Collaboration Teams - Members share responsibility for posting refined answers to the guided readings - succinct, relevant, clear, and with pictures or a video to compliment.
When contributing to the reading guide, follow these steps:
1) First complete the reading guide on your own from the DNA unit page.

2) Write your response to a question in word and then copy it. Be sure to upload pictures and/or video for each question.
3) Click on the edit button and then go to the appropriate question and paste your answer below it.
Sign your contribution with your first name and last initial and TEAM COLOR
4) Scroll to the very bottom and in the Optional comment box, place a summary of what you did and sign it (e.g. "I answered chp 26 question 3" - Tom S.) Th en click Save.
Remember to include pictures and or video for all answersSmiley-02-june.gif

1. What did Garrod mean by “inborn errors of metabolism?”

Garrod postulated that the symptoms of an inherited disease reflect a person’s inability to make a particular enzyme. He referred to such diseases as “inborn errors of metabolism”.

Video about PKU, an inherited disease characterized by a deficiency in the enzyme phelylalanine

2. Describe the Beadle and Tatum experiment with mold in detail – use the diagram below to help. The logic behind both the experiment and the results are critical.

From the growth patterns of the mutants, Beadle and Tatum deduced that each mutant was unable to carry out one step in the pathway for synthesizing arginine, presumably because it lacked the necessary enzyme. Because each of their mutants was mutated in a single gene, they concluded that each mutated gene must normally dictate the production of one enzyme. Their results supported the one gene-one enzyme hypothesis and also confirmed the arginine pathway.

3. What was Beadle and Tatum’s final hypothesis?
why has this definition changed?

Beadle and Tatum’s final hypothesis is known as the one gene- one enzyme hypothesis. This states that each gene is responsible for directing the building of a single, specific enzyme. "One gene one enzyme" has since been modified to "one gene one polypeptide" since many proteins (such as hemoglobin) are made of more than one polypeptide.
external image transcrtransl.JPG

4. Use the diagram below to note the flow of genetic information in a eukaryotic cell – next to each label in the square – write the definition of the term.

Transcription: the synthesis of RNA under the direction of DNA
Translation: the actual synthesis of a polypeptide, which occurs under the direction of mRNA.
RNA processing: yields the finished RNA

5. Why does the “code” have to be in triplets and not singles or doubles?Smiley-02-june.gif

There are only four nucleotide bases to specify 20 amino acids. If each nucleotide base were translated into an amino acid, only 4 of the amino acids could be specified, not enough to code for all 20 amino acids. If a two-letter code was used, only 16 amino acids could be coded for. The triplet code can code for up to 64 (theoretically) amino acids, more than enough to cover the 20 amino acids in existence.

external image codon_GCA.gif

6. What is the template strand?

7. Compare and contrast the codon and anticodon?


8. How did Nirenberg “figure out” which amino acids went with which codes?


9. What is the reading frame?


10. What conclusions can be drawn from the similarities of the genetic code among living organisms?


11. upload a video of transcription and describe the steps.Smiley-02-june.gif

Adam A

12. What is a transcription unit?Smiley-02-june.gif

the length of DNA that is transcribed into an RNA molecule

Zack B.


13. Describe the prokaryotic promoter and terminator.Smiley-02-june.gif

sequence where RNA pol attaches and begins transcription is the promoter. The terminator is the sequence that signals the end of the transcription.

Zack B


14. upload a picture of a a eukaryotic promoter and explain the significance of different components
can you explain the components?

external image 10.1038_nature01763-f1_large_2.jpg
Jackie H. -- Pink Team

15. Contrast termination of transcription for prokaryotic and eukaryotic organisms.

Prokaryotes- transcription proceeds through a terminator sequence in the DNA; RNA sequence functions as the termination signal. Eukaryotes- termination - polymerase falls off DNA. -- Jackie H. Pink Team Need Help please


16. Why is important that the promoter be upstream of the transcription unit?
A promoter should be upstream of the transcription unit because the nucleotides are in certain positions in respect to the transcription unit.
emily a-green team.

It’s important because if the promoter was “downstream” then nothing would transcribe; it’s at the wrong end.
----Brian N


17. Why is RNA processing necessary?
What does "processing" mean?

Its necessary to initiate transcription, create mRNA, and to be translated.

splicing.gifIm sorry but i cant fix this answer i need some one else in my group to do it
-- Brian N.
emily a-green team

18. What does adding a 5’ cap and poly A tail mean and why is it important?Smiley-02-june.gif

Adding a 5’ cap and a Poly A tail to each end of a pre-mRNA molecule is modified in a particular way. It means that the new mRNA is helped to leave the nucleus. It also helps protect the mRNA from degradation. In the cytoplasm, the addition of the 5’ cap and poly A tail, it helps the ribosomal units to attach to the 5’ end of the mRNA.
-- Brian N

19. Define the following terms:Smiley-02-june.gif
a. RNA splicing

The removal of noncoding portions (introns) of the RNA molecule after initial synthesis.

b. Introns
noncoding segments of nucleic acid that lie between coding regions

c. Exons
the other regions besides the introns

d. Spliceosome
snRNP's join with additional proteins to form an even larger assembly.
A complex assembly that interacts with the ends of an RNA intron in splicing RNA, releasing the intron and joining of the two adjacent exons.

e. snRNP’s
AKA: small nuclear ribonucleoprotiens— recognize these splice sites. They are located in the cell’s nucleus and are composed of RNA and protein molecules.

f. ribozymes
site of protein manufacturing contain two subunits.

g. UTR
UTR stands for Untranslated Region, it refers to one of the two sections on each side of a strand of mRNA. If it is found on the 5' side, it's name is a 5 UTR and f it is found on the 3' side, it is named a 3 UTR
Stephanie A

h. Alternative RNA splicing

A type of regulation at the RNA-processing level in which different mRNA molecules are produced from the same transcript, depending on which RNA segments are treated as exons and which as introns.

i. domains
regions of a protein

Emily A,
Brian N -green team

20. Describe the structure and function of transfer RNA.Smiley-02-june.gif

function- to transfer amino acids from the cytoplasmic pool of amino acids to a ribosome
structure- consists of a single RNA strand that is only about 80 nucleotides long.
- Laura C
external image trna_diagram.gifMario Ciao

21. Why is the enzyme aminoacyl-tRNA synthetase important to translation and protein synthesis?Smiley-02-june.gif

The enzyme aminoacyl-tRNA synthetase joins each amino acid to the correct tRNA, because they have to attach to a specific one, which creates a protein.
- Laura C

22. What is “wobble”?Smiley-02-june.gif

A violation of the base -pairing rules because the third nucleotide (5' end) of a tRNA anticodon can form hydrogen bonds with more than one kind of base in the third position (3' end) of a codon.
- Laura C

23. upload a picture of ribosomal RNA and describe the structure and function of it's components.Smiley-02-june.gif

external image ch12c5.jpg

24. Detail the steps of initiation of translation.Smiley-02-june.gif

1. A small ribosomal subunit binds to a molecule of mRNa.
2. In a prokaryotic cell, the mRNA binding site on this subunit recognizes a specific nucleotide sequence on the mRNA just upstream of the start codon.
3. An initiator tRNA, with the anticodon UAC, base-pairs with the start codon, AUG.
4. This tRNA carries the amino acid Met
5. The arrival of a large ribosomal subunit completes the initiation complex.
6. Proteins called initiation factors are required to bring all the translation components together.
7. GTP provides the energy for the assembly
8. The initiator tRNA is in the P site and the A site is available to the tRNA bearing the next amino acid.
- Laura C
external image translation_initiation.jpg
Mario Ciao

25. Use the diagram below to detail elongation cycle of translation. Define terms.Smiley-02-june.gif


  • Codon recognition: the anticodon of an incoming aminoacyl tRNA base-pairs with the complementary mRNA codon in the A site. Hydrolysis of GTP increases the accuracy and efficiency of this step.
  • Peptide bond formation: an rRNA molecule of the large subunit catalyzes the formation of a peptide bond between the new amino acid in the A sire and the carboxyl ends of the growing polypeptide in the P site. This step attaches the polypeptide to the tRNA in the A site.
  • Translocation: the ribosome translocates the tRNA in the A site to the P site. The empty tRNA in the P site is moved to the E site, where it is released. The mRNA moves along with its bound tRNAs, bringing the next codon to be translated into the A site.
external image c8.17x19.termination.jpg
-Corinne DJ

26. Use the diagram below to detail the termination of translation – define all terms.Smiley-02-june.gif

1) When a ribosome reaches a stop codon on mRNA, the A site of the ribosome accepts a protein called a release factor instead of tRNA.
2)The release factor hydrolyzes the bond between the tRNA in the P site and the last amino acid of the polypeptide chain. The peptide is then free from the ribosome.
3)The 2 ribosomal subunits and the other components of the assemply dissociate.
The purple chain is the polypeptide being built from the mRNA (the red strip). The light blue particle is tRNA whch recieves the message to stop building the polypeptide from the release factor (the yellow particle).

27. What are polyribosomes?Smiley-02-june.gif
A polyribosome is a string of ribosomes that can be seen with an electron microscope. The are found in both prokaryotic and eukaryotic cells, and they enable a cell to make many copies of a polypeptide very quickly. external image 138831_polyribosomes.jpg
Sawyer W

Once the ribosome moves past the starting codon another ribosome can also attach to the mRNA. They enable the cells to make many copies of a polypeptide very quickly. Martin A

28. What is an example of a post translational modification of a protein?Smiley-02-june.gif
Post translational modifications are extra steps that may be required before a protein can begin doing its job in the cell. For example, certain amino acids may be chemically modified by the attachment of sugars, lipids, phosphate groups, or other additions. Enzymes may also remove certain acids form the leading end of a polypeptide chain as a post translational modification.

external image protein.jpg
When first synthesized insulin is a continuous polypeptide. It does not become active until an enzyme comes along and takes out a central part of it and then combines the two of them. Martin A

29. What is a signal peptide?Smiley-02-june.gif
A signal peptide is a piece of a protein that indicates that the protein should end up in the endomembrane system, or it should be secreted. It is made up of roughly 20 amino acids near the leading polypeptide. A signal peptide is recognized by signal-recognition particles.
external image signalpep.gif
Sawyer W

Polypeptides of proteins that are going to be secreted are marked by signal peptides that target the protein to the ER. Martin A

30. What is a signal recognition particle?Smiley-02-june.gif
A signal recognition particle is a protein-RNA complex that recognizes a signal peptide when it emerges from the ribosome.

Particle that functions as an adapter that brings the ribosome to a receptor protein built into the ER membrane. Martin A.

31. Use the diagram below to highlight the signal mechanism for targeting proteins to the ER.Smiley-02-june.gif

A signal recognition particle binds to the signal peptide and brings the ribosome to a receptor protein built in the ER membrane. The SRP then binds to the signal peptide, halting synthesis momentarily. Then the ribosome continues translating while the polypeptide goes into the ER. Then a signal cleaving enzyme cuts off the signal peptide, and the peptide leaves the ribosome, folding into its proper shape.

32. Define the following terms:Smiley-02-june.gif
a. Mutation
Changes in the genetic material of a cell.

b. Point mutations
Chemical changes in just one base pair of a gene.

c. Base pair substitution
The replacement of one nucleotide and its partner with another pair of nucleotides.

d. Missense
The altered codon still codes for an amino acid and thus makes sense, although not necessarily the right sense.
e. Nonsense
A mutation that changes an amino acid codon to one of the three stop codons, resulting in a shorter nonfunctional protein.
f. Insertions
A mutation involving the addition of one or more nucleotide pairs to a gene.
g. Deletions
A mutational loss of one or more nucleotide pairs from a gene.
h. Frameshift mutation
A mutation occurring when the number of nucleotides inserted or deleted is not a multiple of three, resulting in the improper grouping of the following nucleotides into codons.
i. Mutagen

A chemical or physical agent that interacts with DNA and causes a mutation.

34. How has a gene been “redefined” and why?
specific example please?

It has gone from a discrete unit of inheritance that affects a phenotypic character to a region of DNA whose final product is either a polypeptide or an RNA molecule. It has been redefined because we know more about genes now, and yes they do affect the way an organism looks and functions, but genes do more specific things than that. For example most eukaryotic genes contain noncoding segments called introns. These introns are not transcribed so they don't effect the phenotypic character, but they do need to be present for transcription to occur.