The nucleic acids include the amazing DNA molecule. It is the source of constancy and variation among species, and is the foundation for the unity and diversity of all life on Earth.

Nucleic AcidsNucleic acids store

and transmit hereditary information

The amino acid sequence of a polypeptide is programmed by a unit of inheritance called a gene

Genes are made of DNA, a nucleic acidGenes

• Are the units of inheritance• Program the amino acid sequence of polypeptides• Are made of specific nucleotide sequences on DNA

The Roles of Nucleic AcidsThere are two types of nucleic acids involved in

inheritance and protein synthesisDeoxyribonucleic acid (DNA)Ribonucleic acid (RNA) DNADNA

– Stores information for the synthesis of Stores information for the synthesis of specific proteinsspecific proteins

– Found in the nucleus of cellsFound in the nucleus of cells– Directs RNA synthesis (transcription)Directs RNA synthesis (transcription)– Directs protein synthesis through RNADirects protein synthesis through RNA

(translation)(translation) RNARNA

– Single stranded nucleic acid which Single stranded nucleic acid which carries the code for protein synthesiscarries the code for protein synthesis

– Found in nucleus, and outside of Found in nucleus, and outside of nucleus in association with ribosomesnucleus in association with ribosomes

The Structure of Nucleic AcidsNucleic acids

Exist as polymers called polynucleotides

Each polynucleotideEach polynucleotide– Consists of monomers Consists of monomers

called nucleotidescalled nucleotides– Sugar + phosphate + Sugar + phosphate +

nitrogen basenitrogen base

3’C

5’ end

5’C

3’C

5’C

3’ endOH

O

O

O

O

Nucleotide monomersNucleotide monomers – Are made up of nucleosides (sugar Are made up of nucleosides (sugar

+ base) and phosphate groups+ base) and phosphate groups– The portion of a nucleotide without

the phosphate group is called a nucleoside

Nitrogenous basesPyrimidines

Cytosine (C) Thymine (T, in DNA) Uracil (U, in RNA)

Purines

Adenine (A) Guanine (G)

Sugars

Deoxyribose (in DNA) Ribose (in RNA)

(c) Nucleoside components: sugars

Nucleotide MonomersNucleoside = nitrogenous base +

sugarThere are two families of

nitrogenous bases: Pyrimidines (cytosine, thymine,

and uracil) have a single six-membered ring

Purines (adenine and guanine) have a six-membered ring fused to a five-membered ring

• In DNA, the sugar is deoxyribose; in RNA, the sugar is ribose

Cytosine Thymine Uracil

Adenine Guanine

Deoxyribose Ribose

Nucleotide PolymersNucleotide polymers are

linked together to build a polynucleotide

Adjacent nucleotides are joined by covalent bonds that form between the –OH group on the 3 carbon of one nucleotide and the phosphate on the 5 carbon on the next

These links create a backbone of sugar-phosphate units with nitrogenous bases as appendages

The sequence of bases along a DNA or mRNA polymer is unique for each gene

DNA Double HelixDNA 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

T A

G C

When guanine and cytosine bond, they form triple hydrogen bonds

H-bonds

When thymine and adenine bond, a double hydrogen bond is formed

• Antiparallel nature: •Sometimes called

complementary” sugar/phosphate backbone runs in opposite directions

• one strand runs 5’ to 3’, while the other runs 3’ to 5’; • One DNA molecule includes many genesRemember, the nucleotides connect together at the hydroxyl group of the 5’ carbon sugar (at the 3’ end)

Scientists can use DNA and Proteins as Tape Measures of Evolution

Molecular comparisons Help biologists sort out the

evolutionary connections among species

How similar are the sequences of nucleotides? The closer the sequence, the

closer the relationship Remember, all life, from the

simplest prokaryote to the most complex eukaryote, contains the same four nitrogenous bases.

It is simply the sequence of base-pairs, and amount of DNA that differs from organism to organism!

Adenosine triphosphate is a common source of activation energy for metabolic reactions.ATP is essentially an RNA adenine (adenosine) nucleotide with two additional phosphate groups. The wavy lines between these two phosphate groups indicate high energy bonds.When that last bond is broken, and the ATP is converted to ADP (adenosine diphosphate), energy is released, and can be used to spur a reaction.Conversely, a new ATP molecule can be built by combining ADP and a phosphate through a process known as phosphorylation using energy obtained from glucose.