Hydrogen bonds

Nucleotide

Sugar-phosphate backbone

Key

Adenine (A)

Thymine (T)

Cytosine (C)

Guanine (G)

Figure 12–7 Structure of DNASection 12-1

NUCLEIC ACIDS are built from subunits called

____________________

Image by: Riedell

NUCLEOTIDES

SUGAR in DNA is________________deoxyribose

DEOXYRIBONUCLEIC ACID

Image from: http://www.tokyo-med.ac.jp/genet/picts/dna.jpg

______________ STRANDED

Backbone (sides of ladder)made of _____________and_____________

DOUBLE

PHOSPHATES

sugars

Purines(2 rings)

Pyrimidines

(1 ring)

A

G

C

T

Phosphate group

Deoxyribosesugar

 Nitrogen bases =“Steps of ladder”

© Pearson Education Inc, publishing as Pearson Prentice Hall. All rights reserved

NITROGEN BASES in DNA

_____________= A

_____________ = G

_____________ = C

______________ = T

ADENINEGUANINECYTOSINETHYMINE

No URACIL

CHARGAFF’S RULES

A = T G = C

Image from: http://evolution.berkeley.edu/evosite/evo101/images/dna_bases.gif

_________ _________At time no one knew why…

now we know its becauseAdenine always bonds across with____________

Guanine always bonds across with ____________

THYMINE

CYTOSINE

DOUBLE HELIX

Hydrogen

Image from: http://evolution.berkeley.edu/evosite/evo101/images/dna_bases.gif

_____________ bondsbetween nitrogen bases hold the two strands together.

• Bases can be in any order along one side of DNA

• Strands are complementary– Complementary – a

DNA strand which is able to bond to another strand according to the base-pairing rule • A always pairs with T• C always pairs with G

Nitrogen Base Pairing

Chromosomes

AP Biology

AA

A

A

TC

G

CG

TG

C

T

AP Biology

When does a cell copy DNA? When in the life of a cell does DNA have

to be copied? cell reproduction

mitosis gamete production

meiosis