Download Messenger RNA (mRNA)

RNA and Transcription 1/5/15
RNA = ribonucleic acid
The structure of RNA consists of a sugar, phosphate, and one of 4 nitrogenous bases.
Sugar = Ribose
Bases = Cytosine, Guanine, Adenine, Uracil (in place of Thymine).
Single-stranded
Intermediary molecule between DNA and Proteins
3 types of RNA: messenger RNA (mRNA), ribosomal RNA (rRNA), and transfer RNA (tRNA).
Messenger RNA (mRNA): copies the information stored in the strand of DNA and carries it to the ribosome.
Ribosomal RNA (rRNA): produced in the nucleus, makes up part of the ribosomes. Ribosomes are the site of
protein synthesis.
Transfer RNA (tRNA): shuttles amino acids to the ribosomes. It's responsible for bringing the correct amino
acids into place at the appropriate time. It does this by reading the message carried by the mRNA.
Transcription: Copying of the genetic code directly from DNA.
Only a piece of DNA is copied. Occurs in the nucleus.
3 phases
1. Initiation 2. Elongation
3. Termination
Phase 1: Initiation
a. Unwind and unzip the DNA strands using helicase.
b. RNA begins transcription at special sequences of DNA called promoters. The promoter contains an initiation
site where transcription of the gene begins.
Phase 2: Elongation
a. RNA is single stranded so only 1 of the 2 DNA strands need to be copied.
The strand that serves as the template is the sense strand and the other strand is the antisense strand.
b. RNA Polymerase brings free-floating RNA nucleotides to the DNA strand.
Guanines pair with Cytosines, but since this is RNA, Adenine pairs with Uracil instead of Thymine.
c. RNA nucleotides line up alongside 1 DNA strand to form an mRNA strand.
Phase 3: Termination
a. Once the mRNA finishes adding on nucleotides and reaches a termination point, it separates from the DNA
template.
The new RNA strand has now transcribed, or "copied", the sequence of nucleotide bases directly from the
exposed DNA strand.
Draw a picture of DNA, then draw a picture of RNA.
Check for understanding
1. The correct sequence for transfer of information in the cell is
a. RNA - DNA - Protein
b. DNA - RNA - Protein
c. Protein - DNA - RNA
d. DNA - Protein - RNA
2. What are the steps of transcription?
a. Initiation - Termination - Elongation
b. Elongation - Termination - Initiation
c. Termination - Initiation - Elongation
d. Initiation - Elongation - Termination
3. Which strand of DNA serves as the template?
a. sense
b. antisense
c. top strand
d. bottom strand
4. What base replaces thymine in RNA?
a. Adenine
b. Guanine
c. Uracil
d. Cytosine