More AP Bio help please!?

Question

If the DNA triplet code for the amino acid alanin is CGA the tRNA anticodon for alanine is:
a. AGC
b. GCU
c. CGA
d. CGT
If you could briefly explain that would be awesome. Thanks!

Answer 1

b. GCU

The complimentry base of C (cytosine) is always G (guanine).
The complimentry base of G (guanine) is always C (cytosine).
The complimentry base of A (adenine) is T (thymine) if its in a DNA. But in an RNA, the Thymine is replaced by U (uracil).

So answer: GCU

Answer 2

The answer is B, GCU. They made the answer easy to see because you can just look for the complement to the CGA sequence, but the sequence given in the answer is in the 3' to 5' orientation (3' GCU 5'), since the codon for alanine is given as a 5' CGA 3' sequence.

Some respondents said that the mRNA is a complement to the DNA sense strand. This is incorrect. The mRNA and the sense strand of DNA have the same sequence (with the substitution of uracil for thymine). Please note that the mRNA and the sense strand of the DNA have the *same* sequence and the tRNA has an antisense (anticodon) sequence. mRNA is not an anti-sense strand. Here is a website that shows transcription and the sense and anti-sense strands:

http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/T/Transcription.html

The original DNA "sense" strand is in the 5' to 3' orientation and the the mRNA strand is read from the the "anti-sense" or "non-coding" (3' to 5' DNA strand) thus making the mRNA an exact copy of the DNA sense strand. The tRNA binds to the mRNA during protein synthesis (translation) due to the anticodon binding to the codon binding in the mRNA. Here is a movie of DNA transcription to make the process of DNA to mRNA clearer:

http://www.johnkyrk.com/DNAtranscription.html

Here is a diagram to make transcription and translation a little clearer:

http://web-books.com/MoBio/Free/Ch3E3.htm

Answer 3

It would be CGA. Recall that if the DNA reads CGA 5' - 3', the mRNA will read 5' - 3' UCG (the bind in opposite directions, and polymerase can only build a chain in the 5' - 3' direction). The tRNA, then, will be the opposite of the mRNA, which is equilavent to the DNA. Since there are no thymines in the original DNA sequence, you don't have to worry about uracils and thymines in the tRNAs. Good luck!

Also, not to bad mouth the other people who've answered (it takes a lot of time to provide answers for these questions, and everybody deserves a pat on the back for trying to help), but many of these answers are giving you the answer for the mRNA codon. Be aware.

Answer 4

Here's some advice: find out all the teachers who are teaching Physics, AP bio and chem and if you like the teacher who is teaching that class, do that class. I'm in the same boat you are, and I looked at all my options and saw that the chem teacher i have this year, who is a really good teacher, will be the AP chem teacher. also note that the AP chem class will most likely have no more than 15 students in the class, which results in more individual attention. bio is pure science, chem is science and math and physics is pretty much all math. If you really like math, physics is the way 2 go. if you don't like math, bio is the way 2 go. If you're in the middle, chem is it. ask around not just in your school but other people you know that are taking AP classes b/c an AP class will be the same whether you live in Maine or California. I don't know if its this way in your school, but in my school, once you sign up for an AP class, you can't drop it. good luck whatever you do, hope i was helpful.

Answer 5

B) GCU

You can figure this out by the process of elimination if you don't know any other way. RNA doesn't have the nitrogen base Thymine, so it can't be d.

Adenine if pairing up with it's complimentary DNA base pair ..it would be pairing up with Thymine. And if pairing up with it RNA pair..it would be pairing up with Uracil, so you can eliminate a and c.

Basically, if you are looking for the complimentary RNA pair from DNA.

It always pairs up..
C-G or A-U

If it's DNA to DNA, it always pairs up..

C-G or A-T

This is due to the sizes of the base pairs. Cytosine will only fit correctly with Guanine and Adenine fits only with Thymine or Uracil.

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I'm sorry to rain on the last person's parade...but here is it straight off wikipedia:

For example, one codon for lysine is AAA; the anticodon of a lysine tRNA might be UUU.

Anticodon
An anticodon [1] is a unit made up of three nucleotides that correspond to the three bases of the codon on the mRNA. Each tRNA contains a specific anticodon triplet sequence that can base-pair to one or more codons for an amino acid. For example, one codon for lysine is AAA; the anticodon of a lysine tRNA might be UUU. Some anticodons can pair with more than one codon due to a phenomenon known as wobble base pairing. Frequently, the first nucleotide of the anticodon is one of two not found on mRNA: inosine and pseudouridine, which can hydrogen bond to more than one base in the corresponding codon position. In the genetic code, it is common for a single amino acid to occupy all four third-position possibilities; for example, the amino acid glycine is coded for by the codon sequences GGU, GGC, GGA, and GGG.

To provide a one-to-one correspondence between tRNA molecules and codons that specify amino acids, 61 tRNA molecules would be required per cell. However, many cells contain fewer than 61 types of tRNAs because the wobble base is capable of binding to several, though not necessarily all, of the codons that specify a particular amino acid[2].

Answer 6

It would be B 90% sure. The GCA code matches with the opposite for RNA GCU normally when you have a A it would match with T but for a reason i cant remember it matches with U. So C matches with G then G matches with C and finally the A matches with U. Basically what is happening is the DNA splits and the tRNA makes a copy of it by matching it up in the way discribed above i think RNA doesnt use T in the matching it replaces it with a U. Sorry i forgot what they stand for it has been a few years but i remember the system of how to match it up. Hopefully with your book you can make even more sense of this answer.

Answer 7

The anticodon is GCU.

C always matches G, and A anways matches T (or U in RNA)

The initial G in the anticodon matches the initial C in the Codon, and so on.

Answer 8

Hm. The mRNA would be GCU and then the tRNA anticodon would be CGA.

So my answer is
C

Answer 9

BillyC is correct.