Section 4.2
HOW DOES DNA WORK?
Vocabulary
 RNA: RiboNucleic Acid . . .
A molecule that is present
in all living cells and plays
an important role in protein
production.
 Ribosome: A cell organelle
composed of RNA and
protein . . . The site of
protein synthesis.
 Mutation: A change in the
nucleotide-base sequence of
a gene or DNA molecule.
Unraveling DNA . . .
 In prokaryotic cells (cells that lack a nucleus), DNA
forms a loose loop within the cell.
 In eukaryotic cells (cells with a nucleus), DNA and
proteins are bundled into chromosomes.
 As we discussed in section 4.1, the structure of DNA
allows it to hold important information for the cell.
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The order of bases (ATGC) on one side of the molecule is a
code that carries information.
A gene consists of a string of nucleotides that give a cell
information about how to make a specific trait.
Genes and Proteins . . .
 DNA is read like a book . . . From one end to another and in one direction.
 The bases form the alphabet of the code.
 Groups of 3 bases are the codes for specific amino acids.
 Long strings of amino acids form proteins.
 Essentially, each gene is usually a set of instructions for making a protein.
 PROTEINS are found throughout cells and cause most of the differences you can see
among organisms.
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Proteins act as chemical triggers and messengers for many of the processes with cells.
An organism could have thousands of genes that code for thousands of proteins.
 RNA (RiboNucleic Acid) is similar to DNA and serves as a temporary copy of a DNA
sequence during protein production.
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Several forms of RNA help in the process of changing DNA code into proteins.
 MAKING PROTEIN . . .
 First, a copy of one side of DNA segment is made (this mirror-like copy is RNA . . . This copy
segment is called messenger RNA (or mRNA). After it is made, it moves out of the nucleus and
into the cytoplasm of the cell.
 Then, the messenger RNA id fed through a protein assembly line. Ribosomes are the “factories”
that run the protein assembly lines. During this process, the messenger RNA is fed through a
ribosome (3 bases at a time). Then, transfer RNA translate the RNA message ad attack correlating
bases (3 at a time) to the messenger RNA . . . This forms the amino acids necessary to produce
protein molecules.
Making proteins . . .
 http://www.youtube.com/watch?v=D3fOXt4MrOM
Changes in Genes . . .
 MUTATIONS: Changes in the number, type, and order of
bases on a piece of DNA are known as mutations.
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Deletion is when a base is left out.
Insertion is when a base is added.
Substitution is when the wrong base is used
 Do mutations matter?
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Three things may happen as a result of a genetic mutation: an
improved trait, no change, or a harmful trait.
 How do mutations happen?
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Mutations occur regularly because of random errors when DNA is
copied.
Damage to DNA by be caused by abnormal things that happen to
cells . . . Any physical or chemical agent that can cause a mutation is
called a mutagen (radiation, UV radiation, asbestos, and chemicals
in cigarette smoke).
Mutations continued . . .
 Types of
mutations
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Sickle Cell Disease . . .
 A simple change in an amino
acid can cause sickle cell
disease.
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Sickle cell disease affects red
blood cells . . .
When valine is substituted for
glutamic acid (both different
amino acid chains), the red blood
cells are changed into a sickle
shape. This is bad because sickle
cells are not as good as carrying
oxygen and are more likely to get
stuck in blood vessels and cause
dangerous clots.
Uses of Genetic Knowledge . . .
 GENETIC ENGINEERING: Scientists can manipulate
genes within organisms (combining traits). Scientists
also use genetic engineering to create new products
(drugs, foods, and fabrics).
 GENETIC IDENTIFICATION: Because your DNA is
unique, it can be used like a finger print to identify you.
DNA fingerprinting identifies unique patterns in an
individual’s DNA. This can be useful in crime scene
investigations, identifying family relations, and
identifying hereditary diseases.
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Only identical twins have the same DNA . . . Except, more recently,
some scientists have created clones, or new organisms that have an
exact copy of another organism’s genes.
Homework
 Now, open your textbooks to page 90 . . .
 Define the 4.2 vocabulary terms
 Then read the section and begin working on the 4.2 packet
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