Download • What does DNA stand for? • Where do we find DNA? • How do

DNA
• What does DNA stand for?
• Where do we find DNA?
• How do crime scene investigators use DNA to
solve crimes?
NUCLEIC ACIDS
Flow of biological information:
DNA
RNA
protein
I.
trait
DNA deoxyribonucleic acid carries the genetic code
(stores and transmits the genetic information
from one generation to the next)
parents
offspring
A. Chromosomes are made of DNA
B. Located in the nucleus only
Model of DNA:
The model was developed by
James Watson and Francis Crick.
They received a Nobel Prize in
1962 for their work.
First picture of DNA (X-ray) –
Rosalind Franklin
The model looks like a twisted
ladder – double helix
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Died in
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Untwisted it
looks like this:
The sides of the ladder are
P = phosphate group
S = deoxyribose sugar
The steps of the ladder are C, G, T, A
= nitrogenous bases (contain N)
Purine
Pyrimidine
A and G = purines
T and C = pyrimidines
Nucleotide
Read from top to bottom as:
3’  5’
5’  3’
Three to Five
Five to Three
prime prime
prime prime
2 H bonds
pairs
A = adenine
T = thymine
pairs
C = cytosine
G = guanine
3 H bonds
One Phosphate + one Sugar + one Base = one nucleotide
Nucleotides are the building blocks (monomer) of
DNA (polymer)
II. DNA Replication
A. Cell division produces 2 daughter cells that are
genetically identical to each other and genetically
identical to the parent cell
B. Remember that for this to happen, DNA in the parent
cell must be replicated (copied) before cell division
-this process occurs during S phase of Interphase
STEP 1
Hydrogen bonds between
base pairs are broken by the
enzyme Helicase and DNA
molecule unzips
STEP 2
DNA molecule
separates into
complementary halves
STEP 3
Nucleotides match up with
complementary bases
Free nucleotides
abundant in nucleus
STEP 4
Nucleotides are linked into 2 new strands of DNA by
the enzyme, DNA polymerase—DNA Polymerase also
proofreads for copying errors
New Strand
Original Strand
III. Ribonucleic acid – RNA -- acts as a
messenger between DNA and ribosomes, and
carries out the process by which proteins are
made from amino acids.
Protein = polymer Amino Acids = monomer
A. Different from DNA:
1. RNA’s sugar -- ribose
DNA’s sugar – deoxyribose
2. RNA – single strand of nucleotides
DNA – double strand of nucleotides
(double helix)
3. RNA has uracil instead of – thymine
When RNA pairs with DNA to get its code:
RNA cytosine (C) pairs with DNA – guanine G
RNA guanine (G) pairs with DNA – cytosine C
RNA adenine (A) pairs with DNA – thymine T
RNA uracil (U) pairs with DNA – adenine A
4. RNA found – inside and outside nucleus
(small – single strand)
DNA found – inside nucleus only
(large – double strand)
B. 3 types of RNA involved in Protein Synthesis–
mRNA messenger RNA
tRNA transfer RNA
rRNA ribosomal RNA
Complete the chart by reading each term or phrase and placing a check in the appropriate column.
DNA
Deoxyribose



single stranded

nucleotides
found in nucleus only
Both

Ribose
double stranded
RNA


found in and out of nucleus
Cytosine

Guanine

Adenine

Thymine


Uracil
double helix

replication
