Chapter 3 Tissues: DNA, RNA, transcription and translation

What are the end products of translation?

A protein chain.

What is an anticodon?

A nucleotide triplet attached to tRNA that base pairs with a complementary codon on mRNA.

Briefly describe the 3 major steps in transcription.

1. Initiation: After RNA polymerase binds to the promoter, the DNA strands unwind, and the polymerase initiates RNA synthesis at the start point on the template strand. 2. Elongation: The polymerase moves downstream, unwinding the DNA and elongating the RNA transcript 5" -> 3". In the wake of transcription, the DNA strands re-form a double helix. 3. Termination: Eventually, the RNA transcript is released, and the polymerase detaches from the DNA.

What is the minimum number of nucleotides that can be in a codon if there are 4 different nucleotides and you need to code for 20 amino acids?

4^3=64. There needs to be a minimum of 3 nucleotides to code for 20 amino acids.

Eukaryotic cells modify their RNA after transcription, how is the 5" end altered and how is the 3" end altered?

5" receives a 5" cap, a modified form of a G nucleotide. 3", an enzyme adds more A nucletides, forming a poly-A tail.

What is a codon?

A codon is the mRNA base triplets transcripted from the DNA strand, written in the 5" to 3" direction.

What is referred to as the central dogma of biology?

Cells are governed by a molecular chain of command with a directional flow of genetic info: DNA ->RNA->protein.

During splicing are introns removed or are exons removed?

Introns are cut out and exons are spliced together.

How is transcription terminated?

Prokaryotes: transcription proceeds through a terminator sequence in the DNA. The transcribed terminator functions as the termination signal, causing the polymerase to detach from the DNA and release the transcript. Eukaryotes: RNA polymerase II transcribes a sequence on the DNA called the polyadenylation signal sequence in the pre-mRNA. Then about 10-35 nucleotides downstream, proteins associated with the growing transcript cut it free from the polymerase, releasing the pre-mRNA.

What are the molecular components of transcription, in particular, what is the role of RNA polymerase, of promoter regions, of terminators, and transcription factors?

RNA polymerase: an enzyme that pries the two strands of DNA apart and joins the RNA nucleotides as they base-pair along the DNA template. Promoter regions: The DNA sequence where RNA polymerase attaches and initiates transcription. Terminators: The sequence that signals the end of transcription in bacteria. Transcription factors: a collection of proteins in eukaryotes that mediate the binding of RNA polymerase and the intiation of transcription.

Does RNA polymerase make an RNA transcript from both strands of the DNA? If not, which strand becomes the template strand, the 3" to the 5" or the 5" to the 3"?

The 5" to 3" becomes the template strand.

What is the difference between the genetic code and a code for a gene?

The genetic code is the overal code contained in the DNA, a code for a gene is a 3-nucleotide sequence that codes for a single gene.

What is the genetic code?

The genetic instructions for a polypeptide chain are written in the DNA as a series of nonoverlapping, 3-nucleotide words.

What do we refer to as a primary transcript?

The initial RNA transcript from any gene, including those coding for RNA that is not translated into protein.

How does RNA polymerase find the specific gene that it will be transcribing?

The promoter attaches to the start point and serves as a binding site for RNA polymerase.

What do we mean by RNA splicing?

The removal of large portions of the RNA molecule that is initially synthesized-a cut-and-paste job.

What is the difference between transcription and translation?

Transcription is the synthesis of RNA from DNA. Occurs in the nucleus. Translation is the synthesis of a protein from RNA. Occurs in the cytoplasm.

What are the end products of transcription?

mRNA.

What are the molecular components of translation? Be able to identify and describe the structure and the function of tRNA, mRNA, and rRNA.

tRNA: function is to transfer amino acids from the cytoplasmic pool of amino acids to a ribosome. mRNA: rRNA: