Nucleic Acids

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WHAT ARE NUCLEIC ACIDS?• Used for:

• Storing genetic information• Assembly instructions for protein

synthesis• Energy molecule (ATP – adenosine

triphosphate)

• Two major nucleic acid polymers:• DNA: deoxyribonucleic acid

• RNA: ribonucleic acid

The distribution of nucleic acids in the eukaryotic cell Two types of Nucleic Acid: DNA and RNA

DNA is found in the nucleus with small amounts in mitochondria and chloroplasts

RNA is found throughout the cell

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NUCLEIC ACIDS

DNA RNA

- Located in the nucleus

- Located mostly in the cytoplasm

- Double-stranded, double helix structure

- Single-stranded structure

- Stable molecule - Less stable molecule

NUCLEIC ACID STRUCTURE

Nucleic acids are polynucleotides

Many nucleotides

Their building blocks are nucleotides

Nucleotides: nitrogenous base + 5 carbon pentose (sugar) + phosphate

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NUCLEOTIDES• Monomer of nucleic acids• Three components:

1. Phosphate2. Pentose sugar3. Nitrogenous base

Nucleotides

Nucleic acids consist of nucleotides that have a sugar, nitrogen base, and phosphate

nucleoside 7

Sugar

Base

PO4

SUGAR

Ribose or Deoxyribose

BASEPURINES PYRIMIDINES

Adenine (A)Guanine(G)

Cytocine (C)Thymine (T)Uracil (U)

Nitrogen-Containing Bases

N

N

N

N

H

NH2

N

N

O

CH3

O

H

H

N

N

N

N

O

H

NH2

H

N

N

NH2

CH3

O

H

N

N

O

CH3

O

H

H

adenine (A) thymine (T)

guanine (G) cytosine (C) uracil (U)

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Purines Pyrimidines

NITROGENOUS BASES

Purines

Pyrimidines

RNA DNA

PENTOSE SUGAR

Sugars

O OHCH2

OHOH

HO HO O OHCH2

OH

ribose deoxyribose

(no O)

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Nucleotides in DNA and RNA

DNAdAMP Deoxyadenosine monophosphatedGMP Deoxyguanosine monophosphatedCMP Deoxycytidine monophosphatedTMP Deoxythymidine monophosphate

RNAAMP adenosine monophosphateGMP guanosine monophosphateCMP cytidine monophosphateUMP uridine monophosphate

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Nucleosides in DNA

Nucleosides are the precursors to nucleotides; they are not phosphorylated

Base Sugar NucleosideAdenine (A) Deoxyribose AdenosineGuanine (G) Deoxyribose GuanosineCytosine (C) Deoxyribose CytidineThymine (T) Deoxyribose Thymidine**T is only found in DNA**

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Nucleosides in RNA

Base Sugar Nucleoside

Adenine (A) ribose Adenosine

Guanine (G) ribose Guanosine

Cytosine (C) ribose Cytidine

Uracil (U) ribose Uridine

**U is only found in RNA**

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NUCLEOSIDE

Structure of Nucleic Acids

Polymers of four nucleotides Linked by alternating sugar-phosphate

bonds RNA: ribose and A, G, C, U DNA: deoxyribose and A,G,C,T

nucleotide nucleotide nucleotide nucleotide

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P sugar

base

P sugar

base

P sugar

base

P sugar

base

Nucleic Acid Structure

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O

N

N

NH2

O

CH2OP

O

O-

O-

OH

O

N

N

NH2

CH2OP

O

O-

OH

O

N

N

AMP

CMP

3

5

3,5-phosphodiester bond

Nucleic Acid Structure

Covalent bond between the phosphate group of 1 nucleotide and the hydroxyl group on the carbon three of the sugar on the adjacent nucleotide

PHOSPHODIESTER BOND• Phosphodiester bond formed between

nucleotides:• Pentose sugar (-OH group)

• Phosphate group

‘BACKBONE’ OF DNA• Linking nucleotides produces a

single strand of DNA

• Phosphate + deoxyribose =

backbone

COMPLIMENTARY BASE PAIRING

• Nitrogenous bases are joined through Hydrogen bonding

• Complimentary base pairs:

• Adenine + Thymine

• 2 H bonds• Cytosine +

Guanine• 3 H bonds

ANTI-PARALLEL STRANDS• Complimentary base

pairing results in double-stranded DNA

• Both DNA strands run anti-parallel to each

other (oriented in opposite directions)

One strand is 5’ 3’ while the other is 3’

5’

COMPLIMENTARY BASE PAIRING

• The 2 anti-parallel strands coil together to form a double helix.

Structure of Nucleic Acids

DNA contains two strands of nucleotides Each strand of DNA has a free

phosphate group at one end and a free sugar at the other end

DNA takes on a helix structure, like a spiral stair case

Bases are always paired as A–T and G-C

RNA is single stranded but it still coils into a helix

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Double Helix of DNA

The sister strands of the DNA molecule run in opposite directions (antiparallel) Purine with Pyrimidine

The sister strands are complementary but not identical

The bases are joined by hydrogen bonds, individually weak but collectively strong

A-T is joined by two hydrogen bonds G-C is joined by three hydrogen bonds

Complementary Base Pairs

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•Two H bonds for A-T•Three H bonds for G-C

Double Helix of DNA

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DOUBLE HELIX

OVERVIEW

Checkpoint

Write the complementary base sequence for the matching strand in the following DNA section:

-A-G-T-C-C-A-A-T-G-C-

• • • • • • • • • •

• • • • • • • • • •

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Answer

Write the complementary base sequence for the matching strand in the following DNA section:

-A-G-T-C-C-A-A-T-G-C-

• • • • • • • • • •

• • • • • • • • • •

-T-C-A-G-G-T-T-A-C-G-31