Transcript DNA and Protein Synthesis lesson

Chapter 12 – DNA and Proteins
DNA Structure:
DNA is made of many smaller subunits
called nucleotides.
A nucleotide has 3 parts:
1.A sugar (a 5 Carbon deoxyribose)
2.A Phosphate group
3.A nitrogenous base - 4 types of these
Adenine (A)
Thymine (T)
Cytosine (C)
Guanine (G)
Always pair up
Always pair up
Adenine and Guanine are purines (bigger)
Cytosine and Thymine are pyrimidines (smaller)
These subunits are arranged in a twisted
ladder called a double helix.
If you untwisted the ladder, it would
look like this:
nitrogen base
phosphate
Sugar
weak hydrogen bonds hold the bases together
The sequence (or order) of the bases in all
organisms’ DNA is what makes them
different from each other.
A gene is a segment of DNA that codes
for a specific trait.
Stop for DNA structure activity:
Be careful with these….they are borrowed
from Mr. Pontzer! Please return them
exactly as you found them! Thank you!
Build a double helix using the drawing you
made in your notes. Look at the example
up front to see how it goes together.
Key is on the next page:
Tubes:
Red = Adenine
Blue = Thymine
Green = Guanine
Gray = Cytosine
Other pieces:
Sugar = black
Phosphate = red
White, round pieces are
the hydogen bonds
bonds.
Yellow tubes are
the phosphate/sugar
bonds.
(correct bases must pair!)
Longest and longer green tubes are to
make a stand for the DNA molecule.
Protein Synthesis
DNA tells our cells how to put proteins
together.
Remember! - Proteins have specific
shapes for specific functions
- Proteins are made from long
chains of 20 types of amino
acids
- Different proteins exist because
amino acids are assembled in
different sequences.
Steps of protein synthesis:
1.Transcription – In the nucleus, the DNA
code is “copied” onto a molecule of
messenger RNA (mRNA) by matching up
base pairs.
RNA contains uracil (U) instead of
thymine(T).
After transcription, the mRNA leaves the
nucleus and moves to the ribosome.
2. Translation – The ribosome reads the
mRNA in 3-base sequences called codons.
Specific amino acids are added to a
growing protein chain. They are matched
up with an anticodon found on a
transfer RNA (tRNA) molecule.
What is a mutation?
􀂄 Any change in DNA
􀂄 Any abnormal change in genetic
material.
Some can be inherited by the next
generation if they are present in sex
cells.
What causes a mutation?
1.) Changes in the environment OR
mutagens
a. ultraviolet radiation
b. pollutants and chemicals
c. tar from tobacco
2.) Errors during replication, transcription,
or translation
Types of mutations:
􀂄 Point mutations
small (but significant) changes, often in
a single nucleotide base.
Example: Sickle Cell Anemia is caused by
a point mutation.
􀂄
Point Mutation
Types of mutations:
􀂄Frame Shift when either insertion or
deletion of one or two nucleotide bases.
When this occurs, the “reading frame” is
changed so that all the codons read after
the mutation are incorrect.
Disorders that result from mutations:
􀂄 Sickle Cell Anemia
􀂄 PKU
􀂄 Cystic Fibrosis
Chromosomal Mutations
End Result:
Different polypeptide or protein chains
can be made from different
amino acid sequences. These proteins
will have different functions!