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Name
_______
Block
13.1 RNA
Lesson Objectives
Contrast RNA and DNA.
Explain the process of transcription.
Lesson Summary
The Role of RNA RNA (ribonucleic acid) is a nucleic acid like DNA. It consists of a
long chain of nucleotides. The RNA base sequence directs the production of proteins.
Ultimately, cell proteins result in phenotypic traits. The main differences between RNA and
DNA are:
The sugar in RNA is ribose instead of deoxyribose.
RNA is generally single-stranded and not double-stranded like DNA.
RNA contains uracil in place of thymine.
RNA can be thought of as a disposable copy of a segment of DNA. Most RNA molecules are
involved in protein synthesis. The three main types of RNA are:
Messenger RNA (mRNA) carries copies of instructions for polypeptide synthesis from
the nucleus to ribosomes in the cytoplasm.
Ribosomal RNA (rRNA) forms an important part of both subunits of the ribosomes, the
cell structures where proteins are assembled.
Transfer RNA (tRNA) carries amino acids to the ribosome and matches them to the
coded mRNA message.
RNA Synthesis Most of the work of making RNA takes place during transcription. In
transcription, segments of DNA serve as templates to produce complementary RNA
molecules. In prokaryotes, RNA synthesis and protein synthesis takes place in the cytoplasm.
In eukaryotes, RNA is produced in the cell’s nucleus and then moves to the cytoplasm to play
a role in the production of protein. The following focuses on transcription in eukaryotic cells.
The enzyme RNA polymerase binds to DNA during transcription and separates the DNA
strands. It then uses one strand of DNA as a template from which to assemble nucleotides
into a complementary strand of RNA.
RNA polymerase binds only to promoters, regions of DNA that have specific base
sequences. Promoters are signals to the DNA molecule that show RNA polymerase
exactly where to begin making RNA. Similar signals cause transcription to stop when a
new RNA molecule is completed.
RNA may be “edited” before it is used. Portions that are cut out and discarded are called
introns. The remaining pieces, known as exons, are then spliced back together to form
the final mRNA.
Name
Class
Date
BUILD Vocabulary
A. The chart below shows key terms from the lesson with their definitions. Complete the
chart by writing a strategy to help you remember the meaning of each term.
Term
Definition
Exon
Coding region of a gene that is
expressed; exons are kept and put
together to form mRNA
Intron
Noncoding sequence of a gene that is
cut out and discarded
Messenger
RNA
mRNA; RNA molecules that carry
instructions for assembling proteins
Ribosomal
RNA
rRNA; RNA molecules that make up
ribosomes, on which proteins are
assembled
RNA
Ribonucleic acid; nucleic acid that
helps put the genetic code in DNA into
action
RNA
polymerase
An enzyme that separates DNA
strands and uses one strand to make
RNA
Transcription
Process in which RNA molecules are
made using DNA as a template
Transfer RNA
tRNA; RNA molecule that transfers
amino acids to the ribosomes
How I’m Going to Remember
the Meaning
Messenger RNA carries the
message of how to make proteins.
B. As you work through this lesson, you may find these terms in the activities. When you
need to write a key term or a definition, highlight the term or the definition.
The Role of RNA
1. Complete the table to contrast the structures of DNA and RNA.
Sugar
Number of Strands
Bases
DNA
RNA
2. On the lines provided, identify each kind of RNA.
a.
b
c.
Fill-in-the blank. Complete the following statements:
3. In DNA,
adenine
__________ is always paired with cytosine.
guanine
uracil
4. In DNA,
uracil
_________ is paired with adenine.
thymine
guanine
5. In RNA,
uracil
_________ replaces thymine.
cytosine
6. In RNA and DNA,
covalent bonds
_________ ________________ form bases pairs.
nitrogen bonds
hydrogen bonds
adenine
BUILD Connections
Master Plans and Blueprints In this visual analogy, DNA is compared with a master
plan, and RNA is compared with blueprints.
The master plan of a building shows how to build and place important parts of the
building, such as walls, pipes, and electrical outlets. On the building site, workers use
copies of the master plan called blueprints to show them what to do. The master plan is
kept in the office.
Explain and evaluate the analogy:
Messenger RNA (mRNA) works like a blueprint in constructing proteins.
Answer the questions. Use the terms DNA, RNA, and nucleus in your answers.
7. The master plan stays in the office. Why is DNA like the master plan?
8. Blueprints go out of the office to the building site. Why is RNA like a set of blueprints?
9. What is another analogy to shows how DNA and RNA information works in a cell?
RNA Synthesis
In transcription, RNA polymerase separates the two DNA strands. RNA then uses one strand as a
template to make a complementary strand of RNA. RNA contains the nucleotide uracil instead of the
nucleotide thymine.
Follow the directions.
10. Label the RNA. Color the RNA backbone light blue.
11. Label the DNA. Color the DNA backbone dark blue.
12. Use the key to label the missing nucleotides marked on the diagram.
Color the nucleotides: A: yellow; T: red; U: pink; C: green; G: purple
13. What enzyme copies the DNA template to make RNA?__________________________________
Color the enzyme orange.
RNA polymerase
Key
DNA
RNA
A = Adenine
C = Cytosine
G = Guanine
T = Thymine
A = Adenine
C = Cytosine
G = Guanine
U = Uracil
RNA Synthesis
For Questions 14–20, complete each statement by writing the correct word or words.
14. The process of using DNA to produce complementary RNA molecules is called
15. The sequence of
in mRNA complements the sequence in the DNA template.
16. In eukaryotes, RNA is formed in the
17. The enzyme
.
and then travels to the
.
binds to DNA during transcription.
18. RNA polymerase binds to regions of DNA called
transcription.
, which are “start” signals for
19.
are portions of RNA that are cut out and discarded.
20.
are spliced together to make the final mRNA.
21. THINK VISUALLY Sketch the sequence in which pre-mRNA is “edited” after it is made on the
DNA template and before it is ready to function as mRNA in the cytoplasm. Show the original
DNA, the pre-mRNA, and the final mRNA. Be sure to label exons and introns.
RNA Synthesis
In DNA replication a cell copies its DNA. Both strands of the double helix are used as templates to
make complementary, or matching, strands of DNA. In DNA transcription a single strand of DNA is
used as a template to generate a strand of mRNA.
Follow the directions.
22. Fill in the missing information. One row has been completed for you.
Template
TTACGG
Complementary
DNA
AATGCC
GGCGGC
Messenger RNA
(mRNA)
AAUGCC
ACGUAG
AGACTC
GATAAG
CUGGCUACA
Create your own example of DNA. Fill in the chart.
Template
Complementary DNA
Messenger RNA (mRNA)