DNA
 Deoxyribonucleic Acid (DNA) is found in what part of
the cell?
Nucleus
What is DNA made of?
 Monomers called Nucleotides
(Biochemical group Nucleic Acid:
3
parts:
 Sugar (deoxyribose)
 Phosphate group
 Nitrogen base
NUCLEOTIDES
 Named for the base it contains
 Looks like:
Sugar-----------Adenine
|
phosphate
THIS IS AN ADENINE NUCLEOTIDE
A nucleotide
DNA Structure
2 Nucleotide monomers are linked by
a bond between the SUGAR of one
nucleotide & the PHOSPHATE of the
next nucleotide. (Dehydration
Synthesis using an enzyme)
More monomers are added on the end
to form a long polymer
Monomers are linked on the end to
form a Single Long Strand
This “backbone” formed by linking
sugar to phosphate forms the
“sides” of the DNA ladder: the
STRONG, backbone of the DNA
strand (polymer)
But DNA is double stranded- How are
the 2 DNA strands held together?
 Pairing of nitrogenous bases(by
hydrogen bonds)!
 The “steps” of the ladder are the same
distance across- ALWAYS a purine (2
ring) with a pyrimidine (1 ring)
 Adenine (pur) pairs with thymine(pyr);
Guanine (pur) pairs with cytosine (pyr)
Bases Bond to Join 2 DNA Strands
(polymers)
 Joined pairs of nucleotides are called
“base pairs”
(PO4)
|
Sugar----A---T----Sugar
|
(PO4)
MORE ABOUT THE BASES…
Adenine always bonds to
thymine
Cytosine always bonds to
guanine
 Adenine –
Thymine (A-T)
 Cytosine-Guanine
(C-G)
DNA is a Double Stranded Molecule
The four bases (ATGC) form
complementary pairs in the double
helix.
This means that:
A always pairs with T.
G always pairs with C.
Double stranded DNA…..
If one strand is ACGCAATTGCATT
The other is
TGCGTTAACGTAA
This also makes it possible for DNA
copy it’s self…
BUT THERE’S MORE…
 The DNA molecule
isn’t flat, it’s 3-D!!!
 The whole thing coils
to look like a “spiral
staircase”
What are Chromosomes?
 Structures the DNA forms (with
proteins) to allow ALL of it to fit in the
nucleus
 All the DNA from 1 of our cells is 61/2 FEET long!!!
 Our cells have 23 different pairs of
chromosomes- 46 total.
 These store ALL the genetic
information to make YOU!!!!
What has to happen before a cell
divides?
All the DNA has to be copied, so
there will be 2 sets of chromosomes
in the cell
This way, BOTH daughter cells
(after division) will contain the
SAME genetic information as the
parent cell.
How does Replication happen?
DNA strands separate at the ‘origin’
& the DNA ‘unzips’
Enzymes (protein machines)
match free nucleotides to each
‘parent strand’
& bonds them to the backbone of
the newly synthesized strand.
Initiation of Replication
Semi-conservative
Replication
Replication is like making a second
identical copy of each DNA strand.
The 2 strands separate, and each is
copied separately.
This makes 2 double stranded
molecules that have one parent
strand and one new strand.
 This is called SemiConservative
Replication.
 Each new ‘Daughter’
DNA has 1 copy of
parent DNA (dk blue)
and one new strand of
DNA (light blue).
Summary:
 DNA replication results in 2 identical
copies from 1 original.
 Each ‘daughter’ DNA contains 1 ‘parent’
strand and 1 ‘new’ strand
 Because base pairing is always
complimentary (A-T; G-C), replication
enzymes can use the parent strand as a
‘template’.
Fill in the Newly synthesized
Strand.
 A T C G T G G C T A ATTGGCC….
T
CCGG….
What is the role of DNA?
Store ALL the information
The material genes are made of…
Gene - segment of DNA that carries
the information necessary to make
a protein.
How is the information stored?
- The order of the DNA bases!!
Genes, cont…
A gene is usually thousands of
bases long!
Because a gene is a series of DNA
bases that codes for a protein,
the information for the protein is
encoded in the sequence (order) of
the four DNA bases, ATGC.
The DNA in a single human cell =
3,000,000,000 bases (3 billion)
However, scientists were surprised
that there are only about 30,000
genes!!
How is the information
used by the cell?
It needs to change languages
to a form the cell uses to do
work- PROTEINS
But first, the gene needs to
be COPIED!
Transcription
 Genetic information in
DNA is copied to mRNA.
 Where does it happen?
 What is mRNA?
 Why is it necessary?
Answers:
Nucleus
messenger RNA
Needed to transport
coding info from the
nucleus to the ribosomes.
How is RNA different from DNA?
RNA= ribonucleic acid;
 Ribose sugar; phosphate;
nitrogen base
 Adenine, Guanine, Cytosine,
and URACIL (base pairs= C-G;
A-U)
 Single Stranded
Transcription has three main
phases:
1.Initiation
2.Elongation
3.Termination
1.Initiation – RNA
polymerase binds to
DNA at the START
sequence (Promoter) &
DNA uncoils
2.Elongation –
Complimentary
nucleotides are added
along the sense strand
3. Termination – When it reaches the stop
sequence in the DNA, the RNA
polymerase is released from DNA
Transcription Animation
 http://www.johnkyrk.com/DNAtranscription.html
 http://www.stolaf.edu/people/giannini/flashanimat/
molgenetics/transcription.swf

mRNA Splicing – Non-coding sequences
(introns) are removed and coding (exons)
are spliced together to make mature
mRNA
Overview of Protein Synthesis
Transcribe!
Write the DNA sequence of a
gene (at least 36 nucleotides
long.)
Transcribe the sequence of
the gene into mRNA
What happens nextTRANSLATION
What do you do when you go
from one language to
another? You TRANSLATE!
Languages? nucleic acid is
translated to amino acid
(protein)
Translation, cont.
Key “Players”:
mRNA
tRNA (transfer RNA)
Ribsosomes
Amino acids
Where does it happen?
The CYTOPLASM
 mRNA is the instructions for building the
protein
 How is the info stored?
 In the order of the bases!!!
(A,C,U,G)
 Translation takes place on the ribosomes
(machine that makes the protein)
 tRNA (transfer RNA) “reads” the nucleic
acid and supplies the CORRECT,
corresponding amino acid
CODON
 These serve as the “words” in the genetic
code
 A codon is made up of three nucleotide
bases (A, U, G, C).
 Each codon specifies an amino acid
(MONOMER) in the protein being made
(POLYMER)
 The codon is “read” by the tRNA anticodon
and the correct amino acid is linked to the
growing polypeptide chain
Quick Quiz
1. The process where genetic
information is copied from DNA to
mRNA is called ___________.
2. List 3 differences between DNA and
RNA
3. List the 3 phases of transcription.
4. Write the complimentary RNA
sequence for the following DNA
sequence:
AAGGCCTTAGACTGT
Quick Quiz, cont…
5. The process of synthesizing a protein
FROM the mRNA is called
________________.
6. How many nucleotides in a codon?
7. The anticodon is part of the
_________.
8. The codon is part of the ___________.
9. What “machine” is necessary for
translation to take place?
10. What is the monomer of a protein?