Protein Synthesis Poster (Part 2)

 

Transcription

 

            Your DNA model represents only a short length of the DNA portion of a chromosome.  An entire chromosome has thousands of rungs rather than only six.  Although your model is only a small part of a chromosome, its replication is the same as that of an entire chromosome during mitosis and meiosis.  As you have already gone through the steps of DNA replication, we will move on to how the cell transcribes the information on the DNA to make RNA and eventually proteins.

            How does a cell “read” and “translate” the chemical message coded in its DNA in the form of specific base sequences?  Part of the answer lies with a second molecule in the nucleus of cells called RNA (ribonucleic acid).  RNA is similar to DNA in that its molecules also form nucleotides.  However, as we have learned, deoxyribose and thymine are not found in RNA.  Ribose replaces deoxyribose sugar and Uracil replaces thymine.

 

Directions:

1.                  Cut out the six RNA nucleotide models.  CUT ONLY ON THE SOLID LINES.

2.                  Open your DNA model along the point of attachment between base pairs (rungs) and separate the two ladder halves.  Move the right half of the DNA strand away from the left half, but leave it in the nucleus.

3.                  Using the LEFT half of your model as a pattern, match RNA nucleotides with the proper nucleotides of the original DNA half.  DO NOT glue down the RNA at this point, but tape the pieces together to keep them in a strand.

4.                  Close the DNA molecule back up with its original left side.  (Chromosomes unzip temporarily during RNA production.)  Glue this strand now in place.

5.                  Draw a large ribosome on your butcher paper / poster paper OUTSIDE the nucleus.  Leave plenty of space to work around it.  Label this:  RIBOSOME.  Also, draw a large arrow leading from the nucleus toward the ribosome and label the arrow:  mRNA leaves nucleus.  Place the mRNA at the ribosome.

 

Translation

            Molecules of tRNA are composted of many base molecules.  However, the terminal (end) three are the important ones (the ANTICODON).  The terminal bases match up with three bases of the mRNA molecules (the CODON).  By means of enzymes, tRNA molecules pick up amino acids.  But only certain amino acids, depending upon the anticodon on the tRNA molecule at that point.  The amino acid is attached to the tRNA at the end opposite the terminal bases.

 

Directions:

1.                  Color the tRNA models already constructed for you and cut them out.

2.                  Color and cut out the tRNA models.  Match these with the appropriate protein and using glue, place one of each of these randomly in the cytoplasm of the butcher paper/ poster paper cell that you have created.

3.                  Label the following:  Leucine:  C-U-G                   Serine:  A-G-C

4.                  Write a label in the cytoplasm near these tRNAs:

                  tRNA and protein found in the cytoplasm.

      When many amino acid molecules are brought to the mRNA by tRNA, the amino acids join together to form a protein molecule.  Thus, joining the tRNA molecules with their attached amino acid to the bases of the mRNA simulates the beginning of a protein molecule.  THIS HAPPENS IN THE RIBOSOME.

      Depending on the type and order of the amino acids, an almost endless variety of proteins can be produced.  Because of the repeated matching of base sequences, the sequence of bases in the DNA chromosomes codes and controls the formation of protein molecules at ribosomes.

 

5.   Move one tRNA that will match up with the end of the mRNA to the ribosome, and put it in place so the bases pair up.  Now, move the second tRNA to the next place on the mRNA matching up those bases.  The two amino acids should be in contact with each other.  Now, tape down the mRNA and the tRNA at the ribosome.  Label this as:  PROTEIN FORMATION.

 

6.   Off to the side in the cytoplasm, place the two amino acids (Serine and Leucine) from your tRNA.  Draw them attached to each other.  Label as BEGINNING OF A PROTEIN CHAIN.

 

UPON COMPLETION:


REFLECTION QUESTIONS:

Answer the following questions on a separate piece of paper per person.

1.                  What is the function of mRNA?

2.                  What is the function of tRNA?

3.                  If the base sequence in a DNA strand is C G T A C G, what will be the sequence of bases of mRNA?  What will be the sequence of bases of tRNA?

4.                  In chemical terms, a particular gene is characterized by its sequence of bases.  How does base pairing  ensure that the genetic message is passed to RNA?

5.                  How do tRNA and mRNA differ in their (a) location within a cell and (b) chemical composition?

6.                  How do DNA and RNA differ in their (a) location within a cell and (b) chemical composition?

7.                  How many bases of mRNA are responsible for the coding of one amino acid?

8.                  Explain how a sequence of bases in DNA can instruct a cell to produce a certain protein.