a genetic             Create a DNA ladder using your
code of the instructions for the entire cell.            DNA pieces in the following order:
How does a cell "read" the chemical                              Cytosine nucleotide
message coded in its DNA in the form of                          Guanine nucleotide
specific base sequences? Part of the answer                      Adenine nucleotide
lies with a second molecule in the nucleus of                    Guanine nucleotide
cells called ribonucleic acid (RNA).                             Thymine nucleotide
         RNA is similar to DNA in that its                       Cytosine nucleotide
molecules are also formed from nucleotides.
However, deoxyribose and thymine are not                Open or unzip one of the DNA
found in RNA. Two other molecules, ribose                chromosomes along the base pair
and uracil, are present. Ribose replaces                 points of attachment and separate
deoxyribose, and uracil replaces thymine.                the two halves.
Looking at their structural formulas and
models, you will see certain similarities               Using the left side of your DNA
between the molecules that they replace.                 model as a pattern, match RNA
                                                         nucleotides with the proper
1. (a) Which base is replaced in RNA by                  nucleotides of the DNA half
uracil? _________________________
                                                  3. Do the RNA half-rung bases pair exactly
   (b) What molecule replaces deoxyribose         as they would if this were DNA replication?
in RNA? _______________________                   __________________________________

2. To which base in DNA do the following                Remove the RNA nucleotide series
RNA bases pair?                                          from the DNA pattern.

(a) guanine ______________________                      Close the DNA molecule back up
                                                         with its original right side. (DNA
(b) adenine ______________________                       molecules "unzip" temporarily
                                                         during RNA production.)
(c) cytosine ______________________
                                                  RNA is a single-stranded (or ½ ladder)
(d) uracil ________________________               molecule. Thus, the series of RNA
                                                  nucleotides formed from DNA represents
                                                  and RNA molecule. After its formation, this
                                                  RNA leaves the nucleus of the cell and goes
                                                  to the ribosomes. It carries the DNA
message of base sequences in the exact same      (c) UGA? ________________________
order. Therefore, the formation of this series
of RNA nucleotides is called transcription.      (d) AAA? ________________________

                                                 Transfer RNA picks up amino acids in a
Structure of tRNA                                series of chemical steps. A tRNA molecule
     Recall that molecules of mRNA              only picks up a certain amino acid. The
       leave the cell nucleus and move out       amino acid is attached to the tRNA at the
       to the cell's ribosomes. Meanwhile,       end opposite the three vases that will attach
       transfer RNA (tRNA) is present in         to mRNA.
       the cell cytoplasm. Molecules of
       tRNA are composed of many base                   Cut out the two remaining models of
       nucleotides. However, tRNA has a                  amino acids, serine and aspartic
       three base sequence (an anti-codon)               acid, from the page provided. Join
       that can match up with the bases of               these models to their proper tRNA
       mRNA.                                             models. Only a specific amino acid
                                                         will fit along the top of each tRNA
       Cut out the two models of tRNA.                  model. Remember that each tRNA
                                                         model has a three sequence base
4. (a) Name the four nucleotide bases                    called an anti-codon.
present in tRNA.
_________________________________                7. What amino acid connects to a tRNA
                                                 molecule with an anti-codon of
   (b) Do these bases differ from those found    (a) CGA? ________________________
in mRNA?
_________________________________                (b) GUC? ________________________
   (c) How does the tRNA molecule differ
from those found in mRNA?                        8. What molecule receives the amino acids
_________________________________                on tRNA?
                                                 9. How many base molecules or nucleotides
       Join the tRNA molecules to the           of mRNA are responsible for the coding of
        model of mRNA.                           one amino acid?
5. What base in mRNA can only join with
the                                              10. What do you notice about the
                                                 relationship between DNA and the mRNA
(a) adenine base of tRNA ____________            pieces?
(b) uracil base of tRNA _____________
(c) guanine base of tRNA ____________
                                                 11. What do you notice about the
6. What order of bases on mRNA will match        relationship between the mRNA and the
a sequence on tRNA of                            tRNA pieces?
(a) UUA? ________________________                ____________________________________

(b) UCA? ________________________                ____________________________________
                                            Names _______________________


Forming a Protein Molecule
During Translation
When many amino acid molecules are
                                              3. A protein molecule consists of the
brought to the mRNA by tRNA, the
                                              following amino acid sequence: leucine,
amino acids join to form a protein
                                              glutamine, tyrosine, leucine, serine,
molecule. When tRNA molecules with
                                              serine. What would be the sequence of
their attached amino acids join to the
                                              tRNA anti-codon bases responsible for
bases of the mRNA, the formation of a
                                              forming this protein? (Use Table 1)
protein molecule is begun. This entire
process is called translation. The DNA
message has been translated into a
                                              4. A ribosome receives the following
protein molecule.
                                              mRNA message: AAA, GCU, CUU,
1. What amino acid is attached to a
                                              (a) What will be the sequence of tRNA
tRNA molecule having a base sequence
                                              bases joining the mRNA molecule?
of (Use Figure 1):
(a) UUU? ________________________
                                              (b) What will be the sequence of amino
                                              acids formed from this code? _________
(b) CGA? ________________________
2. What tRNA anti-codon is needed to
join with the following amino acids:
(a) phenylalanine?__________________
                                               Table 1: tRNA Anti-codon Codes for
(b) valine? _______________________
                                                        Some Amino Acids
(c) glutamic acid? __________________          AMINO ACID          tRNA CODE
                                                    Serine             UCG
Depending on the type and order of                 Proline             CCC
amino acids, an almost endless variety of          Leucine             UUA
proteins can be produced. Because of the        Glutamic acid          GAA
repeated matching of base sequences, the          Tyrosine             UAU
base sequence in the DNA of                       Arginine             CGA
chromosomes codes for and controls the           Glutamine             CAA
formation of protein molecules at               Phenylalanine          UUU
ribosomes.                                         Valine              GUU
                                                   Lysine              AAA
As a review, you should now be able to      Mutations and Base Sequence
transcribe (decode) a message in DNA        Errors
base code into mRNA and then translate
it into a protein molecule.                 Not often are there errors in the process
                                            of forming proteins from the DNA code
A portion of DNA on a chromosome has        of instructions. An error in the process is
the sequence of bases along one strand      a mutation and will result in formation
of DNA as indicated in Table 2.             of a different type of protein.

        Transcribe or decode this          Hemoglobin is a protein in red blood
         message first into mRNA code,      cells. Hemoglobin results from the
         then translate it into tRNA code   proper arrangement of almost 600 amino
         and proper amino acids using       acids. Most humans have the correct
         Table 1.                           type of hemoglobin. However, in some
                                            people the arrangement is incorrect.
     Table 2: Transcribing and              These people have a disease called
   Translating of a DNA Sequence            sickle-cell anemia. Their red blood cells
                                            are sickle-shaped rather than round. As a
CODE OF      CODE      CODE                 result, the red blood cells cannot
BASES                                       transport oxygen as well.
                                                   The following amino acid
                                            sequence represents a portion of the
TAT                                         normal hemoglobin molecule: proline,
                                            glutamine, glutamine, lysine.
CGA                                         5. Translate the sequence of amino acids
                                            in normal hemoglobin into

        Rework the cell’s code language    (a) tRNA base codes. _______________
         backward by completing Table 3
         below.                             _________________________________

Table 2: Transcribing and Translating of    (b) mRNA base codes. ______________
        an Amino Acid Sequence
AMINO            tRNA mRNA DNA              _________________________________
SEQUENCE         CODE CODE CODE             (c) DNA base codes. _______________
                                            In sickle cell anemia, the sequence of
Serine                                      amino acids is slightly different. It is
Leucine                                     proline, valine, glutamine, lysine.
6. Translate the sequence of amino acids     DNA message for sickle-cell
in sickle-cell anemia hemoglobin into        hemoglobin. ______________________

(a) tRNA base codes. _______________         _________________________________

_________________________________            _________________________________

(b) mRNA base codes. ______________          A mutation, therefore, is a difference
                                             from what we consider to be the normal
_________________________________            sequence of bases in a molecule of
                                             DNA. The difference or error does not
(c) DNA base codes. _______________          have to be very great. As you have just
                                             determined, a base sequence of only one
_________________________________            triplet (three bases) can cause the
7. In terms of base nucleotides, explain     formation of the wrong type of
the only difference between the DNA          hemoglobin. A change at only one base
message for normal hemoglobin and the        site of the triplet can cause a mutation.

1. What is the function of mRNA? _________________________________________


2. What is the function of tRNA? __________________________________________


3. How do tRNA and mRNA differ in where they are found in the cell? ____________


4. (a) Briefly describe what happens during translation. _________________________


  (b) What is being translated? ____________________________________________

5. (a) Name four similarities between mRNA and tRNA: ________________________


  (b) Name four differences between mRNA and tRNA: ________________________


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