Download The DNA Connection - Conackamack Middle School

The DNA Connection
Pages 107-112
Key Concepts:
1. What forms the genetic code?
2. How does a cell produce proteins?
3. How can mutations effect an
organism?
Introduction
• The young, white, ringtailed lemur was born
in a forest in
Madagascar.
• White lemurs are
extremely rare.
• Why was this lemur
born with such an
uncommon phenotype?
• To answer this
question, you need to
know how the genes on
the chromosome
control an organism’s
traits.
The Genetic Code
• A review:
– Chromosomes are made up of DNA
– A DNA molecule is made up of four
nitrogen bases: A, T, C and G
– A gene is a specific section on the DNA
molecule that codes for a protein
A single gene could contain
several hundred to a million
or more bases.
The Order of the Bases are
Important
• The order of the bases determines
exactly what protein will be made.
• Every 3 letters (codon) codes for an
amino acid.
• Chains of amino acids build a protein.
Amino acids are like pearls on a
necklace. Pearls are stranded together
to form a necklace. Amino acids are
stranded together to form a whole
protein.
So, how does the cell make proteins?
• The process is called PROTEIN
SYNTHESIS.
– The cell uses the information from a
gene on a chromosome to make a protein.
– Happens on a ribosome in the cytoplasm
• Remember – the ribosome is known as the
“Protein Factory.” This is why.
Ribosomes
Protein Synthesis requires DNA
and RNA to work together.
• What is RNA?
– The “messenger” that carries the code
from DNA out to the cytoplasm.
DNA
RNA
How Are DNA and RNA Different?
1. Number of strands
-
DNA is double-stranded (known as the
“Double Helix”), while RNA is made up of only
one strand
2. Type of sugar
- The sugar in DNA is called
deoxyribose, while the sugar is RNA is
called ribose
3. Nitrogen Bases
- DNA is made up of A, T, C, and G, while
RNA is made up of A, U, C, and G.
Thymine is replaced with URACIL.
•
Types of
RNA
Messenger RNA
(mRNA)
– Job: copies the code
from DNA in the
nucleus and carries it
out to the cytoplasm
A waitress
copies down
the order
from the
customer.
Just like
mRNA copies
down the code
from DNA.
• Transfer RNA
(tRNA)
– Job: carries the
amino acids to a
ribosome to form a
growing protein.
The chef puts together all the
ingredients to build a meal. Just
like tRNA puts all the amino acids
together to build a protein.
How it all Works.
• STEP 1 – Messenger RNA is Made
• STEP 2 – Messenger RNA Attaches
to a Ribosome
• STEP 3 – Transfer RNA Attaches to
messenger RNA
• STEP 4 – The Protein is Complete
STEP 1
• mRNA is
made
– DNA unzips
– mRNA is
made when
bases match
up to the
DNA strand.
(U matches
up with A)
Step 2
• mRNA attaches to
a ribosome
– mRNA exits
nucleus and enters
the cytoplasm
– The mRNA moves
along the ribosome
and every 3-letter
code is read.
(called a CODON)
Step 3
• tRNA attaches to
mRNA
– tRNA carries
over an amino
acid. It matches
up to the codon
with an anticodon.
– The protein chain
grows with each
amino acid.
Step 4
• The protein is
done.
– The ribosome
reaches a STOP
codon.
– The protein is
released out to
the cell to do its
job.
Proteins can be short or very long
(100’s or 1000’s of amino acids).
Here’s how the whole process
works
http://www.pbs.org/wgbh/aso/tryit/dna/shockwave.html
What happens if the wrong
protein is made?
• Mutations occur
– Any change that occurs in a gene or a
chromosome.
• Can occur randomly (naturally)
• Can be deliberately caused in the
laboratory by scientists
• Can be inherited
• Are not always harmful
Types of Mutations
• Inherited
• From
mutations
found in
parent’s sex
cells
• Acquired
• Changes in
body cells
during the
lifetime of a
person
ALBINOS
• Little or no pigmentation
in the eyes, skin, and hair.
• Inherited an altered copy
of a gene that does not
work correctly.
• The altered gene does not
allow the body to make
the usual amounts of a
pigment called "melanin".
• True albinos have pink
eyes and skin.
Mutations can be helpful
• Mutations in potatoes
causes a new variety
to form.
• These Katahdin
potatoes are resistant
to some diseases that
attack other varieties
of potatoes. They also
look and taste better
than other potatoes.