DNA
Deoxyribose
Nucleic
Acid
DNA
• The chemical make-up of genes
• Stores and passes genetic info from one
generation to the next. (heredity)
• Determines your traits
DNA is a long molecule made up of
nucleotides.
Nucleotides have:
• A phosphate
• A 5 carbon sugar
Ribose
• One of four nitrogen bases:
–
–
–
–
Adenine- A
Thymine- T
Guanine- G
Cytosine- C
The DNA Molecule
• Discovered by Watson, Crick, Wilkins, and Rosalind
Franklin. (1953)
• Molecular shape is a double helix.
Double Helix
• Like a twisted ladder.
• Sides made up of sugar and
phosphate (backbone).
• Cross-rungs are made up of pairs
of nitrogen bases.
Nitrogen Base Pairing
• Adenine and Thymine
• Guanine and Cytosine
ALWAYS!!!!
What would the nitrogen base pairs be to
form a double helix?
AGGCCTA-
A and T always pair together.
G and C always pair together.
A-T
G-C
G-C
C-G
C-G
T-A
A-T
What holds the two sides of
the DNA molecule together
(what connects the pair of
nitrogen bases)?
Hydrogen
Bonds
Histones
• The double stranded DNA molecule is then coiled
(helix) and supercoiled (wrapped around proteins
called histones).
• One human cell contains over 1 meter of DNA
Double Helix Activity
Left =
sugar up
Right =
sugar
down
• 3 sections of backbone (other 3 will be
complimentary strand)
• 5 nucleotides on each section
• Complete one section of backbone first, and
then complete its complementary strand of DNA
• Connect the two strands with tape. Use a blue
line to represent hydrogen bonds between the
nitrogen bases.
• Continue with the other two complementary
sections of backbone
Introduction to DNA
• http://learn.genetics.utah.edu/content/begi
n/tour/
Opener 4/23 – pg. 136
1. In your own words describe the structure
of a DNA molecule.
2. Using a ladder as an analogy, what parts
of a DNA molecule can be described as:
a. The sides of the ladder
b. Rungs of a ladder
Opener 4/28 – pg. 136
A single cell in your body has about 2 m of
DNA.
• How does your cell package the DNA so it
can efficiently be copied and transferred?
(don’t answer this yet!)
DNA Replication
• The DNA molecule unwinds.
• The molecule “unzips” at the H bonds.
• New nucleotides attach following the rules
of base pairing.
• Each strand of the DNA serves as a
template for a new strand.
DNA replication is carried out by a
series of enzymes.
• DNA Polymerase joins
individual nucleotides to the
strand and proofreads each
new strand reducing
the chance of mistakes.
DNA Replication Animations
• http://www.youtube.com/watch?v=yqESR7
E4b_8
• http://highered.mcgrawhill.com/sites/0072943696/student_view0/
chapter3/animation__dna_replication__qui
z_1_.html
Warm-up 4/30 –pg. 139
1. People sweat to help maintain body temperature. What
type of feedback happens when sweating regulates body
temperature? Positive or Negative feedback and why?
2. Plants use nitrogen to make proteins. What is present in
the soil that makes nitrogen directly available to plants?
DNA Replication Review
• Make 3 diagrams:
• First: show a labeled 15-base (pair)
section of double-stranded DNA (so 30
nucleotides)
• Second: show what the DNA would look
like during the replication process.
• Third: show the results of replication
*Make sure to label the following: all
base pairs, origin of replication,
replication fork, DNA polymerase
Quick Write
• In a paragraph describe the process of
DNA replication.
– You can use diagrams in addition to help
make your point
– Your task is to prove to me your
understanding of the entire process of
replication with its “key players”