Stores and passes on genetic information from one generation to another.

DNA DEOXYRIBONUCLEIC ACID

DNA STRUCTURE

THE DNA STRUCTURE IS SHAPED LIKED A SPIRAL STAIRCASE, OR TWISTED LADDER.

DNA STRUCTURE(An Overview)

DNA has three main components:• Deoxyribose ( pentose sugar)•Base (there are four different ones)•Phosphate group

The deoxyribose sugar of the DNA backbone has 5 carbons and 3 oxygens.

DNA STRUCTURE

DNA STRUCTURE

THE STEPS OF THE LADDER ARE MADE OF PAIRS OF NITROGEN BASES.

DNA STRUCTURE

They are divided into two groupsPyrimidines and purines

Pyrimidines (made up of 6 atoms 4 carbon 2 nitrogen rings)ThymineCytosine

Purines (larger of the two bases; made up of 9 atoms that make up the fused rings 5 carbon, 4 nitrogen )AdenineGuanine

DNA STRUCTURE

1. ADENINE = A2. GUANINE = G3. CYTOSINE = C4. THYMINE = T

They are represented by their capital letter.

DNA STRUCTURE

There is only one way the nitrogen bases can form

ADENINE pairs with THYMINEGUANINE pairs with CYTOSINE

DNA STRUCTUREQUESTION ?

CAN C JOIN WITH A

AND G JOIN WITH T

YES

NO

CORRECT

MOVE ON

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DNA STRUCTURENucleotides Nucleotides are formed by the condensation of a pentose sugar, phosphate and one of the 4 basesThe following illustration represents one nucleotide

CIRCLE = Phosphate

PENTAGON= Deoxyribose

Rectangle= Base

DNA STRUCTUREDNA Double Helix and Hydrogen Bonding

•Made of two strands of nucleotides that are joined together by hydrogen bonding•Hydrogen bonding occurs as a result of complimentary base pairing

Adenine and thymine pair upCytosine and guanine pair upEach pair is connected through hydrogen bondingHydrogen bonding always occurs between one pyrimidine and one purine

DNA STRUCTURE•Adenine always pairs with thymine because they form two H bonds with each other

•Cytosine always pairs with guanine because they form three hydrogen bonds with each other

DNA STRUCTUREAntiparallel strands

The strands run opposite of each other.

The 5’ end always has the phosphate attached. ’

SAMPLE QUESTION

Which of the following nucleotide base sequences complements the section of DNA modeled above?F. 5′UTCGCA3′G. 5′TTAGCG3′H. 5′GCGATT3′J. 5′TTUCGC3′

3′AATCGC 5′

SAMPLE QUESTION

The Correct Answer: G

G is the right answer because A (adenine) always pairs with T (thymine) and C (cytosine) always pair with (guanine).