Download DNA Structure

DNA Structure
Section 11.2
Nucleic Acids (2 groups)





DNA
Deoxyribonucleic
acid
Stores genetic info
Nucleic Acid made
of nucleotides
ONLY 4 types of
nucleotides make
up DNA



RNA
Ribonucleic acid
Plays key role in
cells (Details to
come…)
Nucleotides

Each nucleotide has 3 parts
1. ring-shaped sugar called deoxyribose
2. A phosphate group (phosphorous
surrounded by 4 oxygens)
3. Nitrogen base: single or double ring
of carbon & nitrogen atoms w/
functional groups
Nitrogen Bases

Pyrimidines



Single ringed
Thymine (T)
Cytosine (C)

Purines



Double ringed
Adenine (A)
Guanine (G)
DNA Strands

To make a strand
of DNA:


The nucleotides are
joined together w/
a covalent bond
connecting the
sugar of one
nucleotide to the
phosphate group of
the next
This makes up the
“Backbone” of DNA
(sides of the
ladder)
DNA’s Structure



Rosalind Franklin & Maurice Wilkins
produced photos of DNA using Xray crystallography
Gives clues to shapes & dimensions
Showed DNA to be a helix
The Double Helix



James Watson &
Francis Crick created
a model w/ the
assistance of
Franklin’s photos:
2 strands of
nucleotides wound
around each other
forming a DOUBLE
HELIX
Hypothesized the
nitrogen bases across
from each other
formed hydrogen
bonds
Complementary Base Pairs

The structure of the nitrogen bases
determine specific pairings b/w the
nucleotides





sizes & ability to form H-bonds
A always pairs w/ T (complementary
bases)
G always pairs w/ C (complementary
bases)
The sequence on one strand can vary:
the sequence of the bases on the 2nd
strand are determined by the first.
http://learn.genetics.utah.edu/units/ba
sics/builddna/
Concept Check 11.2
1.
What are the three parts of a nucleotide? Which parts make
up the backbone of a DNA strand?
2.
List the two base pairs found in DNA.
3.
If six bases on one strand of a DNA double helix are
AGTCGG, what are the six bases on the complementary
section of the other strand of DNA?