High school biology Assignments

Biology 30—Lab III.5 Page 4

tRNA AND PROTEIN BUILDING

RNA produced in the nucleus of a cell moves out of the nucleus to the cell's ribosomes. This RNA is a specific sequence of bases copied from the DNA that carries the chromosomal genetic message to the cytoplasm. Thus, it is called messenger RNA (mRNA). At the ribosomes, mRNA directs the building of proteins. Proteins are made up of smaller molecules called amino acids. How does a cell construct the proper amino acids into protein molecules? Formation of proteins involves another kind of RNA. Transfer RNA (tRNA) brings specific amino acids to mRNA according to the code sequence of bases found on mRNA.

In this investigation, you will

1. Use paper models to show how base shapes in mRNA match only with specific base shapes of tRNA.

2. Use paper models to show how tRNA molecules bring specific amino acid molecules to the ribosome where building of proteins occurs.

3. Learn to transcribe a DNA code to a mRNA message and translate the mRNA to the tRNA—amino acid code.

4. Study the molecular basis of gene mutations.

PART A: RNA Transcription

Cut out the six RNA nucleotide models (cut only along solid lines) on BIOL200-28 Lab Sheet 3. Open or unzip one of the DNA chromosomes along the base pair points of attachment and separate the two halves. Using the left side of you DNA model as a pattern, match RNA nucleotides with the proper nucleotides of the DNA half.

20. Do the RNA half-rung bases pair exactly as they would if this were DNA replication?

Remove the RNA nucleotide series from the DNA pattern. Close the DNA molecule back up with its original right side (DNA molecules “unzip” temporarily during RNA production).

RNA is a single-stranded (or 1/2 ladder) linear molecule. Thus, the series of RNA nucleotides formed from DNA represents an 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 order. Therefore, the formation of this series of RNA nucleotides is called transcription.

PART B: Structure of tRNA

Build a molecule of mRNA using the paper molecules from BIOL200-28 DNA and RNA Lab (from the previous lab). Make sure you are using only RNA nucleotides. Join the RNA nucleotides to form a row of molecules in this order:

Guanine, Adenine, Cytosine, Uracil, Cytosine, Guanine.

Recall that molecules of mRNA leave the cell nucleus and move out to the cell's ribosomes. Meanwhile, transfer RNA (tRNA) is present in the cell cytoplasm. Models of tRNA are composed of many base nucleotides that folds and loops over itself. However, tRNA has a three base sequence (a triplet) that can match up with the bases of mRNA. Cut out the two models of tRNA (cut only along solid lines around the entire model).

1. a) Name the four nucleotide bases present in tRNA.

b) Do these bases differ from those found in mRNA?

c) How does the tRNA molecule differ from mRNA in shape?

Join the tRNA molecules to the model of mRNA.

2. What base in mRNA can only join with the

a) adenine base of tRNA?

b) uracil base of tRNA?

c) guanine base of tRNA?

3. What order of bases on mRNA will match a sequence on tRNA of

a) UUA?

b) UCA?

c) UGA?

d) AAA?

Transfer RNA picks up amino acids in a series of chemical steps. A tRNA molecule only picks up a certain amino acid. The amino acid is attached to the tRNA at the end opposite the three bases that will attach to mRNA.

Cut out the two remaining models of amino acids, serine and aspartic acid. Join these models to their proper tRNA models. Only a specific amino acid will fit along the top of each tRNA model. Remember that each tRNA model has a three sequence base called a triplet.

4. What amino acid connects to a tRNA molecule with a triplet of

a) AGC?

b) CUG?

5. What molecules on the tRNA do the amino acids attach to?

6. How many base molecules or nucleotides of mRNA are responsible for the coding of one amino acid?

PART C. Forming a Protein Molecule During Translation

When tRNA brings many amino acid molecules to the mRNA, the amino acids join to form a protein molecule. When tRNA molecules with their attached amino acids join to the bases of the mRNA, the formation of a protein molecule is begun. This entire process is called translation. The DNA message has been translated into a protein molecule. Be sure to use the tables in BIOL200-28Data.pdf (in Attachments) instead of the textbook tables.

7. What amino acid is attached to a tRNA molecule having a base sequence of

a) UUU?

b) GCU?

8. What tRNA triplet is needed to join with the following amino acids:

a) phenylalanine?

b) valine?

c) glutamate?

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

9. A protein molecule consists of the following amino acid sequence: leucine, glutamine, tyrosine, leucine, serine, serine. What would be the sequence of tRNA bases responsible for forming this protein (use the first code in the BIOL20028Data.pdf tables for each amino acid)?

10. A ribosome receives the following mRNA message: AAA, CGA, GAA, GUU.

a) What will be the sequence of tRNA bases joining the mRNA molecule?

b) What will be the sequence of amino acids formed from this code?

11. A portion of DNA on a chromosome has the sequence of bases along one strand of DNA as indicated below. Transcribe or decode this message first into mRNA code, then translate it into tRNA code and proper amino acids.

Chromosome DNA Code of Bases	mRNA Base Code	tRNA Base Code	Amino Acid Sequence
AAT
GGG
ATA
AAA
GTT

12. Rework the cell's code language backward by completing the following table (use the first codon listed in the BIOL200-28Data.pdf):

Amino Acid Sequence	tRNA Base Code	mRNA Base Code	Chromosome DNA Code of Bases
Proline
Glutamate
Lysine
Serine
Leucine

Analysis

Complete the table by using “x” marks to indicate to which molecule each characteristic applies.

SIMILARITIES AND DIFFERENCES BETWEEN mRNA AND tRNA
	mRNA	tRNA
deoxyribose present
ribose present
phosphoric acid present
adenine present
thymine present
uracil present
guanine present
cytosine present
contains a chemical message or code
carries an amino acid to a ribosome

DNA and RNA

BIOL200-28 Protein Synthesis Lab Page 6 of 7