By: Ms. Jessa S. Arino

NUCLEIC ACIDS

• Nucleic Acids are very long, thread-like polymers, made up of a linear array of monomers called nucleotides. • Nucleic acids vary in size in nature• tRNA molecules contain as few as 80 nucleotides• Eukaryotic chromosomes contain as many as 100,000,000 nucleotides.

Two types of nucleic acids

• Deoxyribonucleic acid (DNA)• Ribonucleic acid (RNA)

DNA• DNA is often

called the blueprint of life.

• In simple terms, DNA contains the instructions for making proteins within the cell.

A HISTORY OF DNA• Discovery of the DNA double helix

A. Frederick Griffith – Discovers that a factor in diseased bacteria can transform harmless bacteria into deadly bacteria (1928)

B. Rosalind Franklin - X-ray photo of DNA.

(1952)

C. Watson and Crick - described the DNA molecule from Franklin’s X-ray.(1953)

Structure of DNA

• Discovered in 1953 by two scientists:

• James Watson (USA)

• Francis Crick (GBR)• Known as the

double-helix model.

RNARNAribonucleic acid3 types of RNA in a cell•Ribosomal RNAs (rRNA) are components of ribosomes•Messenger RNAs (mRNA) carry genetic information•Transfer RNAs (tRNA) are adapter molecules in translation

RNA

DNA has deoxyribose, RNA has ribose;

DNA has 2 strands, RNA has one strand;

DNA has thymine, RNA has uracil.

The distribution of nucleic acids in the eukaryotic cell

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

• RNA is found throughout the cell

The nucleus contains the cell’s DNA (genome)

Nucleus

RNA is synthesized in the nucleus andexported to the cytoplasm

Nucleus

Cytoplasm

NUCLEOTIDE STRUCTURE

PHOSPHATE

SUGAR

Ribose or Deoxyribose

NUCLEOTIDE

BASEPURINES PYRIMIDINES

Adenine (A)Guanine(G)

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

DNA Nucleotide

OO=P-O O

Phosphate Group

N

Nitrogenous base(A, G, C, or T)

CH2O

C1C4

C3 C2

5

Sugar(deoxyribose)

The double-helix

• A twisted ladder with two long chains of alternating phosphates and sugars. The nitrogenous bases act as the “rungs” joining the two strands.

DNA Double Helix

P

P

P

O

O

O

1

23

4

5

5

3

3

5

P

P

PO

O

O

1

2 3

4

5

5

3

5

3

G C

T A

17

One Strand of DNA• The backbone of

the molecule is alternating phosphates and deoxyribose sugar

• The teeth are nitrogenous bases.

phosphate

deoxyribose

bases

THE SUGAR-PHOSPHATE BACKBONE

• The nucleotides are all orientated in the same direction

• The phosphate group joins the 3rd Carbon of one sugar to the 5th Carbon of the next in line.

P

P

P

P

P

P

ADDING IN THE BASES

• The bases are attached to the 1st Carbon

• Their order is important It determines the genetic information of the molecule

P

P

P

P

P

P

G

C

C

A

T

T

20

Two Stranded DNA• Remember, DNA

has two strands that fit together something like a zipper.

• The teeth are the nitrogenous bases but why do they stick together?

RIBOSE DEOXYRIBOSE

CH2OH

H

OH

C

C

OH OH

C

O

H HH

C

CH2OH

H

OH

C

C

OH H

C

O

H HH

C

Spot the difference

Nitrogenous Bases

• PURINES1. Adenine (A)

2. Guanine (G)

• PYRIMIDINES3. Thymine (T)

4. Cytosine (C) T or C

A or G

23

Thymine and Cytosine are pyrimidines

• Thymine and cytosine each have one ring of carbon and nitrogen atoms.

C

N

N

O

N

cytosine

C

N

N

O

O

thymine

C

C

C

C

CC

C

24

Adenine and Guanine are purines

• Adenine and guanine each have two rings of carbon and nitrogen atoms.

C

C

C

C

N

N

N

Adenine N

N

C

C

C

C

C

N

N

O

N

GuanineN

N

C

Chargaff’s Rule• Adenine must pair with

Thymine

• Guanine must pair with Cytosine

• Their amounts in a given DNA molecule will be about the same.

G CT A

BASE-PAIRINGS

CG

H-bonds

T A

How long is the DNA molecule?

DNA IS MADE OF TWO STRANDS OF POLYNUCLEOTIDE

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

They are joined by the bases Each base is paired with a specific partner:

A is always paired with T G is always paired with C“Purine with Pyrimidine”

The sister strands are complementary but not identical

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

There are 10 base pairs per turn

Structure of Nucleotide BasesPurines & Pyrimidines

Nucleotides arelinked by

phosphodiesterbonds

DNA Organization

1. Try the problem from this link:http://www.dnaftb.org/dnaftb/19/concept/index.html

Self-test

2. Use the questions on the following slides

What sugar is used in a DNA?

A) ribose

B) fructose

C) deoxyribose

D) Glucose

What is the base found in RNA but not DNA?

  A) CytosineB) Uracil

      C) Thymine      D) Adenine

What covalent bonds link nucleic acid monomers?

  A) Carbon-Carbon double bonds

   B) Carbon-Nitrogen bonds   C) Hydrogen bonds

D) Phosphodiester bonds

Each deoxyribonucleotide is composed of

  A) 2'-deoxyribose sugar, Nitrogenous base, 5'- hydroxyl

  B) 3'-deoxyribose sugar, Nitrogenous base, 5'- hydroxyl

  C) 3'-deoxyribose sugar, Nitrogenous base, 5'- Phosphate

   D) Ribose sugar, Nitrogenous base, 5'-hydroxylE) 2'-deoxyribose sugar, Nitrogenous base, 5'- phosphate