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Name: ______________________
Date: _____________
Unit 4A: DNA Structure and Replication
NOTES
DNA Structure
DNA (Deoxyribonucleic Acid)
DNA Nucleotide
- A nucleic acid
-
Made up of _______________
DNA is a molecule that must
sometimes be copied.
When/why does the DNA need to be
copied?
__________________________________________________________________
__________________________________________________________________
How many different types of nitrogenous
bases are found in DNA? _________
• What do pyrimidines have in common?
__________________
• What do purines have in common?
_____________________
• If each nucleotide contains 1 nitrogen
base, how many different types of DNA
nucleotides can be formed? ______
• NOTE: Another type of nucleotide,
Uracil (U), will replace the Thymine
nucleotide in RNA molecules.
Notes/Summary:
2
P
Here is an example of a nucleotide:
B
We normally draw a nucleotide using
symbols/letters to represent the parts.
S
• What does the "A" stand for? ________
• What other letters could be used in that position?___________
• What does the "S" stand for?___________________________
• What does the "P" stand for?___________________________
• If the sequence of nucleotides in one strand of a DNA molecule is
T-A-C-G-G-T-C-A-A, what would be the complementary base pairs on the
other strand? ______________________________
P
Phosphate Group
Notice that each nucleotide bonds with a
nucleotide above and
below it. This forms a
strand of DNA.
The two strands run in opposite directions. This is called
_______________________________.
The two strands are then twisted into a spiral shaped, double
stranded structure called a ________________________.
Notes/Summary:
3
The bonds that hold the nucleotides in a strand of DNA together are covalent
bonds (highlight these)
The bonds in between the nitrogenous bases that connect the two strand are
hydrogen bonds (draw these in color)
• Circle a nucleotide on the drawing to the left
• What does each nucleotide have in common?
______________________________
• How do nucleotides differ from each other?
_______________________________
• How many strands make up a molecule of DNA? ______
• Adenine (A) pairs with _____________________
• Cytosine (C) pairs with _____________________
Who discovered the structure of DNA?
• Erwin Chargaff (1950)
– Determined that the percent of A was about equal to
the percent of T in any DNA molecule.
– Likewise, the percent of C was about equal to the
percent of G.
– This is known as “____________________________”
– Why did he see this consistency?
• ___________________________________________________
___________________________________________________
(complementary base pairing)
Notes/Summary:
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Using Chargaff’s Rule:
Source of
DNA
Percentage of Bases in Human DNA
A
T
C
G
Human
• Rosalind Franklin (1952)
– Used X ray diffraction
– Her image hinted that DNA was two
stranded and in a helical shape
• James Watson and Frances Crick
(1953)
– Won the Nobel Prize for
determining the structure of
DNA
– Used info from Chargaff and
Franklin
James Watson
Francis Crick
Human Genome Project (1990-2003)
• Genome: the entire set of _________________________________ that
makes up the DNA of an organism
• Completed in 2003, the Human Genome Project (HGP) was a 13-year
project coordinated by the U.S. Department of Energy and the National
Institutes of Health.
Notes/Summary:
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Goals of the Human Genome Project
• identify all of the approximately 20,000-25,000 genes in human DNA
• determine the _________________ of the 3 billion base pairs that make up
human DNA
• store this information in databases for use by scientists everywhere
• address the ethical, legal, and social issues (ELSI) that may arise from the
project.
DNA Sequencing
• the laboratory technique used to determine the exact sequence of A’s, T’s,
C’s, and G’s in an individual’s entire genome.
What were three surprises for scientists after they sequenced the human genome?
– ________________________________________________________
– ________________________________________________________
– ________________________________________________________
• What were two good things that came from sequencing the human genome?
– ________________________________________________________
– ________________________________________________________
Notes/Summary:
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Forms of DNA and How it is Organized
• Where is DNA located?
– Prokaryotic- _______________________
– Eukaryotic- _______________________
• Every body cell has a complete copy of DNA
Forms of DNA:
• Prokaryotic- 1 circular loop
• Eukaryotic- multiple linear (straight) strands
found in 2 forms depending on the situation.
1. Chromosomes
2. Chromatin
1. Chromosome: tightly packed, or “condensed” strands of DNA. DNA forms
these structures when the cell is dividing. Usually shown as an X-shape or doubled
chromosome.
• Histones - Proteins which act like spools for
thread. DNA is wound around the histones.
Karyotypes
• A picture of all of the chromosomes from one cell of an
organism.
• How many total chromosomes are in the karyotype? __
• These chromosomes are from a _________________.
Notes/Summary:
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Every species of eukaryotic organisms have
a specific number of chromosomes in each
cell:
• How many chromosomes do humans
have? _______
• How long is the DNA in one human
cell?__________
• How does that much DNA fit into a
cell?
Organism
goldfish
chicken
horse
sand dollar
chimpanzee
dog
human
brown bat
corn plant
housefly
fruit fly
Number of
Chromosomes in
each cell.
94
78
64
52
48
48
44
20
12
8
__________________________________________________________________
__________________________________________________________________
2. Chromatin - loosely packed, or “working” form of DNA. The strands are loose
and exposed so that the code or protein “recipes” can be read and proteins can be
synthesized.
Notes/Summary:
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Why have 2 different forms of DNA in your cells?
• Chromosomes are useful because they are ___________________ and easy
to __________ and move when cells are _____________ to make new cells.
• Chromatin is useful because it is ____________________ so genes can be
______________to make proteins (like an open book)
Why is the number of chromosomes different for different organisms?
1) Chromosomes are different ____________________
2) Chromosomes have different ____________________________________
3) Organisms need different ________________ and _________________ for
different functions.
DNA Replication
• DNA must be copied before cell division so that any new cells will have an
__________________________ copy of the DNA from the original cell.
Steps in DNA replication:
Notes/Summary:
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1. The enzyme DNA helicase _______________ and ______________ the double
helix and the 2 DNA strands are separated between the complementary nitrogenous
bases.
2. The enzyme DNA polymerase helps to ______________ free floating DNA
________________________ with the complementary nitrogenous bases on each
of the two strands
3.) Covalent bonds join the nucleotides above and below each other on the new
strands. And, the hydrogen bonds are formed between the complementary
nitrogenous bases (from one strand to another).
4.) Each new DNA strand formed contains ONE __________________ (original)
strand and ONE ______________________(new) strand.
Summary of Replication
• DNA double helix splits into two strands
• Each strand becomes a __________________ for new nucleotides to bind
• Base pairing allows for the correct sequence to be created on the new
“_________________________________” strand
• If an error is made during replication it is called a ___________________.
Notes/Summary:
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Notes/Summary: