Download DNA Structure Notes PPT

You will get your test back tomorrow.
New groups on Thursday.
1. Turn to the last item you put in your composition book for the
Viruses and Cells Unit…
2. On the next page, make a Table of Contents for the new Unit
‘DNA
and Mitosis’
3. I will come around with your colored tab to attach to that page!
DNA and Mitosis
1
DNA Progress Monitoring Sheet
10/25
2
DNA Structure Notes
10/25
Essential Question
• Which part of the DNA molecule
specifically contains your genetic code?
DNA
• Genetic information in the form of a code is held in
the DNA molecules.
• This code holds the directions for making proteins.
Your proteins are what determines your traits.
So what? Why are proteins important????
You are composed of proteins- your skin, hair, eyes
contain proteins….organs, muscles, bones…
(everything that makes you…you.)
• All actions, such as eating, running, and even thinking,
depend on proteins called enzymes.
• DNA is a large molecule made of repeating
sub-units (smaller molecules) called
nucleotides.
There are
three parts to
a nucleotide.
• The simple sugar in DNA is called deoxyribose
• This is where DNA gets it’s name
“Deoxyribose Nucleic Acid”
Sugar
Phosphate
Group
• The phosphate group is composed of one atom
of phosphorus surrounded by four oxygen
atoms.
Nitrogenous
Base
• A nitrogenous base is a carbon ring structure
that contains one or more atoms of nitrogen.
• In DNA nucleotides, there are four possible
nitrogenous bases:
Adenine (A)
Guanine (G)
Cytosine (C)
Thymine (T)
• Double-ringed nitrogenous bases, Adenine and
Guanine, are called PURINES.
• Single-ringed nitrogenous bases, Thymine and
Cytosine are called PYRIMIDINES.
What is DNA made of?
• Thus, in DNA there are four possible nucleotides, each
containing one of these four bases.
DNA STURCTURE
The phosphate groups and sugars of the nucleotides
form the backbone of the DNA molecule
“Legs of ladder”
Phosphate &
Sugar Backbone
DNA STURCTURE
The bonds in the backbone between the sugars and
phosphates are covalent bonds
(strong bonds)
DNA STURCTURE
The nitrogenous bases make up the middle rungs of
the DNA molecule.
“Rungs of ladder”
Nitrogenous
Base (A,T,G or C)
DNA STURCTURE
The bonds between the nitrogenous bases are weak
hydrogen bonds
(indicated by the dotted line)
What else do you notice about the nitrogenous bases?
DNA STRUCTURE
• These paired bases
are called
complementary
base pairs.
• In DNA, adenine
always pairs with
thymine,
A --- T
• and guanine always
pairs with cytosine.
G --- C
• Anti-Parallel
One side of the molecule is right side up (5’-3’)
The other side of the molecule is upside down ((3’ – 5’)
5’ TGCA 3’
3’ ACGT 5’
DNA STRUCTURE
• In 1953, Watson and Crick proposed that DNA is
made of two chains of sugar and phosphate held
together by nitrogenous bases.
• Watson and Crick also proposed that DNA is
shaped like a long zipper that is twisted into a
coil like a spring.
DNA STRUCTURE
• When something is twisted like a spring, the shape is
called a “helix”.
• Because DNA is composed of two strands twisted
together, its shape is called double helix.
DNA STRUCTURE
The sequence of nucleotides
(A,T,C,G) forms the unique
genetic code of an organism.
The closer the relationship is
between two organisms, the
more similar their DNA
nucleotide sequences will be.
DNA STRUCTURE
• Scientists use nucleotide sequences to determine:
Evolutionary relationshipsHow closely related are organisms of different
species?
DNA STRUCTURE
• Scientists use nucleotide sequences to determine:
Family relationshipsAre two organisms of the same species related?
DNA STRUCTURE
• Scientists use nucleotide sequences to determine:
Crime victims and suspectsWho does this DNA belong to?
Talk to the people next to you and make sure you
understand complementary base pairs in DNA.
1.What is the complementary strand for:
5’
ATC GGA TCG 3’
Question 2
Which of the following is NOT a component of DNA?
A. simple sugars
B. phosphate groups
C. nitrogenous bases
D. proteins
The answer is D.
Question 3
Which DNA strand can base
pair with the DNA strand shown
here (Top of pic to bottom)?
A. T-A-C-G-T
B. T-G-C-A-T
C. T-G-C-A-G
D. T-C-C-A-G
The answer is B,
T-G-C-A-T. In
DNA, adenine
pairs with thymine
and cytosine pairs
with guanine.
T
G
C
A
T
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