DNA
Deoxyribonucleic
Acid
THE master molecule of
life!
DNA
•DNA is often called
the blueprint of life.
•Why would we refer
to this molecules as a
blueprint?
DNA Contains instructions for building an
organism like these are instructions for
building the batmobile.
It shows all needed parts and how they fit
together.
The DNA in the nucleus gives instructions
on how to build proteins. Proteins are
how traits (such as eye, skin, and hair
color) are expressed.
Individual Components of
DNA/RNA
DNA
• Nucleotides
RNA
• Nucelotides
– Phosphates
– Deoxyriboses
– Nitrogenous
Bases:A,T,G,C
– Phosphates
– Riboses
– Nitrogenous
Bases:A,U,G,C
• Histones
• Hydrogen Bonds
• Make up Genes
• Is DNA’s message
To get lots of DNA into a small
space…
• We wrap up the DNA• Allow DNA to coil
around histones so that
the coils are even and
safe from breaking!
Click on picture to watch video. Stop after histones (1:40).
Organization of the DNA
Hydrogen
Phosphates
Sugars
Nucleotides
DNA
Genes
Histones
Chromosomes
From smallest to largest
sized structures
Answer these:
Review monomers versus polymers – what
do those words mean?
Which of the previous items are monomers
and which are polymers?
What is the monomer for DNA?
What are the 3 components of that
monomer?
• Genes are a series of nucleotides or a
segment/section of DNA
• There are many genes on a chromosome.
• Humans have 23 homologous
chromosomes. (22 pairs are autosomal, 1
pair is sex)
• Chromosomes are in the nucleus of 2 types
of cells:
– Somatic cells are non-sex cells and are diploid.
(Example skin cells)
– Gametic cells are sex cells and are haploid.
(Example sperm or egg)
Using root words to figure this out,
what do haploid and diploid
mean?
The Shape of the Molecule
• DNA is a very long
polymer.
• What type of organic
compound is this?
• What functional group
would you find on
nucleic acids like DNA
or RNA?
• The basic shape is like
a twisted ladder or
zipper.
• This is called a double
helix.
The Double Helix Molecule
• The DNA double
helix has two
strands twisted
together.
• The nucleotides on
each strand are
held together with
covalent bonds
• The strands are
held together by
hydrogen bonds
Label your DNA coloring
Complementary Bases
• Review the possible
DNA base pairs and
how they bind
together in the
DNA.
• Also, review the
actual names of the
4 nitrogenous base
pairs found in DNA.
Answer These:
• When would you need to make a copy
of DNA?
• Would the copy of DNA need to be
identical or slightly different from the
original?
• In what organelles would you find DNA
or RNA?
• How will enzymes be involved in
copying DNA? In making RNA?
You have reached the end of the note
guide.
For the remainder of this document, you
should take notes on loose leaf paper as
we will be doing this content in lecture.
Make sure to have the notes copied and
prepared for lecture on Tuesday.
DNA Replication
Some basics about the
chemistry of DNA
• The ends of each strand of DNA’s sugarphosphate backbone, is polar.(What does that
mean?)
• The sugar side is slightly positive (OH) (aka 3’)
• The phosphate side is slightly negative (P) (aka 5’)
• Enzymes all build new strands in a 5 (-) to 3’ (+)
direction when they work!
• That means they move along the original strand
from 3’ to 5’
Possible ways to get from original
(parental DNA) to a newly
synthesized molecule of DNA…..
Conservative
Dispersive
Semiconservative
DNA replication Determined by
Meselson and Stahl
Steps to make more DNA (an exact copy)
1. Unwind double helix and break the H bonds
(helicase)
2. Stabilize open strands (use the spooling
proteins called histones)
3. Copy DNA by adding complementary
nucleotides (DNA polymerase)
4. Check for errors (ligase and polymerase)
5. Connect fragments on the lagging strand
(ligase)
Semi-conservative replication
• Each DNA molecule will consist of an old and a new
strand of DNA.
• This means each parental or original strand of DNA
can act as a template to copy.
• However, based on those back bone charges and
the mandatory direction of DNA polymerase, we
have a leading and lagging strand during
replication.
Charges and Copy Issues
• Charges on DNA strands and charges on the
enzymes copying the DNA cause a “leading” and
“lagging” strand during replication. These terms
are used to describe the template strand (one
being copied) of DNA.
• Replication enzymes move along the template
(original DNA) from 3’ – 5’. While building the new
strand from the 5’ – 3’
• So the parental strand (template/original) of DNA
that starts with the 3’ side is called the “leading
strand”.
• The one that starts with a 5’ is called the “lagging
strand”.