Key Concepts:
What forms the genetic code?
How does a cell produce proteins?
How can mutations affect an
organism?
Key Terms:
Messenger RNA
Transfer RNA
Main function of genes is to
control the production of
proteins
Genes and DNA: Chromosomes
are made of DNA.
Genes are sections of a DNA
molecule that codes for one
specific protein. May contain
several hundred to a million
or more base pairs (Ex.
AGGTCACGAATTTTCCGG)
• The order of the nitrogen bases along a gene forms a
genetic code that specifies what type of protein will be
produced.
• Proteins are made of amino acids – A group of 3 base
pairs codes for a specific amino acid
• Ex. CGT = alanine (an amino acid)
• The order of the 3 base code units determines the
order of the amino acids and makes the different
proteins
The Role of RNA
• Protein synthesis takes place on ribosome in
cytoplasm
• RNA acts as a messenger to take the DNA’s
information in the chromosomes to the ribosomes in
the cytoplasm
• RNA similar to DNA, yet different in some key ways:
–
–
–
–
single strand
ribose sugar
Bases – same - adenine, guanine and cytosine
different – uracil instead of thymine
Messenger RNA – copies code from DNA in the
nucleus and carries message to ribosomes in the
cytoplasm
Transfer RNA – carries amino acids to ribosome
and adds them to the growing protein molecule
First Step:
1. DNA molecule unzips between base pairs
2. DNA directs the production of a strand of messenger
RNA
3. To form the RNA strand – RNA bases pair with DNA
bases. Guanine with Cytosine, but uracil pairs with adenine
instead of Thymine
Second step:
1. Messenger RNA leaves nucleus and attaches to a
ribosome in the cytoplasm
2. Messenger RNA provides the code to make the
protein molecule
3. The ribosome moves along the messenger RNA
strand
Third Step
1. Molecules of transfer RNA attach to messenger RNA
2. Bases of transfer RNA read the message by pairing
up 3-letter codes to bases of messenger RNA
3. Molecules of transfer RNA carry specific amino acids
that link in a chain
4. Order of amino acids is determined by order of 3letter code on messenger RNA
Fourth Step
1. Protein molecule grows longer as each transfer RNA
adds an amino acid
2. When done the transfer RNA is released into the
cytoplasm and can pick up another amino acid
3. Each transfer amino acid picks up the same type of
amino acid
A mutation is any change in a gene or
chromosome
Mutations can cause a cell to produce an incorrect
protein during protein synthesis.
As a result of a mutation, the organism’s trait or
phenotype, may be different from what it
normally would have been
If a mutation is in a body cell, it will not be passed
on to the offspring. If it is a sex cell, it can be
passed on and can affect the offspring’s
phenotype
Substitution
Insertion
Deletion
Some mutations happen during DNA Replication:
A single base may be substituted for another
One or more bases may be removed from a section
of DNA or new bases inserted
Some mutations happen during Meiosis:
Chromosomes don’t separate correctly
Cell can end up with too many or too few
chromosomes
Cell could end up with fragments of chromosomes
Mutations introduce change in an
organism and so are a source of
genetic variety
Some mutations are harmful,
some are helpful, and some don’t affect
the organism
Whether a mutation is harmful or not
depends partly on the environment
A mutation causing an albino animal in
the wild would be harmful, but if the
animal lived in the zoo, it would not
matter
Helpful mutations improve an organism’s chances for
survival and reproduction
Ex. Bacteria that have mutations that have given them
resistance to antibiotics are more likely to survive and
reproduce
http://www.sciencewithmrmilstid.com/media/chrom
osomalDNA.png
http://www.medceu.com/images/molecularmachine.j
pg
http://www.accessexcellence.org/RC/VL/GG/images/p
rotein_synthesis.gif
http://faculty.irsc.edu/FACULTY/TFischer/bio%201%2
0files/protein%20synthesis%20overview.jpg
http://www.nature.com/scitable/content/ne0000/ne0
000/ne0000/ne0000/6632005/EssGen_BaseSubstituti
onFig1_MID_0.jpg
