Ch. 10: Nucleic Acids and Protein
Synthesis
- DNA controls the production of proteins
within the cell.
- These proteins form the structural units of
cells and control the chemical processes.
DNA’s 2 primary functions:
1. Store and use information to direct
activities of the cell.
2. Make an exact copy of itself to pass on
to new cells.
Where is DNA stored in the cell?
In the cell’s nucleus.
Structure of DNA
- DNA is an organic molecule made up of
repeating subunits called nucleotides.
- Nucleotide: 3 main parts:
1) Sugar molecule called
deoxyribose
2) Phosphate group
3) Nitrogen base
- There are 4 nitrogen-containing bases
found in DNA nucleotides:
1. Adenine (A)
2. Cytosine (C)
3. Thymine (T)
4. Guanine (G)
- The 4 nitrogen bases are placed into 2
structural groups:
1) Purines: double ring of carbon (A,G)
2) Pyrimidines: single ring of carbon
(T,C)
- DNA is a double helix (twisted ladder)
Base Pairing Rules:
A-T
C-G
Or vice versa
-Double ring always
Bonds w/ single
ring
DNA Replication
- The process of duplicating a molecule of DNA
1) An enzyme called DNA helicase attaches to the
DNA molecule and breaks the bonds or “unzips”
the double helix.
2) In the nucleus of the cell, free-floating
nucleotides bond to the “unzipped” portion of the
DNA molecule.
3) The replication is complete after an enzyme
called DNA polymerase bonds all nucleotides
together forming 2 DNA molecules, both with
one “old strand” and one “new strand.”
Accuracy and Repair
1) The cell has a built-in “proof-reading”
function.
2) About 1 error per billion nucleotides.
3) Body heat, radiation, chemicals, etc. can
damage your DNA.
4) A group of 20 or more enzymes designed
to seek out and replace damaged
nucleotides.
Homework- due Tues.
Research on the web, in magazines or
books something interesting about DNA.
Ex:
- How is DNA used to solve crimes?
- What are some things that can happen as a
result of DNA damage?
- What is the human genome project?
- What are some things modern science is
studying about DNA?
• Some helpful search words for the web:
- DNA
- Nucleic Acids
- Human genome project
- DNA and forensic science
- Neatly write or type 1-2 paragraphs
describing what you found out. Be
prepared to share in class on Tues.
- Don’t forget to cite your sources!
Section 11-2 RNA
How does RNA differ from DNA?
*RNA is a nucleic acid made up of repeating
nucleotides. However, the sugar molecule of
every RNA nucleotide is __________, whereas
DNA nucleotides contain __________
_____________.
*______________, a nitrogen-containing
pyrimidine (one ring of carbon), usually replaces
thymine in RNA. Therefore, __________ pairs
with ______________ in RNA.
3 Types of RNA
• Type of RNA that consists of RNA
nucleotides in the form of a single uncoiled
chain. This RNA is responsible for carrying
genetic information from the DNA in the
nucleus to the cytosol of a eukaryotic cell:
_____________________(______).
• This RNA consists of a single chain of
about 80 RNA nucleotides folded into a
hairpin shape that binds to specific amino
acids. There are about 45 varieties of this
RNA______________(_______).
• This is the most abundant form of RNA. It
consists of RNA nucleotides in a globular
form. Joined by proteins, it makes up the
ribosomes where proteins are made:
_________________(______).
Transcription
Let’s think of transcription as an analogy.
Think of DNA as a reference book in a
library. These books can not be taken out
because they are very valuable and may
risk getting damaged if they leave the
confines of the library. If DNA were to
leave the nucleus and enter the cytosol, it
would enter an environment that would
make it more vulnerable to getting
damaged from radiation and chemicals.
So, how do we get information from the
reference book/DNA without taking it
out of the library/nucleus?
We make a copy.
This is where mRNA enters the picture.
The RNA is the messenger, or copier,
responsible for carrying the genetic
information from DNA in the nucleus to the
cytosol, where it can be used to produce
proteins.
Transcription is…
We will now go through the process of
transcription together. Please fill in notes
where indicated.
http://wwwclass.unl.edu/biochem/gp2/m_biology/ani
mation/gene/gene_a2.html
Some things to remember:
• As in replication, a small section of the
DNA double helix unwinds, and the bases
on the 2 strands are exposed.
• RNA nucleotides line up in the proper
order by hydrogen-bonding to their
complementary bases on DNA.
• The nucleotides are joined together by a
DNA-dependent __________ _________,
and __________ results.
How is Transcription different from
Replication?
• In transcription, only ___ strand of
DNA is transcribed into mRNA
(remember that RNA is a singlestranded molecule).
• The DNA strand that is transcribed is
called the ___________ __________.
What determines where transcription
will begin and end?
• In other words, where does one gene start and
the next begin?
• The starting point of a gene is marked by a
certain base sequence which is called a
_________ ____________.
• These sites act as a “start sign” . Similarly,
there are other base sequences at the end of a
gene that signal a
to mRNA synthesis.
• This DNA region is referred to as a _________
_____________.
What are the products of transcription?
• The transcripts are the different types of
RNA molecules, including mRNA, tRNA
and rRNA.
• Even though the instructions are for
making a protein are copied from DNA into
mRNA, all 3 types of RNA are involved in
the synthesis of proteins.