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Chapter 11 DNA
Within the structure of DNA is the
information for life- the complete
instructions for manufacturing all the
proteins for an organism.
DNA 15min video.asf
DNA is a polymer made of repeating
subunits called nucleotides.
Nucleotides have three parts:
simple sugar, phosphate group & a
nitrogenous base.
DNA polymer known as CGCGTTTTCGCG
The simple sugar in DNA, called deoxyribose,
gives DNA is name:
deoxyribose nucleic acid.
The phosphate group is composed of an atom of
phosphorous surrounded by 4 oxygen atoms.
A nitrogenous base is a carbon ring structure that
contains one or more atoms of nitrogen.
In DNA there are four possible nitrogen bases:
adenine (A), guanine (G), cytosine (c), and
thymine (T).
Replication of DNA
The DNA in the chromosomes is copied in a
process called DNA replication. Without
DNA replication, new cells would have
only 1/2 of the DNA of their parents.
During replication, each strand serves as a
pattern, or template, to make a new molecule.
Replication begins as an enzyme
that breaks the hydrogen bonds between
bases that hold the two strands together,
thus “unzipping” DNA.
Genes & Proteins
The sequence of nucleotides in DNA
contains information. This information is put
to work through the production of proteins.
RNA, like DNA, is a nucleic acid.
However they differ in three ways:
RNA is a single strand – DNA is double
2. RNA’s sugar is ribose – DNA’s sugar is
3. Both RNA & DNA have 4 nitrogenous bases,
but rather than thymine, RNA contains a
similar base called uracil
RNA vs DNA half min video.asf
If DNA is what provides “workers” with
the instructions for making the proteinswhat does RNA do?
RNA is the workers for protein synthesisthey take DNA instructions on how the
protein should be assembled then, amino
acid by amino acid, they assemble the
What are the three types of RNA and
what do they do?
mRNA – messenger – brings instructions from
the DNA in the nucleus to the cells cytoplasm
and then it moves it to a ribosome.
2. rRNA – ribosomal – binds to the mRNA and
uses the instructions to assemble the amino
acids in the correct order.
3. tRNA – transfer – delivers amino acids to the
ribosome to be assembled into a protein.
The diagram below shows a ribosome attach to mRNA,
and then move along the mRNA adding amino acids to the
growing polypeptide chain.
In the nucleus, enzymes make an RNA copy
of a portion of the DNA strand in a process
called transcription.
The main difference between
transcription and DNA replication :
Transcription results in the formation of one
single-stranded RNA molecule rather than
a double-stranded DNA molecule.
Genetic Code
The nucleotide sequence transcribed from
DNA to a strand of messenger RNA acts as
a genetic message, the complete
information for the building of a protein
The process of converting the information in
a sequence of nitrogenous bases in mRNA
into a sequence of amino acids in protein is
known as translation.
translation 2min video.asf
Genetic Changes
Mutations can be caused by errors in
replication, transcription, cell division, or by
external agents
Mutations in Reproductive Cells
Mutations can affect the reproductive cells of
an organism by changing the sequence of
nucleotides within a gene in a sperm or an
egg cell.
If this cell takes part in fertilization. The
altered gene would become part of the
genetic makeup of the offspring.
The mutation may produce a new trait or it
may result in a protein that does not work
correctly, resulting in structural or functional
problems in cells & in organisms.
In rare cases, a gene mutation may have
positive effects, helping an organism by
making it stronger or faster, better able to
survive in it’s environment.
Mutations in Body Cells
If a cell’s DNA is changed, this mutation
would not be passed on to offspring.
However, the mutation may cause
problems for the individual.
Give 2 examples:
stop stomach acid production needed for
2. cause skin cells to lose elasticity
Some mutations of DNA in body cells affect
genes that control cell division. This can
result in the cells growing and dividing
rapidly, producing cancer.
Point mutation is a change in a single base
pair in DNA. A change in a single amino
acid can affect the shape of the protein.
Frameshift Mutation is when a single base is
added of deleted from DNA.
Frameshift mutation is more harmful than
point mutation.
Chromosomal Mutations
Chromosomal mutations can take place
during either mitosis or meiosis.
They result in structural changes in
Causes of mutations
Some mutations seem to just happen,
however many mutations are caused by
factors in the environment. Any agent that
can cause a change in DNA is called a
Three examples are:
1. radiation
2. chemicals
3. high temperatures