Download Name: Date: Per:______ DNA Guided Reading There are two types

Name:_____________________________________ Date:______________________ Per:__________
DNA Guided Reading
Nitrogenous
base
There are two types of nucleic acids called DNA (Deoxyribonucleic
acid) and RNA (Ribonucleic acid). The subunits or monomers of
nucleic acids are called nucleotides, which are made up of a
phosphate group, a nitrogenous base (adenine, thymine, cytosine,
guanine, and uracil), and a five carbon sugar. DNA provides the
information to the cell for making all the protein the cell needs.
Proteins are made of amino acids. The DNA has a specific code for
the amino acids. RNA copies the DNA pattern of nucleotides and
delivers the information into the cytoplasm. DNA is doublestranded, stays inside the nucleus, and has the base thymine. RNA is
single-stranded and moves from the nucleus into the cytoplasm,
and has the base uracil. DNA has the five carbon sugar deoxyribose
while RNA has the five carbon sugar ribose.
1. What are the two types of nucleic acids?
2. What are the four nitrogenous bases that pair together to help make up DNA?
3. List three differences between DNA and RNA.
4. DNA contains five carbon sugar_________________________________ while RNA contains
the five carbon sugar _______________________________ .
Mutations occur when there is a change in the order of bases in an organism’s DNA. Changes in the order
of bases in DNA can occur through errors when DNA is copied or damaged by physical or chemical agents
called mutagens. X-rays and UV radiation are examples of mutagens. Three types of changes can occur in
the order of bases in DNA: substitution, (bases are exchanged) insertion (a base is added), and deletion (a
base is left out). DNA codes for the traits, which are inherited, on genes made up of specific orders of
different nucleotides. Some nucleotides do not code for anything. Not all mutations are harmful.
Mutations can be helpful, harmful, or have no effect on organisms.
5. What causes mutations to occur?
6. What are physical or chemical substances that cause mutations called? _______________________
7. What are two examples of mutagens?
8. List the three types of changes that occur in the order of bases and describe what happens in each.
Watson, Crick, and Wilkins were given the Nobel Prize for identifying the structure of DNA. Their model
showed DNA as a double helix, or shaped like a twisted ladder. They based their findings on Rosalind
Franklin’s work which determined the structure of DNA as well as a rule which states that the bases of
DNA are always paired in a specific order. Adenine is always paired with thymine and cytosine is always
paired with guanine.
9. Describe the structure/shape of DNA.
10. How are the bases of DNA always paired? List the two pairings.
Mistakes in the process of meiosis can result in a new organism with more or fewer chromosomes than
normal. Individuals with Down’s syndrome have an extra copy of chromosome twenty-one. This results in
a variety of physical and/or mental conditions.
Many genetic disorders are caused by recessive genes. It is a disease or condition that results from
mutations. If an offspring receives two recessive alleles from parents, the child inherits the disease. If a
person is heterozygous, he/she does not show the symptoms. Sickle cell anemia is one such disease. It
results from a substitution at the base level of DNA. It commonly affects people of African, Indian, and
Mediterranean descent. The disease causes the red blood cells to become sickle-shaped. This prevents the
blood from passing normally through the capillaries, resulting in oxygen not being passed on to the
tissues.
11. What causes Down syndrome?
12. Why would both of a person’s parents need to carry the sickle cell gene for them to have it?